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According to my pdf files, up to 2001 they used the same pushrods on the LS1/LS6 engines. GMPartDirect.com shows they use that same length rod on everything Gen3 up through 2003. PN 10238852
Lance, can you measure the base circle on your aftermarket camshaft? I have the 98 cam I will measure and post the size of it shortly.
Okay, the base circle on a 1998 F-body camshaft is 1.551 for what its worth.
Called Comp and they say that their base circle is 1.509.
1.551 - 1.509 = .042" or .021" per side
I guess I need only .021" milled off my rocker trays. The tech rep at Comp says that they recommend the 7.400" pushrods for all the LS1 engines in stock configuration.
Okay, next question, how much does aluminum grow when it heats up to operating temperature. Since aluminum grows faster and further than steel, makes me wonder how much valve lash you lose at temp.
see heres the thing as stated earlier, on my engine who knows about the pushrods since i have stock 5.3 heads. But, 7.4" pushrods may be too short on an LS6 engine w/LS6 heads and cam, but could be long enough on a 5.3 head.
You see guys......this is why I failed math, my inability to figure this shit out! :grr:
Chris
What matters is the base circle size of the stock cam vs the base circle of the replacement cam. Divide that by two and that is how much you need to change your pushrods if all you change is the cam.
I get within .001" of what you have for the base circle Greg. My concern is the 0.6 mm longer valve stems in the LS6 heads. To me that would mean shorter pushrods, right?
That's gonna be a tough one to calculate. I could do it with optics when you send it to me.
TRTturbo, thanks for the link! I still have a little confusion but will have this figured out by tomorrow.
Can you measure a stock pushrod? I can send one with the trays. I don't have anything larger than 6" calipers unless I take one to work.
Well, that's a .024" longer valve. With a 1.7:1 rocker that would mean the cup end of the rocker would be compressed .014" more than the shorter LS1 valve. So, if you had stock heads 7.400 pushrods would be like they were 7.414 long.
Lets work this out....
heads milled -.055
longer valve at 1.7 ratio .014
needs .069 shorter pushrod or 7.331
Good luck finding that length! 7.350 is available.
Now I have to go back to why MTI says a 7.4 would work fine with the LS6 heads.
The stock pushrod is 7.4. I compared my stock to the hardened ones when I put them in and they were the same length.
LS6 and Ls1 pushrod lengths are both 7.4"
I'll get back with you tomorrow on this Greg.
7.4" long pushrods on stock LS6 heads makes sense to me. 7.350 long for heads milled .055" also makes sense.