I know somebody on here has done this exact thing already. If I retro fit an LT1 roller cam using the 3.1 lifters, how long will the pushrods need to be? Online I find info of 7.3 AND 7.5, which is it?

 

Your adjustable push rod will tell you for sure. No need to depend on some yutz on the Interwebz like me.

 

Well, I'm kind of in a time crunch. Pushing to make my MSE driveable by April 15.........and my block and heads JUST went to the machine shop! Just thought somebody probably already went through this.

 

why guess ? Just measure and order a set of push rods

 

You'll be in a worse one if you put the wrong push rods in and destroy things.

Not with YOUR parts in YOUR motor. Which is all that matters. What fit somebody else's parts and motor won't necessarily fit yours.

 

You need a pushrod that will give you a proper valve train geometry. The only way to know the proper length is with an adjustable pushrod. I think 7.3 and 7.5 can be measured with the same adjustable pushrod.

There's a difference between assembling an engine and building an engine. If you're building an engine, it would probably be stripped down at least 3 times do get proper machine work measurements.

Like mentioned above, it's your engine with your parts. Nobody can tell you what part to use because it's not OEM. Swapping parts usually means other that have also changed.

 

Found some info through research this morning. ASSUMING stock block and heads.
Stock gen1 sbc pushrod length +/- 7.8" with oe style hydraulic flat tappet lifter seat height of +/- 2.0"
87-up with factory roller cam use a +/- 2.6" lifter seat height and a 7.2" pushrod.
MOST retrofit roller lifter are around +/- 2.5" seat height requiring a 7.3" pushrod
The 3.1/3.4 v6 oe roller lifters have a 2.26" seat height, requiring a +/- 7.5" pushrod.

Again this would be assuming STOCK heads and valve setup. Your results may vary.
I hope this helps anybody else trying to retrofit a rollercam into a gen1 block.

 

with all the assumptions, just check. It’s the right way

 

Yes, I will once I start putting the engine back together. Would just like to have the right length on hand so as not to wait any longer than absolutely necessary.

If all else fails...........I'll TOW it to the show and enter in "under construction" class.

 

Those numbers are still going to be ballpark.

Has the deck been milled for squareness?
Have the heads been milled for squareness?
Has the camshaft been changed? A higher lift cam does not increase the lobe height. To get more lift, the base circle is ground down. That means a longer pushrod is required to achieve proper valve train geometry. That's why you can't guess at the length and pushrod length needs to be measured. Too many variables to just guess at a length. An adjustable pushrod will be cheaper than buying a set at the wrong length.