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My mechanic was nice enough to let me shadow his guys while they did a heads/cam/intake install on my ‘02 C5. Great bunch of guys, made some new friends, but just had some questions about the last few steps where I’d like to see if the forum here agrees with my gut. The build is based around TrickFlow 215 heads, milled to 61cc, using CamMotion Titan 4 cam, Harland Sharp SLS17 roller rockers and Johnson 2110R lifters. My mechanic wasn’t fully familiar with the procedure for measuring proper pushrod length and preload, although he’s done an absolute ton of cam swaps and LS work before. He called in another mechanic who builds serious drag motors, races and seemed to really know the procedure that I’d only read about extensively. Using an adjustable length pushrod, feeler gauges, referencing the cam build sheet, doing some calculations, he arrived at a pushrod length of 7.425. Using the adjustable pushrod, the wipe pattern was perfect, centered. I know that TrickFlow used 7.5” pushrods IF you don’t mill the heads and use you use stock lifters. Johnson lifters are apparently longer by a bit. .018” was milled from the heads to arrive at 61cc volume. Pushrods should be shorter than 7.5 by a bit, but I couldn’t figure out why he arrived at a number so much shorter than I expected based on other’s experience and my calculations using amount milled, different lifters, etc. I ordered the 7.425 lifters and we installed them today after testing the first set for wipe pattern. He says the pattern is fine, his engine builder guy that measured said it was fine, but I have my reservations on it. The wipe pattern while using the adjustable pushrod was perfect. This one, according to my research, indicates a pushrod that is too short. This would cause increased valve guide wear and less than optimal performance horsepower wise if the valves are not fully opened. What say the forum?
Pushrod length on an LS anything does NOT affect wipe pattern. On a traditional SBC, yes. On an LS, no. The only way to change wipe pattern on an LS is by adding material (shimming) to the rocker stands, or removing material (machining) from them. Of course, changing distance from the fulcrum to the rocker tip would also do the same thing, but I'm not aware of anyone who's doing that. On the Gen 1 SBC, changing pushrod length changes 2 things: Lifter preload, and, consequently, fulcrum height..... On an LS, the only thing changing pushrod length does is change lifter preload, because the fulcrum does not move in relation to the valve stem tip. Hope this helps......
at zero lash turn torque wrench 3/4 turn to 1 1/4 turn to tighten rocker arm 25 ft lbs. this ensures correct push rod length INCLUDING .050" pre load
less than 3/4 turn = push rod too short
more than 1 1/4 turn = push rod too long
the competition cams tool has an overall length of 6.8" (guage length is even more). each 360 degree turn is 0.05". also add in pre load (when ordering pre load) .05" to .07"
Pushrod length sanity check
