Catbypass, Cup pipe, G pipe...which one would you go for?

[NormalNorm]

Hi guys, im sure I have asked this question before, just need a bit of assuring before I do it!

Obviously I have a standard exhaust system on the car, but ive seen and heard a few of you guys have changed the odd things for noise enhancement and 2-3bhp more with a nicer flow in the system.

Some say if you changed all pipes then the car is too loud.

I was thinking just to change the Cat bypass, what do you think, as this will freeup the system, maybe 2-3bhp more, which Im not that much bothered with, but do want it a touch nicer in sound, but not too loud!

Talk boys!

 

[Steve Brookes]

Mine came with cat, primary and G pipe bypass. Personally I didn't like it - too 'American muscle car sound' for me. And there seemed to be no guts at low revs. So I put an original silencer on. Much better performance (seat of pants kind of way) but a bit quiet. So when the opportunity arose I changed the big middle silencer for a cup pipe. Nicer sound, no loss of seat of pants power and a big weight loss right in the middle of the engine. Noise comparison of my standard and cup pipe systems on youtube:

http://www.youtube.com/watch?v=4m1a3JPkmbw

This makes the exhaust 102 db on a static noise test. Next I will probably go for a partial decat which should keep it below the critical 105 db.

 

[Dave Wilkinson]

Norm,

From what I've seen of your previous posts it looks like your car is a '92 on a K plate. If this is so you will not be able to pass the MOT emissions test without a cat (the test is much more stringent for August '92-onwards). Your only choice would then be to fit a less restrictive cat such as a 200-cell sports cat. Changing the cat will not make a huge difference to the sound as there are two massive silencers between it and the outside world. Fitting bypasses to both is ridiculous and likely to get you stopped by the BiB. You can hear the car from over a mile away!!

If you plan to use the car on track you need to be careful as some mods will take you over the required sound levels - particularly Bedford Autodrome and Goodwood being the difficult ones. A Cup Pipe, to replace the silencer across the back of the car is the most effective and is marginally quieter than using a G-Pipe (which replaces the secondary silencer behind the right rear wheel). The G-Pipe produces a more "growly" sound and is marginally louder than the Cup Pipe.

The other option is to fit a completely different exhaust system and there are a lt of after market systems available from the likes of Dansk, Fabspeed, Hayward & Scott and others. Just be sure to watch the dBs if you plan to track the car.

Regards

Dave

Edited to correct the MOT emission date to August 1992.

 

[tim_haskins]

I personally would go with a cat bypass pipe first and see if your happy with the sound. That's what is fitted to mine!

I would then probably go for a primary bypass as I have heard the gpipe secondary bypass is quite loud.

I haven't bought the primary bypass for mine as I am going to get the fabspeed rear box...prob is that it's £700!!!

don't go for all 3 ie catbypass 1st&2nd bypass as it will be too noisey.

Tim

 

[colin129]

Since this is an exhaust post, perhaps someone can help me on an exhaust question.

I do not know what sort of system I have on my car, I suppose I just assumed it was a standard system. When I had my last service I required to replace an exhaust section, as it was corroded. The section was a 'de-cat pipe', the part number is JZ Machtech number rather than a Porsche number, a £260 touch, I guess it could have been worse [8|]

I guess, therefore, I had/have a modified system. I find it quite quiet, to be honest, from the inside, outside, at idle it sounds quite fruity!

Explanations please?

Perhaps, when I come along to Curborough, someone will be able to tell me.

 

[Dave Wilkinson]

Colin,

A "de-cat pipe" is the same as a cat bypass. £260 doesn't sound (!!) too bad as Design 911 list them at £199 + VAT. Some of the cat bypass pipes are designed to look like the original cat (so the heat shields fit) so it's pretty difficult to tell them apart without looking inside.

Regards

Dave

 

[NormalNorm]

Thanks guys, especially Steve and Dave! yes mine is a 92, so thanks for the advice.

I was speaking to Chris today at Tech9 a personal friend of mine who said I could do either the Cat bypass which is situated on the left and side of the rear of the car, am I correct? which would be more effective. But by the sounds from Dave and Steve, your recommending the middle section which takes away the middle box, which runs right in the middle of the rear just behind the rear bumper, correct?

Getting excited already! But hearing you guys talk about the car being too loud scares me, because I dont want to be heard from a mile away![]

 

[Mjonzo]

Thats correct Norm, that rear box that runs along your rear bumper, long box with pipe exiting each end. I replaced that on my 964 with the 'cup primary bypass'. Sounded ace, gave the car a proper Porsche sound but wasnt loud when not 'on it'. It was generally quiet in the cockpit and you only got the exhaust sound benefit with the windows open.
Had bought the CAT bypass to also go on but now i have sold the car. The CAT bypass is up for sale if your interested (brand new and boxed).