exhaust performance upgrade
Thread Starter
Racer
Joined: Nov 2007
Posts: 302
Likes: 0
exhaust performance upgrade
hi? What difference in performance and HP will i gain if i add a headman long tube headers, remove cat and put on dynomax super turbo mufflers and keeping most of the oem pipes? And or keeping stock headers and remove cat and put on dynomax mufflers? what gain in hp/performance will i get from either methods.
Le Mans Master
Joined: Sep 2004
Posts: 5,116
Likes: 5
From: Livonia MI
Depending on the condition of your cat converter, could be up to 20 hp. Old style converters are quite restrictive from the start, and running them on carburated cars, isnt doing their life any favors. My buddy with a 79' L-82, went with true duals through most of the factory exhaust, and can definitely feel the difference, especially in high rpm breathing. He also re-jetted the carb, and opened up the air filter hose inlet a bit. He still kept it hosed in fresh air, which is what you're wanting to do.
Melting Slicks
Joined: Aug 2010
Posts: 2,487
Likes: 10
From: Palm Beach Florida
St. Jude Donor '12
Depending on the condition of your cat converter, could be up to 20 hp. Old style converters are quite restrictive from the start, and running them on carburated cars, isnt doing their life any favors. My buddy with a 79' L-82, went with true duals through most of the factory exhaust, and can definitely feel the difference, especially in high rpm breathing. He also re-jetted the carb, and opened up the air filter hose inlet a bit. He still kept it hosed in fresh air, which is what you're wanting to do.
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Le Mans Master
Joined: Oct 2007
Posts: 7,441
Likes: 964
From: Tennessee/Rhode Island
Keeping in mind that my 78 L-82 had 220 Net HP when new which is about 180-185 RWHP on a dyno, I have made minor tweaks to a basically stock motor (66,000 miles) over many years with the biggest change being McJacks shorty headers, 2.5 inch duals, and Monza Turbo mufflers. On the dyno last October 2011, the motor produced 233 RWHP. The only other changes are Comp cams roller tipped 1.5, not 1.6, rockers, and a 4175 OEM Spreadbore replacement carb with no modifications to it. I hope my example gives you an idea of the HP potential that exhaust changes can make-it can be very substantial!
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
With a well-designed system, realistically ~20 HP/TQ. To keep it quiet, invest in a good crossover to soften the exhaust note. Matched with an intake, the gains can be more substantial. Budget for a dyno tune after installation.
Drifting
Joined: Sep 2006
Posts: 1,986
Likes: 21
From: Columbus MN
In my case, a new accelerator pump cam, bigger squirters and a very light vacuum secondary spring balanced the carb with the exhaust, and very light springs on my distributor brings the timing advance in sooner too. NOW I am getting the most from GM Performance 350 HO.
Melting Slicks
Joined: Dec 2009
Posts: 3,220
Likes: 651
From: Thunder Bay
Depends on what the streets are like in your area. I have Hooker Super Comp headers and I certainly wouldn't be lowering my car with the roads we have around here. I have to be careful with speed bumps, but the headers aren't the lowest point under the car. Corvettes don't have much ground clearance to begin with. My headers didn't change that much.
Last edited by drwet; Apr 14, 2012 at 10:14 AM. Reason: Kant spel
Drifting
Joined: Sep 2006
Posts: 1,986
Likes: 21
From: Columbus MN
Here are a couple of pictures to show you clearance (about 4") with long tube headers.
And here is a picture of my '80 showing how low it is in front. (I lowered the back end another inch since this picture was taken.)
