'66 427CI 390HP block - how large can I bore safely?

[Georges C.]

I live in the south - HOT weather! Just how large can I bore a 427 CI 390 HP block and not impact structural integrity or abiity to cool properly? As the question indicates, I am a novice at the rebuild process.

[Michael H.]

Re: '66 427CI 390HP block - how large can I bore safely?

I would'nt go any more than .030 to help with the cooling. The more material you can leave on the cylinder walls the better.

Mike

[Georges C.]

Re: '66 427CI 390HP block - how large can I bore safely?

Thanks Michael, I've been told the blocks are so thick that they can be bored beyond .060 safely and many of the guys racing do this as well. Also been told there's a new coolant out that reduces the heat problem. Anyone else out there want to chime in? Appreciate any ideas about this.

[Joe R.]

Re: '66 427CI 390HP block - how large can I bore safely?

I live in the south - HOT weather! Just how large can I bore a 427 CI 390 HP block and not impact structural integrity or abiity to cool properly? As the question indicates, I am a novice at the rebuild process.

Georges,

Please provide a bit more information so that we can better answer your questions. Is the block original to the car? Why does the engine need to be rebuilt? What are your plans for the engine? Generate as much power as possible while appearing stock? Or are you planning to go back together bone stock other than oversize pistons? Are you planning to have the car judged by the NCRS? Or are you just wanting to drive and enjoy? I believe .060 over is fairly safe. You probably should have the cylinder walls sonic tested. That will tell you for sure.

Joe

[Joe R.]

Re: '66 427CI 390HP block - how large can I bore safely?

Georges,

I've seen Zerex G-05 recommended here, I think by Duke Williams maybe. Here's a related thread:

https://www.forums.ncrs.org/showthread.php?87009-Antifreeze-Change-Over-to-G05&referrerid=2667

I'm not sure what you mean by heat problem.

Joe

[James B.]

Re: '66 427CI 390HP block - how large can I bore safely?

Joe Raine made some very good points. Very important you have the block sonic checked as core shift was common problem on 427 blocks. I had 66 425, needed to go over .030 to clean up but found we couldn't go to .040 so went to 0.035 over and had to use special pistons. Also on rebuild of 425 I got talked into lowering CR (that probably was needed), compensating with 454 crank, going from solids to hydraulic lifters, roller cam and followers, 'new design' cam, etc. motor made power but the rebuild completely changed the character of the car- I liked the original, responsive, high reving 425 and I didn't have that any more.

[Michael H.]

Re: '66 427CI 390HP block - how large can I bore safely?

Thanks Michael, I've been told the blocks are so thick that they can be bored beyond .060 safely and many of the guys racing do this as well. Also been told there's a new coolant out that reduces the heat problem. Anyone else out there want to chime in? Appreciate any ideas about this.

True, the walls are thicker and yes you can go to .060 or more, but like I said the more material you leave on the walls the better heat dissipation you'll have and as we all know Big Block's don't like heat. Take the least amount of material off that you can. The cooler they are the better they run.

Mike

[Georges C.]

Re: '66 427CI 390HP block - how large can I bore safely?

Thanks, to all. I am restoring the car to the original 427ci 390 HP engine that came in it -- is impossible to find the correct numbers for blocks. That being said, I have found the correct block with date and appears t be clean - supposedly little drive time but it was not correct for his car - he is supposed to have found a correct engine. The engine I found has been bored to .060. I intend to use it to drive, have had the car since 1976 mechanical restore then driven about 15,000 miles with current LT1 type engine. Am doing complete interior to original, and engine compartment with -this - engine, and some minor other mechanical re-news.