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Exhaust Mod Idea

illusiVe

By illusiVe,
in Engines & Forced Induction

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illusiVe Proficient

illusiVe

Posted
Posted

Ok, now everyone says that N/A needs backpressure and stuff and i've been doing some testing with my exhaust and my car.

Basically i have a STOCK R34 25 GT (non turbo)

with the exhaust from factory i have a very nice torque for 2k-4k which then drops

but after i modified the exhaust to bigger and more free flowing

i LOST that down low torque, however gained alot more from 4k-redline.

Im just thinking if i could basically run 1 stock exhaust and then have a flap to a 2nd exhaust with the same diametre, and have a flap open as i hit 4k. so down low, i have the low torque. but if im doing some foot to floor driving, i get the higher range or torque.

sound good? (also should help put this debate of backpressure to rest)

(more power without back pressure, however thats only at redline/high revs.. to an extent of course)

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Eug Grand Master

Eug

Posted
Posted

just to clarify someone explained to me quite a while ago here in SAU that its not backpressure, but infact volumetric vacuum.

my R33 has something similar with the stock exhaust - basically has a flap with a pulley set up and opens up around 3500-4000rpm

you can hear the thing rattle a bit too..

http://www.hks-hokkaido.co.jp/movie/muffle...hipower_sky.avi

i think this is what ant95GTR is talking about (correct me if i'm wrong)

i reckon this has more to do with silencing than low rpm torque - sounds tough as though!!!!

eug

scathing Grand Master

scathing

Posted
Posted

There are a couple of OEMs (Aston Martin is doing it on a couple of their cars in their range these days, off the top of my head) that do something like this.

At a certain RPM a valve opens in the exhaust, providing more flow up top. I don't know if it just bypasses the centre muffler or if it opens a completely separate set of pipes, but either way the Vanquish and V8 Vantage get a whole bunch of noise high in the rev range.

I'm considering doing something similar in my car if I ever replace the exhaust again. I was going to set up a bypass valve to route gasses around the centre mufflers at high RPM. I'd have it automatically controlled (say at a certain RPM above a certain speed. So on a stationary noise test or in first, and perhaps second, gear it wouldn't open at all) but with a manual override for when I hit the track.

illusiVe Proficient

illusiVe

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Posted

sound similar yes, if its turbo u hear the turbo spool which alters the sound of the engine quite abit, but if u have an ear for it you can still tell its a skyline :P

but no WRX have the distinctive noise because its a boxer engine.

ignuz Mentor

ignuz

Posted
Posted

Yea.. my stock exhaust had that flap thing.. I remember when i bought it I was checking out the exhaust going.. ok someone riced my exhaust and only one is open...

Meh it sounded like crap and looked like crap tho...

As seen below..It's actually a pretty cool shot, except my new exhaust looks alot nicer.. no pics of it atm though because, my car is in repair.. Wet roads and my stupidity... :(

oidmqv.jpg

scathing Grand Master

scathing

Posted
Posted
but no WRX have the distinctive noise because its a boxer engine.

Not exactly, as lingering soul pointed out.

The "boxer throb" you get from Subies is because of the crap design of the exhaust, which is forced upon them by the crap design of the engine. I could just as easily make any sound like that. The difference is that its a packaging requirement on a turbo boxer 4, and stupidity on any other kind of engine.

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