Too much air going out?

[HuntingtonFRS]

I have the Tomei UEL, Invidia Q300 2.5" exhaust, and just added JDL over pipe/front pipe but it's 3".

I'm running the HKS supercharger. My question, is this too much air going out now? Not enough back pressure? Is that really possible being boosted?


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[D_Thissen]

It's fine, don't worry.

Edit: In regards to back pressure. Here's a comparison between a 2.5" and 3" exhaust.
[ame="https://www.youtube.com/watch?v=_PVXvHkr-Vs"]The Power of 2.5- vs. 3-Inch Exhaust - Engine Masters Ep. 9 - YouTube[/ame]

[HuntingtonFRS]

That's really interesting. Does it make the same difference on lower horse power vehicles though? I feel like there are more factors than just what they tested when comparing vehicles.


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[FRS Justin]

Forced induction takes the worry away from back pressure loss..
Running forced induction forces the air into the cylinder and that offsets the need for exhaust scavenging..

[KoolBRZ]

Originally Posted by HuntingtonFRS

I have the Tomei UEL, Invidia Q300 2.5" exhaust, and just added JDL over pipe/front pipe but it's 3".

I'm running the HKS supercharger. My question, is this too much air going out now? Not enough back pressure? Is that really possible being boosted?


Sent from my iPhone using Tapatalk

Too much air no, too much velocity, maybe. Valve timing controls the flow of air and fuel through the cylinder. Air Intake and exhaust restrictions affect the velocity of that flow. Remove some of the exhaust restriction and you change the velocity of flow through the cylinder. Before I complicate things with AVCS valve timing, Injector angles and other complicated stuff, answer me this, how does your car sound now? Is it more brassy sounding, like a trumpet? Or is it more brrrrrraaaaappppppp'y? There is a happy medium between the two which makes the most power. The only way to make sure, is to use tunes ranging from too little AVCS advance to too much advance. The tune between brassy and brrrrrraaaaappppppp'y is the one making the most power. Then the challenge is making the same sound throughout all loads and rpms.

Chances are if your exhaust has changed your restriction too much, your car will sound more brassy, and have less low end torque under medium to heavy loads. If this is happening, contact whoever made your tune and see if they will adjust it for you.

[Poodles]

There. Is. No. Such. Thing. As. Backpressure.

[swarb]

Originally Posted by Poodles

There. Is. No. Such. Thing. As. Backpressure.

You is wrong

[HuntingtonFRS]

My car has constipation? Lol


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[wparsons]

Originally Posted by KoolBRZ

Too much air no, too much velocity, maybe. Valve timing controls the flow of air and fuel through the cylinder. Air Intake and exhaust restrictions affect the velocity of that flow. Remove some of the exhaust restriction and you change the velocity of flow through the cylinder. Before I complicate things with AVCS valve timing, Injector angles and other complicated stuff, answer me this, how does your car sound now? Is it more brassy sounding, like a trumpet? Or is it more brrrrrraaaaappppppp'y? There is a happy medium between the two which makes the most power. The only way to make sure, is to use tunes ranging from too little AVCS advance to too much advance. The tune between brassy and brrrrrraaaaappppppp'y is the one making the most power. Then the challenge is making the same sound throughout all loads and rpms.

Chances are if your exhaust has changed your restriction too much, your car will sound more brassy, and have less low end torque under medium to heavy loads. If this is happening, contact whoever made your tune and see if they will adjust it for you.

Removing restrictions too far (most common from too large of a diameter exhaust) will typically give lower exhaust velocity, not higher. There's a sweet spot for velocity for good scavenging (and maximum power).

On a turbo car, the turbo itself is much more of a restriction than anything after it, so the best exhaust is typically the one that has the least restriction possible.

On a supercharged car you can still have benefits from scavenging, but it's not as important.

As for the original question, going to a 3" front pipe isn't going to change overall flow/velocity much since it still has to go through the 2.5" Q300 to get out. That said, testing shows that a good 3" exhaust will make more power than a good 2.5" exhaust, even N/A, on these cars.

[churchx]

wparsons: testing, 3" win, .. you mean perrin one? But IIRC it was with stock header, no? Don't know if it would be same way with 3" exhaust AND catless aftermarket headers .. rather i'd bet on bolt-on mods cumulative gains hitting diminishing returns and there to be of little difference between 2.5" vs 3" NA.

[wparsons]

Originally Posted by churchx

wparsons: testing, 3" win, .. you mean perrin one? But IIRC it was with stock header, no? Don't know if it would be same way with 3" exhaust AND catless aftermarket headers .. rather i'd bet on bolt-on mods cumulative gains hitting diminishing returns and there to be of little difference between 2.5" vs 3" NA.

Look at the dyno thread(s) from the nameless header, definitely more important with an aftermarket header than the stock one.

There is a point of diminishing returns, but the point was that going to a 3" exhaust isn't going to make you lose power over a 2.5", there's still plenty of exhaust velocity.

[churchx]

wparsons: thanks for info.
I won't go 3" it route anyway though, as it usually is reported as being louder, hence bad companion to exhaust that will be already louder due catless aftermarket header, hence combo might get above reasonable noise level, from what i see seeing several posts of users switching back to stock or Q300 when they installed header after catback.

[COO86L]

Backpressure is a myth created by hotrodders.
Scavenge effect is real.