I autoX alot and have been getting beat (by hundreds of a second!) by a good friend in a 1996TT. I need more low/mid power. Can't mess with computer and stay in same class. Exhust is free. Any suggestions on Headers, Cat-bypass, sport mufflers. My buddy got a new exhaust for his TT with sport cats and lost 10hp. I don't want to make the same mistake.

I have an engineer friend in the aerospace field looking at designing a header with optimal wave-pulse flow. I don't understand exhaust gas theory, but he designs stuff for tanks and airplanes and knows his biz. I'd love to hear educated responses.

 

From my uneducated understanding, a better flow (larger tube dia.) will improve your top end, but diminish back pressure, hence low to mid efficiency.
Nowin te real world, perhaps getting rid of all the emissions controls crap (cats and co.) will improve torque all over the range.

One interesting device is the Exup from Yamaha. I think they stopped making it (have no clue why), but they used to put that on their crotch rockets up until a couple years ago. Definitely an interesting way to have a big top end ad not compromise the low end. But how will the EFI behave with that? This is the question!
After a quick google search, Suzuki uses a similar system on the GSXR1000. They claim a 6% torque gain (vs convetional) at low rpm (from 3k ... considering redline must be well over 10k).
Here's a bit of official write-up on the Exup : http://ymedc.introweb.nl/en/archive/...000_exup.shtml

Is ignition free? Perhaps some high power plugs and wiring could help out your torque span...

 

Does anyone know if Porsche or any 3rd party companies offer a shorter gear ratio to improve pickup? I've tried other cars with this mod and it's made a significant improvement at low speed acceleration in 1st and 2nd, with of course a drop off in the higher gears. Just curious...

 

Zorro and 996Garagage - thanks for the responses. The yahama idea sounds great, but its complexity is out of my friends capability. He is using a program call Ricardo Wave Tuning to help determine the best header design. It may get expensive for one pair, so I'm thinking about having a dozen or so made, along with cat bypass pipes. Let me know if anyone is interested.

The gearing is another great idea, unfortunately it will put me in the modified class, unless the gearing was a factory option. What I really need is a taller first gear and lower second gear. I do have info on gears if you need it.

 

i am assuming your car is normaly aspirated, since you posted here. if so there isn't much except a light weight fly wheel and sport clutch, wouldn't f$#k with the gearing, 100 cell cat also not a bad idea. for autox i would just run the stickiest tires possible like the corsa or ps2 cups and shave as much weight from your car as possible, this would make the biggiest difference. the headers are a waste of time. best bang for the buck is the ecu even though you don't want to screw with it.

just noticed your sig, your running hoosiers, thats about as sticky as they get.

 

Like Don said, if you're running an NA engine, changing the headers on your 996 isn't going to do much of anything (except maybe hurt you). Start getting rid of some weight from the car to gain those hundredths!

 

Agreed, and BTW the gearbox on the 996 is "sealed" with no parts available. Even if you messed up one of your OEM gears yo cannot replace it, only replace the whole box.
Weight drop is your only viable option IMO

 

Headers probably will not help any in an AutoX. Spend your money on tires.

 

Already Running Hoosier AS304's. Suspension is done and tuned. Just need a little bit more low and mid torque. I'm getting beat by cars with close to double my HP by .050 to .5 of a second. Just need a little. Was thinking about going with 17's and a lower profiel tirem to increase the low range of gearing. Unfortunately the tires I need don't seem to exist. 245/35/17 and 285/30/17. I go with 40/45 series then my overall diameter will remain the same (or close to it).

I'll keep you posted on the exhaust set up. I just gave my friend all the info: ie, bore, stroke, displacement, peak torque, compression, rpm, peak torque, intake and exhaust valve diameter. He did ask for the following and I haven't provide yet. Could use help:

Cylinder firing order...
Intake Valve lift...
Intake Rocker Arm Ratio...
Int. Duration at .050 lift (deg.)...
Intake lobe center line...
Intake opens at (BBDC)...
Exhaust lobe centerline...
Exhaust opens at (BBDC)...& closes at..

To all: We probably won't end up with much more hp at all, our goal is increased torque, with a flatter curve that rises at a lower rpm.