Question: Correct exhaust size for 4AGZE running 12psi?

[PooJou]

Hey guys,
As i've got my GZE running all nice again, i've noticed one thing. It's too bleedin' loud! Now I'm fairly sure that the exhaust on there atm is something like a 2.5" from the extractors back - which I think is too large a diameter? My mechanic thinks that there is too -little- backpressure from this system - bear in mind the previous owner had prepped this car for an incoming turbo setup, so this might be the cause of the slightly large exhaust?

What do you guys think? Is a 2" too small? what about 2.25"?

Not sure what type of muffler is on there atm, think it's a lukey turboflow, but it may well be straight-through.

Thanks in advance!

[Ben Wilson]

I had a 2 1/2" system on my mr2 and it was bloody loud, if I was going to do it again, I'd try 2 1/4"...

[TooF]

on my 4agze ive got 2.5" and im pretty happy with it.. all be it with quality mufflers in there. passes road legality no stress.

that said my new one is 3" from the turbo back.

[PooJou]

Thanks for the input guys - So you think 2" is a tad small? I'm not sure exactly what is under my car as i said earlier, but I guess I'll take it down to the exhaust shop and see what they think.

It's not necessarily a road legality question, as plenty of super riced other cars with 5" cannons are louder, it's just that, for a 2.5" system its ... quite loud lol.

[Poggy]

2.5 to 2.5inch cat, then 2.25inch cat back. Use a glasspacked perferated resonator and then a lukey turbo muffler. Should keep a constant back pressure and keep the soundwaves nice and smooth instead of short, sharp and buzzy.

[BeRad]

*waits for "backpressure" abuse *

[PooJou]

*waits for "backpressure" abuse *

Lol actually, the backpressure thing was just mentioned by my mechanic, I'm more interested in seeing how I can quiet it down without restricting the GZE's breathing.

[Ben Wilson]

Backpressure is great for reducing noise, the higher the backpressure, the better a muffler will work..

[The Real Roadrunner]

its not so much the pipe dia that makes the difference noise wise but the mufflers and how many of them.
i have built plenty of 3.5' systems on turbo cars that are under the db limit and sound great.
i would look for the largest poss straight thru centre offset muffler you can find with fglass or stainless packing 4"x9"oval about 16"with 2.5"id.
i know genie have these and get that fitted under the car should still have a crisp note and knock down the db aswell as in cabin drone.

[Poggy]

actully, when you get pressure drop such as having the same size exhaust on an N/A car or supercharged car the exhaust gases cool the further down the exhaust they get, which gives you low backpressure spots which changes the wave lenghts of the sound waves, thats why you get buzzy exhausts, because the exhaust is to big and the waves are just bouncing around "short and sharp", to keep a good efficent exhaust not to mention a good sounding exhaust you need to get smaller towards the end to avoid low backpressure sports where the waves will go from long and smooth to short and sharp. we like long smooth waves.

In summery you need to get smaller towards the end, because the exhaust gase cools and takes up less space, so thats why you get a smaller exhaust cat back, to compensate for the gases takign up less space, this keeps the gases flowing better and not just boucing around

Flame me if you want but ask any proper exhaust buff

[PooJou]

The car sounds great high up in the rev range, it just gets a bit ummm boomy down low? even idling its a bit loud.

It has no tip or anything on it, muffler is a lukey of some description as i said before - thanks for the help so far guys, I'm becoming more clued in about exhausts with each post

[Poggy]

mufflers are important, very important, they limit the noise heaps, but even good mufflers on a system with backpressure low spots will sound shit and buzzy

[mojo_type]

my gze has 2.25 and its not that noisy its a cat -> hotdog -> muffler
try a different muffler

[Kebin]

My 4agze is running all 2.25 to 2.5 cat (off cressy) then 2.25 to two straight through mufflers. It is very quiet around town with a nice overall tone not buzzy or anything and a little droney when traveling 100km/h+

[Rex_Kelway]

The exhaust of Rex for His AW11 consists of:



Its a 2.5inch segmented-bend stainless system with an SW20 Tanabe muffler and stock cat (de-cat for trackdays). The muffler shrinks to 2 inch but logic dictates by this time that is plenty for a 150 odd Hp. The first metre should be the biggest then after that it can smaller with no effect at all.

When He made it Rex was expecting a bit of volume (Rex dislikes obnoxious road exhausts) He was pleasently surprised that it is only a fraction louder than stock, if that. It has a killer note with no drone, bark or buzz at all.