Is there anyone on here that has or know someone with a large displacement all bore LT1 motor? I'm not talking about a 355, something much larger. I'm considering another engine buildup for fun.

 

Cylinders are thin on an LT1 block. Mine's bored 40 over, and that's farther than I'd like but was done for convenience at the time. I couldn't find a spare block quickly and wanted to get it done. To compensate, I have partially filled the block. Most engine builders don't like to see more than 30 over. Early production gen I SBC's are often bored 60 over, but to do this and expect decent ring seal and block stability you need to have the block sonic checked. Exactly how thin cylinders can be before they are "too thin" is a matter of some debate. They need to thicker on the "thrust" side anyway. But even at 60 over (bore = 4.060") it would only be ~360ci.

Aftermarket and Bowtie small blocks are designed for a bore of up to 4.125". That equates to 372ci with a 3.48" stroke.

Rich Krause

 

Thanks Rich...I wasn't aware that the LT1 had thin cylinder walls.

 

yeah me neither darn it.

 

Mark Montalvo has built two 421's, with different bore x stroke combos. One was a 4.090" bore x 4.000" stroke. In order to go this far, he had to have a complete thickness check on all eight cylinders, then recenter the bores to maximize wall thickness on the thrust side... a heck of a lot of work and $$$. Can be done, but it isn't worth it. I held my overbore to 4.020" (381ci) to maintain the cylinder wall thickness with a large N2O shot.