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Replacing your exhaust submitted by Brucey

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Replacing your exhaust submitted by Brucey

Post by bcadmin » Sun May 09, 2004 3:12 pm

Choosing, buying and fitting a stainless steel manifold/exhaust system for a UKbspec model BMW 635CSiA

By; Bruce
Dance, a.k.a.

<img width=425 height=174 src="/tech/exhaust/image002.jpg">

Fig1. My Beemer,
the Bee-hee-mer-moth

Q. Why buy a new exhaust?
A. Because the old one is broken, or you want some aspect of the
exhaust performance to be different. Sometimes it is a little of each, as in my case.

This article describes how and why I changed my exhaust system on my otherwise
fairly standard RHD car. I hope it is of interest to others with similar
vehicles, and of some usefulness to those of you in other countries with LHD vehicles, for whom much of the fitting work would be
very similar, even though the manifold itself would be of a different design.

Anyone who does this job using these notes will probably manage
it in about a third of the time it took me. I spent a lot of time working out
what to do next, doing things in the wrong order, searching for tools I
didnt know Id need, and sliding in and out from under the car a
zillion times to get another tool that wouldnt be quite right for the
job either&. If just one or two people get any benefit in time saved, I
shall feel as if I have not wasted my time writing these notes up.


In the previous twelve months, my standard exhaust had gone from OK to knackered.
Also, the #4,5,6 manifold had: a) leaked (not for the first time in the life of
the car), b) mysteriously still sounded like it was leaking even when it
wasnt, and c) had cracked near one of the bolt holes. I had previously
resealed the #4,5,6 manifold to the head temporarily with exhaust jointing
compound, and had noted that I would have to do something major with the exhaust at some point. However, the centre box (OE BMW part, lasted ~seven years) eventually blew in spectacular and noisy fashion, and this kind of forced my hand a bit. Having looked at it, I was not optimistic that I would be able to replace the middle box on the system without destroying the rear box (which was OK) and/or the link pipes (which were original, and although OK, must be weakened by corrosion). One way or another, I knew I was in for a lot of work and/or expense.

In the course of my searches, I heard that the M30 cylinder head is prone to cracking on cars that are raced. This sometimes happens on enthusiastically driven road cars, too, even if they dont seem to have any special problem with the cooling system (which would certainly cause it). The problem seems to be the stress from differential thermal expansion of the manifold and the head. This is presumably one reason BMW made the manifold in two parts, to allow some movement on the crush ring joint (although casting it in one go would have been tricky, too).

The standard RHD manifold has to clear the steering box, the master cylinder, AC pipes (if fitted). In order to do this, the routing from ports #1,2,3 is up, then back on a collector pipe; #4,5,6 go onto another collector pipe parallel to and below this one, and both sweep down and back together. Just by the bend, the collector pipes are squashed from round to a very flattened oval, then back to round for the link pipe flange joint. In situ, the squashing looks like overkill, and it is; however, the manifold presumably has to clear the steering box if/when the engine is fitted or removed with the manifold attached, and this requires a very weirdly shaped manifold indeed, because of the way the steering box sticks out. Although the flow path is not badly constricted in this region per se, the shape change in the pipes is very undesirable. Furthermore, the #4,5,6 manifold is really a sort of 4 into 2 arrangement with all the exhaust going through this small casting, it must run extremely hot indeed, and I gather they often start to leak (as mine has done,
several times) at this point. The link pipes are stepped in size, going from a small size at the flange to a larger size at the first silencer box.
Depending on the gasket that is fitted at this flange, there either is or isnt any sharing between the link pipes at the flange. I dont know if this makes
any real difference. The currently supplied genuine BMW gasket does not allow sharing, as it has a centre rib. The one that came off my car didnt.
Heat shields above the manifold prevent too much radiant heat from getting to the AFM, which sits right above the manifold. Convection is still there though, and for this reason I would not have only a thermostatically controlled fan on this car, if I was going to do a lot of town driving; the standard fan is always turning a bit, and this helps keep the
worst of the heat from the manifold out of most things. Despite this, it is not unusual to see peeling paint on the steering box and inner wing, all from the heat of the manifold.

It gets pretty toasty in there.
<img width=512 height=384 src="/tech/exhaust/image004.jpg">

Fig 2.
the standard RHD manifold, in situ. The AFM and one of the
heat shields have been removed. The AC hose in its original position is just visible bottom centre right.

<img width=236 height=339 src="/tech/exhaust/image006.jpg">

Fig 3,
The standard RHD manifold system, a.k.a. the Dingolfing Engine Strangler. The part at the left is the #4 ,5,6 manifold, viewed from the rear. Note the squashed section- it is so flattened that in places the outside of the casting is actually narrower than internal diameter of the collector pipes elsewhere in the manifold. Although they did a good job, (considering, as the internal swept area remains roughly constant, since the opening is stretched a lot in the other direction,) this is still not a very good design.

Despite the obvious compromises in this manifold arrangement, BMW dont report a performance drop in the RHD UK models vs LHD Euro models as such, and nor do independent road tests. However it goes without saying that this arrangement could be improved upon, and would probably have to be for cars that are tuned for significantly more power, if the risk of manifold blowing and head cracking problems are to be avoided.

I spent a while looking around before I bought the Fritzs Bits
system. For some details of this, see the appendix, which contains the postings some of you may have seen on this website already.

<img width=512 height=384 src="/tech/exhaust/image008.jpg">

Fig 4
The new manifold arrangement. Nice, isnt it? The
outrageous bend in the #1 header is absolutely required on a RHD car. The steering box stops the obvious route to the collector, so #1 has to loop below the RHS engine mounting instead. I dont know if a similar LHD manifold is available from the same source, with a more sensible #1 header pipe. Note there are no access points for sensors as there are on OE manifolds- not that these ever got used on my car.

<img width=508 height=262 src="/tech/exhaust/image010.jpg">

Fig 5.
This is the space it has to go into- the main space-thieving culprit, the
steering box, is even attempting to elbow its chief accomplice, the engine
mounting, out of the way. It is like having a very fat cuckoo in the
nest. The exhaust has to fight for every square inch of room.

Fig 6.
F1 manifold for comparison. This is made in titanium.. (photo coming soon)

<img width=299 height=466 src="/tech/exhaust/image012.jpg">

Fig 7, the old and the new compared (the new #1 header pipe clearly turned shy, ran off and hid in the corner when I took this picture). Using my uncalibrated hands, I estimate the new one weighs about to 2/3rds the old one. It took longer to get the old system off in one piece than it did to fit the new, once everything was prepped right. Note the slim single-bolt clamps on the link pipes; you cant buy them like this because they are Brucey specials, Im afraid.

On the manifold, I ended up using brass nuts on steel studs with copper ease to help stop seizure. I find that brass nuts (if you can use them) are less prone to complete seizure. I think this will work well, with my new exhaust (and has done so for about 300miles so far). However, I think the OE exhaust manifold runs hotter, so I would not recommend brass nuts on one of these. The fabricated manifold I now have has excellent thermal contact between the flanges and the head via OE gaskets, but limited thermal contact between each header tube and its flange, by virtue of the size and location of the welds between the parts. I suspect the flanges and nuts will therefore run 100 to 200 degrees Celsius cooler than with OE parts.

I made up my own clamps for this system. I did this for several reasons; 1) because I can,
2) there are no stainless steel clamps available to buy for this job,
3) I think ordinary steel ones will rust relatively quickly,
4) space is limited, particularly where the collectors join the link pipes, so slimmer clamps would be a good idea
5) A single-bolt clamp, if it can be removed at all, is often easier to remove (and fit) than a double bolt clamp. My design is in stainless steel,
laminated from several layers of thinner material to give the thickness
required, and welded only at the ends. This way they are very slim indeed, and flexible enough to be removed if required, but are still very strong. After noting that the stainless steel captive nuts I originally fitted to theseclamps ALL diffusion bonded to, (and seized up on) stainless bolts during welding, I went off the idea of using stainless bolts and nuts anywhere really hot. Thus my clamps use stainless bolts with non-captive brass nuts where necessary. This seems to have worked OK so far.

Fitting the system:

Below follows a potted guide to what is involved, as far as I can recall (it is now a few days since I did the job).

If you are fitting a system similar to the one I did, think carefully about the condition of the head before you fit the system; you may decide to rebuild the head anyway, as this will allow you to remove and fit the studs more easily, and to match the exhaust ports to the manifold properly. If you do the latter, note that you will need different gaskets; the headers are a little larger than the ports, and once the ports are opened up to match, the OE gaskets wont be a good fit any more. I think these gaskets should not be opened up owing to their construction. I didnt bother with this- Im not after massive power with this upgrade.

Before you start; make sure you have
1) all the parts you need,
2) all the tools you need,
3) all the time and patience you will need,
4) a good contingency plan if you run into problems, eg. A sheared-off stud in the head.

the exhaust I purchased came with a rear box hanging strap, and new three-bolt clamp rings. In addition to this you will need; 6 off exhaust gaskets, (I used genuine BMW, but I am told that there are some available from GSF (Victor Reinz?) which have integral heat-shields), link-pipe to centre-box seal rings (1ea. of two types), 4 off 54mm dia. Clamps, new exhaust hanging rubbers (if required), new exhaust studs, and 12-off 12mm hexagon nuts, seven M8 bolts with nuts and washers (6 off pref. caphead type ~40-50mm for the exhaust clamps, one
shorter one for the rear box strap), exhaust sealing paste. Copper-ease.

Also, you may choose to put a 44mm dia. clamp on the #1 header sleeve joint (not as per instructions, but I did this for extra security). You may also choose to remount the original heat shields from the exhaust studs, for which you will have to make suitable heat-shield mounting brackets, and supply new bolts etc for same. Again an option, you may
choose to insulate the exhaust with a suitable wrap- I couldnt get hold
of exactly what I wanted to use in time, so I used woven glass-fibre, secured with stainless steel wire and further one-off clamps in stainless steel.

You will also need any other exhaust brackets that cannot be re-used. The
T clamp and bolt on the link pipes will probably need to be replaced, for example.

You will need the following at the least: A good jack, capable of raising the car at least 12 off the ground. Four (or preferably five) good quality axle stands. Open-ended + flat ring (pref. full hex in 12mm) spanners in 12, 15, 17 and 13mm sizes, 10mm socket, 17mm socket, 12mm socket, drive 13mm full-hex socket, medium length, good quality drive wobble
bar. Various screwdrivers, a good quality socket set. Scrapers
for cleaning gasket faces. A junior hacksaw.
A set of files including one for dressing screw threads.
An M8x1.25 #2 tap. An M8x1.25 die.
A stud extractor. An air impact wrench is useful for freeing
off the exhaust fittings. A small angle grinder (or dremel tool) with cut off
wheel is handy for exhaust bolts that wont shift at all.

first remove the AFM, air filter, the heat shields, and the plug caps. Remove the ignition leads altogether, or tie them up well; otherwise they will flop down at intervals and drive you nuts. (This is what happened to me.)

Next jack:
the car up one end at a time, and support it with the four axle-stands under the subframes so that it cannot move. Check the condition of the exhaust fittings carefully and note any new parts you have yet to obtain.

You will probably have run the engine briefly in order to move the car to the spot where you will be working. This is fine. When the engine is still a little warm is a good time to loosen the manifold nuts. Do this carefully. See how the wrench you are using fits the nut before you haul on it. Preferably use a full-hex ring spanner, as the manifold nuts will be undersize through corrosion, and prone to rounding off. Some of these nuts are difficult to access; I found one of the best tools for the job (although it is a bi-hex design) is the Heyco 10-12mm ring spanner from the original BMW toolkit, which has an exceptionally
slim ring. Mine was missing from the toolkit when I got my car, and Im now glad I spent the 5 quid or so on it a few months ago.

Also loosen the nuts connecting the two halves of the manifold.

The nuts on the bottom side are best accessed from below. Now is a good time to remove the RHS engine mount, as this will considerably ease access to the lower nuts on #3 ,4,5,6. Jack up the engine, and use a fifth axle stand and/or a packing piece between the engine and the front cross member to make absolutely certain the engine cannot move.

Also drop the anti-roll bar from its body mountings (13mm socket), and remove the tubular cross-brace (15mm combination spanner and 17mm socket).

If you are lucky, all the manifold nuts will come loose, or the nut will be seized on the stud, and the stud will unscrew instead. Only back the fasteners off a turn or so at this stage. On mine, I was lucky, and they all came undone, with about half the studs still in the head. If you are unlucky one or more will shear off, and then it is either off with the head, or out with the right-angle-drill. Incidentally, the holes in the head are much deeper than they need to be, and even if a thread is damaged when drilling out a stud, there may be enough depth in the hole to retap and use an over-length stud. Maybe you can use an oversize stud (but remember you cant necessarily go any bigger than a 12mm headed nut with this manifold). Otherwise it will have to be helicoiled; difficult but probably not impossible in situation

Having loosened the manifold nuts a turn or two only, now is
a good time to tackle the rest of the exhaust. Loosen (or, like me, shear off) the link pipe T clamp. Loosen the link pipe support from the back of the gearbox. Next, loosen the nuts on the link-pipe to manifold flange. There are three, with a very non-standard 13mm hex on an M10 thread. Although they will be very tight indeed, two can be accessed line of sight with a simple socket and extension. The third cannot. Nor is there space for any ring spanner. Nor can the parts be easily removed from the car without removing this nut, unless the link pipes are severed (or perhaps just released from the centre box, although this would be a tight (maybe impossible) squeeze, and the car would have to be about 18clear of the ground). The only way of removing this nut safely is to use a full-hex socket and a wobble bar. It is, I have to say, a right bugger, even with the correct tools and an air impact driver. If you dont have the right tools it is nigh-on impossible to improvise with this one nut. As I didnt have these things at first, there was much wailing and gnashing of teeth, as various alternatives were tried, to no effect. Eventually I gave up, and resigned myself to a twenty-mile round trip to go get the right things for the job & Once these nuts are undone, any remaining seal between the head and the manifold will likely be broken.

Remove the centre exhaust rubbers. Now release the back box. I ended up cutting the support strap (someone had borrowed the Dremel tool I would otherwise have used to cut the seized bolts). Support the back box on some wood, then lower the exhaust from the front, by removing the link pipe support altogether. If you do it this way, you have a complete exhaust which could be refitted in an emergency. This is preferable to other ways of removing the exhaust also because the chances of disassembling other joints in a used exhaust without extensive damage are rather slim. Note you might be able to refit the old manifold temporarily with one or two studs missing and run the

OK - with the tubular manifold this isnt possible. Having the option
to refit the old system might get you out of a jam if you bust a stud and
cant fix it in the time you have.

Now remove
the manifolds completely, and clean and inspect the gasket faces. Run the tap
through any of the threads where the stud has come out. Dont overdo it,
or the tapped hole will be too deep for the standard studs. Run the die over
any remaining studs, and assess if they are good enough to re-use. A normal die
holder cant be swung in the gap you have, but you can probably hold the
die using slip-joint pliers if the cut is not too big; I fabricated a new
die-holder that I <u>could</u> swing in the gap OK, but I probably didnt
really need to. Remove any studs that are not fit for further use. You must
shorten the lower studs, otherwise you will not be
able to fit the nuts on these studs when the manifold is in place. Cut about
5mm from the length of the lower ones that remain in situ. I extended a junior
hacksaw handle for this, after losing most of the skin on my knuckles on the
first one. Dress the ends carefully, and check you can spin a nut on easily
with your fingers. Fit/trim remaining studs.

<img width=501 height=255 src="/tech/exhaust/image014.jpg">

Fig 8.
Shortening the exhaust studs, or how to skin your knuckles in
seconds&In this view you can
no longer see the now re-routed AC compressor hose. I later mounted a heat
shield on the bracket on the rear of the AC compressor- the #1 header runs very
close to this and a heat shield here is probably essential. Hmm, must fix that
oil leak, too.

Now is the
time to insulate or wrap the new manifold if you have not already done so; I
would say it would be almost impossible to do this properly once the manifold
is fitted.

<img width=490 height=260 src="/tech/exhaust/image016.jpg">

Fig 9,
Freshly-wrapped manifold. Stainless steel wire secures otherwise loose woven
fibreglass wrap. Stainless steel clamps secure ends of wire and help stop
fraying at ends of wrapping.

Also, check
to see how the AC hose (if fitted) to the top of the
compressor is routed. You may need to re-route this hose, and/or install a heat
shield here, as the #1 pipe will run much closer to this than before.

Now fit the
gaskets over the studs. They only go on one way, metal face outwards, small flat
downwards. Use a little gasket compound to stick them in place, or they will
fall off;- you dont need it to make a good seal.
Apply copper ease to all the studs. Fit the rear #4,5,6,
manifold, then fit and fully tighten all the nuts. NB! You <u>must</u> do this
before fitting the next parts, as access to the lower nuts on #4
,5,6 is more or less impossible later on.
Next, fit #2,3 manifold, and again
tighten the nuts fully. Now fit #1 header pipe and tighten, using sealing
compound on the sleeve joint. Refit the engine mounting. You may need to do the
last two steps the other way round, depending on the access to the engine
mounting bolts. Remember to include the heat shield brackets you have made (if
applicable) on #1,#3,#4,#6 upper manifold studs as you fit them.

Marvel at
the fit of the headers through the small gap they have to go

<img width=492 height=119 src="/tech/exhaust/image018.jpg">

10, manifolds fitted. Note special brackets to refit OE heat
shields. With these re-fitted the engine bay appears completely standard unless
subjected to close scrutiny. Between the steering box and the engine, the space
is so full of tubes you cant spit through there and hit the floor.

Now, fit
the link pipes, and the clamps (loosely). Likewise
mount the link pipe support, and the T clamp. I made up a stainless
steel strap clamp here; this is more secure, and also has the effect of packing
to stop the pipes from fretting on the link pipe support bracket.

<img width=453 height=343 src="/tech/exhaust/image020.jpg">

Fig 11.
Link pipe support bracket and revised clamp arrangement, viewed from behind.
Golden-brown colour of pipes is real enough after 300miles.

Fit the clamp
ring and the soft seal ring to the RH link pipe (mine needed chasing out with a
file before it would fit). Hang the centre box, and assemble the three-bolt
clamps and the remaining seal ring loosely. Note access for tools, and position
bolts accordingly; if you use caphead bolts and put them the right way round
(nuts forward), you will be able to access them all with a long series Allen
key and a slim (3/8 drive, pref.) socket. I used stainless steel bolts
and matching nylock (ran out of ordinary ones, would you believe&) nuts

Hang the
rear box loosely. Adjust and tighten all the clamps, starting at the front and
working back. Check everything is snug. You may be able to adjust the height of
the system by moving or modifying the centre box hangers- they are adjustable.
I didnt do this (rushing near the
end&), and may have to go back and adjust this at some point, as the
system isnt hanging quite as neatly as I would like.

underneath, refit the cross-brace and the anti-roll bar.

Refit the
heat shields, the ignition leads, and the AFM/filter assy. <u>Dont,</u>
under <u>any circumstances</u> forget the earth strap on this assy.- without
this, a fault in the HT king lead or coil could fry your AFM <u>and</u> your
Motronic ECU; trust me, you dont want this to happen&.

Run the
engine up, and check exhaust for leaks. Dont be worried if there is a bit
of smoke to start with, it is probably just contamination burning off the

Now, go
enjoy&&-I did, I drove 250miles in the first two days, mostly with the
windows open and the radio turned off- the new exhaust note is soundtrack
enough to drive to&.

<img width=318 height=329 src="/tech/exhaust/image022.jpg">

Fig 12.
The business end. The tailpipes are ~2 &frac14; (57mm) OD, slightly
slash cut, and nicely polished.

The exhaust
note is quite different (see comments in appendix). However, at tickover, there
is now a definite lollop to the exhaust note that wasnt
there before. I can only think of three reasons why this might be; 1) The
mixture strength at tickover has changed (and it probably has, everywhere else,
too), 2) I perhaps have an unrelated fault of some kind, maybe a small air leak
3) The uneven header lengths are responsible. At the moment I am assuming 3),
as #1 and #5, for example, fire sequentially, but now have header lengths
almost 2 feet different in length. This is bound to sound a bit odd, and at
least one person has commented that it sounds a bit like a five cylinder car at
tickover (which I agree with to some extent) and wonder if there is a misfire
on one pot (which I dont think there is).


I posted a
several times re. this on the BigCoupeGroup website.
Below follows an essentially unedited version of these posts; any comments I
have added later are in brackets and marked with a <u>single</u> asterisk,
thus; *. Multiple asterisks have an altogether different meaning&.

Before #1-
exhaust stud/nuts query

-I've just splashed out on a full new exhaust system,
complete with six-branch tubular manifold, well designed (ie less-restrictive)
boxes etc, all in stainless steel, which is looking nice and shiny right now;
(I know it won't last once fitted) <br>
- The manifold some might consider a needless expense;
ahh, but my car has the steering wheel on the 'right' (read into this what you
wish) side, which is definitely the wrong side so far as the exhaust manifold
goes. You LHD guys don't know how lucky you are; RHD cars have a completely
different manifold that is 'designed' (I use the word loosely) to clear the
steering box. It does this OK, but fails in its main purpose, which is to allow
efficient expulsion of the exhaust gases without causing problems. <br>
-Basically this manifold is what some have described as
'a barbaric piece of ****'. Certainly not one of BMW's finest moments. Mine has
shown signs of overheating locally near the 5-6 region,
and has sprung leaks in this area too. And it is a ROYAL pain in the rear end
to mess with. <br>
So (finally) I get to the point; does anyone have a
bought or modified FULL hex 12mm wrench design that will allow this (manifold
removal) to be done a little easier? I am probably going to have a go at making
one (I have all the required facilities), but if someone has done this already
it could make life easier for me. <br>
Also; has anyone got any top tips re.
materials for the exhaust studs and nuts? I can go to
stainless studs with brass nuts if I want, but I don't know if this is going to
seize up worse than the steel/steel arrangement. Likewise, is there a better
anti-seize material for these studs than copper-ease? <br>
Any comments welcome

Before #2:
choosing a system- background info.

I did a lot
of looking around (although I would not claim it to be exhaustive
-ho ho) before
buying the system I did. If you think of the system in four bits;
Manifold, link pipes, front box, back box:

it boiled down to ~200-300 quid for both boxes (pattern, will last about
two-three years) in steel. ~double this for genuine boxes (will last five years
or so) (*minimum expected or guarantee periods), and then there were various quotes
from reasonable to astronomical for stainless systems. The stainless systems
went from only a bit more than OE price for the boxes, to full on one-off
custom jobbies, manifold and all that were in the ~1500 quid range (* or even
more; it just got silly in some cases).

nationwide chain of stainless exhaust fabricators (who usually go for the
slammed hot-hatch, wide wheels, underside neons, tailpipe (etc etc etc
zzzz....) market) declined to even quote for a system, part or whole. They gave
two reasons; 1) The near tubework required is larger than they normally
use on any of the boy-racer systems they specialise in, and 2) The chap I spoke
to candidly revealed that he thought his boxes 'were a bit crap really' and
that the 3.5 straight six would 'probably blow them to bits in no time'. (*
this may have been just the branch I contacted- I have since heard of others
who have had silencers from this chain, but have heard no running reports

Several of
the basic stainless pipes available are made partly or wholly in 400 series
stainless. Typically the pipes will be in 400 series and the boxes in 300
series if there is a mix. On the plus side, 400 series is typically cheaper and
stronger than austenitic stainless steel (300 series), but on the minus side it
will corrode superficially (no big deal) and the material next to the welds
will be harder and more brittle after welding. This last point means that
systems welded in 400 series are a little more susceptible to breakage right
next to welds.

This means
that it is a very good idea indeed to buy a stainless exhaust with a lifetime
guarantee against breakage, especially if the pipes are in 400 series material.
I bought one like this last year for my Land Rover, and it (for the two boxes
(* actually two parts, just one box) in stainless) was cheapish (~170quid
without fitting kit) and has a lifetime guarantee. However, in the small print,
it says the guarantee will only be honoured if the mountings were in good
condition. This isn't surprising, but might be very annoying if a two quid hanger
rubber goes, breaks the exhaust and then the warranty is void.

* addendum; See
picture below-

<img width=509 height=218 src="/tech/exhaust/image024.jpg">

Fig 13. This is
a shot of the 400 series stainless steel pipe on my Landy after just one
winter. (you can also see the infamous A
frame in the background; I have an ongoing struggle with its middle ball-joint,
which is something Im sure other Landy owners can sympathise
with) For scale, the pipe is just over 2 OD (58mm).
This corrosion after such a short time
looks awful, but is in fact pretty harmless. The part of this exhaust that is
actually visible, at the back, is made of 300 series material.
By contrast, a good 300 series stainless
steel will only corrode appreciably in salt spray if the metal is very hot
indeed; Ive seen this for myself, because the 300 series stainless
header pipes on my Moto Guzzi have actually pitted due to mad winter usage some
years ago, but bear in mind they will run at dull red heat at times, so
corrosion can proceed many times faster. The clamp in the picture is 300
series; the brown marks are not corrosion, they are left over from welding. I
did this one in a bit of rush, but improved versions of this clamp design are
now holding the BMW exhaust together.)

You can
tell the difference between 300 and 400 series because a magnet will stick to
400 series, but not 300 series material. Strictly there are dozens of different
grades within each series, not all of which are suitable for making exhausts at
all, so you have to take it on faith that a suitable grade within the series
has been used.

Since I
preferred to have a decent manifold (the old one has leaked in the past, and is
a basically poor effort anyway) this eliminated most of the systems available.

The one-off
systems might be really good, but past experience tells me that to make one
that fits at all is difficult enough, even when there is loads of space (which
there is not on this vehicle). To make one that works well also usually takes
several goes or a lifetime of experience. So a one-off system is likely to be a
bit risky as well as expensive.

The system
I bought came from Fritz's Bits who are down in the west
country. I have spoken with them several times and they have always been
friendly, helpful and knowledgeable. E.g. my system turned up without the rear
box strap, and this was rectified quickly without any drama.

They tell
me they have developed this system (which (*of course) fits E28's too) over a
few years in collaboration with a fabricator who makes a lot exhausts for
exotic cars. From what they tell me, the system I have is certainly heavily
revised from the earlier versions they made (supporting my concerns
re. one-offs). The whole thing (manifold flanges aside)
appears to be in 300 series material, via a mix of TIG and MIG welding.

The weld quality would doubtless be
sniffed at it if these tubes were part of a vacuum physics experiment, but for
a car exhaust they are pretty darned good.

On the
minus side although a standard fitting kit can be used (*with extra clamps,
there wont be enough in one kit), there is no matching fitting kit
available with stainless pipe clamps (four or five are needed) etc, so I shall
be custom fabricating some of those (if a job's worth doing etc) to fit this

manifold looks a flippin' good job; an absolute beauty: given that the optimum
design ( six equal length headers into two) is not
possible without extensive modifications even on a LHD car, the RHD
design is little compromised; basically
there is an unequal length six into two (actually two 3 into 1s) arrangement,
the main discrepancy being a huge loop (round the steering box(* and the engine
mounting)) in the #1 header which comes off separately. All the bends are
smooth and well-radiused, and the collectors are
beautifully formed. Where there is an undressed weld bead on a gas-washed part
of the pipe, it is clear that good care has been taken to avoid a
'dangle-berry' style underbead which would otherwise make for a hot spot.

I am
privileged enough to have also had the opportunity of examining a full titanium
5 into 1 tubular manifold for a current F1 car (a real 'bunch of bananas' style
one) made elsewhere; this was obviously built to a far higher standard, but not
by as much as you might think.

'silencer' boxes are of a revised design to standard; both are the 'absorber'
(i.e. straight through) type rather than the 'baffle' type.
Both the rear box (a little) and the
front box (a lot; it is ~2ft long) are larger than
standard spec (* -addendum- there
is no centre box at all on the new system I fitted&.). Both
have cunning dinks in them to give better clearance from various bits that
stick out underneath. I would guess that the system is variously a little
(boxes) to a lot (manifolds) lighter in weight than the original parts.

I anticipate
that the overall result will be considerably more efficient, and pleasantly
'fruity-sounding' (hopefully without being obtrusive (* it is actually a bit
obtrusive, but the only one of my neighbours who has commented to date says she
quite likes it&..).

The boxes
will fit onto a standard manifold and link pipe set-up, and they are about
600quid the pair- about the same as OE parts. Although buying the boxes, link
pipes and manifolds together is cheaper than separately, by the time UK
carriage is added, the whole lot gives you just enough change to buy a few
gaskets, seal rings etc that you will need out of a grand (ulp!).

This is a LOT of cash, admittedly, but it is
still loads cheaper than any one-off quote I found, and although I will have to
fit it and get various clamps and things separately, I suspect that the end
result will work as well or better than any road-legal custom system I could
have bought, at any price.

It'll be a
couple of weeks (at least) before I've made up the clamps and fitted the system;
I will probably post again when I have done this.


posting; initial reactions;

-just a quick post to give initial reactions on fitting of complete new
stainless exhaust system, including tubular manifold.

-it took a
long time to fit it properly; I decided to make up a load of brackets, clamps
and things in stainless steel, plus getting the old system off took ages. Once
I had everything ready, fitting the pipes was relatively easy, although fitting
the manifold was fiddly, as anticipated.

- basically
the job is a good'un; the new exhaust is a lot lighter in weight [ I could
hardly pick up the old system , it weighs so much; boxes plus link pipes came
off in one lump] and is clearly less restrictive. The new headers are 1
1/ bore, the main pipes 1 7/8. The pipes give a reasonably
subdued, but 'definitely means business' fruity burble. It sounds more TVR that
standard BMW from the inside, and at tickover when you
are behind the car you FEEL the tickover rather than hear it. At first I
worried it was too loud, but a couple of drive-bys with a friend listening
persuaded me it was OK, and wouldn't unduly attract the Law (*only time will

downside is that there is some boom in the cabin, certainly enough to notice. I
think this is most obvious at 50-60mph in top, although it is also there at
lower speeds. At 80mph there is no sign of it- in fact you wouldn't know much
difference between this and a standard pipe from the inside at this speed.

-I was
worried about the possibility of 'chirruping' from the relatively thin headers;
I have had this before, and although it usually subsides with mild steel pipes
(eventually) I have found that with stainless ones it usually does not.
Plus I was concerned that there might be
heat from the manifold, so to address both, I insulated the headers. There is
some noise despite this, but it is only evident at all on more than 1/3rd
throttle, and is never too intrusive. Cruising at motorway speeds you can't
really hear it at all, until you want to accelerate hard.

-the fit of
the pipes was pretty good, with just one place (link pipes to front box) where
there was any straining to get everything lined up, and all the original
mounting points pick up perfectly. However, the whole system probably hangs
about half an inch lower than the original one (* I may yet adjust this).

-the fit of
the manifold is nothing short of miraculous, given the space it goes into, and
that you still have some access, rather than none to the lower manifold nuts; it
really is a tight squeeze in there.

- In the
end, for the manifold, I used brass nuts and stainless washers on 12.9 grade
steel studs, with plenty of copper-ease. After calling four fastener suppliers
to obtain 12mm headed M8x1.25 nuts, I gave up. They are standard equipment on
the BMW manifold (but in steel, and I fancied brass), and you won't find a 13mm
M8 (the ISO standard) on any Honda car or motorbike- they are all 12mm, every
one of them (you don't even get a 13mm wrench in the tool kit- no need).
Despite this, none of these 'professionals' had 'ever heard of a 12mm headed M8
nut'. In the end I did what I should have done in the first place- I milled my
own from larger ones.

- I used
genuine BMW manifold gaskets; these look like they can be put on lots of
different ways, but only one way is the right way. I discovered that one of the
old ones had been put on the wrong way round (another 'professional' job,
incidentally), and this may have contributed to my earlier problems with the
exhaust manifold on 4,5,6. The incorrectly fitted
gasket would almost certainly have made the manifold run hot, and it also made
a weird sound, like it was leaking (which it also was at one point) even when
it wasn't. (* I actually spotted this ages ago, but
didnt twig that it was a problem&doh! You can see the
gasket edges from the top, and it should go head, gasket sealing material,
metal gasket layer, manifold, in that order. I could clearly see that one of
the gaskets had been fitted the other way round when I looked closely, but
didnt realise the effect this might have&.)

performance seems a bit quicker at the top end, with maybe a bit less midrange.
But it is difficult to say for sure. It does sound good (if you like that sort
of thing), though the cabin boom might get wearing if you do a lot of slow
work. For longer runs I don't think it will make any difference, as the car is
not appreciably louder at motorway speeds.

- I shall
submit a tech article at some point on this, as I'm sure anyone fitting this
system would benefit from a little warning about a few things, and the
instructions supplied are a little, erm, concise.


Copyright Bruce Dance 2004.
Please feel free to reproduce all or part of
this document, provided suitable acknowledgement is made.


Post by horsetan » Sun May 09, 2004 10:19 pm

Addition to shopping list:

1 x Fritz Bitz stainless steel manifold set.... *tick*


Post by commander_obvious » Tue May 11, 2004 6:29 am

while i understand that clearance may be necessary...

from what i understand the best manifolds for NA applications are equal length designs.
so why waste money on anything else?



Post by commander_obvious » Tue May 11, 2004 6:35 am

manifold looks a flippin' good job; an absolute beauty: given that the optimum
design ( six equal length headers into two) is not
possible without extensive modifications even on a LHD car
ok, i just saw that you noted that but i saw a header by veilside that looked to be an equal length design. the way they do it is basically to throw in extra tubing to the pieces that hook up to the 4-6 cylinders.

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Post by Brucey » Wed May 12, 2004 6:36 pm

-maybe I should rephrase that comment; you can get and fit an equal branch length manifold of the type you describe (and I think there is a nice picture of one currently next to Josecoy's post on spark plug wires) to a LHD car: but you probably either don't need it or won't get the best out of it without extensive modifications.

First thing is, do you need it? The standard Euro 635CSi has about 220BHP, which is ~63bhp/litre. Standard Federal spec is well short (over 35bhp...) of this. A realistic target for a na car with standard(ish) fuelling, mild head work, and a road-biased cam is probably 250bhp, which is still 'only' ~72bhp/litre. [If anyone is genuinely running a lot more than this on the road from a 12V motor, without compromising driveability at all, please let us all know how; I'm sure it would be a very popular upgrade.] Even at this specific power output, the gains to be had from fitting an equal branch length manifold over one that is simply less restrictive are likely to be small.

Over this sort of power output, maybe its a better idea; still not exactly vital though; with a system of the type I have, I understand it is possible to get near M6 levels of power without making the car a complete nightmare on the road.

An equal branch length manifold may be a right so-and-so to fit; for example, the one depicted in Josecoy's post appears to have loops that come very close to the block which will obstruct access to the lower nuts.

Also note that an equal branch length manifold will throw heat out into the engine bay like crazy; way worse than a standard manifold, (or an unequal length version) and if this heat gets into the intake system you'll get losses, not gains in power.

The real problem for me was that (and I did try to stress this in my posts) my car is RHD. I tried to find the best manifold I could at a reasonable price, and I didn't find an equal branch length one available to fit a RHD car; with the steering and brake master cylinder in there, there simply does not seem to be enough room. I think I could have had one custom made, but it would have raised some major (i.e. unacceptable) difficulties, like having to alter the intake system, maybe restricted access to the spark plugs, or having to grow a third tiny hand on the end of a spindly extra limb in order to be able to fit it....

If anyone knows of an equal branch length manifold that will fit a RHD car, without serious shortcomings, I'm sure others who visit this forum from my side of the big pond would love to hear about it.

As it is, the manifold and exhaust system I have just fitted will not give me a big power hike by themselves, but then that wasn't entirely the point: I replaced a load of stuff that was both inherently problematic and knackered anyway with a system that should last well, improve reliability, and allow plenty of potential for tuning in the future should I desire to do it.



Post by sohlman » Sun May 16, 2004 4:02 pm

I've just herd the system. At first i though Bruceys car had an exhaust blow, then he reved it and it sounds more like a V8 then a flat six. The exhaust looks the business and i have added it t my shopping list. It sounds dirty and thats a good thing in my book.

Great article Bruce


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Post by Brucey » Wed Dec 15, 2004 7:09 pm

Running report:

After about eight months and ~4000 miles there is little to report really. The exhaust and manifold have not needed to be fiddled with at all; after carefull fitting, it has all just worked, and worked well.

As predicted the fuelling has been changed a bit by the pipe, so there has been much fiddling with AFM bypass and TPS settings. I shan't go into details here (another tech article planned) but with various adjustments of these, you can get BIG gobs of low down torque at a price- the fuel consumption goes eye-wateringly, wallet-cripplingly bad- up to 25% worse than normal- and you wouldn't notice that much from the drivers seat. On one particularly poor trial adjustment I only got about 190 miles out of a tankful.... I wonder how many 6ers are set up like this all the time?

I digress: The absorber baffles have not got noticably noisier (a problem on some systems of this type), and I've had no clunks or rattles.

Power is very adequate, thank-you....

Initially I was a bit concerned about the amount of sound outside the car, but I needn't have worried- it isn't too loud, just very nicely throaty. Inside, there is cabin boom at some speeds, but it isn't at all bad.

The noise isn't isn't like other straight-six exhaust notes; it sounds kind of funky and offbeat, not quite so smooth and civilised. Maybe not so 'sanitised' is a better word. Maybe its the unequal length headers. Anyhow, I like it. I like it a lot....

I can't deny I throughly enjoy driving along with the windows open, and every now and then I cannot resist a modest prod on the throttle, just to hear that gorgeous sound. In fact today (midwinter) I was doing exactly this, with the heater on full blast. I might grow up too, one day....

Pretty much everybody who hears it running likes the sound, and several times I have received unsolicited comments, ranging from James' in the post above, to;

'that sounds ****in' luvverly mate......'

-just the other day.

If I ever get a second 6er, one of these pipes is on the shopping list, no question.



Post by UKDaveJ » Fri Dec 17, 2004 5:48 pm

Thats quite a recommendation there mate!

pleased you like it so much.

Dave 8)

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Running report addendum;

Post by Brucey » Thu Jan 06, 2005 8:32 pm

As you can tell I am quite happy with this system, but if I were to be critical of it;

It will be a little boomy in the cabin for some tastes.

The manifold does not have equal branch lengths.

The manifold does not match the cylinder head ports perfectly.

The last of these may be mitigated by careful blending of the ports, but this in turn will make subsequent re-fitment of the original manifold problematic. I have a small step in the exhaust at this point and this may affect the efficiency and fuel consumption of the engine slightly.

Although an otherwise standard engine like mine isn?t likely to be especially sensitive to tuned lengths in the exhaust, this will change if a longer duration cam is installed or other tuning is carried out, at which point a properly designed equal branch length manifold would be a better solution.

Although I didn?t locate a source for an off-the-peg item (maybe there is one and I just didn?t find it??), I believe it should be possible to design and make an equal branch length manifold for a RHD car, albeit that it would almost certainly have marginal clearance, and be a pain to fit. Also, since some of the pipes would have to go up before they went down, this would probably necessitate some major changes to the heat shielding arrangements for the AFM etc.

I reckon if ten or more UK owners were to go down this route we could get a reasonable price on such a manifold even from a custom fabrication shop. If anyone is keen please contact me or start a new thread.


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Post by Brucey » Fri Sep 16, 2011 9:03 am


for some reason the picture links seem to be broken above- is this just me?

Also; I have made sounds recordings of the exhaust note for those who are interested




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Post by wattsmonkey » Fri Sep 16, 2011 1:34 pm

This is the article which made me get one of these systems! Thanks Brucey, I must have read and re-read it ten times before purchase.

I LOVE it, although it does encourage childish driving! Boom is noticable at trundling-through-built-up-areas speeds, say 1,500 rpm, but the noise above that is wonderful!

Thanks again,

"Most of it necessary; all of it enjoyable[!]" LJKS
'84 635CSi, dogleg fun


Will FRITZ'S BITS exhaust manifold/headers fit US SPEC 88 M6

Post by M6SCOTT » Sat Oct 15, 2011 10:05 pm

Will the exhaust manifold / headers made by FRITZ'S BITS fit my 1988 US SPEC E24 M6 ? Will they fit without a great deal of modification and what can I expect in performance gain ? The exhaust manifold / headers will be running into a new OEM BMW exhaust using the Frank Fahey track " X " pipe with no cats !


Post by sohlman » Thu Oct 20, 2011 3:26 pm

The system by Fritz is for RHD cars as there was not a system available for these cars. For a LHD system that does not require the awkward bends around the steering box there would be better manifold systems available and there would appear to be more options available in the US with exhaust then what is available over here in Blighty.

I hope this helps


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Post by Brucey » Thu Oct 20, 2011 9:13 pm

re the M6 headers- I'd vote for a set of BMW OE LHD M635 headers; they spent a fortune developing these and as James says the RHD ones are likely compromised because of the steering box....




Post by Griffter » Thu Apr 19, 2012 8:44 pm

Fantastic info thanks Brucey. Have you (or others with the system on the m30) ever had a noise test? I'd be very interested to know the db noise level measured please.

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Post by Brucey » Fri Apr 20, 2012 8:39 pm

maybe Fritz's know?

100db may be a bit touch and go....



Post by Griffter » Tue Apr 24, 2012 7:55 am

Fritz say 91-93dB


Post by sohlman » Tue Apr 24, 2012 11:50 am

I tested mine using my iphone App.

measured at idle from recollection my car was delivering around 80db 10cm from the exhaust tip at iddle. This is with a Frits manifold and standard exhaust system with no stuffing in it due to a flamming exhaust down to a faulty ECU some 5 years ago.

By contrast i have a track car which has a scorpian system and a standard BMW manifold and this was measured at Three quaters max revs (4500) was measured between 87 - 89DB 1 meter from the exhaust depending on the circuit.

I would say the track car is similar noise wise to Brucy's car. Brucey can comment on that as he has been out in the track car and hear it circuit side at full chat.


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RHD Headers

Post by peterpilot » Sat May 26, 2012 7:22 pm

Just in case you gents missed my recent post on my RHD headers I made up. About 430 mm to the junction and works a treat.
IMG_4821.JPG (25.22 KiB) Viewed 18304 times
IMG_4830.JPG (24.67 KiB) Viewed 18304 times
IMG_4823.JPG (23.36 KiB) Viewed 18304 times
1981 635 CSI Euro Manual
1985 635 CSI Euro Manual
1998 540 I Steptronic
2004 K1200 RS

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RHD Headers

Post by peterpilot » Sat May 26, 2012 7:36 pm

Here are a couple of pics of the exhaust fitted. One Pic is without the heat shield and the other is with the heat shield.
IMG_4839.JPG (27.96 KiB) Viewed 18300 times
IMG_5089.JPG (26.64 KiB) Viewed 18300 times
1981 635 CSI Euro Manual
1985 635 CSI Euro Manual
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2004 K1200 RS

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Exhaust and RHD Headers

Post by peterpilot » Thu May 31, 2012 10:16 pm

I know this original post is pretty old, but the RHD setup is not at all impossible to have equal length headers.
For those who are interested, and who may have missed it, check out my post in "My Project". (RHD Headers)
1981 635 CSI Euro Manual
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Replacing Exhaust

Post by peterpilot » Thu May 31, 2012 10:20 pm

I know this original post is pretty old, but the RHD setup is not at all impossible to have equal length headers.
For those who are interested, and who may have missed it, check out my post in "My Project". (RHD Headers)
1981 635 CSI Euro Manual
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Post by ron » Fri Jun 01, 2012 5:58 am

Have you thought of going into production with the manifold (headers)?
They are ALWAYS rustier than you thought!!!!!!
'85 M #228
'87 M #367
'88 High line.
'80 735i
'10 X5

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RHD Headers

Post by peterpilot » Fri Jun 01, 2012 7:59 am

Hi Ron,
Yes it seems I should make up at least 5 sets as your countrymen are definitely showing some interest as well as here at home.
I have a daughter in London. I'm sure she could be my agent.

With work prospects as they are too, there is a good possibility I could bring them over myself on a fairly regular basis.

The next one I do, I will make an accurate costing; The flange cutting, the mandrel pipe bends and of course the labour. I'm sure I can come close to the Fritz price.
It's probably better for you guys over there to decide on having them coated in whatever you please.

If one goes into the theories of stainless steel and its heat dissipation properties, it is not ideal for headers. Having them polished like chrome,in my opinion, is a waste as you cannot see them, what with the angle of the engine and of course the need to have a good heat shield. (I use a piece of 2mm brushed stainless, and on top of that, spaced with 2mm washers, a 2mm piece of brushed Aluminium. (When I'm answering you guys to the west, I will say Aluminum! heh heh). With my '81, I managed to adapt the original ally cast ones, so it looks pretty standard from above.

As mine are 38 dia 2mm mild steel pipes up to the 3 into 1 collector, and a lower grade (forget the spec now, 312??) 50mm dia. 1.5 mm SS thereafter, (all the way to the tail pipes), I have had mine thermally metal sprayed purely to keep them looking clean. This is expensive though (cost me in your terms 150 quid for the two), but it lasts forever and remains a white-ish silver as in the pics with no heat discoloration.
The set on my '81 6 has just a high grade of heat resistant paint and it still looks/feels fine after more than a year.

Fitting is not a real sweat. I have a spare engine on a stand in my garage, and was able to build these on that and have the car right there to check the fit. So it is well clear of everything.
On my '85, I had to bend the metal power steering pipes slightly down ( 5 mm) to make sure of a good clearance, and when I fitted my '81 set, I made a 3mm washer spacer, slotted the hole and slid it under the engine mount as it was a little close to the steering box. However, the future ones will be well clear of the standard bits.
During manufacture and to finally fit both of these, all I had to do was lift the rt side of the engine by placing the jack where the rt mount meets the engine. By loosening the gearbox rubber mounting nut/s, the left engine rubber mounting nuts (slightly), the rt engine rubber mount bottom nut, but removing completely the upper nut, the engine must be lifted, rt side by about 2 inches (50 to 60mm) and with a little patients they go in with hardly any foul language required.
The manifold studs must just be long enough for the job, as if they are too long, it will not help getting them into position.
I had to take all of mine out and clean up the treads in the head, 1 inch deep. I slotted the top of the studs and screwed them back in with a screw driver with some mild locktite.
All the manifold nuts are accessable and for final tightening, some can be reached from under the car.
I use three bolt flanges with captive nuts welded in position so that they can always be ground off and replaced. I have used SS Cap screws.
The advantage here is that the exhaust can be removed very easily and replaced with ease, with only two new gaskets required.

Ok, the sound?? With this equal length system, I have to say that in my opinion, it does not sound anything like the original 6 with the cast iron system. To me it sounds more like a singing 3 series. A much smoother note which starts to howl from 4000 upwards, depending how "free" the flow is. A deep boom at lower rpm 1500 - 2500.
We had an E30 333i in this country in the late 80's, and the sound reminds me of this car.
I would imagine the Fritz system to possibly sound strange, what with that no 1 pipe diversion. (Maybe not?)
Anyway, enough waffling?
I'll get to it. Should definitely have some later in the year or in the new year.
Last edited by peterpilot on Fri Jun 01, 2012 8:29 am, edited 1 time in total.
1981 635 CSI Euro Manual
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2004 K1200 RS

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Post by ron » Fri Jun 01, 2012 8:17 am

Hi Peter, Thankyou for the very in-depth reply. Looking forward to hearing from you closer to the "production " date.

Regds. Ron.
They are ALWAYS rustier than you thought!!!!!!
'85 M #228
'87 M #367
'88 High line.
'80 735i
'10 X5

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