OK so then we can conclude that my 5 inch straight out pipes are the best? Need I show you guys the flames again?!?!

 

Craig, what are u going to call ur pipes?

Fabpipes or Eurospeed?

 

Mike, I originally planned to use a 10 inch muffler in a nearly straight run from the turbo to the tip (2 inches off axis). However, the general concensus was that it would be too loud (although quieter than straight pipes). Now, I will be using 17 inch long mufflers, which should remove considerably more volume.

Fabspeed appears to use 3 or 3.5 inch mufflers (outside diameter), which means they have 1/2 - 1 inch of sound absorbing material with a 2.5 inch inside diameter. I will be using a 4.5 inch outside diameter muffler, which means I will have 1.5 inches of sound absorbing material (with a 3 inch inside diameter). Therefore, with more sound absorbing material, I should not be louder than a Fabspeed exhaust, and I may be quieter.

Craig

 

I prefer Speedpipes!!!!

If it works out, my exhaust shop will be building a template so they can reproduce the exhaust for anyone else who might be interested.

Craig

 

Europipe Stage 2 -- that's the ticket!

 

Craig - I hope you're right. The exhaust this Guy made was screaming loud. I can't imagine what straight-pipes would be like. It definately made the EP2 Loud sound like OEM. Have you considered trying to get Europipe to make an exhaust for you like they did for Chad? I believe the piping is 85MM.

Mike

 

I would not be interested in a Europipe exhaust that uses a chamber muffler, regardless of the pipe diameter -- chamber mufflers rob power. ALL racing mufflers are straight through designs. For example:

Borla Racing Mufflers:




Burns Stainless Racing Mufflers:



MagnaFlow Racing Mufflers:



Now look at the Fabspeed exhaust, which was independantly proven to produce the most power of the 996TT exhausts available at the time of the test:



Not surprisingly, Fabspeed uses straight through mufflers similar to the racing mufflers depicted above. IMHO, that is the predominant reason why the Fabspeed produces more power.

Now look at the Europipe:



Europipe uses a chamber muffler, presumably because it is quieter. Europipe sacrifices power for sound attenuation, presumably because that is what most customers desire.

I am trying to strike a balance. Straight pipes produce the most power, but the volume is intolerable. Chamber mufflers sap too much power. A properly used straight through racing muffler will hopefully strike the right balance. I would use the Fabspeed exhaust, but for the restrictive 63.5mm piping.

You wrote that CJV is using 85mm piping? That is really big. If that figure is correct, Im sure it comes from the turbo books he has utilized (I forgot the name) and I will not disagree. However, my exhaust pro thinks 85 mm is too large for my car. While larger diameter piping reduces restrictions, it also can slow down the velocity of the exhaust gases, which can reduce power and increase turbo lag. The key is to strike a balance, such that the diameter is large enough to permit a free flow, while not reducing velocity too much. Thats how we came up with 76 mm for my application. A larger diamter may be appropriate for CJV's higher horsepower application.

Craig

 

it has less to do with the actual design and more to do with flow velocity and characteristics. Only a flow bench will measure this accurately. By design the stright through inherently appears to flow better intuitively...but that doesn't mean it actualy does or has to. With the right tools and testing (ie...time and money) you should be able to design a chamber system that flows just as well...but then it would probably be just as loud. If the is getting through the sound probably is too...

dave w

 

I have a Fabspeed exhaust for the GT2 for sale, let me know if your interested.

 

Years ago I read a dyno test on 2 1/2" mufflers behind a modified 454 Chevy dyno motor. The reverse flow OEM Corvair turbo and Chrysler Hemi mufflers produced as much or more power than the straight thru glass pack mufflers. They were also much quieter. Part of the problem with the turbo is that there isn't enough room for an ideal muffler. The chambers have to be too small.

 

there is a huge theoretical difference in system air flow through a turbo and NA motor. Itis very common for NA motors to loose power when flow is increased beyond a specific point due to a number of reasons. Generally with turbo apps this in not as common because you are using forced induction to get such a large volume in you need to evacuate it as fast as possible and the turbo itself is the bottleneck. continually increasing flow volume seems to yeild an optimal point and then level off vs decreasing. My point is that you can't really compare 454 chevy dyno results to a twin turbo application...

dave w