[Briancanadiano]

So I read somewhere that installing catless downpipes actually affects performance at low rpm, torque is affected.. High up you get more power but at the bottom of the rpm range you lose torque...
Is this actually true? Or just BS?
Let me know your thoughts! Thanks

[JStang]

Edit: Damn it you caught it!!

[Briancanadiano]

Ya stupid iphone auto correct

[MDORPHN]

Reducing backpressure -- and increasing exhaust velocity -- does not reduce torque on forced induction set-ups.

Neil

[Briancanadiano]

Originally Posted by MDORPHN

Reducing backpressure -- and increasing exhaust velocity -- does not reduce torque on forced induction set-ups.

Neil

Thanks, it's crazy what people make up sometimes, that's what I was thinking to...
Thanks for the clarification.

[tennis_pr0]

I'm not a veteran when it comes to this but I would think reducing back pressure and allowing the turbo to spool faster would increase low end torque. More immediate power no?

[135Pats]

Originally Posted by tennis_pr0

I'm not a veteran when it comes to this but I would think reducing back pressure and allowing the turbo to spool faster would increase low end torque. More immediate power no?

Yes, the efficiency gains in terms of evacuating exhaust gasses helps with spool up.

[SoFlo_BD]

It definitely does not decrease low end torque.. Boost builds alot quicker and since installing catless dps it got rid of any conceivable turbo lag I had

[HeavyMetalRocker]

My tires say, no!

[brewnami]

Catless downpipes, JB4 G5, DCI, map 5 and a little E85 I put 463 pound feet of torque to the wheels. More torque than my 255 pilot super sports can handle through the first 2 1/2 gears. I'd say that article was smoking crack.

[roadkillrob]

It probably just feels that way to some people as adding more power up top but only a bit more down low makes the difference seem more drastic from low rpm to high rpm and that can make the bottom end feel like it has less power even though it doesn't.

[Tiago@VRSF]

You'll increase torque throughout the powerband with catless downpipes, there's no loss in torque

[Allen@MOTIV]

I'm sure you're referring to one of many articles claiming that reducing back pressure somehow reduces exhaust flow. That's a complete misunderstanding of basic fluid dynamics and totally false.

[blackbeast06]

Originally Posted by Allen@PTF

I'm sure you're referring to one of many articles claiming that reducing back pressure somehow reduces exhaust flow. That's a complete misunderstanding of basic fluid dynamics and totally false.

Poiseuille's law.

Originally Posted by Allen@PTF

I'm sure you're referring to one of many articles claiming that reducing back pressure somehow reduces exhaust flow. That's a complete misunderstanding of basic fluid dynamics and totally false.

Would that still hold true for N/A engines?

[Allen@MOTIV]

Originally Posted by FCobra94

Would that still hold true for N/A engines?

Yes. Piping must be sized properly(intake or exhaust) to promote gas flow while maintaining enough velocity to prevent it from being "lazy" at low engine speeds. Back pressure is an unfortunate side effect of the smaller piping that favors low engine speed(torque) not the cause of the increased evacuation(This has more of an impact in manifold runners/primaries than it does further down the exhaust stream.)

[Briancanadiano]

Thanks everybody for the clarification!

[coti]

What is the proper piping size for this car and why? 2.5", 3", 3.5" etc

[Lotus99]

Originally Posted by Allen@PTF

I'm sure you're referring to one of many articles claiming that reducing back pressure somehow reduces exhaust flow. That's a complete misunderstanding of basic fluid dynamics and totally false.

So along the lines of this logic, then it's BS also I assume that some people claim BMW's reason for putting in the exhaust valve (where it's closed in the low RPM's / lower throttle pedal values) is to build more torque in the low end, and by keeping it open ("golf tee mod"), then you're reducing torque.

Right?

[Allen@MOTIV]

Originally Posted by Lotus99

So along the lines of this logic, then it's BS also I assume that some people claim BMW's reason for putting in the exhaust valve (where it's closed in the low RPM's / lower throttle pedal values) is to build more torque in the low end, and by keeping it open ("golf tee mod"), then you're reducing torque.

Right?

Correct.

[Tiago@VRSF]

That's absolutely for sound and nothing else. These cars can be a bit loud at idle, incorporating the valve keeps things a bit quieter on cold starts.

[JP.Williams]

But the valve is open on idle, and shuts once you start driving along. Well mine does anyway. So what is its true purpose? Its still open once warm on idle and shuts once im moving on part throttle.