Jeff's Performance IMCA Modified Engine - Horsepower IMCA Style

Once the pistons and rods are fully assembled, they can finally be tapped into place. The pistons are 0.040 over at 4.040 inches, and the final displacement will be 383 ci with the 3.750-inch stroker crank (0.250 over stock).

The camshaft is degreed in for the 103-degree centerline.

Jeff's Performance checks piston-to-valve clearance with a dial indicator because it's much more exact, but they also squished a little clay for this article because it's a lot easier to see what's going on. Hill says minimum piston-to-valve for an engine with solid lifters and steel valves should be 0.080 inch for the intake and 0.100 inch for the exhaust. These have a few thousandths more clearance than that, but not much.

Rocker arms are Crane aluminum units with roller tips. The 1.5:1 ratio produces 0.561/0.572-inch valve lift.

Shop owner Jeff Hill handles setting the valvetrain himself. Crane recommended setting the lash relatively tight at 0.014, and the engine seemed to respond to it.

The engine was run with both gasoline and alcohol, and although different carburetors were used, both were 750-cfm four-barrels.

On the dyno, the engine was set up with 131/44x34-inch headers with 10-inch collectors. Peak torque on alcohol was 558.3 lb-ft at 4,500 rpm, while horsepower peaked at 530.4 at 5,900 rpm.