sshenton1975

Hi guys

Thanks for your advice - decided to go for it and took a trip to Porscheshop this morning in Birmingham to purchase my shiny G PIPE
As you know, this is being coupled to the Cup pipe I alreadh have fitted.

The results are fantastic - it sounds like an American V8 - very loud!! I must admit to being a bit embarrassed this afternoon when I took it out - it certainly turned heads.

BUT.................

It may be me, but the car does seem slightly down on power. When I changed to just the Cup pipe a few months ago, i noticed a positive difference. However, today with both pipes, there seemed to be a bit less urgency about the car. Could this just be down to the new sounds getting the better of me?
Obviously there is less back pressure:
a) can this really affect power substantially? What are we talking %?
b) could this damage the engine long term?
c) MOT failure?

I would like to keep this set up (I do few miles) but I don't want to suffer power loss.

What are you views - am I imagining it??/

Sounds the D*gs B*llocks though!!!!!!!!!!!!!!

964russ

i did the same a month ago. NO its daft! well 2 LOUD IMO.... 2 loud for me, well 2 LOUD!!! the feds r gunna b all over u!

rroobbcc

I recently posted a similiar reply to the following on the 996 board in response to a guy who experienced the same issue w/muffler bypass on his 996...

The general consensus is that these engines need some back pressure in order to develop torque to its full potential, especially in the low end. What you have done by adding the bypass pipes is removed most of the back pressure. So you have sacrificed your low-end torque in exchange for a little top-end HP and lots of noise. I would recommend going back to one of your two mufflers.

Chris M.

The 964 Cups have no cat, no primary, and no secondary. I doubt Porsche would have done this if it made the engine lose power.

SimonExtreme

It's not as simple as that! Changing the map for the ECU (DME) would mean the effect could be different. Therefore, what works on one car might not work on another. In addition, I haven't seen the cup parts but it could be that, although they have no silencing, they are shaped so as to ensure there is no loss of back pressure. And this can be the problem with aftermarket parts.

whakiewes

Simon,

Back pressure is needed in all engines in order to help the piston complete its 4-stroke cycle. On turbo engines you don't need much of an exhaust because the turbo causes a large amount of back pressure itself. On NA engines though back pressure is needed in different ways. Because of the RPM's and how NA engines create power, what is more important is the pulsing action. This is achieved through design not restriction.

There is a but though to the whole back pressue idea - how it helps. Where an NA engine suffers from back pressure is at low rpms where the pressure doensn't exceed the rotating mass. This is the 'torque' that you lose. The engine struggles to keep spinning essentially (although this really isn't the case). At upper RPMS though, typically above 4000, the engine has enough speed to not be disrupted by a loss in back pressure. This can also be further helped with ECU tuning that advances the timing to help the engine gain back what is lost.

So on cup cars exhaust aren't needed because how often do you see below 4000 rpms. On the street we are constantly starting from a stand still and shifting a lot. Its not feasible and responsible to run at 4-5k plus all the time. For short runs, but to cruise at 5500rpms is just a waste. This is why we pay so much for engineered exhaust systems. They help it so we can enjoy the car as much from 1000-5500rpms as we can from 5500-8000rpms. Unfortunately though there aren't many engineered exhausts, but more of 'fabricated' exhausts.

I love the sound of bypasses installed on air-cooled flat-6's. Its a sound that is rivaled even by American V8's. If you enjoy it, then all it good and well.

Wes

N51

There's no way I'll tolerate my modified RSA sounding like an American V8.

Noah

SimonExtreme

I personally think you are mad driving this set up on the road. I think you are asking for a whole heap of trouble. This is how I understand the law.

1. If the vehicle exhaust produces more noise than standard then that's an offence under the Construction and Use Regs. Magistrates will accept the opinion of a police officer that the exhaust is noisier than standard, no reference to dB meters, no reference to BSI/EN marks.

2. The law states "Every vehicle propelled by an ICE shall be fitted with an exhaust system including a silencer and the exhaust gases from the engine shall not escape into the atmosphere without first passing through the silencer. Reg 54(1) MV(C & U) Regs 1986." By removing all silencers, your car is illegal.


3. If you cause your car to not meet the CU regs, youcould be invalidating your insurance. You need to declare this mod, or you are in trouble. For instance, I declared my decat and cup pipe and these are noted on my policy. However, my car is still legal if in the opinion of a police officer, it is not too loud. Your car is illegal because it has no silencer and therefore, even with your declaration, your unurers might not pay up.

3. Not declaring the mod is, theoretically, illegal as you have obtained your insurance by deception. It is rare for the police to throw that one at people, but they have done.

I really do think you are bringing a whole heap of trouble on yourself. I would be very suprised if you don't get stopped. At best, you will be given 15 days to replace the STANDARD system, at worst, you will be done for driving an unroadworthy car and having invalid insurance. Because of the chav ellement in UK society driving riced up "Max Power" cars, the courts aren't very sympathetic to this type of thing at the moment.

Good luck!!

Marc Shaw

Is this supposed to be a good thing?

Marc

Devils_son

I tried the same setup (+ catbypass) last week. Too loud. Way too loud... Removed the G-pipe a little later and now the secondary is back in place.

Not only did I think it was too loud for the neighbourhood, I think it is too loud for me sitting in the car. Good fun for a few kilometers, but after that... no. Not only that, you will be kicked of most circuits because of the noise... I don't like to be a spectator at the Nordschleife.

Devils_son

p.s. an RS pipe may cure the power loss...

sshenton1975

Mmmm - Thinking of changing back purely because of power loss not because of noise - that' great!

What is the RS pipe?

Any other way of getting back my lost torque without removing the g pipe?

MassGuy

I just bought a gpipe from Marc and I look forward to putting it on my car. I will then have both pipes bypassed. I know this is going to be loud...real loud.

So when I want loud the pipe will be on. When I want quite the pipe will be off. Real simple. No need for a big debate. One more reason to love my 964. One more thing I can can play with to help ME to enjoy my car.

I hope this thing sounds like a pack of harleys.....louder than an american v8........in fact I hope women grab there children and run them in the house.

This is the effect I want.....temporarily.......then I will put the pipe on when I am done playing. YAY.

bjorne

I have both primary and secondary bypasses, yes car is loud, but I love it, car is 75%track/25 street, you get use to the noise, its all in what YOU like, and I have noticed NO power loss in any rpm range
just enjoy, just my opinion
Jason

fstockcarrera

Jeff and I have done extensive dyno work there is absolutely no loss of power with Primary and secondary bypasses only INCREASES with stock headers. If you replace the cat with the europremuffler you will gain MORE POWER. These Engines need very little back pressure

Bob