killlerkc

Looking to upgrade my L98. The 1.6 3/8th rockers will do well. Just can't find out exactly what the proper Pushrod length, width, and threads I need.
I'm pretty sure they need to be 5/16th.
Any guidance at this point would be much appreciated. Thank you Kc

bosshog8

Why won't stock pushrods suffice? I have never needed to change from stock pushrods unless I have done a cam change, new heads, etc. If you have made other changes that require a different from stock pushrod length then it is unlikely anyone knows your exact situation. There is a pushrod length tool you can use to determine your particular size.

vettespecial

Yes Bosshog8 is correct, I am driving my fresh overhauled L98 Cam and roller rockers, and other stuff, i had my engine machine shop do this step
before i took it home to assemble, using a adjustable push rod with cam chain and one lifter and rocker installed you just turn over the motor thru full valve deflection intake and exhaust and see that rocker arms stays on true center of valve stem. adjust push rod untill it true center then measure
length of test push rod, then you know proper length you need to order.
The machinist call it valve train geometry check.

mtwoolford

jeeze, just try the stock push rods first; if the block hasn't been decked, or the head milled, or something else done to alter the oem dimensions, you should be fine.

all the above advice is right on , but...since you are running hydraulic lifters right?....you'll need to purchase some very light weight valve checking springs to install on each valve as you check the geometry. Why? without the engine running and oil pressure pumping up the lifters, the stock valve springs will compress the plunger down into the lifter body, rendering the measurements pretty much useless.

or if that's too much of a problem, take an old lifter, disassemble it, pull out the inner piston and stack small washers inside the lifter body, so that the lifter is in essence an uncompressible "solid" lifter and use this one lifter to check pushrod length for each valve.

DouglasC

ALWAYS replace the old Pushrods when changing the Rockers !! Measure with the adjustable piece and go from there. The new rods will in effect "seat" just to perfectly fit with the new Rockers. The old rods won't have the correct length (geometry) and are worn in to mate with the old rockers. Also keep in mind that IF you are leaving every other part of the system stock (as in stock Cam, Lifters, Springs Heads etc.) you won't get a large HP gain. Perhaps 2 to 5 though this varies. Many just think by increasing the lift by going from 1.5 to 1.6 that there will be 20 ish HP gains as "some" manufacturers claim. NOT in my experience.

C409

..... When I changed rocker ratio on an '93 F-body LT1 in a '74 'vette , it picked up 0.14 seconds in the 1/8th mile with no other changes ... I don't recall what the MPH change was .....