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. Parts List Description PN Source Price Edelbrock Victor Jr., L92 28457 Jegs $349.99 Kwik alternator kit, Camaro K10194 Kwik Performance $167.00 GMPP L92 stock heads, pair 12582713 Scoggin-Dickey $899.90 GMPP L92 CNC heads, pair 88958698 Scoggin-Dickey $1,099.90 GMPP racing lifters 88958689 Scoggin-Dickey $226.85 L92 rocker, intake (8) 12569167 Scoggin-Dickey $95.84 L92 rocker, exhaust (8) 10214664 Scoggin-Dickey $98.80 L92 rocker support (2) 12600936 Scoggin-Dickey $15.92 Rocker arm bolt (16) 12560961 Scoggin-Dickey $72.80 Comp 281HR hydraulic roller 54-428-11 Summit Racing $354.75 Comp 277LR hydraulic roller 54-458-11 Summit Racing $396.95 Comp 281LRRHR13 roller 54-469-11 Summit Racing $396.95 Comp valvesprings 26918 Summit Racing $174.95 Comp retainers, steel 1772-16 Summit Racing $153.95 Comp pushrods, Hi-Tech 7955-16 Summit Racing $115.75 Edelbrock Victor Jr., LS1 29087 Summit Racing $269.75 Holley carburetor, 950 cfm 0-80496-1 Summit Racing $714.95 Edelbrock Victor Jr., LS1 29087 Summit Racing $269.75 Edelbrock headers, LS1 65073 Summit Racing $519.95 Autolite race plugs AR474 Summit Racing $21.52 MSD truck plug wires 32829 Summit Racing $68.95 Wilson tapered spacer, 1 1/2 004130 Summit Racing $178.95 ARP metric studs 400-8034 Summit Racing $151.95 WCRCH ported 6.0L head WCCH-6.0L West Coast RCH $1,575.00* *Requires core-$1,865.00 outright with valves and springs SOURCES Scoggin-Dickey Parts Center 5901 Spur 327 Lubbock TX 79424 800-456-0211 www.sdparts.com Rock Auto 6680 Odana Road Madison WI 53719 866-762-5288 www.rockauto.com Summit Racing 800-230-3030 www.summitracing.com Mahle Motorsports Fletcher NC 888-255-1942 www.mahlemotorsports.com GM Performance Parts P.O. Box 33170 Detroit MI 48232 800-577-6888 www.gmperformanceparts.com West Coast Racing Cylinder Heads Reseda CA 818-705-5454 www.proheads.com Kwik Performance Springfield MO 417-955-1467 www.kwikperf.com Wilson Manifolds Ft. Lauderdale FL 954-771-6216 www.wilsonmanifolds.com « | 1 | 2 | 3 | 4 | 5 | View Full Article By Jeff Smith Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!