502 overbore, how far can it go?
 

i have ta chance to trade some parts for a bare genV 502 block with main caps. the block is bored at .060 over and the guys machine shop says it just needs to be honed to be ready to go. i have read conflicting info online, some people say you can take a bbc to .100 or even .125 overbore and that the 502s had siamesed walls so they can take it even more. but then i read other places taht say .060 over is risky? my goal with the motor is to get into the 600-650hp range n/a with a stroker crank, after market heads and custom cam. all forged internals, H beam rods.... all the goodies to keep her strong and dependable. nothing too insane, no plans for boost at all. or am i better off snagging a 454 block and doing a 496 with it? thanks in advance for any advice

i wouldn't use a 502 bored more than .030'' ,but that's just me

if i am reading that right that says you can only go 30 over but i am finding pistons and rings all over that for 60 over. here is one for example

http://www.ebay.com/itm/PISTON-RINGS...item20b7c65886

sure way to find out is to look at gm parts catalog...if they dont sell them,its because they know better...i work in harleys,and they dont go over .030'' in evolution engines...jobbers sell the +.040'',but i wouldn't use them,as the cylinders get too thin and distort under heat....but then again,jmo...

I don't know about a Gen V block but I did see someone that has taken a Gen VI to 4.560 to make a 555 stroker. That was pushed to the limit for a GM block.

Here are the typical stroker bores, typically 540 is where most marine engines stop with a GM block, anything after that is usually aftermarket. Also, these are all typical for 9.8 standard deck blocks, if you get a tall deck aftermarket block you wouldn't even be thinking about these low numbers.

4.470" Bore Size is Standard 502 (actually about 4.466) depending on hone job.

4.500" Bore Size to Make 540 cu in ..OR in 4.530" Bore Size to Make 548 cu in..OR in 4.560 Bore Size to Make 555 cu in .. OR 4.600 Bore Size to make 565 cu in

A lot of guys do .060 over, I have been looking for a bare 502 block they are getting hard to come by. How much will you have in the block or in your case about how much are the parts you are trading worth. Be sure you have a machine shop check it out first.

Your really .030 past whats reccommended already. I wouldn't build a 502 production block out to 4.560 as you are getting the cylinders walls pretty thing and you will either get cylinder distorion under a load or worse. The reason you see 4.560 and bigger pistons is the aftermarket blocks like the merlins and darts can use the same bores and strokes and can be bored further safely, Smitty

More than one of the engine builders that are advertisers here on OSO, have personally told me that going .090 to .100 is perfectly safe even on a blown motor.

we have bored the gm gen5-6 blocks to 4.530 have not had any problems,i would be a little nervous going to 4.560 would be a good idea to have the block sonic tested

I have taken them to 4.600 on more occasions then I can remember. I wouldn't go over 4.560 on a salt water block since you have to worry about corrosion from the back side of the cylinders. If you are going to go to 4.600, then you have to sonic test the block to check for core shift. I can count on one hand how many I have seen that won't go to 4.600.
With that being said, I didn't choose to go straight to 4.600. I only did it because we had to. Now, I will not hesitate to take one straight to 4.560, and do with most all of them to unshroud the valves with aftermarket, big valve heads. That makes a 524 with a 4" crank and a 555 ci with a 4.25" crank. I have literally done hundreds of them since that block hit the market. It's still a good idea to have it sonic tested. You really need a minimum of .250 wall thickness at least.
I know a few drag racers the have taken them to 4.625. I wouldn't do it, but it has been done. And they didn't fill the block.
Good luck.
Eddie

well seems like conflicting info here also lol. i am wiating for more info, if it is a clean bore at 60 over i am gonna go for it, if there are issues then its a no go. i have been looking for a affordable 502 block for over a year and a half, they are not easy to come by and i do not have pockets deep enough to spend 1800+ on a new one. thanks for the info guys :)

I'm running 4.565 and pushing 650+ hp, no problems. I had a reputable engine builder check the block before and after, no issues.

The operative words here are inspection and testing! Inspection of the existing condition of the block and importantly the conditions of the internal water jackets with respect to rusting and deterioration is critical along with the sonic thickness testing. Even core shift in new cast blocks can lead to bore wall thickness issues and believe me when I say in casting there are no always right blocks that make it to market!
Our new 675HP upgrade for the HP525efi engine is based on a 540 cubic inch with a 4.530 bore and that seems to be a safe place on the average 502 Gen 6 block especially since these are freshwater closed cooled engines. We have as many other builders gone to 4.560 -4.600 on these blocks on many occasions but only after careful inspection and sonic testing. Depending on how long of service life you will expect from the block and how many times you expect to freshen the bores will also be a determiner as you will need addtional material in the bore for re-bores in the future so starting at 4.500-4.530 has some addtional advantages at starting there especially when you consider the cost of a replacement or new core block.
Just some addtional builder advice here.

Best Regards,
Ray @ Raylar

How far can you cut down the decks?.. :party-smiley-004:

We don't cut them as much in the North as they do down south!!:evilb:

I have bored many genVI blocks to 4.560 and boosted them with 10 to 12 lbs of boost with no problems. Rob

4.600

this is one of those cases that ray go savaged over in an earlier post. yes , the info is conflicting but you have two guys that have built more motors sucessfully than the rest of this board combined, telling you the answer.

so, really, what is the question ? is another 20 or 30 thousandths of bore with the associated few cubic inches gain worth introducing variables that will involve a lot of work and effort and expense to check for and even when you are done, you will be taking a substantial risk for absolutely no gain what so ever.

i have said it before and i say it again now. the difference between professionals and home builders is not what that they know what to do , it is that they know what NOT to do.

two of the best professionals in the industry have told you what not to do.

believe them

wow dude?? did you not read all of this or what? the block is already at 60 over, i am not trying to gain cubes! i want a usable block for a mild stroker build. and the pros just said they have taken it 60 over so i am not really sure why you are hammering me?? pretty sure the deal has gone south anyways