Pushrod Length Question - Intake/Exhasut measure different...
Pushrod Length Question - Intake/Exhaust measure different... I measured lifter 4 intake and 4 exhaust pushrods to zero lash. I used the adjustable length checker, and moved in increments of 1/4 turn (0.0125"). I'd find the length that was slightly too short, and the length that was too long, so it was between those two, and I averaged the lengths. I did that for all 8 lifters I measured for. The most that I could be off using that method is less than 0.00625", which is close enough for pushrod lengths.
I came up with 7.269" intake, and 7.244" exhaust. All 4 intake were identical, all 4 exhaust were identical. Then add on preload to those numbers. I tried a few different pushrod lengths and figured out what the preload would be.
Prelaod with 7.350" pushrods:
Intake: 0.081"
Exhaust: 0.106"
Preload with 7.325" pushrods:
Intake: 0.056"
Exhaust: 0.081"
I have a few questions. First, why is the length of the intake and exhaust pushrods different? Second, which length pushrod should I choose? Would it make sense to use a different pushrod length on the intake and exhaust? If I was shooting for 0.080" preload it would seem as if that would be the right decision. I would appreciate any pros on the subject to shed some light.
A little info on my setup: LS1 with stock bottom end (pistons flycut with Lindy tool), PRC stg. 2.5 5.3l heads with 59cc chambers, MS4 cam, LS7 lifters, stock rockers. Need any more info please ask.
I came up with 7.269" intake, and 7.244" exhaust. All 4 intake were identical, all 4 exhaust were identical. Then add on preload to those numbers. I tried a few different pushrod lengths and figured out what the preload would be.
Prelaod with 7.350" pushrods:
Intake: 0.081"
Exhaust: 0.106"
Preload with 7.325" pushrods:
Intake: 0.056"
Exhaust: 0.081"
I have a few questions. First, why is the length of the intake and exhaust pushrods different? Second, which length pushrod should I choose? Would it make sense to use a different pushrod length on the intake and exhaust? If I was shooting for 0.080" preload it would seem as if that would be the right decision. I would appreciate any pros on the subject to shed some light.
A little info on my setup: LS1 with stock bottom end (pistons flycut with Lindy tool), PRC stg. 2.5 5.3l heads with 59cc chambers, MS4 cam, LS7 lifters, stock rockers. Need any more info please ask.
Last edited by Kevin Doe; Nov 6, 2008 at 08:30 PM.
Could be the way the valve seats were cut. If not going with custom pushrods, I would either go all 7.350 or two lengths. The 0.106" preload won't hurt you and I have had two engine builders (well known) tell me that dyno testing has been showing more preload helps with power.
Well I looked at the next shorter length as well.
I could go with 0.081" preload and use 7.350" on the intake and a 7.325" on the exhaust.
Or I could go with 0.056" preload and use 7.325" on the intake and 7.300" on the exhaust.
What is the overall consensus?
I could go with 0.081" preload and use 7.350" on the intake and a 7.325" on the exhaust.
Or I could go with 0.056" preload and use 7.325" on the intake and 7.300" on the exhaust.
What is the overall consensus?
Staging Lane
Joined: Aug 2008
Posts: 71
Likes: 0
From: Miami, near the U.S.A.
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Glad to help, Kevin! You've been very patient with delays in your build and we appreciate customers like you who are understanding of these things!
ZMonster: GM sets them up with quite a bit more preload than .010"....closer to .100" in most cases!
ZMonster: GM sets them up with quite a bit more preload than .010"....closer to .100" in most cases!
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Largest Stocking Distributor of LS-x Engines / CHECK OUT OUR NEW WEBSITE!
COMP - FAST - PACESETTER - DIAMOND RACING - EAGLE SPECIALTY PRODUCTS - CALLIES - COMETIC GASKETS
RAM CLUTCHES - MOSER ENGINEERING - KOOK'S HEADERS - ARP - GM BOLTS AND GASKETS - MSD - NGK
POWERBOND - ASP - AND MORE!
Its no problem. True customer satisfaction will come after I tune it and get some numbers! You guys have been great so far, and I expect nothing other than good numbers when its up and running.
FormerVendor
Joined: Nov 2001
Posts: 3,065
Likes: 6
From: Houston, Tx.
The valve tip heights are probably just slightly different as well too as 90 percent of heads are like that so you need to check as you did and do then get the right pushrods like you did. You can put a pushrod or straightedge across the tips of the valves and see which are higher or lower. I have many L92s that with the rev valves end up .025 different as well. Some cam companies keep the base circles the same and some will keep the nose the same so it depends.
