# Cutouts HP and TRQ numbers



## dustyminpin (Jun 19, 2006)

August '11 issue of High Performance Pontiac ran an article covering a topic that I've been wanting to know about for over a year now. They did a test comparing a full aftermarket exhaust vs. cutouts on a dyno. I put DMH Low Profile electric cutouts on my goat last summer right before the Power Tour and talked to lots of peeps on tour about the possible gains of them and nobody really seemed to know. I remember getting mixed answers here on the forum as well. Hell, the guys running the dyno at the Dyno-Challenge didn't even know. The results the magazine got back were a gain of 11 HP and 8 lbs-ft. with the cutouts open, over several runs to verify consistency. As they say on G.I. Joe, "Now you know, and knowing is half the battle."


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## Gotagoat (Jan 6, 2006)

Given this info, I wonder if the reduced back pressure from my Kooks Afterburners add a horse or three.


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## dustyminpin (Jun 19, 2006)

I'm sure they do. My Borla guy told me on they phone they saw an average of 5 hp increase on the GTO 5" tip model (they didn't offer a 4" tip back then although it would yield the same bump).


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## svede1212 (Nov 1, 2005)

It's time we stuck the "back pressure" with a pick axe in the head and buried it. Back pressure reduces air flow and power. In my opinion altho a MAF can help adjust for the change in air flow a different tune might yield better results yet.


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## SWGOAT (Nov 9, 2010)

What Hp/torque gains would shorty headers, stock mids with stock cats, resonator delete and muffler delete yield as this exhaust is rather unrestricted and flows well with CAI and Diablosport tune. This exhaust mod should reduce back pressure and increase flow, anyone have an idean of HP/torque gains? I plan on getting car on dyno this summer.


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## 87GN06GTO07IRL (Aug 10, 2009)

dustyminpin said:


> My Borla guy told me on they phone they saw an average of 5 hp increase on the GTO 5" tip model (they didn't offer a 4" tip back then although it would yield the same bump).


I'm thinking he gave you a line of crap. I can't see how a tip would reduce back pressure. Bends of a smaller degree in the system would help, a bigger tip, not so much.


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## svede1212 (Nov 1, 2005)

I would call BS on the tip thing too. Sometimes a _smaller_ tip can be used. Exhaust is a balance between keeping as low of a back pressure as possible while at the same time keeping exhaust velocity as high as possible. As the gases travel the length of the pipe they start cooling and slowing down. A larger tip just slows it more. IMHO a tip shouldn't be larger than the pipe that feeds it. It makes exhaust sense and anti-ricer sense. There are lots of articles on exhaust design that aren't forums and give real data.


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## svede1212 (Nov 1, 2005)

SWGOAT said:


> What Hp/torque gains would shorty headers, stock mids with stock cats, resonator delete and muffler delete yield as this exhaust is rather unrestricted and flows well with CAI and Diablosport tune. This exhaust mod should reduce back pressure and increase flow, anyone have an idean of HP/torque gains? I plan on getting car on dyno this summer.


Not much if the rest of the engine is stock and you keep the stock cats


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## dustyminpin (Jun 19, 2006)

87GN06GTO07IRL said:


> I'm thinking he gave you a line of crap. I can't see how a tip would reduce back pressure. Bends of a smaller degree in the system would help, a bigger tip, not so much.


You and Svede misinterpreted my post. The Borla rep was telling me that their model yielded a 5 hp bump over the stock exhaust, period. I was merely throwing the 5" tips in there to let the readers know which model I have. At the time, Borla only made the 5" tip model. For the first several years of production that was it. Now they offer a 4" tip and a 5" tip because some customers didn't like the looks of the "coffee can" tips, said they were too ricey. My ass. They're goddammed beautiful.


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## svede1212 (Nov 1, 2005)

I'd believe a 5HP bump. The tips. . . to each their own but anything larger than the pipe is trying to give the impression that there's something there that isn't IMHO hence the rice tag.


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## dustyminpin (Jun 19, 2006)

I see your point, but I hadn't really thought of it like that since the stock tips were bigger then the rest of the pipe as well. 2.5" to 3" if memory serves. My stock exhaust has been up in the attic for years.


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## Poncho Dan (Jun 30, 2009)

Stock catback sucks because it weighs almost 70 pounds. Not to mention it sounds like its packed full of a bunch of wet socks.

If exhaust pulse speed (and sync) must remain as fast as possible from port to tip, then in theory, glasspack/resonator/magnapack style is superior to chambered.


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## svede1212 (Nov 1, 2005)

Poncho Dan said:


> Stock catback sucks because it weighs almost 70 pounds. Not to mention it sounds like its packed full of a bunch of wet socks.
> 
> *If exhaust pulse speed (and sync) must remain as fast as possible from port to tip, then in theory, glasspack/resonator/magnapack style is superior to chambered.*


That's the idea. Gases leave the cylinder extremely fast and you want to lose as little of that speed as possible. Cut-outs are best :~)


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