The production valvetrain on the Gen III V-8 is non-adjustable, but geometry issues can be addressed by installing different-length pushrods. In general, most Gen III V-8 builders say a stock valvetrain with the proper geometry will require the rocker holddown bolts be turned another 1 1/2 turns beyond the point where the pushrod will not spin between your fingers. This is considered the valvetrain "preload" with the components "hot." These same engine-builders have found power by running less valvetrain preload. The general consensus is that power exists in valvetrains with a preload of about 3/4 turn of the holddown bolts. On a stock head, this would mean you'd run about a 0.040-inch shorter pushrod to achieve this--but always measure your valvetrain for this measurement. Most of the aftermarket valvetrain companies offer Gen III pushrods in multiple-length increments to allow geometry tuning. You could buy adjustable rockers, but they will just add valvetrain weight (not good for high-rpm applications) and cost that can be rectified with the proper pushrod length. The LS6 heads were first released in '01 on the Z06 Corvette and are available today in assembled form from GM Performance Parts (PN 12564824, casting number 12564243) loaded with hollow stem valves (these were factory pieces from '02 to today) and LS6 valvesprings. To learn more about the Gen III V-8, check out www.cartechbooks.com to order How to Build Performance Chevy LS1/LS6 V-8s. Gen III Cylinder Head Casting, Machined and Final Part Numbers RPO Year Size Casting Part Numbers Machined Final Assembly LS1 '97-'98 10215339 12558806 10215339 12558806 10215337 12558808 '99-'01 '01-'04 12559853 12564241 12559853 12559854 12559854 12564242 12559856 12559856 LS6 01-04 12564243 12560800 12569315 12564824 12560802 LQ9 '02-' 04 12562317 12562318 12565363 LQ4 '99-'00 12581873 12561874 12561876 '01 12562317 12562318 12562320 '02-'04 12562317 12562318 12565364* 12565363 LM4, LM7LR4, L59 '99-'01 12559862 12559863 12559865 '01-'04 12561706 12569862 12561708 12559863 12563678 *(this PN also good for RPO KL5; the natural gas engine) The LS1 (above) and LS6 (below) combustion chambers look different and have slightly different volumes. The port and chamber design work for these heads was done mostly with supercomputer modeling, some flowbench and dyno testing, and a little in-vehicle tuning.The LS1 (above) and LS6 (below) combustion chambers look different and have slightly diffe A quick way to narrow down the type of cylinder heads on your Gen III V-8 is to look at the bolts holding the valvecovers on the heads. The '97-'98 LS1 Gen IIIs had "perimeter" located bolts...A quick way to narrow down the type of cylinder heads on your Gen III V-8 is to look at th ...while the '99-and-later Gen IIIs had "centered" bolts. The centered bolts were to be the design all along, but the engineering validation process was not complete when the LS1 went into production in mid-'96, so these engines used the proven perimeter bolt pattern....while the '99-and-later Gen IIIs had "centered" bolts. The centered bolts were to be th « | 1 | 2 | 3 | » | View Full Article Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!
