1974 Nova Backfire HELP!!

Alan Roehrich · 06-22-2012, 02:52 PM

Valve springs?

Valve sticking in a guide?

TDC on balancer wrong?

Wrong timing tab?

Timing set machined wrong?

Compression test?

Leakdown test?

Actual HEI spark test at the spark plug end of the wires?

Vacuum reading at idle?

Those 292 magnum cams just plain suck. You need 11:1 just to make one run decent. If you do not have at least 11:1, it needs to be advanced a full 4 degrees, verified. It needs hot extended tip plugs, a ton of initial timing (like 20 degrees at 650-750, and around 44 total, all in by 3000) a 33-36 squirter (with the high flow screw), an aggressive accelerator pump cam, and maybe even a 50cc pump. If it's not a vacuum secondary, it needs all that on the secondary side, too. They're usually better off with 4 corner idle circuits, and 0.060 holes drilled in all 4 throttle plates. Try about a 4.5 power valve.

Even if you have an honest 11:1 or better, you're usually better off ditching that cam. For a hydraulic flat tappet, in a small block, anything more than around 236-238 degrees is almost always a joke, there more for sound than power. At that point, I go solid lift. I never use a shelf cam that has more than around 236 @ .050" in anything, at that point, it is serious enough to warrant a real custom grind.

Set the valves at no tighter than zero lash plus 1/16 to 1/8 turn, or hot and running, make the rocker stop clicking, and go 1/16 turn max. Use poly locks or double rocker nuts.

The local speed shop sold dozens of those cams years ago. Usually, after we tuned on them and crutched them for a while, the customer had the 292 pulled out and replaced with a nice custom cam about 12 degrees smaller at 0.050". The car often picked up 2 tenths in the 1/8, ran better in town, got double the fuel mileage, and about ten times the plug life.

If it is an automatic car, it needs a good 3000-3500 stall converter, and at least a 3.73 gear.

06-22-2012, 02:52 PM	#4
Alan Roehrich Veteran Member Join Date: May 2006 Location: Murfreesboro TN Posts: 5,105 Likes: 1,561 Liked 1,784 Times in 407 Posts	Re: 1974 Nova Backfire HELP!! Valve springs? Valve sticking in a guide? TDC on balancer wrong? Wrong timing tab? Timing set machined wrong? Compression test? Leakdown test? Actual HEI spark test at the spark plug end of the wires? Vacuum reading at idle? Those 292 magnum cams just plain suck. You need 11:1 just to make one run decent. If you do not have at least 11:1, it needs to be advanced a full 4 degrees, verified. It needs hot extended tip plugs, a ton of initial timing (like 20 degrees at 650-750, and around 44 total, all in by 3000) a 33-36 squirter (with the high flow screw), an aggressive accelerator pump cam, and maybe even a 50cc pump. If it's not a vacuum secondary, it needs all that on the secondary side, too. They're usually better off with 4 corner idle circuits, and 0.060 holes drilled in all 4 throttle plates. Try about a 4.5 power valve. Even if you have an honest 11:1 or better, you're usually better off ditching that cam. For a hydraulic flat tappet, in a small block, anything more than around 236-238 degrees is almost always a joke, there more for sound than power. At that point, I go solid lift. I never use a shelf cam that has more than around 236 @ .050" in anything, at that point, it is serious enough to warrant a real custom grind. Set the valves at no tighter than zero lash plus 1/16 to 1/8 turn, or hot and running, make the rocker stop clicking, and go 1/16 turn max. Use poly locks or double rocker nuts. The local speed shop sold dozens of those cams years ago. Usually, after we tuned on them and crutched them for a while, the customer had the 292 pulled out and replaced with a nice custom cam about 12 degrees smaller at 0.050". The car often picked up 2 tenths in the 1/8, ran better in town, got double the fuel mileage, and about ten times the plug life. If it is an automatic car, it needs a good 3000-3500 stall converter, and at least a 3.73 gear. __________________ Alan Roehrich 212A G/S Last edited by Alan Roehrich; 06-22-2012 at 02:55 PM.