custom exhausts

[jaywood]

How many of you guys have made your own exhausts? I'm thinking about running 2.5's straight.

How much piping did you need? I was thinking 2 four foot straight tubes, and maybe a couple 45 degrees.

Thanks guys/

[33xander33]

It's not much for performance but I straight piped my 325i and it sounds incredible.

[brody]

It's not much for performance but I straight piped my 325i and it sounds incredible.

It's not much for performance, you are right. You will actually lose power unless you retune your car.

[e30trooper]

It's not much for performance, you are right. You will actually lose power unless you retune your car.

You lose low end tq, but gain Topend response. Depending where you live you will get pulled over.

[azael325i]

I just went to the Castros shop and they did a great job. I got a spin tech and love it.

[nando]

You lose low end tq, but gain Topend response. Depending where you live you will get pulled over.

what? You won't lose torque from a single 2.5" pipe, unless the engine is going lean because it needs retuned (which is what broday was getting at).

[brody]

what? You won't lose torque from a single 2.5" pipe, unless the engine is going lean because it needs retuned (which is what broday was getting at).

It doesn't go lean, the power loss come from it going too rich.

[nando]

it could go either way depending on what's going on with your exhaust scavenging.

in my case, the exhaust made the car run 10% leaner because it was scavenging more on the intake stroke.

it could also read rich if you were overscavenging because it would be sucking part of the intake charge out the exhaust, but that's unlikely on an M20.

Hoveringuy's M54 went rich with the euro S50 headers. Maybe it's a MAF thing? going into an untuned part of the MAF transfer curve?

[MonkeyMadness]

Where and how much $$$ ????

i just went to the castros shop and they did a great job. I got a spin tech and love it.

[Killacortes]

what? You won't lose torque from a single 2.5" pipe, unless the engine is going lean because it needs retuned (which is what broday was getting at).

So single gains more low end torque? or does dual have a better gain? I have a NV m50 and its all top end. some low end torque gains would be bueno

[azael325i]

Where and how much $$$ ????

Castro's customs
North Hollywood ca
Ask for chris great guy and prices. He has done just about everything on my car. With the spin tech exhaust system complete was about 400$ which other places wanted 500-600$. It's not to loud too...

[u3b3rg33k]

it could also read rich if you were overscavenging because it would be sucking part of the intake charge out the exhaust, but that's unlikely on an M20.

Wouldn't that cause it to read lean? unburned fuel / air mix has extra O2, not less. just like spark blowout reading lean.

[nando]

So single gains more low end torque? or does dual have a better gain? I have a NV m50 and its all top end. some low end torque gains would be bueno

No, there's not more/less torque from single/dual. there's no difference at all, it's all the same after the X or Y pipe assuming it's not too small.

[StereoInstaller1]

No, there's not more/less torque from single/dual. there's no difference at all, it's all the same after the X or Y pipe assuming it's not too small.

Nope, not true.

Larger tubing has less scavenging at lower RPM, THAT is where the torque loss happens. Larger tubing has less exhaust velocity; how could anyone see it differently? Until the RPMs go up to the point where the tube(s) can properly scavenge, larger tubing WILL decrease torque due to less frequent gas pulses causing slower exhaust velocity. This is not debatable, it is fact.

It is all about the resonant frequency. Smaller tubing has higher Fs, even if it is dual, with or without Xs or Ys.

Smaller tubing also means less cabin drone (that higher Fs again), which is why BMW did it on their higher performance models, not to mention better ground clearance.

IF your goal is street driveability and torque, do dual tubing. If your goal is high RPM performance, go large single tube. Either way, match your exhaust to your useage.

[Killacortes]

Nope, not true.

Larger tubing has less scavenging at lower RPM, THAT is where the torque loss happens. Larger tubing has less exhaust velocity; how could anyone see it differently? Until the RPMs go up to the point where the tube(s) can properly scavenge, larger tubing WILL decrease torque due to less frequent gas pulses causing slower exhaust velocity. This is not debatable, it is fact.

It is all about the resonant frequency. Smaller tubing has higher Fs, even if it is dual, with or without Xs or Ys.

Smaller tubing also means less cabin drone (that higher Fs again), which is why BMW did it on their higher performance models, not to mention better ground clearance.

IF your goal is street driveability and torque, do dual tubing. If your goal is high RPM performance, go large single tube. Either way, match your exhaust to your useage.

street driving and torque is def the goal. The guy who owns exhaust pros here close to where i live recommended dual 2 x pipe with dual in dual out magnaflow muffler. does that seem about right? or is dual 2 inch too small