396 L78 block

[the427king]

Sonic test it to be certain .....cylinder wall thicknesses can be all over the board on the same block even within the same bore,so be sure to measure 4 places on each bore . 854s are decent for boring to 427 but #962s are the best.....

[big gear head]

I've got a 854 L78 block. I removed the center plug and checked the space between the cylinders with a pencil and it went through. I don't think I would bore this block to 4.250.

[EZ Nova]

Originally Posted by chris slawski

Hey folks-
Can a L78 4 bolt block 69 vintage accept an over bore to 4.250 for 427 displacement or will it become unstable?

asking for a friend

For the cost, WHY?? you could probably buy a ready to go 4.250 or 4.280 bore block for less?

Keep the L78 for L78 stuff or people.

IF your looking to go fast, the added bore will help some, but in the end is it really going to be worth it? I myself see no reason for this unless to mislead people or a class by claiming to be a L78/396 and be stroked? Like some sort of stock-block class.

FYI I did a mild 402 to 575Hp back in the 90's with mostly GM stuff. Used OEM L78 short block, Ported sq port closed chamber heads, strip dom intake and comp .660 solid roller. Ny '69 Nova would run 10.40's with 9" slick, thru muffler and 4.56 and M21. I'm sure with what we know now, I could put that deal in the high 9's or low low 10's, WITH A OEM "163" intake.

So tell us WHY your thinking this bore?

Thanks, John

[EZ Nova]

There is a reason why stock and super stock guys use SLEEVED 454 blocks to go back to 396 also!!!!!

Your friend could very well run into a overheating issue too with that thin of a cylinder wall.

[Vortecpro]

Originally Posted by chris slawski

Hey folks-
Can a L78 4 bolt block 69 vintage accept an over bore to 4.250 for 427 displacement or will it become unstable?

asking for a friend

NO

[Vortecpro]

Originally Posted by EZ Nova

There is a reason why stock and super stock guys use SLEEVED 454 blocks to go back to 396 also!!!!!

Your friend could very well run into a overheating issue too with that thin of a cylinder wall.

The reason there sleaved down 454s is to move the bore away from the intake valve. My engines are aways filled for NHRA stock.