Jarren_b

Alright guys I ordered my new cam and im trying to determine my pushrod length. Ive done this before but there is a new variable that is throwing me off and I simply cant remember exactly how to do it.

I will also be measuring with a length checker to be sure but last time I did this, my measurment and math was spot on and nothing has changed this time except for my new LS7 lifter (.050 taller than ls1) and a slightly smaller cam base circle.

So here it is.

Stock LS1 base circle is 19.7mm/.775 in

Old BTR cam was 17.95 mm/.706 in

New Cam is 17.97 mm/.707 in

The thing thats throwing me off is that My lifters are now taller being ls7 but can also handle more preload than stock ls1.

Right now im running I have a 7.450 pushrod that I measured to be correct with my BTR cam and .070 preload on the ls1 lifter

Someone help me make sense of all this! Im pretty sure ill need shorter pushrods than what Im running now

Jarren_b

nobody?

fsvaasam

I can try to answer or at least give my oppinion. When you build new set up, there is too many variable measures such as gasket thickness and lifters depending on manufacturer. So only right way to be sure and not guessing, is to measure with lenght checker. I did it and have my piece of mind.

Jarren_b

I havent removed heads so the only thing that has changed is the lifters but they also can take more preload

fsvaasam

Its quite hard to change lifters without removing heads.

Jarren_b

sorry I mean Im replacing with a stock size head gasket .051.. I had a brain fart for a second.

Jarren_b

but last time I measured and used the math method and they were dead on with eachother

fsvaasam

All advertised thickness and lengths isnt nearly always absolute truth. Thats why people measure it to be sure. I have fresh example from head gaskets which advertised to be .054 and i measured them .049 So allways measure dont count on expectations. Its more labourious, but all worth it at the end result.

speedtigger

iTrader: (16)

If there is only .001" difference in the base circle, then the pushrods you have should be fine. The LS7 lifters are a direct replacement for your existing lifters, so no change should be needed.

Jarren_b

really the only thing im concerned about is bottoming out the ls7 lifter. how much preload can they take? cause if im thinking of this correctly, the preload would be like .110
I think factory recommendation is between 60-91

fsvaasam

In theory i would say like speedtigger, but isnt it easier to check and to be sure, so you leave no guesses?

In this thread you can find some lifter differenses:

https://ls1tech.com/forums/generatio...plunger-4.html

speedtigger

iTrader: (16)

25 thousandths shorter pushrod would put you at .085" preload then.

Jarren_b

I just read through that whole thread and now im really confused because of what people are saying turns equal in terms of preload. some say .047 some say .075.. I guess my only option is to measure but I definitely dont want to have a lifter fail or mess up my expensive cam.

fsvaasam

If you look at the soundengineer post #75 in that thread, you can see LS7 lifter part number 17122490 preload is 2.09mm. It is 0.082" I think its optimal measure to shoot for from factory, but you could be fine with little less or more.

01ssreda4

iTrader: (96)

I thought ls7 lifters were overall taller but the distance from the roller to the cup where the pushrod sits is identical to the older style?

fsvaasam

Correct. If you want to shoot in the middle of lifter travel you need shorter pushrods with LS7 lifters. Bottom lenght is same with LS7 lifters, overall not.

Jarren_b

If I keep my pushrods the way they are (7.450) ill be right at about .100 preload. Ive seen some guys run this and ive seen some only run .040 and some that run .120.. the full travel is .200. so is it safe to be %50 of the total plunger travel? This will be my 4th time changing pushrods and I really dont want to have to change them AGAIN. I called LG today to get another opinion and he said I should be just fine with the same size pushrods and ls7 lifters

poltergeist 02

iTrader: (65)

Before I switched to Morels I used LS7's. I measured the difference using a dial indicator and the lifter cup in the LS7's sat about .050" higher than the LS1 lifters.

01ssreda4

iTrader: (96)

Thanks, I couldnt remember its been so long.

fsvaasam

Jarren_b, you can be sure when you measure.