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Simple question: Is anyone running headers + high flow cats with a center bypass? Or is this a total faux pas on these cars?
I do realize that the "golden ticket" is to do headers + cats with side muffler delete and OEM or upgraded center muffler, but if your car already has a center bypass and you want to retain the functionality of the valved side mufflers, would it be insane to install headers + 200 cell cats as well?
Tye has the EVOMS and Sharkwerks bypass on his car. I'm sure he'll chime in shortly.
A buddy of mine who doesn't post here has GMG headers with 200 cell cats and a GMG bypass. I've driven my friend's GT3 with the GMG setup and it sounds nice.
If you want to keep exhaust valve functionality while minimizing weight, various companies like Fabspeed and TPC sell valved side muffler bypasses.
After going from Track exhaust, to Bypass, and now Bypass plus Headers, I can say this is the best combination. From a sound perspective, there is ZERO drone. This thing is track exhaust loud when WOT, yet bypass quiet when just cruising around. The best way to describe it is imagine being able to turn the volume up on the bypass. At WOT, the sound is a very clean wale, much cleaner sounding than the track exhaust which i thought was a little muddy.
More importantly than sound, with the retune optimized for this setup, there are significant gains across the range. The mid range pickup is significant to tell by the butt dyno, where i dont feel the need to have to gear down if im not in the ideal gear.
The Sharkwerks/Evoms Headers come with 200 Cell cats. They are fully modular so you can remove the cats when you go to the track and replace with a test pipe, which is nice so you arent burning your cats out.
I also added the Carnewal Remote Valve switch so I could control the functioning of the valves at any time.
Also, another option that wasn't available at the time I did all this, but is now, is the Dundon long tube header and custom center muffler option. With or without cats depending on your preference. Verified power gains across the rev range. Its very tempting
FWIW.
I have GMG catless headers / my center bypass / oem side mufflers.
Did a 2 pulls against a 997.2 3.8 gt3 - 3rd gear, 45 - 120, i got about 1 car length on him down low - at about 120, right before shifting - he was 1/2 car behind me. My car has a lot of front aero as well. FWIW. No tune. I don't want to mess w/ that stuff.
I have side muffler delete. Cargraphic headers with 200 cel cats with valves. I was going to go with a Cup center muffler or bypass but I was told the stock center is very similar to the Cup and it's not very restrictive. When my stock center splits I'll probably switch to a bypass; I like loud cars. My CGT and Stradale with valves bypassed were favorites. However for now I'm happy with the huge weight reduction and sound I get with the Cargraphic headers. And like the guys I'm running 100mm tips. They fill out the exhaust exit perfectly. Be sure to get 997 specific 100mm tips. Otherwise it just looks wrong. GL! Best JBO
When my stock center splits I'll probably switch to a bypass; I like loud cars.
Weld reinforcement plates onto the stock center to reduce the risk of cracking. I have about 12-14 trackdays on my reinforced stock center, BBI side muffler delete, and Fabspeed headers with 200 cell cats exhaust setup with no issues.
Did you guys lose and throttle response by going with 200cell cats or catless setups? That is my biggest fear!
The headers themselves are pretty innocuous about that on these cars, bolting them on by themselves won't cause issues, and doing the headers plus an appropriate tune for them (like our Stage 3) is all gravy--more power and better response than stock across the board.
What does kill low end power and throttle response is doing one of the track exhausts with no rear muffler or valves. See the dyno chart below; you'll pick up power over ~4000rpm and save some weight, but low end power gets hit pretty hard:
Thanks for the quick response! That's cheap horsepower. Sounds like a good value based on the gains shown on the graph. I'll give you a call. Best Josh
10-11-2017, 05:13 PM
Headers + High Flow Cats and Center Bypass?
