327 Chevy Maximum Bore Size

I just picked up a 1965 Corvette 327 engine with the camel hump heads. I am installing the engine in my 40 sedan delivery and wanted the engine to represent my first Corvette with the L79 motor option. (327/350) Upon disassembly, I found a very clean engine that has been bored .040 and the cylinder walls look good so far. I have the heads at the machine shop and am not sure about boring the block to .060 as I am afraid of building a heater motor (runs hot). My question has anyone bored to .060 and had any problems with overheating? The machine shop said they do it all the time but that doesn't mean they don't run hot.

If you can offer some advice I am listening even if it means to hone the current block and put it back together. I don't know about the taper but there are no ridges or scoring in the cylinders.
Thanks,
Lynn
Pewsplace.com

 

I wouldn't go .060" if it doesn't need it. If it needs it a .060" works, but be sure there's no core shift in the casting before going there. If it can be honed and re-ringed I'd do that, rather than bore it more.

 

I've had multiple .060 over 4" bore 327 and 350 engines and a few .080 overs. No heating problems ever. The only heat problems I've ever experienced had absolutely nothing to do with the bore size. Most of the time it's a timing or radiator issue.

With the correct radiator and timing, a .060 or even .080 over SBC will live forever.

All this from my cars (and trucks), not hearsay.

Just sayin'....

 

going to forged pistons may help if you got some clearance, i dont like them for street but a few thousandths gets ate up with the clearance required
i did that to a 327 .o30 vette block put in a 331 kit and it was a great engine

 

My personal rule is .060 as a last resort max bore on all sbc's except the 400 (.040).

 

I ran a 12:5 to 1 .060 motor for years on the street with no cooling issues at all, I'd stay .040 if I could why take it out if it will live at the current size.

 

.060 on a 327 is not a problem, but if the cylinders are clean you shouldn't have to go that far.

 

Whats the casting number and stamp code on the engine block?

 

hone it,new rings,your good to go

 

My cousin and I built a 327 a few years back for him. 40 over would've been good enough to clean the cylinders, but he insisted on going 60...no matter what I told him. Anyhow, after going .060 over we got the block back from the machine shop and notice some pinholes in one of the cylinders. We took the block back and they sleeved that cylinder. We built the engine and dropped it in his truck. After running it a few times in his garage it started to miss... pulled out one of the plugs and water poured out. I'm thinking more cylinders had these pinholes. Maybe that block was just a bad cast (I'm not sure of the casting numbers off hand) but ever since then, I do not recommend .060 over unless absolutely necessary.

 

Don't take bore measurements for taper too seriously if you are measuring without torque plate.
Don't use a 3 stone hone without a torque plate either.

 

The difference between .040 & .060 is only.010 on each wall, if it was junk at .060 it was already junk at .040. That being said I have bored well over 300 SJ 327's to .060 and at least 20 to .080 every one good to go. .060 isn't a recommendation it's a fact of life.

 

I put one in my dads 55 Stude. .060 over, KB hypereutectic flat tops, 69 Z-28 solid cam, runs cool in the 100 plus degree Fresno summers

 

You might want to sonic test it first, every block is a bit different in casting let alone what kind of life it might have had with age

 

Word... keep it simple and don't make extra work for yourself.

Bob

 

Thanks for all the great responses. The block is a 65 vintage and has casting number 3858180 and was used in the 275 hp motors. I think I will see if I can get by with just honing the cylinders and putting in new rings. I have the pistons removed and will take it to the machine shop on Monday. I really appreciated the advice from all of you. I would like to keep the motor intact rather than pursue a new block with a standard bore. The engine has had great care for the last 30 years in a 62 Corvette that was pampered.

Tim, I will call you later today.

Lynn

 

Did anyone else look at those sonic test numbers Hot Rod published on the 350 block a couple months ago, and think "if that block was shifted to the minor thrust side, 1/8 would be a go"?

 

hone with tourq plate and install new 040 pistons with file fit rings.
problem can be not heat but loss in hp if cyl walls is flexing when warm and cyl is not perfekt round as pistons and rings

 

x2!!

 

Lynn, another option is non shelf or a custom set of pistons. We do this all the time with race engines ordering + .005" over. In your case they would be .045" oversize.


NOW- before everyone starts screaming about the price of custom pistons, you did just save around $200 for a bore job. Any good machinist will only hone with plates the additional .005", which you would need to anyway if you went .060" over. You increased the value of your engine with a nice set of forged pistons as well. You also saved the $60-100 on the sonic test, which should be mandatory on the .060" over bore. It is a old wives tale that this alone would cause your engine to run hot.

This is NOT some cobb way of slapping something crudely together, this is done in very high end engine shops like mine on a daily basis, TR

 

Thanks, I did not know you could order special pistons. I am waiting for a report on the block.
Lynn

 

And another plus to doing this is you can order whatever ring grooves you want.