1996 LT4 Chevy Corvette Bullet Engine - Under Pressure

Performance Q&A

Kevin McClelland Dec 1, 2006 0 Comment(s)
0612_chpp_01_z 1996_chevy_corvette_lt4 Cylinder_head_valve 2/1

This week at work we finally got an engine running on the dyno that had been pushed back many times by other projects. It was the original development engine for the GM Performance Parts HOT engine. It started life as a '96 LT4 Corvette bullet. We developed a cam for GM (the HOT cam) and worked with them on the dual-plane carbureted intake for the Gen II reverse-flow-cooling engines. We freshened up the engine, zero-decked the block, cleaned up the cylinder heads (minor porting), and bored the block 0.020 inch over. With the zero deck and the shave of the heads, the final compression ratio came out at 11:1. The final home for this engine is my bracket-racing '80 Malibu wagon. Back in 1996, when we originally built the engine, it produced 420 hp and ran extremely well in my '65 El Camino.

I'm a firm believer in the stock oiling system of a small-block. The only simple mod that the oiling system had was the installation of a 70-psi white pressure-relief spring from the 302 Z28 and 350 LT-1 engines. Well, when we ran the engine in and set the timing at a very conservative 28 degrees total, the engine produced 441 hp through 211/42 dual exhaust! I was very pleased for an engine this mild to produce that kind of power, and have over 15 inches idle vacuum at 750 rpm. As I was looking over the dyno sheets, I noticed that the oil pressure was hitting 82 psi at the peak rpm of 6,600 with 200-degree-F 10W-30 Castrol. This was with a stock-volume 31/44-inch pick-up and production pump. Well, we promptly removed the pump and put the production late-model Corvette pressure-relief spring back in the pump. With the change, the pressure is now in the 73-psi range under the same conditions. Now here is the fun part: The horsepower jumped from 441 to 448 just from reducing the pressure by approximately 10 psi. This was due to the load of the oil pump on the distributor and camshaft and the reduced windage in the oil pan. I'm very tempted to remove the pump again and clip a coil off the spring. I would be happy with 55 to 60 psi, and see where the power would go. Please stay away from high-volume oil pumps in small-block Chevy engines. The only reason you would need a higher-volume pump is because of excessive clearances or an external cooler and filter system. This change really got my attention.

Klickity Klack
Q I have rebuilt my engine and I installed a noisy geardrive. I tried to adjust my valves by loosening and listening for the clatter with and without earplugs. I just can't hear it. Every time I think that I have it right, I shut the engine off and the rockers are loose. The engine is a 350 small-block with a Comp Cams 280 Magnum hydraulic flat-tappet cam. The rest of the valvetrain is rounded out with a Comp Cams kit. Do you know of another way to adjust the valves or have any other suggestions?Steve Summers

A Nothing is worse than a clicking tappet noise that you can't hear! You can't hear the valvetrain noise over the geardrive whine? That sure is one loud gear drive. OK, get those covers off and let's lash the valves.

Have you ever heard of the exhaust-opening/intake-closing method (EOIC)? This is when you adjust the valves on one cylinder at a time. You rotate the engine until the exhaust valve just starts to open. This is when you adjust the intake valve. Loosen the intake adjuster until you have excessive lash. Slowly tighten the rocker adjuster while rotating the pushrod between two fingers. As you tighten the adjuster you will take up the lash until the pushrod has resistance to rotation. At this point you have achieved zero lash. Then you should tighten the adjuster a half-turn past zero lash. Now rotate the engine until the intake valve just closes. Repeat the procedure to find zero lash and give the exhaust a half-turn preload. Go on to all the other cylinders. (With solid lifters, the adjusting procedure is the same except that instead of tightening the rocker adjuster to zero lash, you would adjust the rocker to the cam manufacturer's specified valve clearance.) This should give you a good performance valve adjustment. Don't burn your fingers!


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