Push rod length
11-11-2022, 02:35 AM
#1
Teching In
Thread Starter
Push rod length Hi guys, need a bit of advice. I’ve had an LS1 rebuilt and i had the heads shaved 0.020 off. I’ve upgraded the cam with a stage two sloppy and i have dual springs. The rockers are new but stick with the brian tooley trunion kit installed, I’m getting conflicting advice with regards the pushrod length. Some say i need the shorter 73750 whereas other say the stock 74000 length is ok as there is adequate travel in stock style lifters. I’m just concerned the stick length push rods will keep the valves open on zero compression
11-11-2022, 06:10 AM
#3
Like the video shows.. no one can tell you what length pushrod you need as you actually have to check it yourself and figure it out. Head gasket thickness, milled heads, standard or short travel lifters, valve seating depth, cam lobe size/design, and many other things I'm not listing affect push rod length. you MUST check them yourself, on your engine.
I'm curious why you chose the dual springs as opposed to something like the Pac 1218's... do you plan on spinning it at 7K+ often, or? I'm asking because I had dual springs, and when I moved away from them my engine picked up horsepower.. Not a lot, but definitely noticeable.
I'm curious why you chose the dual springs as opposed to something like the Pac 1218's... do you plan on spinning it at 7K+ often, or? I'm asking because I had dual springs, and when I moved away from them my engine picked up horsepower.. Not a lot, but definitely noticeable.
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andyedgar1970 (11-11-2022)
11-11-2022, 06:35 AM
#4
Teching In
Thread Starter
it was just something i was advised to do, was told to put duals in. It’s a 230/238 585/585 112LSA cam with just 20 thousands off the heads, stock type followers and standard gaskets
11-11-2022, 06:52 AM
#5
Yes definitely measure what lifter preload a stock pushrod will give you.
I've measured lifter plunger travel and stock lifters have over .200, and the theory is more preload equals less oil under the lifter plunger. Less oil means less chance to for it to get aerated (don't know if I agree that it gets aerated) And the theory is aerated oil compresses and loses lift.
One engine I'm running now I thought was never machined but stock pushrods gave it .130 preload and it was fine for a few years. Then I saw the video above and thought I'd try shorter pushrods to pick up low end. Kind of opposite of what's going on in the video.
I went with 7.350 which gave it a "correct" .080 preload. The only difference I noticed is the exhaust seems quieter at idle, idle seems more tame.
No difference otherwise, no additional noise, no power difference that I could tell.
A lifter plunger bleeds down when preload is set and then it stays there. It never moves. Unless it's over revved and you get valve float they can "pump up" and be a problem. But at that point it doesnt matter what size your pushrods are.
I've measured lifter plunger travel and stock lifters have over .200, and the theory is more preload equals less oil under the lifter plunger. Less oil means less chance to for it to get aerated (don't know if I agree that it gets aerated) And the theory is aerated oil compresses and loses lift.
One engine I'm running now I thought was never machined but stock pushrods gave it .130 preload and it was fine for a few years. Then I saw the video above and thought I'd try shorter pushrods to pick up low end. Kind of opposite of what's going on in the video.
I went with 7.350 which gave it a "correct" .080 preload. The only difference I noticed is the exhaust seems quieter at idle, idle seems more tame.
No difference otherwise, no additional noise, no power difference that I could tell.
A lifter plunger bleeds down when preload is set and then it stays there. It never moves. Unless it's over revved and you get valve float they can "pump up" and be a problem. But at that point it doesnt matter what size your pushrods are.
The following users liked this post:
andyedgar1970 (11-11-2022)