what exactly does a muffler do??

[[Zero-S]]

Right. Or at least thats what I got from tms, and I believe his explanations more than most peoples.

[Spidey]

I'd have to agree with lessthanjake. Bigger pipping on an N/A car will cause you to lose the scavenging effect not backpressure as previously stated "backpressure is not your friend" wehter it be turbo or N/A.

It is all about your exhaust gas velocity.

Also For a certain car speed the loss in power increases as backpressure increases.

lets say for example with 2lb backpressure at 70mph, the power loss is 4 hp, when backpressure is at 4lb power loss is 8 hp.please correct me if I'm wrong

[MrFox]

Running no exhaust while at first seems like a great idea is not so on the inside, because the exhaust can't provide the scavenging effect that the exhaust provides. You say that the back pressure will hold the fresh air in? well if there is back pressure how is the exhaust gas supposed to excape in the first place?

Factory cars are designed to work with a certain amount of backpressure - because they have to put a damn muffler there to quiet the sonovbich down. Cam profiles are selected so that optimized scavanging occures with this amount of backpressure at a specified RPM. if you take away this backpressure because you dont care about the noise, than the cylinder becomes overscavanged at that RPM.

lets say for example with 2lb backpressure at 70mph, the power loss is 4 hp, when backpressure is at 4lb power loss is 8 hp.

It depends. Backpressure in a modified car is not a case where more is better, nor is less better. its system optimization. Less backpressure always decreases the flow resistance of the system. But if your system (cams, intake, header, ports, exhaust, muffler) is optimally scavanged at whatever RPM you are looking at, than increasing or decreasing backpressure will cause a loss of torque and power at that RPM. However if its not optimal to begin with, then you stand to gain or lose by modifying backpressure. Just beware that while one RPM point is being improved, other RPM points are moving away from optimal.

backpressure is beneficial to a certain point on NA cars to enhance torque. Selecting the right exhuast for NA is important. Things like header pipe size, lenth of the runners, collector arrangement, main pipe size on the exhaust pipe and muffler design all impact where you are making power and how much you make.

[corn322]

yep, mrfox is right. to get the most out of the system, you have to change everything. you can either have power at low rpm, or power at high rpm. but you can't have power everywhere.

[Cyberkreig]

but you can't have power everywhere.

unless you drive a toyota.

[lessthanjakejohn]

yep, mrfox is right. to get the most out of the system, you have to change everything. you can either have power at low rpm, or power at high rpm. but you can't have power everywhere.

You could have like a 10 stage vtec and a varibale diameter exhaust

[[Zero-S]]

What about the SR20VET? I know its more trouble than its worth, but I'm just asking.

[themadscientist]

a vacuum operated variable valve on a slightly oversized exhuast would give you the best of both worlds, by closing against spring pressure with the vacuum present off idle and then allowing the sping to overcome it and swing open the valve as vacuum falls off with increasing RPMs thereby increasing system flow you would see a thick powerband from idle to redline with no sacrifices made anywhere.:thinker

[[Zero-S]]

Ok...I understand that. But what about the whole variable valve timing stuff? Does that compensate for the differences with low/high rpm power (as described in an earlier post)?BTW this thread has gotten a little off-topic hasn't it. Informative though...

[themadscientist]

well as rpms increase everything must move faster to keep up. By have a system that can advance cam timing in the higher RPMs you can enjoy optimum cam timing at all engine speeds.

[Onizuka]

ok i didnt feel like reading the last 2 pages so....

i drove around with just the stock header on my car for about 1 minute befure i really realy wanted to hook up my exaust again.

[themadscientist]

felt a little light in the sack area didn't it. I bet your neighbors hate you:pface