"High Flow" Custom Exhaust suggestions...

[16v of E30]

Im thinking I want to get a bit more power out of my m42...I used to have a 16v Vdub that I pretty much straight piped, and it added a lot more pickup/torque thru the lower rpms.  Im wondering if anyone here has experienced a "high-flow" exhaust system on their car, and how the performance was affected.  I already have a K&N cold air intake so shes inhaling pretty well...i just want to blow it out the back with less restriction.

Not knowing jack s*%t about the m42 engine yet, how much backpressure is required to not mess up the engine?

I had a 2-1 DP into a resonator then 2.5" pipe back to a Flowmax muffler.  It was way louder and way more powerful as stated above.

Can some of you give me an example of your custom exhaust systems, as I know a great welder/fabricator..

Thanks
Ryan

[AcSchnitzer318is]

sorry no help for you, but bump as I am interested too.  I am about to switch to magnaflow muffler and have all my piping redone from the header back since I have so many exhaust leaks in the cat back.  

Should I go hi-flow cat or just straight pipe to muffler?  Legality is the only concern not really volume.

[16v of E30]

i had no cat, but where i live (out in the boonies) we dont have to pass aircare.

throw a resonator in there just to give it some tone, otherwise your neighboors will hate you as it gets pretty loud

[DRtothE]

are you telling me nobody on this forum has done the calculations for the back-pressure on the stock M42 engine, and custom fitted fabricated pipes w/ or w/out converters and/or resonators?

[Boyracer]

My custom exhaust + exhaust manifold secondaries:

[E30_318is]

I replaced cat. and stock resonator with Simons Tubex resonaator. 2,5" (lenght ~25")
The rest of the exhaust is stock (not for long).
It only sounds a little raspy when the engine is cold.
1500-4000 rpm sounds almost like stock exhaust.
4000-7000 rmp ( i have a chip) its louder but not 2 lound or like a ricer.

i was suprised how restrictive the stock cat. is, my  m42 revs up much faster now. + i recycled the cat. and got 105 Eur for it :eek:.

And i gained low end torque also.
Im planning to replace the stock muffler with simons free flow muffler.


Sorry for my English

[Boyracer]

I am bit unsure what the required backpressure means? :confused:

I think little bit of back pressure on very low revs might help emissions but on higher revs it is a bad thing that hurts cylinder scavenging. And since my car is destined to spend 99% of time above 3000 rpm on track, minimal backpressure is a good goal.

Current 2 liter BMW E90 320si racers (in used WTCC etc) actually have 2 x 2,5" or 3" pipes coming from the engine. They seem to think that backpressure is not beneficial

[P. Kennedy]

Boyracer:  Who makes the exhaust system you have pictured above?  I doubt that it is available in the U.S. of A., but it sure does look interesting.

[Boyracer]

It's not available anywhere, I made it myself few weeks ago

2" secondaries with 2.5" exhaust. Cat is 3" 200 CPI metallic Catco.

[xwill112x]

ive been told these motors like it being "hard to breathe" and it will hurt it with a real high flowing intake and exhaust...

[Boyracer]

Yeah, right

That's why BMW Motorsport fitted their S42 race engine with veeeery restrictive exhaust system and veeeery poorly flowing carbon fiber intake plenum and individual throttle bodies :rolleyes:

Simple experiment you can do by yourself... Try to breathe trough garden hose while running and see how much faster you are going to be that way :p

[Gray S.]

Yeah, right

That's why BMW Motorsport fitted their S42 race engine with veeeery restrictive exhaust system and veeeery poorly flowing carbon fiber intake plenum and individual throttle bodies :rolleyes:

Simple experiment you can do by yourself... Try to breathe trough garden hose while running and see how much faster you are going to be that way :p

Thats not completely relevant.  Those are race motors designed to live their entire lives in a very high and narrow RPM range.  Straight piping an m42 with a large diameter exhaust will result in huge loss in low end tq (which we already are short on).    For a street car it is really impractical to put something like a 3 inch on an m42.

[EN318isPDX]

Thats not completely relevant.  Those are race motors designed to live their entire lives in a very high and narrow RPM range.  Straight piping an m42 with a large diameter exhaust will result in huge loss in low end tq (which we already are short on).    For a street car it is really impractical to put something like a 3 inch on an m42.

Sounds right to me! I believe i read somewhere that the only restrictive part of our exhaust is the muffler. You can tell we have the best header bmw could have given us! Does anyone know why BMW decided to kink our exhaust just before the muffler? I've seen it on different BMWs besides E30s. The only reason i can guess is for clearance to make it past the frame?

[Boyracer]

Thats not completely relevant.  Those are race motors designed to live their entire lives in a very high and narrow RPM range.  Straight piping an m42 with a large diameter exhaust will result in huge loss in low end tq (which we already are short on).    For a street car it is really impractical to put something like a 3 inch on an m42.

I agree that on low revs little bit of backpressure might be beneficial.

But if your main concern is low rev torque, why bother thinking modifying exhaust at all? Because stock exhaust propably has more backpressure than aftermarket exhausts. You can even get more backpressure simply by putting restrictor to end of muffler

But if you want your car to go faster overall when pushed, backpressure is not good because it really hurts in high revs where small engines like ours make the power.

Novel solution would be exhaust that has variable backpressure depending on revs like E36 328i or Ferrari 550 Maranello etc.

[Gray S.]

Exactly, I'm sure there is a suitable compromise somewhere. 2.25" piping perhaps?  I'm not sure what the ID of the stock exhaust is.