GM 502 Gen VI Sonic Test
 

I was wondering how far I could bore a 502 block. Just by measuring the thickness of the cylinder walls through the water passages in the deck, it appeared that 4.600 was easily obtainable. I had my machine shop sonic test it for me and here are the results. This is a very thick block. If I was to bore it to 4.600, the minimum thickness in cylinder 3 would be .264.

With a 4" crank that would take a 502 to a 532.
With a 4.25" crank that would take a 502 to a 565.

565 sounds good. and just a tad more expensive than a 540. With a JE flat top piston the compression would be 9.4/1.

Re: GM 502 Gen VI Sonic Test
 

Picture for 500EFI Overbore Thread

Re: GM 502 Gen VI Sonic Test
 

Linster,
I have a Gen V block and a few years back I was looking to open it up.. My guy went to 4.520" which is oddball size, and had to do a lot of ring work because of it.. I was told at that time 4.530" was max on the standard production block.. we never did a sonic test. Problem being that when cylinder wall scoring happens, then the block is done. If you take it all the way to the limit, your gain in hp due to cu is minimal when you consider that you can get one more hone or bore to clean up a messed up cylinder bore.. Just my .02 on the subject..

Dick

So linstar - what did you do here?

What are your recommendations on the 502 max punch minus on size smaller?

Triple Nickel !
 

Linster:

My opinion and suggestion is to keep the block bore at 4.500" on overbore and use a bigger stroke crankshaft like 4.50" and that way you'll have bore left over for a possible future re-bore need and still have the big cubes needed for big torque. Its a "Triple Nickel" 555 cubic inch size BBC as we call them at 4.50" stroke and a great engine configuration. Also 4.50" piston sizes in standard strokes are many times shelf stock at piston houses as well as crankshafts and less expensive than custom bore sizes or strokes.

Best Regards,
Ray @ Raylar

Hopefully he has already figured out what he was going to do. Considering that this thread is 6 years old. :drink:

Sorry about that but i was researching what has been done in the past and was curious what he went with and if he was successfull in the new bore. I plan on upgrading mine next winter and am undecisive on exactly what I am going to do. I have a plan but not enough facts to base my decisions on yet.

Yep! Next time I should pay more attention to the original post dates. Some of these new OSO question hounds dig up some old ones don't they!

Best Regards,
Ray @ Raylar

A 4.5 bore and 4.5 stroke is 572", not a triple nickell 555 "as you call them". It is also not a good combo for a standard deck 502, especially in a marine app. It drags the piston too far out of the bottom of the bore and causes clearance issues as well as a bad rod angle among other things. A 4.375 stroke and 4.5 bore is a 557 and that is a good combo. People on this board think you know what you're talking about so you should probably be a little more careful when dispensing advice. It could cost some poor guy a ton of money to try and build a 4.5" stroke standard deck disaster..