what does exaust really do for a stock engine besides sound good and keeping the engine cool. I'm running a stock 305 HO in a '84 Trans Am w/700r4 and 3.73 gears. I've added Headman shorty 4-1 headers , 2.5" Y-pie. 2.5" high flow cat,Borla 3" adjustable cat-back. on a bone stock engine,which delivers 190hp to the rear wheels stock. what can I expect these exaust mods to do? with the Borla plate closed?,open? is it neccessary to advance timing and use a different grade of gas to accomodate the differences in back pressure to see any benifit? thanks everyone,for yet another INFORMATIVE POST!!

 

You will gain about 15-20hp on that engine do to the crappy manifolds and small exhaust pipes they used stock. No need for higher octane gas, but advanced timing a few degrees is not necessary but it is a free mod worth a little hp. If you do advacnce then you might want to run a little more octane to prevent knock

 

So I can rightfully claim 205-210hp!!??? your kidding me! that's awsome! what next? cam,intake? I'm gonna have to get this dynoed for rock solid proof! I didn't mention the K&N and air silencer delete, I thought the air silencer made a big difference at WOT. the K&N allows me to go months without changing the air filter.

 

The stock engine did NOT produce 190HP at the rear wheels. The factory rates the horsepower at the flywheel. Probably made 160HP at rear.

 

This is the 4 brl right? You might have to rejet it to get some more power out of the engine. Ask the carb board, they would know. I don't know crap about carb.

 

hey jyd I did the same mods you have with the same car(84 Z28)almost with a rebulit carb and I pulled 173hp at the dyno. if this helps.