The article cited makes reference to the "bellmouth". This is typically a feature on a down pipe in a single turbo application, like a subaru WRX for example. The Porsche does not use a bellmouth - the turbos bolt directly to the cats, not a bellmouth. As for the "divorced" bellmouth/wastegate comments....some bellmouths have splitters to smooth the flow out of the turbo and some do not, but the Porsche exhaust system is a completely different animal and does not utilize this type of hardware or feature.

Likewise the 2.5" vs. 3" pipe diameter information appears to be based on a single turbo application and the examples cited are based on the exhaust pipe handling the entire engines gases through a single pipe. Again, this is not the case with the 911 twin turbo cars. The pipe diameter on our cars only handles 1/2 of the engine HP, thus 2.5" diameter would be good for 500 HP or more on a flat 6 911 twin turbo, using the data cited in the article.

There is some good information in the article, but it does not seem to address the Porsche style motor and exhaust system. For instance, our 100 cell cat, 2.5" quiet exhaust system really wakes up the 997TT, especially when the car is flashed and that is over 500 HP.

 

Bosco,

You are absolutely right. I stand corrected.

Initially, I did not look too closely and saw markings on the exhaust can that looked to me like Akropovic markings.

The picture is below:



After reading your post, I went back to the workshop this morning for a closer look (to avoid making a more of a fool of myself ) and this is the result:



I apologize for my confusion.

Regards,

Karim

 

Totally understandable error...dont know why they would use the same symbols as Akrapovic...definitley misleading

 

thanks for the feed back i learn something new every day. this post was for more informative then specifically for a 911 turbo engine, just the basics, but you do have good points though.

 

Very interesting topic & very nice article Ronnie. In theory, you should not lose power when back pressure is reduced, such as by using a more free-flowing exhaust.

In practice, yes there have been reports of at least a subjective sense of loss of low end punch with a change from stock to after-market exhaust. The 3 cars that I know about have nothing in common, in the sense that a different brand of exhaust was used in each car. Even though the problem is real to owners, its subjective nature makes it extremely difficult to prove one way or another.
In one of the car mentioned above, I vaguely recall that owner (used to post here - if still lurking pls correct me as needed ) mentioned he had dyno'ed car before and after and there was a slight loss of torque below 3000 after exhaust was installed. Dyno's were not posted but still to me they are not sufficient proof, as the change could be dyno to dyno variation, and one needs to show it in more than just one car, and, proves (how?!) that sense of loss *is* related to that loss of torque on dyno.
In addition, there are other things going on with a more free flow exahust, such as the seemingly faster spooling up of engine; is it possible this subjective sense of loss is not real, but a by-product of the faster spooling up?

Also, a couple of knowledgeable and experienced tuners (who have worked with more than just Porsche Turbo's) have told me, yes, too much pressure reduction *could* lead to less low end torque. Are they right or wrong? I don't know. Could it be before the Turbo kicks in, the engine acts as NA engine and therefore does not like the reduction in back pressure? Could the back pressure reduction somehow affects the scavenging effect? I don't know either.

Despite of vendors advertising gain of such such with an exhaust mod alone, when I installed my after-market exhaust, not only was I not looking for *any* horsepower gain, I was ecstatic and relieved I did not feel any loss of punch!

 

Here's a link to Stephen Kaspar's 996tt 2003 study of exhausts. The exhausts that showed lowest backpressure showed greatest tq gains at lower end (fabspeed track sport, europipe, turbo-exhaust.com). The greatest overall gain was with the one with the lowest backpressure (fabspeed track, $600). Interestingly, the expensive ones like Europipe were not a whole lot better than stock and Ruf was even worse.

http://www.rennlist.com/imagineauto/<!-- google_ad_section_end -->

 

Thanks for the informative write-up. It's rare to find anyone who actually understands the whole system and the physics behind it

 

Not sure I agree. The EP was much better at typical driving engine speeds, ie, below 4500 RPM and the biggest gains were lowest. That makes for a very streetable power curve. I have a stock pipe, but the EP had the power curve I'd want on a street car.

 

c'mon Paul let's see if we can get a group discount on those bad boys!

 

These are the HP gains of the Europipe Stage 2 over a stock exhaust in this Imagine Auto Dyno test :

2500 rpm : + 20 HP

3000 rpm : + 31 HP

3500 rpm : + 58 HP

4000 rpm : + 71 HP

4500 rpm : + 0 HP

5000 rpm : + 7 HP

5500 rpm : + 0 HP

6000 rpm : + 24 HP

6500 rpm : + 3 HP

7000 rpm : + 20 HP


So after 4000 rpm the waste gates open and all the gains are gone...

If the EP Stage 2 is free flowing at 4000 rpm it is free flowing at 6500 rpm as well. The maximum backpressure of the EP stage 2 at 7000 rpm is 60% less than the stock exhaust.

So overall the Europipe was not a whole lot better than the stock exhaust , that is correct but it wasn't a fair test either.

Also the Ruf exhaust is a nice exhaust with a great sound , no drone and decent HP gains. But if your wheels are slipping on the rollers the HP gains won't be pretty.

What can we learn from this ? Get a proper ECU tune for your specific engine mods and exhange the data logs with your tuner.

Hope this helps.

Cheers , Stef

 

stef

please correct me if i am wrong but if it was stage 2 then it should be 72 % less then the stock ? and 60 % for stage 1 based on my calculations
ronnie

 

thanks for sharing

 

Haha.....no, not yet ronnie. Maybe something i will do in future though...time and money permitting. Too many other priorities at the moment.

So true. Good to see you're on to it.

I totally agree with you on that xseal. My butt dyno certainly felt the car was better than stock everywhere after the EP1 install. After back to back testing the stock versus tubi versus EP1 i found that the tubi lost power and the EP1 gained power slightly over stock. EP certainly had more down low and was sharper and crisper under throttle everywhere. At the time i removed the tubi i was highly critical and was even prepared to forget the EP if it didn't live up to expectations and go back to stock. Thankfully i was pleasantly surprised.
I would agree a tune would make an aftermarket system work better but my findings on the EP1 was the car felt like it was given a mild tune as such after instal. In all honesty i was even contemplating not bothering with a tune after the instal. The EP made enough of a difference to be satisfied with.
The tubi, and i understand many others remove a bit of power until a tune is added. And i believe that fact is now out of the bag.

Great thinking there Boggy. But it'll have to wait till im back in Aus....im out of town for a long time. Am currently sipping cafe in Paris so time to respond to threads and think of future mods is limited at the present...but that time will come

 

The only real benefits in HIGH performance are tuner packaged systems where R&D has been intense because it is profitable and every tuner wishes to remain reputable...
This is not to say longevity will not be reduced (for those of you swapping cars every few months not a problem)..

So unless you're willing and the pant pockets are able...

 

Do we have video footage of software tuned versus software/AM exhaust?