Quiet Cat Back Systems For Under 98 Db Track Usage

[Chris Wilson]

Looking for advice on quiet (under 98 Db drive by at full throttle, on track, measured trackside) systems. I have tried a Trust / Greddy Power extreme II which made 102 Db, a doubling of the perceieved noise allowed, so no good at all, and nor is an HKS Hiper Silenced, with a similar noise level. It's the fairly large turbine size I am running, I guess, that's the issue. The exhuast that's on it is a bit ropey, and mild steel. No ID on it, obviously commercially made, but I have never seen one like it before, it came on the car as bought. I need to have a replacement for it soon, and on the new engine about to go in the turbine housing will be bigger, the capacity bigger, and a lot more cam and revs.... Do I need to make a custom system? Do you have noise issues in Oz? How do you meet them without killing too much power?

Thanks.

[AlexCim]

Fujitsubo Legalis R (not the Super R version)

[Roy]

Holy crap...102db? I have an external gate and i dotn get pinged when at the track, i think they are checkign for 95dB???

What turbo setup are you running? ID be tempted to go twin system, with twin mufflers. You can pack it up nice and tight to the underside, you can the flow benefits of a 4" system and you can share the gasses accross two mufflers

..LOL well the theory sounds good on paper

[R31Nismoid]

If you wanna make it quiet, twin system is the way to go. All the gains... none of the noise

And its gonna be a custom job and pricey

All the big HP GTR's here in melb are doing it

Twin goes ok into the GTR floorpan aswell.

Not sure on the GTS-t layout, but it couldnt be any worse

Im doing the same aswell

[siba33]

when you say twin system, do you mean like two mufflers?? or like two pipes into one muffler or somethng different??

[Andi]

I believe they mean from the cat two pipes run towards the rear of the car. So two pipes and two mufflers. I believe if its 2x 2.5" that equals to about one single 4" pipe?

I've considered doing this as well but can't imagine it being too cheap.

Since we're on the topic of exhaust (sorry to OP, don't mean to hijack) is a 3.5" fine for a GTT? Or should I just got 3"? I'm afraid 3.5" might be 'too' big?

[R31Nismoid]

siba33 - Twin... wether that be a single dump or twin dumps (single or twin turbo) and then have it twin all the way to the rear.

With a cross-over pipe somewhere along the line.

2 cats (smaller obviously) and then 2 or 4 mufflers somewhere along the system depending on whatever you choose with the exhaust shop etc.

No such thing as "too" big for a turbo car IMO.

[9krpm]

can you guys post pics of what the twin system looks like from the rear?

twin all the way from the turbo will be awesome to look at but probably add a lot of weight.

[Abo Bob]

You could always get it made out of titanium.

I have a Fujitsubo system. Not sure what it's called but I was at a shop once and there was a car there with it so I said I want that one and they got it for me.

My system is 3" from the turbo back (GTT) and is not restrictive. I have 255rwkw at only 0.9 bar of boost from a highflow turbo so I think that proves it's lack of restriction. 3.5" is just louder if you ask me but in terms of power you can't relly go wrong going bigger.

[saliya]

Anything that's 3.5" or over is a bastard to shut up. In my .sig I have an 100mm exhaust that flows, for sale, but I've

never measured it trackside on full noise. It's 95db @ 3500 no load, (with cats/resonator/muffler)...

On the back of a napkin:

2 x 3" exhausts (ok, 2.82") should flow as much as a single 4"

So if you could find a 3" exhaust configuration that was 95dB on full noise, 2 of them _should be_ 98dB.

Some things to think about:

* are most of your competitors within the 98dB limit? If not, how loud are they on full noise trackside?

* you'll probably only get pinged if you're noticeably louder than other cars in your class or your competitors complain.

* are other car noises (induction/tyre/gearbox/etc) included in the level? If not, how are they eliminated?

* if you're in with a bunch of other cars, there's no way they can measure just you

* if you're alone in front, button off past the measuring device

I've heard plenty of racecars that are louder than 98dB (this seems to happen a lot with rotors

and smaller-capacity engines). I've only ever seen one car get chucked off the starting grid

because it was too loud, but I've seen a few get pinged because competitors complained.

There are a few genuine competitors on this forum, might be worth

PMing them for their experiences as threads can sometimes get lost in the noise...

I'd probably try building a twin 3" system, then add muffling till the competitors stop complaining.

Regards,

Saliya

Edited April 30, 2006 by saliya