RHD Exhaust decision down under

[SWAUS6]

The exhaust on my RHD 1986 635 has begun to fall apart, not unexpectedly. Now I have a choice to make about replacement, which is not necessarily straightforward way down here in Western Australia.

I'm not interested in the OEM system, and would like your opinions and sage advice please on whether to A: A complete Fritzbits SS headers and system Ex UK, and have my local exhaust shop fit it; or, B: have my local exhaust shop custom build an SS system from the stock headers back. BTW - the local exhaust shop is familiar with older BMW - doing work for others with E9, E12, E34 etc. My particular questions are: is there much of an advantage with the Fritzbits headers, and is there a problem or performance loss/limit with a custom system from stock headers back? I gather drone can be an issue with custom systems. Also costs and potential hassles (removal of stock headers and fitting FB SS) are likely greater with A. B is potentially the most straightforward and less exxy option.

Have dug my way around in the forum looking for the answers to this without any real success, I did however find Brucey's Fritzbits system fit instructions comprehensive and very informative.

Thanks all.

[GazM3]

The headers do work nice on the m635 but are pretty expensive. Headers are always a good thing to get. Probably the best sounding local exhaust is the Motorsport down under headers and full system. Sounds fantastic. But hard to get.

Otherwise try these.



https://www.ebay.com.au/itm/192211358374

Brand New Bmw M30 RHD E28 E24 535i M535i 528i 635csi Extractors Headers

Geez they look even similar to fritZ bitz. Then get a local rear exhaust system built. Hell I'd even consider offloading mine it's a custom 2" but it's going to be restrictive on a worked over m88/3. Prob ok for a worked m30. If u get one built get a j pipe expansion chamber slotted to The rear muffler. I just had one done on my supercharged e34. Sounds really high end. AMG's are using them and even their turbo v8 sounds so much better than the BMW equivalent

Good luck

[SWAUS6]

Gaz,

Thanks, that's great! They look the goods - and they are down here in Oz - with ceramic coating available.

Also appreciate your tips about the exhaust and the expansion chamber fitment, Sound is critical, has to match its look with the black Schnitzers.

The M30 in mine is pretty cammy, sounds serious at idle and revs like billyo. Not sure if that's stock, one of its four past owners may have fitted an aftermarket cam, its unlikely been rebuilt - done 240,000km (I acquired it at 211,000 7 years ago) - which I don't think is huge travel.

Cheers,

[GazM3]

Cheers.
The J pipe expansion chamber moves the sound up a few octaves in frequency killing the bass. Without it the twin 2.5" on the 540 sounded like real bassy like an American v8. Now it sounds more European.

Good luck getting hold of Motorsport down under. If u can't the eBay headers from NSW look good but will require the drivers engine mount removed. The fritz ones for memory run similar path but have the first pipe removable.

[SWAUS6]

Gaz,

Good, thanks again for the added info. The image of the NSW headers did indeed suggest that the engine mount had to be undone and lifted or likely removed to allow fitment and then replaced. Bruceys explanation of his FRitzBits system fit clearly shows the No 1 pipe removeable. I'll contact the NSW makers.

Motorsport Down under have never answered any of the emails I've sent, which is somewhat offputting.

Cheers

[Brucey]

yes the e-bay manifold is built differently even though it is the same shape, so fitment is going to be different.

In a perfect world I'd have bought a manifold where all the primaries were the same length as the #1 pipe. Unfortunately such things are not easily found to fit RHD cars.

A consequence of the uneven lengths is that the cylinders are not all working equally hard all the time, it seems. The #1 cylinder appears to be working harder than the others under a wide range of normal driving conditions.

A couple of yeas ago I had an intermittent, then persistent, misfire. The #1 plug had failed (but because I am running LPG, didn't look bad ) and in the course of my investigation (moving parts around) I ran the engine with a bad plug in several of the other cylinders. The effect on running quality with a bad plug was far less in (say) cylinder #2 than #1. [I even checked all the compression values etc, all good.]

Other than that I don't have much to add to my original write-up. Except to say that

1) (esp if you have a pre 9/86 LH master cylinder and if you are prepared to re-route the inlet, both of which would make things easier) I think it might well be possible to make an 'up, over and down' style exhaust manifold with equal length long primaries to fit a RHD car. It would be a lot of work though.

2) if you fit a system with an X-pipe, the secondary length from the collector on 123 to the X will usually be different (by about 10" or so) to the length from the collector on 456 to the X. I don't know how much this will affect performance or sound quality but it seems to me that you could make the secondary lengths equal by building a 'staggered X-box' where the entries from each part of the system into the X-box are also staggered. Never seen this done though, so maybe it is a daft idea for some reason....

BTW I'd be interested to see how the J-pipe is done, any pics?

cheers

[GazM3]

The J pipe I guess is best described as a hermholz resonator to cancel out the problematic bass frequencies. Imagine an extra small chamber on top of a round muffler with a small slot cut between the 2 chambers.

In the e34 it's on the rear muffler. Next time I'll do a pic of it when it's jacked up. Kind of hard to explain why it works and I wouldn't have believed it. But it firstly made it a little quieter. Not much but it took the nasty part of the bass out and still kept the crisp part of the bass.

It's always a problem running large dia exhausts for power. It runs now dual 3" from the collectors to the high flow cats then dual 2.5" to the tip. With the big bore pipes it lifts the exhaust down several octaves creating bass due to the low velocity. . The j pipe basically makes it sound at idle like it's got a size or 2 smaller in dia exhaust then u have the big scream at full power.

Probably not so much of an issue on twin 1.75" or 2". I thought of going 2.25" but was probably going to restrict power when hitting over 450bhp. The twin 2.5" won't be an issue to probably 600bhp.

[SWAUS6]

Thanks Brucey and Gaz, some useful ideas there.

I had a look around online for anyone's use of the EMS headers and could find none, do you know of any examples of their use Gaz?

Cheers