1979 Cat delete?
Race Director
Joined: Nov 2006
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From: Sunshine Coast, Queensland, Australia
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Cruise-In VIII Veteran
Don't waste your time. Seriously, any exhaust shop can make up a "test" pipe. But putting on a true dual exhaust is good for 50 - 80 H.P.
That 2 into 1 back into 2 system just plane sucks!
That 2 into 1 back into 2 system just plane sucks!
Le Mans Master
Joined: Jun 2019
Posts: 7,658
Likes: 2,470
From: Indiana
https://www.corvetteforum.com/forums...79-4speed.html
agree, do not waste yourtime for 2 reasons
at least when i was looking..all unobtainium ebay etc..
you will be 1/4 to 1/3 into the cost of duals…
your 79 still has holes for duals..
While at it remove the exhaust diverter on passenger side when adding duals
good luck
Race Director
Joined: Sep 2001
Posts: 10,560
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From: Wellington, FL
St. Jude Donor '11 thru '25
Don't know about the rest of the country but there's a HEAVY fine for exhaust shops here if FL that are found performing any work involving eliminating a car's converter.
Drifting
Joined: Mar 2006
Posts: 1,263
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From: Wabasha Mn
Very true! When I lived in Tampa years ago Hillsborough County had smog regs so somebody always knew somebody else that could take care of you if you wanted a "dirty" exhaust up grade. Probably much harder to find today but they are around!
Melting Slicks
Joined: Jul 2019
Posts: 2,296
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From: MA/NH Seacoast
Take that heavy pos off and throw it in the woods!
The cats on these era GM cars are mostly all the same shape. I had a test pipe off a 78 Vette fit a 77 Trans Am. I'm sure there's a company or two that are still making them.
I would suggest going the dual route and getting rid of that horribly restrictive Y-pipe though. I couldn't believe how small and poorly routed the original was on my 78 I'm building.
The cats on these era GM cars are mostly all the same shape. I had a test pipe off a 78 Vette fit a 77 Trans Am. I'm sure there's a company or two that are still making them.
I would suggest going the dual route and getting rid of that horribly restrictive Y-pipe though. I couldn't believe how small and poorly routed the original was on my 78 I'm building.
Burning Brakes
Joined: Jan 2006
Posts: 1,223
Likes: 174
From: Fort Wayne IN
Alternatively, take the cat off and mash all the guts with a crow bar, dump it all out, and reinstall. You just turned your old cat into a resonator for free and it will still pass visual inspection.
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From: Warren, Mi
I have a 79.i purchased a dual exhaust system by Pypes SCC10S with x pipe and street pro mufflers and chrome tips. I literally bolted right in. I did it in my garage with nothing more than hand tools. It looks and sounds amazing. As far as the person claiming to gain 50 - 80 HP. I call bs. There is absolutely no way to gain that much Hp from an exhaust system. 5 - 8 HP maybe.
Race Director
Joined: Jan 2000
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From: San Jose CA
I have a 79.i purchased a dual exhaust system by Pypes SCC10S with x pipe and street pro mufflers and chrome tips. I literally bolted right in. I did it in my garage with nothing more than hand tools. It looks and sounds amazing. As far as the person claiming to gain 50 - 80 HP. I call bs. There is absolutely no way to gain that much Hp from an exhaust system. 5 - 8 HP maybe.
Realistically, there is probably 10-20 hp to be found on a stock motor, a bit more if you have removed the factory manifolds and replaced with long tube headers.
That said, modern cats are very efficient and even on a high performance motor lose very little power, assuming they are appropriately sized to the engine along with the rest of the exhaust system.
What did you do with the heat riser? Also, is there a clearance issue with the speedometer cable and the driver side pipe?
Race Director
Joined: Nov 2006
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From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
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Cruise-In VIII Veteran
No typo. lose factory exhaust with it's super restrictive Cat. 50 - 80 HP. No ****! Many a thread on this forum over the years on this very topic.
Racer
Joined: Oct 2001
Posts: 474
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From: Portage La Prairie Manitoba
Upgrading to true duals only without changing anything else...... 20-30
Le Mans Master
Joined: Feb 1999
Posts: 8,351
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From: Tampa Bay FL
When my local shop installed my dual exhaust, they had to label it as 'cat back'; on the paperwork due to regulations. However, they installed a 2.5" header connected, custom bent, true dual system with h-pipe all the way to my Super Turbo mufflers. That was late 90's. That aluminized system lives today. Worth every penny of the $250 I spent then (on top of the cost to Jet Hot coat my Hedman full length headers).
Melting Slicks
Joined: May 2021
Posts: 2,274
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From: Fleming Island, FL
Does anyone here have time slips of their before and after exhaust modifications? I don't think the 2-1-2 is all that terrible. To the OP, a new monolithic catalytic converter will probably free up 15-20 HP.
Last edited by Fly skids up!; Jan 4, 2022 at 04:32 PM.
Le Mans Master
Joined: Jun 2019
Posts: 7,658
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From: Indiana
test if clogged first, i think a vacuum gauge and an IR gun will work..
if clogged maybe 40 HP.. if not my WAG is cat pipe replacement 10-15 hp, go to duals 2.5 inch no headers..15-35 hp, torque?
the original is a pass through bed design with beads..mine actually was working fine.. but fried the floor
