[Zeta]

最初由 turbos86 發表
But ok, I'm confused on one thing. Some people say back pressure is bad, other says you need it. And what's it got to do with torque/power lost.

awww, screw it, do I/H/E and get a straight pipe, who needs back pressure anyways! LOL

back pressure is bad, those who say that u need it are likely to have confused by the fact that excessive size in exaust piping cause lose in low end power. so they assume that the lose of low end power are caused by the reduced back pressure. that's not the case, the lose in low end power are due to reduced exahst gas velocity (by increasing the exaust piping u increase the exaust gas capacity, but the exaust gas travels slower in the larger pipe) and the turbulence at the wall of the exaust pipe.

so basicly i don't think u "need" backpressure

[NTG P5]

lol....the Master has spoken...hahah...Yoda that is...

I know that for NA cars, you dont need really large diameter pipes and exhaust to achieve performance...going with too large pipings and exhaust will cause loss in low end power *just like Zeta had mentioned

but for FI'ed cars, the bigger the pipes the better
*but that doesn't mean you'd get a 12" exhaust pipe...

Back pressure is both good and bad. A little bit of back pressure in a 4 cycle engine helps down low but it loses power up high. Too much back pressure decrease power and can create detonation.

A brief explaintion of how backpressure works.

When your exhaust valve opens near the end of the exhaust stroke. The exhaust gas must be push through against a positive pressure in order to get out of the combustion chamber. Energy must be used to overcome the initial pressure within the exhaust system. After that exhaust gas starts to travel faster and creates a negative pressure. The more negative a pressure becomes means that you are creating more suction or a vacuum in the system. The system is literally sucking or pulling out exhaust gas from the combustion chamber. This sucking or scavenging effect not only helps remove more exhaust gas from the cylinder. It also helps suck in more intake air & fuel mix at cam overlap. The faster the exhaust gas travels the more vacuum it creates. You want to get as much as negative pressure created before cam overlap.

[NTG P5]

oh...very technical oh...Initial-D really into carz and how they work...

so that's why cars like the Nissan Maxima are equipped with exhaust that has a butter-fly flap in the muffler that opens/closes as the engine is pulling diff loads

a little back pressure when the car takes off, then buffly opens as more exhaust gas flows throgh

engenious

Yup that's called Variable back-pressure Exhuast. It switches between different length exhaust pipe.

[RSX]

最初由 頭文字D 發表
Back pressure is both good and bad. A little bit of back pressure in a 4 cycle engine helps down low but it loses power up high. Too much back pressure decrease power and can create detonation.

A brief explaintion of how backpressure works.

When your exhaust valve opens near the end of the exhaust stroke. The exhaust gas must be push through against a positive pressure in order to get out of the combustion chamber. Energy must be used to overcome the initial pressure within the exhaust system. After that exhaust gas starts to travel faster and creates a negative pressure. The more negative a pressure becomes means that you are creating more suction or a vacuum in the system. The system is literally sucking or pulling out exhaust gas from the combustion chamber. This sucking or scavenging effect not only helps remove more exhaust gas from the cylinder. It also helps suck in more intake air & fuel mix at cam overlap. The faster the exhaust gas travels the more vacuum it creates. You want to get as much as negative pressure created before cam overlap.

NICE.....

to me.... this is most reasonable since i study physics....

hehehheee

[turbos86]

Thanks guys, totally understand now:)