Quiet or otherwise aftermarket exhausts

I just wrote this in answer to a question on a Skyline forum and thought it might be useful here with track days looming.

If you just drop the tailpipe or mid secction diameter with a tiny bung or even a flap valve all you do is create monumental back pressure, which will send EGT's skywards and probably cause det' and kill your engine. You need pipe length and lots of baffled boxes to give silencing without much added backpressure, it being a myth that back pressure is needed to make an engine run efficiently, even an N/A one. Backpressure is mixed up with tuned resonant length in this particualr myth. Most aftermarket Jap exhausts are overpriced, undermade junk, with a captive audience ripe for being ripped off. Think about it, you need to build a system with a big pipe diameter, one medium sized back box, and maybe a small resonator. It can hang low and catch sleeping policemen, but no one worries, and you can charge a fortune for a simple, cheap to make package, and people queue at your door to buy them. Or, you can make a multi boxed, well tucked up, complex system, that's quiet with little back pressure. It will be more efficient than the stock one, but as quiet. It will cost a lot more than a stock one, which is expensive anyway, but you need to recreate the silencing effect of the missing cat within your exhaust system. Only a few people will want it, `cos it's not noisy or bling, and it's VERY expensive. So you don't make it...

`Fraid your back to a stock exhaust or get one made up specifically Abbey Motorsport, with whom I have no connection, were talking of doing this. I make my own, but it's not commercially attractive for me to make them to sell.

I investigated this in the Trust catalogue, but none of the importers had first hand experience of what their quieter systems sounded or performed like, and physically they looked to have too big a bore with too few baffled boxes to do much, sound reduction wise, and they were too expensive to buy in as an unknown quantity. 98 Db drive by is pretty quiet, and hard to meet. Take into account induction nose made by your hot air gobbling, inefficient, none tuned length HKS air filter or similar, and you're onto a hiding for nothing unless you do noisy days only at track days, which are limited in quantity and expensive.

I have been thinking about this for when I go single. I would like a car that I can use on trackdays - that means the screamer pipe routed into the exhaust and a quieter exhaust. I would also like it to pass emmisions tests, to make it a fully road legal package that is as close to OEM as possible.

Will be very interested to see how this thread progresses.

Interesting. I have always felt they were overpriced.

What about the Trust one I bought from you - that has some kind of cat-like silencer in the midpipe. Anything interesting about it?

I was actually thinking about coming trackdays this year whilst in the bath last night And I was wondering about the effect of backpressure caused by a baffle.

Is it possible to setup a map that will allow for the increased backpressure and ensure the egts don't rocket etc ? Kind of the reverse to a race map. I know the baffle route saps power aswell, but I want to do trackdays with the Supra this year.

Apologies in advance if this is a daft question

How does the stock exhaust sound with the CATs removed??

im interested in this thread too, also would like to how standard exhaust sounds with 1st cat removed as i will be doing this, i won't be getting an aftermarket exhaust (was looking at hks draggers as not 2 loud) until a few months after.

The stock exhaust, even with both cats out, should pass most track day noise tests with ease. I'd recommend that over fitting any bungs or flap valves in an attempt to drop noise levels. Re mapping won't help, fit a quieter system! The Trust ones are pretty efficient and very well made, the small box is just an added silencer. I doubt the one you bought would pass a noise test on a single, it MIGHT on a TT.

******** BE AWARE MECHANICAL NEWBIE **********

This kind of thread interests me no end but I don't understand some of this Chris.

If I understand right, you're saying that aftermarket exhausts are a waste of time & money. With the added danger of causing damage to your car.

What if, I was not a purist, I wanted the car to sound a little more throaty, bit of a masculine roar (I want to stress, NOT LOUD) then surely the company manufacturing the aftermarket exhaust has met my expectations. The stock exhaust did not sound as I like so I change it.

What's wrong with that? Assuming it is fitted by a specialist (who would point out if it was going to damage my car)

Just not understanding "Back pressure" etc. too well might mean I misinterpreted the post.

It's not fitting the aftermarket exhaust that Chris is saying can damage the car, it's attempting to then silence it with some form of bung to meet trackday noise requirement levels.

So what about baffle's, does that mean for example the Blitz Baffle for the Nur Spec R once fitted will cause alot of back pressure and raise the EGT's too high...... or are exhaust specific baffles ok to use?

I have been thinking and following the same lines regarding quetening my system.. it's 4" dp and straight through... very noisy.

My old subaru GTB had the pipe sectioned into 2 at the back box with a butterfly plate that opened when you put your foot down, but that is of no use on the track, and a pita to fit to a sup...

I have had a good look on mine and the 4" pipe virtually touches the car all along the underside - the only possible room for a baffle is the section behind the rear subframe... but most of that is taken up by the back box.. I was looking for a mother of a good back box to put on the end - any recommendations chris?

The only other option I thought was to fit an off axis baffle in the middle - but there is only a little room on the one of the 4 sides...

Even with a 3 inch system - to get a good baffle that is not too big must be a challenge...

just reminded me of bung backpressure....

I put my foot down while being harassed by a scooby on the A38 once - I had'nt done the screw up on the bung tight enough.. the pressure at wot spat it at the scooby who only just missed it.

time for a quick getaway!

All i can say is in an effort to quieten my exhaust, Zigan evo, not terribly loud, i just like quiet:) i made a baffle, and found it sapped 60 odd bhp:( so i have now made a slightly less restrictive one, but i think my next step is to try an Apexi ECV , and possibly change the exhaust.

Tanabe MEDALION TOURING acheives extremely high levels of exhaust system efficiency, while maintaining a street driveable, extremely low frequency and deep tone that is well under 93db for discreet sports driving.

is it 4" matey?

I was (and still am) tempted by a custom job by Hayward & Scott - price-wise they quoted around £500 for a full system iirc, tuned to how I would prefer. I've also heard a lot of good things about them.

Tanabe MEDALION TOURING acheives extremely high levels of exhaust system efficiency, while maintaining a street driveable, extremely low frequency and deep tone that is well under 93db for discreet sports driving.

yeah ive heard that too, so thats the exhaust ill be looking at when I come to BPU. I had a chat with Chris about the Trust exhausts and he suggested that they were excellent quality whilst not being loud enough so the police can hear you coming a mile off. At the end of the day, I want more power without the noise, as on a daily driver, it would only annoy me.

I was (and still am) tempted by a custom job by Hayward & Scott - price-wise they quoted around £500 for a full system iirc, tuned to how I would prefer. I've also heard a lot of good things about them.

They did the custom down pipe from my turbo back to the Veilside Ti.

I am thinking about going back to them and having a silencer fitted in that section.

Tanabe super hyper medallion, Tanabe medallion touring and Fujitsubo Legalis are the quietest - I did MAJOR research when buying my exhaust as I wanted one that was as close to stock quietness as possible.

I have heard all 3 in person (and own one myself), and they sound VERY close to stock on idle/low revs, but have a really nice tone/growl when you step on it - however NOTHING like the stupidly loud cannon-muffler style exhausts that flood the market (apexi, greddy, blitz etc).

Hope that helps!

How does the stock exhaust sound with the CATs removed??

On my U.K. TT there is hardly any increase in sound level compared to when the cats were fitted.

Who stock Tanabe and Fujiwhatsit exhausts in the UK? Thanks for the info.

Can't help you with UK suppliers Chris, but Taka Kaira (http://www.takakaira.co.jp) sell Fujitsubo and MVP Motorsports in the US sell Tanabe's!

Thanks Inferno!

OLD THREAD RESSURECTION ALERT

Chris at the begining of the thread you state it being a myth that back pressure is needed to make an engine run efficiently

now i allways accepted on N/A engines some backpressure was good but on turbos everything i have read says you want zero backpressure,

I dont usually drive my car with the cat in at MOT time and just get the garage to fit and then remove for the test, but this time i am driving the car and i am stunned what a transformation it has made, i am only talking about low down grunt off the line and realise that at high boost/revs EGT's are going to become an issue. The car is almost back to BPU in terms of drivability and low down pull, it normally makes positive boost at 3200 rpm (with 3200 hi-stall) but now its 2800 rpm, obviously the backpressure the cat is creating is allowing the turbo to spool much ealier and 400 rpm down the rev ranges makes a hell of difference.

My car is a T61 so i dont know if this effect would be as pronounced on bigger turbos but i am going to look at replicating this effect with an Apexi ECV maybe linked to a pressure switch to open at a preditermined boost pressure (this is how i presume the defunct DEC's system worked i presume)

Interesting as the general idea behind turbos is zero back pressure allows the turbo to spool quicker, and generally speaking bigger is better.

I guess the area of the map you are talking about is where there is no boost ie sort of NA so yeah I guess it could benefit from some back pressure which it turn possibly generates more torque/power and higher exhaust volecity and therefore spooling the turbo quicker, hmmmm.

This could get interesting.