Hi all. I'm into a 455 build as I see many here are. This is a 1971 low comp motor that needs boring, etc. I've had the crank cleaned, fluxed and takin down 10 thousandths. I have an Edlebrock Performer Intake w/750 Holley. Cam not purchased yet. I'm going to use either Edlebrock or Mondello Alum heads. I'm looking for around 400HP/but a big torque cruiser w/out HUGE lope. Street cruiser. My question is will it make any difference if I go 60 over on the bore as opposed to 40 over. And does KB (so far my piston of choice) make a 10:1 that big? Sorry, but so many choices! Any and all advice greatly appreciated. Thanks in advance. wfg4u@aol.com

 

I would go no more than needed, like .040. That way if you have a problem down the road, you can bore it again. If you go .060,and need to bore it again, you will have to sleeve it.

 

Here's the way I look at it. It's generally accepted that the max overbore on these blocks is .060 in. If you bore the block .060 then that will be the last rebore you will get from that block. If you only bore it .040 or .030 then you may have a good chance of re-boring it again. This may not seem important, but consider what might happen if you broke a ring or something and damaged a cylinder wall. If you had bored to .060 the block would be junk. If you had only bored it the minimum amount to clean it up, that block would have a second chance. They aren't making 455 blocks anymore.
The 6 extra cubic inches is not going to make much, if any, difference in HP output.

 

X2, don't bore any more than necessary and don't bore at all until the machine shop has the pistons to fit them to each cylinder. Boring more than necessary gains very little in performance, makes the cylinder walls thinner which lessens the chance of boring again if needed and some say may make the engine run hotter.