RRhodes1

LS7 lifters, t-rex cam, dual springs etc etc.

i had bought & installed LS7 lifters along with a t-rex camshaft this past spring. I recalled hearing that LS7 lifters were "different" than the stockers.
i contacted the shop i was buying parts from, and mentioned said "difference".

he called me back the next day claiming i needed 7.425 push rods.

this contradicts everything else i have read on here about these lifters needing shorter pushrods.

cars valve train is dead silent.

i wonder about this as the car is soon to be getting PRC 1.0 LS6 heads and yella terra roller rockers. i will be using a PLC this time around.


so needless to say, is he right telling me that length, or should i take my business somewheres else?


Thanks !

vipvegas

iTrader: (13)

The LS7's lifter cup is seated different then the stock cup. Often to obtain correct preload on the lifters a shorter rod then stock is needed. For example in my setup with ls7 lifters in the ls1 most guys run 7.4's but after measuring 7.3 was optimal for me. But your shop is claiming you need longer ones??? Doesnt sound right to me, are you able to check pushrod length yourself?

Johnnystock

iTrader: (6)

Isnt true that bigger cam needs taller PRs? Trex is pretty big indeed.

RRhodes1

the car is coming out of winter storage this april , and i will be checking push rod length then when i swap rockers & the cylinder heads.

all i am going to want to do is to get the cam on its base circle, put in a weak spring to hold the valve uptorque the rocker stud to 22 ft/lbs., adjust the push rod checker to zero lash. take out and measure.

then id add .050" for preload plus whatever it takes to get my roller wipe pattern center? Or is it when its @ zero lash it is at ideal wipe pattern location?

the shims that come with the yella terras... what are they for?

just a few details i need to get figured out.

needless to say, im not going back to that shop.


Thanks!

XtraCajunSS

iTrader: (2)

With the base circle of that cam, in a stock application (stock block, stock gasket, STOCK head) a 7.425 pushrod will probably give you the optimal preload with those lifters. If any of the factors change, for example, valve job, milling, different gaskets, etc... all bets are off. FWIW I use "LS7" lifters GM PN 12499225for almost all my builds now and check lifter preload everytime. Please be aware, this lifter is the '97 and up replacement lifter for any LS series engine. I also use them in all of my normal LT1 builds.

In cases such as yours, a cam over .600" lift with stock heads 7.425"s seem to work best. You'll end up with approximately .050" preload. You can run 7.4" no problem but you may end up a little noisy. These lifters are very forgiving and will work with a wide range of preload specs. If memory serves, GM calls for .055"-.085" preload. I like to stay on the low end for high RPM apps. Hope this helps...

Shane

RRhodes1

smaller base circle i assume?

Gnarly , maybe i wont need new pushrods once i slap new stuff on there.
i will check just the same.

here will be the valvetrain set up.

Trex cam, LS7 lifters, 7.425 push rods (hopefully), 1.7 yella terras, PRC dual gold springs & titanium retainers, on a PRC LS6 stage 1.0 head sitting ontop of a GM MLS gasket. all on a stock LS1 block.(soon to be dual timing chaing and ARP rod bolts.)

i hope no one sees any potential problem with this set up?

as far as i understand the PRC heads are the same EXTERNAL dimensions as a 243 casting, same valve diameters etc. i will be getting the valves recessed a bit just for a bit more PTV clearance

Thanks alot guys !

01ssreda4

iTrader: (96)

aftermarket cam = smaller base circle. .050 smaller on the ones I have measured. divide that by 2 and you need .025 longer pushrod then stock. Lifter cups on LS7 are taller so that kind of negates this. However like Shane said, they are a forgiving lifter.

XtraCajunSS

iTrader: (2)

You'll definitely need to check PR length with the YT's. As long as the new heads have stock valves in them and are not milled, basically meaning stock valve drop or more, you should be golden...

Shane