I have 7.4s right now

Plan on having my heads mill .02 with .04 gaskets

So a total of .03 shorter than stock height

Is there a rule of thumb for example drop the head height .02 go with 7.375 pushrod length?

What size pushrods did yall use for you milled heads?

 

For what its worth I had .020 taking off my heads, stock MLS gaskets and have been running a 7.4 PR for some time with zero issues. Your going to get answers from both sides here I would imagine.

 

My other issue is I have the Ls7 lifter which are .05 taller than the stock lifters.

I am doing the swap in a weekend at a friends shop so I dont have time to use a pushrod checker and wait for the correct pushrods to get in since it is my dd.

I do think the 7.4s with .02 milled taller Ls7 lifters will be to much pre load but I cant decide whether to go 7.375 or 7.35

I have been told the true gm stock pushrods are 7.38 dont know if that is true or not

What can happen with to much preload? What are signs there is to much pre load

 

The new lifters seem to have the masses fucked up LOL. Again your going to get mixed answers. The cups are what is taller. I would say run a stock length rod, I do believe it is 7.38. But it would be best to actually measure since you did change things up. Nothing says anything about replacing PR's when you switch to the new style lifter, as it is a OEM replacing part...To much PL will not let the lifter pump fully, will or could damage the cam, rockers, lifters. Not enough can make for a louder valve train.

 

"The new lifters seem to have the masses fucked up LOL." Hahahaha so ture! It's like i read the direct replacement info then get scared by the .05 taller info

Are you running Ls7 lifters on your set up?

I currently have 7.4s with 20,000 miles no issue, so I think im going to order 7.375s b/c Im thinking about putting .04 cometic gaskets on as well

 

Any milling of the head or thinner/thicker gaskets corresponds directly to the pushrod length. So in your case, you would want a 0.03" shorter pushrod to maintain the same lifter preload.

FWIW, my heads are milled 0.022", LS7 lifters, and LS9 head gaskets (stock thickness), and I am using 7.325" pushrods to get around 0.075" lifter preload.

There seems to be a LOT of variability, so you will want to measure for the correct pushrod length.

 

No sir I am running old style ones.

 

Is .1 preload ok?
What is to much preload?

Is there more power to be gained from being lower on preload then over. <nothing dramtic hp wise like 1-2 I guess

For example lets say anything under .050 preload will be valve train noise and anythings over .1 preload will break< so from the above question would It be more efficient/power if I was around .6 preload vs .95 preload

 

The "correct" amount of preload varies depending on who you ask. Do a search on LS1Tech and you will find what most people are running. There is no power to be gained or lossed via preload. Generally, less preload is noisier.