Got a '91 RS V8. If i were to replace my cat-back, is there a big (if any) difference in HP gains between a Dynomax or a Borla (or any other performance brand)?

What can i expect out of replacing my cat-back in terms of HP and Torque?

 

Dont expect too much from a catback, other than a nice sound. While it will increase horsepower some, it wont do much because the problem with stock exhaust is in the manifolds and cat. They are the major restriction. Headers, a high flow cat, and a catback would probably give you anywhere from 30-60 hp increase, while a catback alone would probably give you less than 30.

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1983 Pontiac Firebird SE
LG4-Based Chevy 400
700R4 Tansmission
Modified 4 Barrel Q-Jet Carb
Accel Super Stock 8mm Wires
Edelbrock Pro-Flo Air Cleaner
3.23 Posi Rear
14X7" Cragar SS/T Wheels
Clarion 45X4 CD/AM/FM Head Unit
100WX2 Amp
2 Pioneer 12" Subs in Custom Box
Third Gen Performance
"A four cylinder is only half an engine"

 

I agree with Ward. You will gain very little in that dept. but you will get a nicer rumble from the back. I think Dynomax makes not the best, but the best affordable catback systems there is.

 

is it really 30-60 simply by replacing the whole exhaust? i didnt think it was that much.

 

yeah, 30-60 hp is definently possible by just bolting on headers, a cat, and a nice cat-back muffler. The main restriction on these third gen f-bodies were the exhaust. I already have a hi-flow cat and a flowmaster muffler....next is the edelbrock TES for my little 305 to complete the set-up. Overall I'm expecting at least 30 hp from all of it.

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1988 Pontiac GTA 5.0 TPI
-K&N Filter
-Hypertech Air Foil
-Hypertech Perf. Chip
-2.5in Flowmaster Muffler

Kills
94 Probe GT, 95 Mustang GT, 86 Trans Am, 96 Impala SS, 85 Thunderbird 5.0, 95 Thunderbird 4.6, 95 Accord V6, 98 Integra VTEC, 70 Chevelle Malibu

 

You might get 30 horse with everything if you were lucky as hell! I'd say more like 20 tops.

 

If your looking for the best power out of a cat back system, get a single out system. These systems may not look as good as a dual out, but they are more efficent then a dual system. BTW, I have a bran new Dynomax cat back system for a 91 RS, still in the box.

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Convertible, L98, Mini-ram, ZZ9 cam, Comp Cams 1.6/1.52 steel roller rockers, Trick Flow 23* heads, K&N's with chopped airboxes, March underdive pulleys, Edelbrock ceramic coated TES, Flowmaster cat-back exhaust, Dynomax high flow converter, MAC subframe connectors, Accel box & coil, Fastchips custom chip, 3.23 rear gears, white face gagues, and NOS!

 

None of the thirdgens have a crappy enough exhaust on them stock to pick up anywhere near 50-60 hp.

I would think 30 hp would about it for a whole exhaust swap.

You won't get over 10hp w/ a cat-back alone IMO, which isn't too say it's not a good mod though.

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Ray87Z
-Vortec headed 350.
86 IROC w/ a cammed 305 TPI.
Formerly Ray86IROC.
www.inter-scape.com/Ray

 

Lol I can pick up 60 hp with an exhaust system... I have pretty much a stock 305 exhaust system on a SB 400 :P.

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1983 Pontiac Firebird SE
LG4-Based Chevy 400
700R4 Tansmission
Modified 4 Barrel Q-Jet Carb
Accel Super Stock 8mm Wires
Edelbrock Pro-Flo Air Cleaner
3.23 Posi Rear
14X7" Cragar SS/T Wheels
Clarion 45X4 CD/AM/FM Head Unit
100WX2 Amp
2 Pioneer 12" Subs in Custom Box
Third Gen Performance
"A four cylinder is only half an engine"