Exhaust Q

[chrisf5]

what would the result be if you put 3inch exhaust on a non turboed neon and uhh whats the benefit from going from 2.25 to 2.5 (approx)

[Neon4Life]

well ive heard that even if your turboed and you go to a 3inch exhaust that it can hurt you performance wise.

and if you go from 2.25 to 2.5 not sure what the diff would be but probably only a little diff in exhaust air flow.

[excon]

3 inch piping is overkill and will hurt performance on a non-turbo car. Exhaust gas is hot, and your exhaust system is made to remove that heat and gas as quickly as possible. The stock piping size is plenty big: at 2.25". Unless you have done major mods to the intake track, which would therefore increase the volume of air coming out of your engine as well; such as a turbo, you do not need the larger pipes.

The reason it would hurt performance is because as your exhaust gasses cool they become harder to move and thus create backpressure. You want your exhaust gas coming out quickly and efficiently because it will create less backpressure on your engine and give you more power.

[60trim]

You need a little bit of back pressure. 3" is overkill hands down. 2.5" is appropriate for an upgrade. Intake, 2.5 inch exhaust, plugs, wires. That is a super mild path. I would only do 3" on a fully built motor with hi compression pistons, velocity stack runners, header, spray in N/A form.

[racer12306]

I thought exhausts were all 2.5, instead of the 2.25 they used to be. Or was it 2.25 instead of 2?

[OB]

Exhaust will always be controversial. I've talked to engineers who claim the "back pressure is needed" myth is total BS. A lot of people (non engineers) will argue otherwise. I've done my fair share of research and i've decided that the engineers make a valid point, so I settle on their side of the discussion. However, regarding velocity, a smaller exhaust is always better. Basically, the smallest exhaust piping possible without hurting flow or gas velocity. Anyone who claims that 2.5" is beneficial because you installed a CAI and a mild header is full of shit. The stock exhaust piping diameter is probably good to 175hp NA. Forced induction changes things a bit; 2.5"-3" for mild turbo setups is realistic due to the drastic change in exhaust gas characteristics. Temp, velocity, flow, etc. all change a lot from stock.

Bottom line is, without a longtube equal length runner header coming off of a race ported head, exhaust performance isn't worth much effort. Upgrading the stock muffler and getting a decent header are good basic upgrades. Changing pipe diameter should be considered an advanced upgrade that should only be done when everything else has been addressed. i.e. The car has been tuned, and exhaust system engineering programs have been used to compare data, giving reason to increase pipe diameter.

[60trim]

Can we get some dyno graph comparisions here?

[OB]

I was gonna ask the same thing