I'm in the middle of a rebuild. I've searched the board, and haven't easily been able to find out how big LT1 blocks can be bored? 0.030 over? 0.060? More? What is, safely, the limit?

 

wwhyyyyyyyy you just weaken the block. go .010 over if you can find the correct pistons for it and they arent too much more.

People have gone .090 over to make 42x cid LT1s but I'm sure they didnt last too long

 

On the new style blocks over .030 is pushing it. Then the cylinder walls might crack or heat very badly.

 

.060 is the max, most people do .030

 

What does 0.030 over make the CID?

 

355 is .030, 357 is .040, 360 is .060... I have a 360 in my 89 formula, but i had to have the cyl sleeved to handle it... so i wouldnt go over .030 if i were u try and find .020 pistons if u can

 

Unless you're looking for Cubic Inches, bore the minimal amount necessary for a good rebuild.

.060 over is about the MOST you'll want to run in a street/strip LT1, and even that's pushing it.

 

actually, I remember seeing a guy on this board long time ago (old account) who claimed to have over 80000 miles on a .090 bore....

Don't know about that. but I don't think .030 is sacrificing much. I never had any problems.

I wouldn't go over .040

 

Another vote for 0.030 over... I think that is more than safe. You wont have any problems with that. I don't know about .060 over or even .090 over though.. damn that seems high.

 

.040" would be my last resort, and I'd only do that if it absolutely needed it. If it needed more than that, I'd find a new block. I'm a big fan of only taking out what you need.

Sleeving is another possibility, but I haven't heard much of that with LT1 blocks.

 

If you're looking for more cubes a longer stroke would be the way to go. Stock bore x stroke is 4 x 3.48 so there's not much room on the boring side, but you can fit a longer stroke crank in without too many problems.

Maximum acceptable bore is .060, any more than that is pushing it and would probably not be acceptable for maximum reliability.

 

Cool. Thanks for all the input. Next question: I see guy's with 400+ ci LT1's. On LS1tech there is a guy right now with a 410ci LT1. Yet, the biggest stroker crank I've ever seen is a 3.875. With a 4.060 bore, that would make a 401ci motor. ???

 

I think that's 401 or 402 you'd be at with that combo...

 

bore^2 * stroke * 8 * .7854

 

There was a guy who used to post on here that claimed to have built two different versions of the LT1 at 421ci. One was a 4.030" bore x 4.125" stroke. The other version was a 4.090" bore X 4.00" stroke. I saw the dyno sheets for the 4.090 bore motor, and it made over 800HP on the juice. He had to have the entire block soniclly checked for wall thickness, then recenter the bores to put most of the meat on the thrust side of the cylinder. Seems like a huge waste of effort.

There was a performance shop that used to sell a 409ci short block LT1, but he no longer has it in his catalog.

There is also a person who posts here that has a 427ci LT1 (4.120" bore X 4.00" stroke), built with a sleeved LT1 block. Can't remember his name, but I know he posted some info on a thread on Advanced Tech about sleeving the LT1.

Do not bore any more than you need to.... I'm real happy knowing that my 381 (4.020 X 3.75) has the wall thickness to withstand a 300-shot, and could be rebuilt in the future if necessary.