BigVette427

I'm thinking about swapping my OE LS7 lifters for Morel 6504's when I do the heads and I'm interested in any opinions or lessons learned with these on the the LS7? I am otherwise inclined to switch to 7.775" PR's while I was at it, as well. They say they are drop in replacements for LS lifters, but I can't find a whole lot of data on these as far as how they may affect PR length on the LS7.

jayyyw

Those Morel lifters should be .045" preload, +/- .005. I believe they are something like .027" shorter than the OEM LS7 lifter. When you install them, face the oil fill holes towards the oil passages in the block (header side).

Definitely measure after you have the heads assembled.

BigVette427

Got it, thanks. I was thinking of swapping new PR's and going from OE 7.800" to 7.775". How will these shorter lifters affect pushrod length?

Unreal

Shorter lifter will need a longer PR.

You can't say crap about going from 7.8 to 7.775 without measuring. The question to how long of a pushrod is needed is always measure. No excuse or reason not to.

BigVette427

Preferably I'd like to have the correct set of PR's ready to go ahead of time, but I agree that I will want to measure to be sure.

What I was thinking was going down to 7.775" to reduce preload to around .100" vs GM's preference at .125", so theoretically if I were to go to the Morel 6504's at .027" shorter than OE LS7 lifters, I'd need to bump up my PR's back up by the same amount, (back up to the 7.800", correct?) Just trying to make sure I understand the math. Thanks.

Unreal

Pushrods can be had overnight, or a day or two at most. Most local shops stock a good variety of sizes. Having them ready is basically impossible, unless you buy 3-4 sizes, and return the ones you don't use. If you need to do it fast, order multiple sets and return what you don't use.

0HP RESEARCH

There is no real way to know 100% for sure, you have to measure like Nick said.

There are a number of different things that will determine pushrod length, and who is to say the ones in the engine now are actually correct or the desired ones?

Ideally you would want to have the lifter bled out dry so you can feel the travel and how much preload you have when you do it. With the lifter completely bled dry it also will allow you to see how much room you have in the lifter from seated to fully collapsed. The adjustable checkers come in handy but we check every engine here with a real one piece pushrod and measure it until it is right. By doing it this way you eliminate the chance for error, as long as you are using the same company to get the final ones as your checking pushrods. Of course for the home using having tons of different length pushrods around is not a real option.

Pushrod checkers come in handy and you will need to be able to measure them once you are done. Also be sure to check with who ever you buy the pushrods from if they are really what they are stated. Some pushrods will vary from manufacturer as to what they really are.

Dan_the_C5_Man

Who says "GM preference at .125"? What is your reference?

I fear this thread will go the same way the spring and retainer thread went..

BigVette427

What are you talking about? I eventually figured it out! Just trying to piece everything together when I do my heads here soon.