Q&A / Tech

Mailbag: Timing is Everything

Got questions? 

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..

C.S. • Currie, NC
Q: I have a 1967 Ford Fairlane. It’s equipped with a 1968 390 GT engine that’s bored .030 inches over. The engine uses the stock heads, a COMP Cams 294S Magnum camshaft kit (248/248-degree duration at .050 inches and .605/.605-inch lift), an Edelbrock Performer RPM intake manifold, an 850 cfm Holley carb, and Hooker headers.

The ignition consists of an MSD distributor, an MSD 6AL box, an MSD Blaster 2 coil, and MSD plug wires. The transmission is a C-6 auto with a 3,000-3,500 stall speed TCI Street Fighter torque converter. The rear-end is a Ford 9-inch with 3.00 gears and an open diff.

What should the timing be at idle? Currently, my timing is 38 degrees at 1,000 rpm. I have to retard the timing to get the engine to turn over, but while accelerating, the engine backfires through the carb. Do I need a new starter?

A: Engine timing should be 10-12 degrees at 800 rpm. Total timing should be 34-36 degrees at 3,000 rpm. Reduce the timing to these specs, and you’ll find the engine will turn over easier and run a lot better.

There are a couple of other concerns here. First, the stock heads are insufficient for use with the COMP Cams 294S cam. At a minimum, you should perform some port work and install new valves and related valvetrain components to keep up with the demands of the cam. Another option would be a set of Edelbrock Performer RPM heads (part number 60069), which will outflow OEM ported heads by a large margin. They also come with all the necessary components to support a camshaft with .605 inches of valve lift. Plus, they’ll shave about 45 pounds of weight off the engine.

Second, you’re giving up a lot of acceleration with the open diff and 3.00 gears. You can fix this by installing a Detroit Locker and Richmond Gear 4.11 gears.

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