Thanks Stef for the informative post, as always I enjoy reading your thoughts on exhaust. Your point about dyno only a reflection of WOT testing, and the turbo reducing scavenging effect, are very good and well taken.

The complaint about torque loss at low rpm is indeed rare but I have heard of a couple of different owners mentioning it. I actually drove one of the cars: I was auditioning mainly for sound and was not aware of the possibility at the time, but after the test drive, the car's owner asked me of my impression, without mentioning anything specific. I told him great, but somehow the car felt like there is loss of torque in the low range. At which point he said he felt the same thing!
On two other cars, owners PM'ed me with the problems. I didn't drive those cars, but the description from their owners is same. While anecdotal, the number of complaints versus the very small number of owners here make me feel like it's worth a warning to be presented.

The subjective torque loss was in the same lower rpm range that you mentioned. It is always a puzzle to me, and its subjective nature and where it happens (part throttle & lower rpm) do make it very hard to prove one way or another.

 

Stef I take on board and agree with what you say about turbo and naturally aspirated engine characteristics and their respective exhaust system pro's and con's. An atmo engine is certainly far more susceptible to power loss from an under restricted exhaust for sure. I have experienced that for myself in atmo cars with AM systems. From the outset it is reasonable to expect that a turbocharged engine should have better flow and therefore performance characteristics with a less restrictive system (that is if the system is truly less restrictive than stock) so i was kind of surprised when i found my last AM system was removing some sting out of the midrange and upper rpm range. The engine certainly felt like it had lost some of its previous zippiness at WOT especially when the boost kicked in....no question about that in my mind. The thing about the 997tt engine is it's so powerful to begin with so it can naturally make any adverse changes in power delivery a little harder to detect for certain users....as the car is so damn quick anyway. But for all of that i definitely know i certainly wasn't imagining it....that is for 100% certain. What i felt was unmistakeable and the longer i drove the car and familiarised myself with its new driving characteristics the more and more obvious it became. Right from the get go i knew something was definitely missing from the first WOT drive....but i just couldn't put my finger on it at that stage so needed more seat time. It felt like up until @3500 the car felt less restricted, if not by a huge amount, so it was better there, but after @ 3800rpm upward, the thrust of the car simply didn't feel quite as strong as what it was before with the stock system.....like the sharp blade had been somewhat dulled. And the longer i drove the car the more conclusive it became. As i said, the car felt better under 3/3500rpm than before, but beyond that it had become dulled in an unexciting kind of way. So Stef i don't know how you can answer for that. Maybe with your experience in finding the magic balance of the EP you have come across this problem in your r and d processes? I note your comments on a system with shorter length tubes for example...as deadening the midrange. So maybe some of these AM systems have somehow wound up with shorter tubes or something. Anyway, one thing that is 100% for dead certain is that after the back to back changeout of removing this very well known AM system and fitting up your EP1 system the difference was unquestionably immediate!!! And right from the moment i pulled out of the driveway onto the road. And further driving through the rev range at partial and at WOT the difference was incredible...it was like WTF!!! (and in a good way thankfully....and phew). I honestly wasn't expecting such a dramatic difference. And in fact to begin with i was very skeptical that your system was going to cut it.....to the point that if your system didn't hit the spot i had resigned myself to having to revert to the stock system. But like before with the previous AM system, the longer i drove the car, and over the following days it was absolutely unmistakably conclusive the car had gained more thrust everywhere!!....at part throttle, wot...EVERYWHERE!. In fact it felt so much stronger and zippier than that last POS AM system it was absurd. I was honestly very annoyed with myself for putting up with that last POS AM system for as long as i had, which wasn't very long at all...but let me tell you seemed like a damn eternity at the time. I must admit i had no idea that a decent exhaust could make such a huge difference to this 997tt car and my car was running the stock tune file so i had no tune as such to contaminate my findings. I have no answer for it. Maybe Stef you have an answer? I know one thing for sure though. The manufacturer of that last AM system sure has a hell of lot to answer for. No wonder they dont/won't offer money back satisfaction guarantees. The bloody thing was also a bastard to fit to boot. The cat flanges were too thick at the turbo housing so you had to bend the small turbo heat shields which also left two of each 4 studs with barely enough nut purchase. The straps were a bad joke...ridiculous....i could go on... how they can charge what they do for this rubbish is outrageous.....and to say an EP is expensive in comparison to whats on offer...is completely.. And what is it with people and chromed up shiny stuff????....some manufacturers evidently know some people seem to just love this shiney chrome **** and are prepared to pay all sorts of silly money for it thinking it has to be better when it's not. Oh well... all that i can say to that is there are them's that know.

 

Hi Paul, whow what a post !

Sorry I have no answer to your questions about your previous Tubi exhaust. I'm not that familiar with this system really.

Don't worry too much about the past and enjoy what you have now.

Cheers, Stef

 

I have heard a few anecdotal reports of CELs with GMG's cross flow exhaust. Not sure if this is a problem with the exhaust cats or the owner's cars. You can PM me for more details if you need them.

The stock exhaust is 65mm if I'm not mistaken. I have to believe in a turbocharged application you'll make more power with less back pressure with a 76mm exhaust.

 

Yeh, well I'm known for a good rant.
Now Stef are you sure about not knowing anything about why some of these systems are taking the sting out the car....or are you just being too politically correct with this silence.