Exhausts and Headers

[BimmerToad]

For the same cross sectional area, a single pipe will flow better than two pipes, since fluid dynamics assumes the flow at the surface of a pipe is almost zero due to a boundary layer.

1 2.5" single pipe = less surface than 2 1.75" pipes, but comparable flow cross sections. Less cost too, though 2 pipes looks cooler than a single pipe

[SA E30]

How much power do you have and what is the cars purpose? There is no need to reinvent the wheel. Why not just buy a header that is appropriate and put an exhaust on that will either meet your autox noise requirement or pass emissions, or both...

It's not so much the power, I'm just asking in general... and the reason that we dont just buy a header is the RHD headers that are available, are to small for my ports, hence why I'm looking into a bigger one.

Power I dont really know anymore, had it on 4dyno's and got 4 completely different readings... from 140kw to 162kw, wheel KW .

All I know is in a straight line it's strong enough to run a E36 3.0lt Euro M3 about a fender ahead till the end of 3rd, on a 3.63:1 Diff.


Ok, but I would think that putting an x pipe into the exhaust would also reduce the scavenging affect, as the back pressure is equalised ? along the 2 pipes...

I dont really care which looks cooler, as u can always just run a twin tip, and most ppl wont be the wiser, I'm really curious how a single pipe would affect performance.

[e30polak]

looks like u guys have this covered, but i'll put in my two cents and experience, basic rule of thumb i've stuck to is the bigger u go in exhaust, the more back pressure u lose=torque loss, but gaining freer flow=more top end hp, once u go too big u don't gain any power and u car runs like SHIT! i swapped and s52 into my e30 and wanted to gain the most possible power with all bolt-ons before doing heavy internal upgrades or any forced induction...the stock exhaust on the s52 m3 comes with 2: 2 1/4" pipes going all the way from the header back, so because of a lack of room, i'm running a custom 6-1 turbo manifold as my header, which has a 3" opening, when we first got the car started with only the header on, the car sounded like a dragster and didn't perform as great as expected it to...the answer was the exhaust, i was losing WWWWAAAAAAAYYYYYY too much back pressure, keeping no gas velocity in the system, essentially running way too lean....i opted to match up a 3" exhaust pipe all the way back, with a 3" vibrant high flow cat, a 3" borla hollow race muffler as a resonator, and finally a 3" vibrant street power turbo muffler, results were amazing, gained lots of back pressure, throttle response, etc....granted most people doing the swap will run 1: 2.5" pipe straight to the muffler, i felt that would create excess back pressure, and with the turbo manifold, i wanted to be able just to chop the exhaust later and add a turbo...so from my experience going bigger in exhaust helps, but my car is quite loud...yet it has the sexiest exhaust note i have ever heard:woowoo: