Q: I have a 1981 Pontiac Firebird with a Chevy 350 in serious need of some more low-end power!
It has a Holley Dominator manifold and a 750 cfm car, 305 heads, a .480”-lift cam, Hedman Hedders into a 3” Flowmaster exhaust, a Powertrax limited-slip differential with 3.73 gears, and a TH-350 tranny with 2,200-2,500 stall converter.
The thing is, my ’71 Camaro (also a 350) jumped harder off the line with just a cam and a Holley 650 Double Pumper.
I was thinking about adding an H-pipe to my exhaust setup, replacing the existing manifold, and swapping out the cam for something with a little more grunt to boost throttle response.
Do you think this will give me the “jump” I’m looking for?
A: It sounds like your bird may be suffering from a classic case of “bigger isn’t always better” syndrome.
The 750 cfm is too much carb for your engine, which is causing it to bog down off of the line rather than take off like your Camaro used to.
But before you replace the carb, check out those 305 heads. Chevy produced both a low- and high-compression version, and if you’re running the high-compression heads, some diligent carb tuning could you achieve your goal. Holley’s installation and tuning video might be able to help with that.
On top of that, your 3” exhaust system is too big for your setup. It’s actually hampering exhaust flow and low-end torque.
A 2½”-diameter system will help restore your lost power and you can find them with a built-in H-pipe that will further increase exhaust flow and net a few more ponies down low.
Finally, an intake manifold tuned for maximum performance from 1,500-6,500 rpm will be perfect.
Keep your cam and see if your Firebird is ready to take to the skies!
Gear ratio? My 79 trans am has 340-something gears and it will spin the tires all the way through the intersection. My 77 trans am has 240 something Highway gears and it will not break the tires loose.
My 80 bird has a 350 sbc. Smog motor .454 lift Comp cam 882 heads 194/150 valves.2200 stall and 3:42 gears with 2-1/4 exhaust. 600 cfm vac secondareies. Runs pretty good. Had to put MT drag radials on it to keep it from breaking loose.