LS Engine Build - The Garage-Built LS Stroker, Part II

This graph shows the major torque and horsepower differences between the stock 6.0L heads and the GMPP-ported L92 castings.

This graph shows the major torque and horsepower differences between the stock 6.0L heads

What We Learned
The biggest surprise of the day was the torque improvement with the larger cylinder heads. When we originally tested the L92 heads on the 6.0L engine (May '07), these big castings killed the torque. But when we bolted these same heads to the 404ci engine, the torque exceeded that of even the WCRCH-ported 6.0L heads. Note how the average torque for both big port heads exceeds even the ported cathedral head by no less than 4 lb-ft. While we didn't achieve our 575hp goal, we did see an amazing 81 peak-to-peak horsepower improvement over the stock 6.0L heads.

While the CNC-ported L92 heads at first glance don't appear to be worth the additional cost over the stock L92 castings, we didn't really give these heads a chance to succeed. We would need to add a camshaft with another 6 to 8 degrees of duration and valve lift upward of 0.670 inch to take full advantage of what these heads offer. However, a bigger cam would definitely hurt the torque and make street driveability more of a compromise. One solution would be to improve the exhaust port flow on the stock L92 heads. The exhaust flow numbers on the WCRCH-ported 6.0L heads already outflow the CNC-ported L92 heads, and the L92 stock exhaust ports are supposed to be better than the stock 6.0L versions. It's a good bet that a stronger exhaust port would allow the engine to make more peak power without sacrificing the torque, and we'd have more horsepower without having to spend big money on expensive heads.

After the test, we dug a little deeper in the Comp Cams catalog and discovered a 281LRR HR13 cam that uses a 231-degrees-at-0.050 intake but adds a much longer duration exhaust at 247 degrees at 0.050 with 0.617/0.624-inch lift. This cam would probably carry the power out another couple hundred rpm and improve power at the peak. If you are considering replicating our combination, this is the cam we'd choose.

Finally, to put our 560 hp in perspective, we plugged the power into the Quarter Jr. dragstrip simulation program using our 3,200-pound Orange Peel '66 Chevelle running 3.55 gears and a 200-4R trans. The program spit out a low-11-second pass at 122 mph, assuming we could actually harness all this power. Sounds like fun.

By Jeff Smith

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