Exhaust Mod Idea

[illusiVe]

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)

[Ant97GTR]

Already been done by at least one Japanese tuner(HKS).

Works but very expensive to setup...

[Eug]

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

[Ant97GTR]

Yeah thats it.....I don't know how exactly it works whether its controlled via the ecu or a separate system (it would have to open at the right RPM to maximize its use) but it is available.

[Maxx]

u will have a separate controller like EVC in the car to control the RPM the shuttle work

[Eug]

not sure about the R34 GT, but if the standard exhaust has the same mechanism as mine - might be able to utilize it?

[bnr#@]

That movie is of the HKS driving performer GTR (fully street leagal). that valve is there so the noise can be minimised for legality. It is controlled from an in cabin switch

[Maxx]

apexi got something similar too

http://www.apexi-usa.com/product_exhaust_d...d=217&pageNum=1

http://www.apexi-usa.com/product_exhaust_d...d=238&pageNum=1

[gatty]

my stock r33 exhaust has a flap etc that would open up as stated above, you can buy it if u want

[illusiVe]

not quite the same....

[AlexCim]

dont r34 gtt's come with dual tip mufflers that have flaps in them?

when cold, the muffler is only 1 tip open, as it warms up etc, both tips open.

This could do what you are talking about. For a fact, i know S2 manual stageas have these.

[scathing]

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]

just have it full open @ 4k.. closed below that, manual override for hoon + track times.

[ImPuLsiVe]

sorry to hijack, but does the sound (exhaust note) the same for all rb engines rb25 in particular regardless if its turbo or not? Like a distinction from all other POS. Similar to that the WRX got that distinctive sound also.

thanx

[illusiVe]

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

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

[lingeringsoul]

funny how porsches don't sound like WRXs tho........

[ignuz]

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...

[scathing]

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.

[illusiVe]

ferrari also have V8.... but it does sound like a v8.. its just the tuning and the exhaust.