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M90 v M30 - again!

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Mark E
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Posts: 365
Joined: Wed Aug 24, 2005 10:33 pm
Location: South Australia

M90 v M30 - again!

Post by Mark E » Wed Aug 17, 2016 5:49 am

Hello group... long time no post, and apologies for dragging this topic up again.

The time has finally come to refresh / rebuild the engine in my 1982 Euro 635 with the famous/infamous M90 (with early Motronic).

My concern has always been finding someone here in little old Adelaide who knows about these engines and what you can and can't do with them, as I'm hoping to build a few extra 'horses' into the old girl.

I contacted a local BMW "specialist" who I know personally and is a previous E24 owner. I thought he had some idea, but after explaining what I had and what I wanted to do, he came back to me saying there is no such thing as a M90! Grrrrr!

Anyway, I need to source as much data and information about the M90... engine spec's; differences to the M30; performance upgrade options etc etc... anything I can use to educate this individual (& myself) about the M90.

If Bert K is still on this forum (who I thought was rebuilding his M90) - any issues / tricks / shortcuts / pitfalls you discovered?

For any of the Aussie guys reading this... I obviously have very little confidence in this individual being able to achieve what I'm after, so if you know of any really good engine builders who understand the M90 and aren't 2 million miles away from Adelaide - please let me know.

Thanks so much in advance...
Mark E
'82 635csi
In the Land Downunder

GazM3
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Re: M90 v M30 - again!

Post by GazM3 » Wed Aug 17, 2016 6:18 am

Sounds like a good plan. I dont know of any engine guys in SA. They all seem to play with holdens there. Perhaps try willall racing? (spelling).

There is plenty you can do with the old m90. Items to consider.

Is it a Daily driver, cruiser, or Sat Night special?
Are you intending to race/trackday?
Do you want good economy?
Are you going to run the OEM manifold / weber carbs / ITB
What sort of power do you want, Factory 200bhp (ish), warm 240bhp, hotter, 300bhp, crazy 400bhp?
Is the rest of the car up to installing an upgraded engine. Things like suspension, clutch, fuel system, body (suspension mounting points) etc etc

And of course what sort of budget do you have in mind.

I can understand doing your due dilligance on who to get to build your engine as there are horses for corses. Some well known shops really have no idea. For example, I picked up a 2002 with Stroker (2307cc) M10 over a year ago. The chap who built the expensive engine intalled it with only 8.5:1 compression, and used a head gasket that was for a smaller bore factory engine, had a distributor that was stuffed, had way too small carbs on it, but with a bigish 307deg camshaft. Specs were over the place. It made a lousy 85hp @ rear wheels which is barely more than the factory 1990cc engine. Lots of money spent, lots of name brand parts, and in critical items such as rockers used no name ones!!!.
BMW’s
74 2002 2.3ltr
84 E24 M635csi
94 E34 540i/6 SC
97 E36 M3 euro SC U/C

OTHERS
02 Landrover D2 td5
08 Holden Ute 6.0
11 Audi S5

Mark E
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Joined: Wed Aug 24, 2005 10:33 pm
Location: South Australia

Re: M90 v M30 - again!

Post by Mark E » Wed Aug 17, 2016 7:12 am

Thanks GazM3... all good points.

I do know of the guys at Willall Racing... but not sure of their classic BMW knowledge. Might call & discuss.

It is a weekend cruiser that's had everything underneath done including suspension, rubbers, brakes & drive shafts. Some existing mods including a big bore throttle body & hi-flow exhaust have got me about 230bhp (dyno'd) currently, but would like to push it into the high 200's maybe low 300's.

It's done over 200,000 miles so the bottom end particularly needs some attention if I'm going to try an draw that sort of bhp.

Economy is not a real issue as I was thinking of even going 'old school' and hanging some triple Webers off it, as it currently runs early Motronic and there's not much you can do with that.

But the biggest issue the apparent uniqueness of the M90 with its over-square block from the M88 and the early single cam M30 head and what can be done in the way of crankshaft upgrades, cam grinds, head work etc.

All and any info greatly appreciated.
Mark E
'82 635csi
In the Land Downunder

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Brucey
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Re: M90 v M30 - again!

Post by Brucey » Wed Aug 17, 2016 7:54 am

the M90 is a variant of the M30. Nearly all the tuning methods that are used on other (motronic) M30s are applicable to M90 too.

The motronic engine you have was used between mid 1980 and 5/82 and it shares bore and stroke dimensions with the earlier L-jet fuelled M90. The later M30B34 engine (5/82 to 6/87) has a slightly higher CR (in Euro form), a smaller bore and a longer stroke. BMW moved to this bore/stroke because they felt the heads/head gaskets weren't 100% reliable with the earlier larger bore, (but it didn't stop them from using the same bore and stroke in the M88 engine).

So basically almost any M30 cylinder head work (NB anything that works on an M10 is also applicable in terms of porting) and any M30 camshaft can be made to work in your engine; the only snag is that the distributor drive on the end of the camshaft needs to match your setup (if you choose to use a standard distributor); there are three styles, for L-jet, for early motronic ~80-~84, and later motronic ~84 onwards. There are various adaptations possible between these versions but any easy solution is to use the distributor that matches the cam you have.

Like Gaz says there are plenty of options for tuning, e.g.

-CR increase (head skim), adjustable cam sprocket, reworked cylinder head/inlet manifold, revised camshaft, decent exhaust manifold etc can net another 50-80 bhp or so and this may be within the scope of the original ECU and fuelling. Past that you will definitely need a remap (difficult now with early ECUs) or revised management. [NB In truth you will benefit from that anyway, regardless of the state of tune.]

- at the other extreme you could build a stroked motor with forced induction and stand alone management.

It all depends on how deep your wallet is, really. You would have to figure that expecting a 35 year-old motor's bottom end to survive (when the motor is tuned for more power) is perhaps a bit of a stretch; this being the case, you may end up concluding that you may as well buy another engine outright (which could come from anywhere) rather than refurb the extant one. If refurbing the extant bottom end, do remember that there are numerous small differences in the M30 engine depending on when it was built; the sump varies, the oil pump varies (and needs to be matched to the sump), amongst other things. The RH engine mounts vary too (in where they attach to the block; not all M30 blocks will accept all RH engine mounts). In addition the cylinder head castings vary (eg in how thick the port walls are, and how big the ports themselves are) as do the inlet manifolds.

Regarding the sump; your car presumably was built pre 5/82. This means it has a different chassis from the later (post 5/82) cars, and the crossmember is different. I can say from personal experience that your motor won't fit a later chassis because the sump fouls the crossmember but I don't know if a later motor/sump would fit your chassis or not.

Re the chassis and running gear; the early E24 chassis is basically the same as an E12 and also shares many parts with the E3. It is somewhat more frisky on the limit (in good part because the toe setting of the rear wheels is less well controlled in hard cornering); the later (E28-based) chassis had a few significant improvements to both the front and the rear suspension; several owners of early cars have successfully transplanted the later style of rear subframe/trailing arms etc to their chassis, but if you use stiffer swingarm bushes the early back end can be improved at cost of NVH. At the front a later version suspension transplant is both more difficult and arguably pointless; other than availability of parts, there isn't that much to be gained.

The options for upgraded brakes are also chassis-specific; the E12 brakes are pretty good (for that era of car especially) but if you are going to have 250+bhp (and use it) better brakes would be an excellent idea. However IIRC almost no brake setup from another standard BMW will bolt on and give a significant benefit; larger discs from later BMWs will bolt on OK I think, but the caliper mounts will need to be revised accordingly and indeed the brakes may need to be entirely replumbed with most later/alternate styles of caliper. The reason for this is that the E12 models have front calipers that have fittings for a split feed; the front and rear pistons in the front calipers are on different brake circuits, so instead of a diagonal split, the dual circuits work half of the front brake caliper (each side) on one circuit and the other half plus the rear brakes on the other. Unless the front calipers are a) four pots and b) tapped for this split you can't retain this style of dual circuit layout.

So there is much to consider; you need to ask yourself what you really want and how much time and money you are prepared to chuck at it.

[edit; much of the above was drafted before your post above, apologies if I've covered old ground there.]

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Mark E
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Location: South Australia

Re: M90 v M30 - again!

Post by Mark E » Wed Aug 17, 2016 12:54 pm

Thanks Brucey... extensively detailed, informative and right on target as always.

Mine is a January '82 build and I am keen to keep the existing motor in the car, so a transplant is not on the radar.

And chassis, suspension and brakes are all pretty well sorted for the moment too.

In summary... I'm needing a rebuild of the bottom end. So on my potential shopping list is: totally refurbished bottom end with possible re-bore; new lightweight pistons to match; maybe an 86mm crank - all balanced; ported & polished head (not necessarily bigger valves); cam grind to match. If that's achievable within the scope of the existing ECU - then great. Otherwise I would consider losing the AFM & Motronic and just throwing on a set of triple side-draft Webers(?) Hand made exhaust headers are also part of the plan.

So, to those like Brucey et al who have way more technical & engineering knowledge than I, I hope that all sounds do-able.

If I'm leading myself up the garden path, then please let me know. :D
Mark E
'82 635csi
In the Land Downunder

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Brucey
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Re: M90 v M30 - again!

Post by Brucey » Wed Aug 17, 2016 1:44 pm

I don't know all the answers (not by a long chalk) but I have a few comments;

- if you stroke the motor it may take a lot of detective work to come up with a standard set of BMW pistons and rods that will work OK. Maybe someone knows of something that will work? Otherwise you will have to buy custom/specialist parts.

- re regrinding cams: The cam lift from a stock cam (or any cam made using one or a stock blank) is limited by the fact that the rockers are designed to work with a certain base circle diameter, and the lobe height is constrained by the fact that the lobes for cylinders 5 and 6 have to pass through the bearing aperture for the second to last cam bearing. IIRC this limits valve lift to around 10mm.
The standard way around this is to grind the base circle smaller so that you can get more lift without having bigger cam lobes. The rocker is then modified (e.g. by adding an oversized eccentric) so that it still works OK. This seems to be OK but I think the rocker geometry isn't perfect any more and furthermore it is essential that the exact nature of the rockers that should be fitted is known beforehand; the valve lift curve is perfectly symmetric with a stock cam, but the cam lobes are nothing like symmetric; the cam is ground for a particular rocker geometry and changing that will spoil the lift curve.

- you can fit a longer duration camshaft (with more overlap) and this will make the top end wake up a bit. However there are problems because the bottom end torque will be lost and the idle quality will be affected too. This will give a lumpy idle on both batch fired single-body plenum injection, i.e. motronic (because the charge gets shunted around in the plenum) as well as on carbs.

-increasing the CR will prop up the bottom end torque even with a longer duration cam.

- if you wish to avoid a lumpy idle with a longer duration cam, this can be done, using fully sequential injection, or by using TBs, keeping the original injection.

- If you replace the injector rail with a later version that uses a 3.0bar FPR (in place of the 2.5 bar one) then you can have enough spare capacity in the fuel injectors for about 100bhp more than standard.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

GazM3
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Re: M90 v M30 - again!

Post by GazM3 » Wed Aug 17, 2016 8:50 pm

What an exciting upgrade. Webers sound like a good cost effective plan. They will sound great and be very tuneable. They may not have the drivability through the rev-range as injection would have.

Compression is king when it comes to making good HP and making the best bang per unit of fuel. It's all got to work together with the cam and valve train. Compression has the smoothing effect on bigger cams. There would be similar drivability with a 10:1 comp engine and a moderate cam as there would be with a 11.5:1comp and a much bigger cam and u have more everywhere.

It should be relatively simple to make a 330+bhp streetable m90 that will pull the e24 really hard. If you change your Pistons well it will make it easy to use the 86mm crank. I'd consider getting a m30b35 from the e34 then you can build the engine on the side to minimise the downtime. It comes with the 86mm crank and can be made as period as u want

My guy I use here in Victoria is not for everyone. The advantage is he is local to me, very low cost, and a brilliant engine builder. There are plenty of downsides as communication on occasion is non existent, things go along at a pretty slow rate as he does it part time and depending on what else is going on for him. If you are a local it's probably not so bad but if you are from out of town it's probably not ideal.

Also while u are browsing the net have a look at racehead engineering in Sydney. They have custom Itb setups and his m20b29 that makes 300rwhp is an orsome engine in his e21. Imagine what could be done with a hottie m30b37 with similar spec.
BMW’s
74 2002 2.3ltr
84 E24 M635csi
94 E34 540i/6 SC
97 E36 M3 euro SC U/C

OTHERS
02 Landrover D2 td5
08 Holden Ute 6.0
11 Audi S5

davem6
Posts: 83
Joined: Thu Aug 13, 2015 1:06 am

Re: M90 v M30 - again!

Post by davem6 » Sat Aug 20, 2016 8:27 am

Hi Mark
I bought JE Pistons from Steve Nelson at Topend Performance in the US. He knows BMW engines and will custom make any piston you want, price was very reasonable, they also sell Cometic gaskets and head stud kits, this will keep it all bolted down tight and should deal with the gasket issues Brucey raised.

Follow Brucey's advice regarding cams, don't get sucked in to going too big with the cam if you want reasonable road manners. The loss of drivability will outweigh the power gain.

Personally I would not go with carbs, Injection will give you better drivability. Go standalone and lose the AFM. If you have the cash go with ITBs. Talk to Rama at Race Head Engineering. He makes really nice ITBs in a range of sizes but I don't think he has manifolds for M30s yet but he will be able to get something custom made for you.

Another advantage of the injection is you can lose the distributor too, run wasted spark with a 6 post coil and that will get you over the issue of the the distributor drive on the front of the cam. Fit an E34 crank wheel with the 60/2 tooth arrangement and mount the engine speed sensor on the front, this will do away the old sensors on the flywheel.

This approach will give you all modern electronics and retain the classic look.

Good luck, sounds like fun.
Dave
1987 M6
NSW Australia

Markos
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Joined: Mon Jun 15, 2015 8:28 pm
Location: Seattle, WA

Re: M90 v M30 - again!

Post by Markos » Tue Feb 13, 2018 6:05 pm

Hi Mark,

I just dug this up while searching for something. Where did you end up with your M90?
'71 BMW E9

Pasocb
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Location: Paso Robles CA

Re: M90 v M30 - again!

Post by Pasocb » Sun Feb 25, 2018 1:21 pm

I am with Marcos. Nice write up. Would really like to hear more on this also.
1980 633 Polaris (Passed on to family member)
1980 633 Alpine (Passed on to family member)
1981 635 Hennarot (Project 1)
1980 635 Polaris (Project 2)

Drew
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Location: Hiding in the garage, South Bucks, England

Re: M90 v M30 - again!

Post by Drew » Tue Mar 06, 2018 11:35 am

as a word of caution with any head work, make sure you get the correct M90 head gasket as the M30 one is not correct. A 1982 M90 motronic 635CSi came to me as a breaker, and (I think) the reason it was a breaker was overheating issues caused as a garage had fitted the M30 h-gasket to the M90 engine. Engine was in terrible shape with oil sludge in the head and signs of overheating, which may have been related.

and as a shameless plug, I have an M90 motronic ECU (Bosch 002 ECU) going spare. pm me if interested

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