We’ve got the answers—the Summit Racing tech department tackles your automotive-related conundrums. This week, we’re dialing in timing and straightening out a few cam/valvetrain issues..
D.B. • Basom, NY
Q: I own a 1977 Chevy 1/2 ton 4×4 with a 350 engine. I’ve had the engine bored .030 inches over, installed flat top pistons and 305 heads (10.0:1 compression ratio), a Summit Racing cam kit, double roller timing chain, high-volume oil pump, and a Holley dual plane intake manifold with a 600 cfm carburetor. I also installed headers, a dual exhaust, and 3.73 gears in the axles.
Currently, the engine pings during acceleration. I’ve tried using premium fuel and octane booster to no effect and have re-timed the engine and tuned the distributor, too. The truck also has very poor low-end performance and that’s where I need power the most.
A: The detonation (pinging) you’re experiencing can be caused by many things. Was your cam degreed properly during installation? Are you sure your compression ratio was calculated correctly? Is the carburetor providing the engine with enough fuel? It’s possible one or all of these problems exist, causing the air/fuel charge to ignite before the ignition system is ready to fire. This condition is known as pre-ignition.
First, we would suggest swapping out your existing Summit Racing cam with a Summit Racing K1102 cam kit. Its 1,500-4,000 rpm power range is ideal for a heavy truck with 3.73 gearing, and its lower powerband (compared to your current camshaft) will boost low-end performance. When installing your new cam, take the time to degree it properly and double-check your compression. Periodically check the color of your spark plugs to determine if you have the correct air/fuel ratio in the cylinders. If the color of the spark plug is different, you’ll have to tune the carburetor to work with the new engine combination.