Blue Meanie

iTrader: (3)

I was talking to a friend of mine that told me I am probably losing 15-30 horsepower with my GMMG vs True duals or cutouts. Is it really that much? I was thinking maybe 15 with cutouts. He said GMMG doesn't flow that well, I thought it was one of the best. It certainly sounds like it flows well with the insane volume of sound it makes. I am considering switching to true duals if the difference is that high. With the new cam and electric waterpump on top of that it could possibly put me close to the 490-500hp range.

Ls1CamaroGuy87

iTrader: (7)

lol, no way! The horsepower difference betweet y-pipes and true duels is too close to measure....Now when longtubes enter the picture...there could be I am guessing a 3-7 HP difference between the two. I think your friend is wrong.

99Hawk262

iTrader: (19)

I would say maybe 5-10 max difference between GMMG and TD's. GMMG is a great catback and does make great power. Put cutouts on and call it a day. Nothing flows better than cutouts. You'll have the power when you want it, and the sound for cruising.

300bhp/ton

If that rwhp is on a Mustang Dyno then I think a set of duals would in theory offer more HP, but by how much is difficult to tell. There are many people who have mde well over 650rwhp with a 3" Y pipe in the past.

Having said that you are at a level of HP where a 3" Y is a restriction in terms of flow.

As for the mufflers, well usually straight thru chambered ones as used by GMMG are pretty decent. However some neck down and reduce flow. Also for some reason GMMG use smaller tubing after the axle and presumbly smaller core mufflers so there is a chance it isn't flowing as well as some other catbacks. But I bet it is better than most.

An easy way to tell is just pull the GMMG out of the Y (same affect as a cutout) and slap it on a dyno, then recouple the GMMG and dyno again to compare results.

If you want duals, it might be worth utilizing the rear half of the GMMG and get some custom lengths going from the collectors on the LT's via an X pipe to the two pipes for each muffler on the GMMG and simply bin the rest.

2.5" duals will out flow a 3" Y

3" duals probably are needed for another 100 or so rwhp.

Blue Meanie

iTrader: (3)

Well if it isn't as bad as he was saying, which I didn't believe it was I will just leave it. I'll do some cutouts when I switch the cams. Your idea about cutting up the GMMG and making duals out of it sounds intriguing though.

Poltergeist

My car is just a bolt on but when I open my cutout (just before the axel) I only gain 5rwhp over my GMMG. A friends H/C car only gained 4rwhp when he opened his cutout with his GMMG.

Weekend Racer

The GMMG will flow as good S ANYTHING OUT THERE!

300bhp/ton

Yeah but are you guys at or near the same HP level as this guy? Personally I really like the Y pipe setup, but once you start approaching 500rwhp duals really do make sense if you're after every pony.

300bhp/ton

Care to back that up? Do you have any CFM numbers for the GMMG? And BTW there are plenty of setups that will easily out flow the GMMG TSP Rumbler X for starters.

JustAnIlluzion

iTrader: (60)

agree,

the gmmg has too many bends and the smallish mufflers.

nexvctm2001ss

iTrader: (8)

WOW this must be a joke GMMG=restriction True duals only made me gain 8rwhp over GMMG and a cutout with GMMG set up only 5rwhp over this exhaust.Like some one else stated unless every hp counts 2 you or you are making alot of hp then GMMG will be just fine. My car=418 rwhp without the spray so all I can say is WOW to all this

Poltergeist

Exactly which part of "my car is just a bolt on" did you not understand?

Z2K_MrJ

If your Car Is Pushing 8XX HP then you might Gain 15-30 Hp Like your Friend SAId.

300bhp/ton

Sorry but I really don't understand what you are know getting at. Bolt on or not makes no odds to CFM flow rate. The GMMG may not be restrictive at 'x' bhp level. However the thread starters setup is far beyond that level, so claiming its still not a restriction is an inaccurate conclusion.