i was just wondering what kind of hp gain would i be looking at i have 89rs 305tbi basicly stock just got open air thing done and transgo shift kit and the 80 series muffler no cat back. If i got the flowmaster cat back and gutted the cat or removed it completely i would gain about how much hp. And slp headers would then add aproximatly how much hp. Thanx for ure help these estimates can be at the fly wheel.

 

I am not too sure about horsepower numbers. But I can say that my cat-back reduced my 1/4 ETs by .3 and then when I installed the headers they went down by another .4, I do have the stock cat non-gutted though.

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1987 Chevy Camaro IROC-Z
L98 TPI 350 (5.7L)
TH 700R-4 Transmission
Borg Warner 7.75" 9 Bolt Rear End

Current Mods: LT4 Hot Cam, Comp Cams 1.52:1 Roller Rocker Arms, Edelbrock TES 1 5/8" Headers, Hooker 3" Aerochamber Cat-Back System, Performance Resource Chip, Accel Ignition Coil, Cap, Rotor, 8.8mm Wires, K&N Filters, JET TPI Air Foil, All Free Mods, Falken ZIEX Z-Rated Tires.

Best ET (w/o LT4 cam): 14.32 @ 97.7mph
(corrected for elevation)

7.5" 10 Bolt with 3.42s soon to come!