ringmaster

iTrader: (1)

I am going to upgrade my exhaust for better flow and less weight but I want something quiet. I have an amazing fabricator friend who can build me a full mandrel bent system with the straight through muffler of my choice.

I want to use 2.5" pipe to keep it quiet but will I be giving up HP by not going to 3"? Keep in mind this car will have a stock turbo, just upgraded with a Flash and IC piping.

Please no wild guesses or "bigger is always" better comments. Is there any dyno proof out there that 2.5" makes less power than 3" (assuming the same muffler) on a ~300whp car?


Thanks

steveevo8

well i'd assume a 2.5" makes a significant amount less less air flow but i'm not a tuner so i could be wrong

bluebanana23

iTrader: (26)

actually there is a dyno in the turbotrix section. The larger exhaust produced a significant amt. of more power. I could have sworn factory dia. was 2.5 inches. Would post the link but world history hw is calling...

ringmaster

iTrader: (1)

This is the answer I am trying to avoid! No sh*t a full 3" TBE will make far more power than the stock ~2.5" exhaust, but what about if both the 2.5" and 3" systems use the same mendrel bent tubing, same flowing muffler, etc...will there be much, if any, difference in power output on a car with 300whp? Obviously a 500whp car will need a huge exhaust, but maybe not with less power?

bluebanana23

iTrader: (26)

the dyno was comparing a 2.5 buschur exhaust and a 3inch and that car was making 300 whp.......... so I don't see how that doesn't answer your question

steveevo8

stock exhaust is 2.25"

ringmaster

iTrader: (1)

Sorry about that, my mistake I couldn't find the thread on the Turbotrix section so I didn't know it was a 2.5" vs 3" aftermarket system test. Do you remember the results? How much more power did the 3" system make? Were they both cat-less?

Thanks

bluebanana23

iTrader: (26)

I can't find it either but I do remember both were with hi flow cats. As for the 3inch being a buschur...I don't remember. The hp difference was around 15 but i'm not sure. The reason why I remember is because I have the same mods but with a different ecu flash and was thinking of changing at that time.

ODB4G63

iTrader: (6)

Is the only reason you want to stay with the 2.5" for sound reasons? Just wondering because I was really surprised at how quite my 3" was just by adding a magnaflow muffler. I almost wish it was louder!

ringmaster

iTrader: (1)

Let me put this another way

Assume were are dyno testing a slightly modified EVO (maybe ECU flash, 20psi, I/C pipes, stock turbo, etc) that makes 300whp with no exhaust system after the turbo.

Next we bolt on a full 3" cat-less TBE (mandrel bent, straight through muffler, all the good stuff). What power do we get? Still 300whp or maybe a bit less?

Next we bolt on a full 2.5" cat-less TBE (mandrel bent, straight through muffler, all the good stuff). What power do we get? Still 300whp or maybe a bit less like the 3" test or have we really lost/given up some power by going down to the 2.5" size?

Has anyone ever done a test like this to confirm that these cars, around the common 300whp level, really benefit from the large 3" exhaust tubing?

AMSTuning.com

iTrader: (9)

On a stock turbo, with stock boost, downpipe, cat-delete pipe, straight exhaust/turbo muffler the diameter of the piping would not change the numbers so much that 3" can be crowned king. The 2.5" piping has its own benefits.

ringmaster

iTrader: (1)

For me a 10whp gain (say 310whp vs. 300whp) by going to the 3" would be worth the extra noise, etc.

When you say the 2.5" piping has it's own benefits, do you mean less noise and easier to fit or are you talking about some kind of performance advantage?

AMSTuning.com

iTrader: (9)

Precisely. I was talking about Noise levels and fitment as a ratio to HP gains. Alot of people are willing to sacrifice that additional 10hp for better sound and fitment. It's actually seems to be the premier deciding factor when someone is shopping for a new exhaust.

hkfeet

iTrader: (20)

Im going with a 2.5" hks downpipe, and 2.5" UR hfc with my hks hi-power exhaust. I was really thinking about getting a 3" setup but since Im not going to upgrade my turbo nor am I going to be drag racing, and the possibilities of getting my 03 evo over 350hp is slim. I really like the low end torque I would gain from this setup. Besides my experience with a 3" B&B downpipe in the past makes me want to avoid getting another 3" dp. The rattling was real messed up, and I couldnt handle it.