Track exhaust on m52'd e30

[ThomasGTT]

Didn't knew whether to post this in motorsport or the m50/m52 section, but i could use some advice on an exhaust setup.

I run a track dedicated e30 with an m52 and e36 m3 manifold (LHD car). The manifold is welded up to a standard e30 type 1 midsection and back box, but it hangs quite low and it is leaking a lot. So i am looking for a new setup that connects to the m3 manifold. What should i do?

It is a track only car, so no MOT issues regarding the cat. But don't know whether to decat or to use a race cat. Any decat experience with the m52? Also the question is if i should use a single pipe (2.5"?) or a dual pipe system. The car needs to pass noise regulations at Zandvoort, Zolder, Spa (92dB at 4500 rpm i believe), so cant be extremely loud.

Any advice? I live in the Netherlands and so does the car, so tips on local exhaust shops are kinda pointless.

Thanks in advance!

[ThomasGTT]

Anyone?

[DanThe]

I use an aftermarket E30 M3 system on my M52 car, twin 50mm tube, I wouldnt advise anything less tbh, certainly not 2.5 inch single pipe.
It has only a backbox, no middle silencer, not too loud, I do have a reading from testing equipment somewhere, will have a look.
Crap pic, but its the only one I have

[ThomasGTT]

Thanks for the picture!. You know what kind of aftermarket exhaust this is?

So taking out the cat is no problem (with regard to power)? Did you use a x-pipe?

[DanThe]

Im not sure what the make is, there are no markings on it, it has an x pipe at the front just behind the joint to frontpipes, unless you have emissions rules to stick to theres no point using a cat, I seem to remember it being around 87db when ive had it tested at track days

[Neilios]

What is the advantage of the X pipe, can a system be made to run well without one?

[Mikey_Boy]

You need the X pipe to fill in the torque curve otherwise the car will be as flat as a fart until about 4500rpm...

[Neilios]

Thanks. Why is this?

[MillRat]

I am very late to this post I know, and please ignore this if you have already found the solution.

Anyway, basically the X-pipe allows the gases travelling through one pipe to create a pressure difference behind it (or a vacuum) and helps to draw any unburnt or standing gas from the other pipe with it. Without this, the gases escaping from the opening exhaust valve will see a wall of high pressure (the gases from the previous exhaust cycle which have not yet escaped the pipe) which will significantly slow down the gas passing from the cylinder into the exhaust. With the X-pipe in place, the gases escaping from the cylinder see a much lower pressure zone instead which will help to scavenge the burnt gas from the cylinder. These gases (which will have higher velocities as a result) will then create the same conditions for the other pipe.

Obviously this set-up requires that the runners feeding the 2 pipes are alternated according to the firing order of the engine (not normally a problem on an E30 as the factory exhaust manifolds already takes this into account - that is the front 3 cylinders on an M20 or M50, etc. feed one pipe and the back 3 the other pipe).

It is interesting to note that this effect actually produces a significant benefit and this low pressure "scavenging" effect that is produced running the X-pipe is actually beneficial over a very short exhaust setup (extractors directly to atmosphere for example) as the pressure in the exhaust should be lower that atmosphere. The trick is to find a runner/exhaust length that best accelerates these gas velocities, but not too long to not allow the gases to escape the pipes quickly enough and thus start to create some back pressure further along in the pipe.