At what point does the factory or a GT500-style closed muffler start limiting power?

Uncle Rusty

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Hey guys, I was wondering if anyone had experience with running different mufflers with Supercharged applications? Specifically, I recently re-installed my factory Mustang Mufflers coming from the more open and much louder Roush ones. I'm still running an offroad X-Pipe, so the exhaust is still mostly open flowing aside from that.


I know that in an N/A car, the difference in power here would likely be zero or less than 1-2HP or something along those lines. My question is though, doesn't that change once you're at a certain level of power? I know that this probably has an effect moreso on a Turbo car where backpressure is an important factor, but am I losing power running my TVS at 10psi on E85 with the factory versus the Roush Mufflers?


I'll mention I recently switched over to E85 at the same time I swapped the factory's back on, so I don't have a good butt dyno benchmark to compare, but power-wise it felt the same on corn as it did on 93. It also might just be the weather though, it was getting up there around 85-90 with 75% humidity so that might be it.


In either case it's a nice change of pace going from a car that you can hear 5 miles away to more of the sleeper mode with the TVS being much louder than the exhaust, which you can't hear more than a few blocks away in comparison.
 

Uncle Rusty

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Good to hear some real-world examples from you crazy high HP guys... I'm not gonna worry about it at all then, lol. I don't think there's much of a difference between the Factory GT vs GT500 Mufflers aside from the sound.

I'm considering getting electric exhaust cut-outs, more so for the fun factor, but if I do I'll definitely dyno the comparison when I have the chance since I'm definitely curious if it's any different at all.
 

Sizeth3

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I would be curious to see, just because a car makes 600 rwhp with the stock mufflers, doesn't mean it wouldn't make 620 or 630 with a free flowing exhaust. On a forced induction car, you can always just turn up the boost, however I would be surprised if there isn't something to gain with a freer flowing exhaust.

I remember on my last Camaro, swapping from a high flow Magnaflow 3" muffler to a 3" bullet muffler picked up 2 mph and 2 tenths in the 1/4 consistently.
 

Doug1227

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I have QTP electric cutouts, but we never opened them on the dyno. In theory, I could make the MAX HP that I want to make (what I'm making now) with a more free flowing exhaust or with the cutouts open. HOWEVER, if I can make it through the stock quiet stuff, then I'll just leave it alone. I may do some testing where I run a lower boost setting, but open my cutouts to see if that makes a big difference.
 

MRSUPRA

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/\Well said. And I was surprised myself to see that power made through GT500 mufflers.
 

11Sec_Lx

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My exhaust consists of stock manifolds, cat deletes, stock H, stock over axles and a GT500 axle back. I added cutouts last winter. On my car, making mid 700's on Pump/Torco the cutouts added 9 rwhp.
 

11Sec_Lx

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Btw... Here is a pic of my exhaust.
cf7de9fee94b56d01731dd57846821bb.jpg
 

burke985

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I have a set of JBA on now and i changed them for some single tip GT 500 muffs and maybe it was just my mind playing tricks on me but the gt500 made it feel restricted a lil. I took em off and put my JBA's back on
 

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