Kevin Doe

iTrader: (1)

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.

ZMONSTER!

iTrader: (9)

Different lobes on the intake and exhaust? Like LSK intake and XER exhaust? Only way I can think of. Either way if you measured it that way thats what it needs!

vettenuts

iTrader: (4)

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.

Kevin Doe

iTrader: (1)

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?

Kevin Doe

iTrader: (1)

After talking with Matt at TSP I ended up going with 8 7.350s and 8 7.325s to give me 0.081 preload all around.

Grimes

iTrader: (3)

Good decision - and props for "doing things right".

Clevite Kid

. . . and kudos to Matt for helping his customer (who is one smart cookie in his own right !!) reach the correct endpoint.

ZMONSTER!

iTrader: (9)

Way to go man!
But since this is still open Im going to hijack the thread for a quick second...isnt GM preload .010? Why would you put more preload than the GM specs?

Sales2@Texas-speed

iTrader: (5)

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!

iTrader: (9)

Ok my mistake!

Kevin Doe

iTrader: (1)

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.

racer7088

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.