forhamilton

So the back story is this. I have GMG headers on my RS, side muffler delete and M&M exhaust. The bung broke and I pulled the header off to have it welded back on. In doing this I realized the packing from the cats is falling completely out. So I emailed GMG. I didn't get much help. They want to charge me $1200 per side to rebuild. Car only has 13,000 miles. They blame it on abuse.

I've heard that the power gains are not found in the headers, but the side muffler delete and a high flow center exhaust. Others claim they come from the headers.

I started looking at the factory headers. There really isn't that much difference and it makes sense that Porsche would put the most powerful, lightest and highest flowing header they can get to make emissions and last. They went as far as to make the center out of titanium!

So my real question is who has done actual testing and has data on the factory headers versus after market with side muffler delete and high flow center exhaust? What does the data show?

I really don't want to hear from anyone that is guessing or someone trying to sell there product. I want the whole truth and nothing but the truth so help me God!

bmwtye

While I dont have data on side muffler delete, I have the Sharkwerks/Evoms Headers, high flow cats in conjunction with OEM side mufflers and Sharkwerks center bypass. Here is the data:

https://rennlist.com/forums/997-gt2-...s-unicorn.html

I have also previously run the oem headers/cats with sharkwerks track exhaust which replaces the side mufflers.

I can tell you comparing that setup to the header setup i have now, the header setup put out more hp and tq, and im not talking just peak numbers. With the track exhaust, low end tq went down since the side mufflers were gone.

I am extremely happy with the Sharkwerks/Evoms setup.

forhamilton

I would be curious to see how much power your car would make if you deleted the side mufflers and went back to stock headers.

NorthVan

Power is made from limiting the restriction of air flow. Cats create the most resistance, mufflers create the least.

I have some custom made Cat less Headers that run to the factory mufflers. When I want it loud, I hit the sport button, when I need it quiet, I turn if off.

My experience with 200 cell cats are they will all fail, then you run the risk of sucking pieces of the cat back into the engine.

Spyerx

Tune + headers with high flow cats = about 20-25hp, 15lbs torque.
My results with a COBB tune + Cup 100 cell headers are almost identical to bmwtye. (I went with the motorsport cup parts for OEM quality)
The key is the high flow cats + tune to optimize for them.
Side delete only is more about weight and heat, not power, you may pickup a couple HP but not really measurable.
In the link Tye posted, he has that, stock tune, headers, side mufflers, only center bypass which gives no power.

ShakeNBake

OEM Tune, I lost 10-15hp going back to stock headers from GMG.

forhamilton

Shakenbake, do you have side mufflers?

bmwtye

Deleting the side mufflers will cause a loss in low end tq, and these cars already lack that so having even less isnt the best idea. While you can compensate this a bit with tuning, its still a loss. The loss in tq is up to about 3700 rpms.

bmwtye

The beauty of the sharkwerks/evoms system is the 200 cell cat is modular so you can just pop it out and replace it with the straight through test pipe for track days. You can buy the header setup with both the cat and the test pipe

forhamilton

I didn't even realize these cars functioned below 3700 rpm!

Seriously though, I'm most concerned about power at the track. I rarely would be in the low rpm range.

bmwtye

Yea I'm rarely under that but u wanted data so providing you with it. If u don't have noise restrictions at your tracks run the Sharkwerks track exhaust

sterlingc1975

Going to be playing on the dyno with some of these scenarios myself real soon..

surlynkid

I have the FVD RSR system by M&M with headers, side deletes, 200 cell cats and center muffler. Just look at the design of the oem headers versus real headers. The oem design sucks. The M&M headers are nice and designed to provide equal length of each cylinder and equal back pressure. There is no balance to exhaust flows with oem. I was 390 at the wheels at a shop well known for low dyno readings. I definitely have more power over stock. I would guess on a proper dyno, I am 405. 3700rpm - they meant for pit lane.

I have my dyno data if you want to see it. I have the FVD tune with the exhaust.

FLT6SPD

Any fabrication facility can produce headers, but its not just about welding pipes and flanges and removing everybit of backpressure (unless its a turbo), it's a science, some get it right, others do not.

As far as cats falling apart I would look into the mfg and not use them again, If the pieces get sucked back into your engine you have other problems with scaveging...

ShakeNBake

Yes, GMG headers + Side Mufflers + GMG center section. Car made 425HP on local dyno SAE adjusted, then produced 410 on same dyno with oem headers.