Without going dart. If I was gonna tinker with building some motors what would be the best 502 to start with. Gen 4,5 or 6? Just curious.


Let me also add say I was thinking 600-650 naturally aspirated

Gen 6. Already set up as a roller cam. 4 bolt mains.
Forged crank and rods if you find a short block

They made the Gen v and VI in a production style block. I would take a Gen VI over a Gen V.

As for Mark IV 502, you'll only find them in a "'bowtie" block style. The Mark IV bowtie is a good block. Finding budget parts for mark iv style is usually more common. Things like used oil pans, cranks, etc are a little more common.

Main thing I would look for in any of the above, is a GOOD block. As in, NOT saltwater, std bore is always nice, and other things of that nature, and of course price and availability.

I think any 502 block is going to have 4-bolt mains. I have read that the older Mk IV blocks were thicker on the deck surface, which makes them stronger in this area, but like MT said, they may be hard to find in a 4.5 inch bore. The Gen V was somewhat of a compromise - not really any advantages over the Mk IV block aside from the 1-piece rear main seal, and you lose the ability to run a mechanical fuel pump if you were planning to do that. The big improvement with the Gen IV was the provisions for factory roller cams (more accurate lifter bores and the taller lifter bosses offer a little more support for the lifters) and priority main oiling - meaning the oil passages were reconfigured to give the main bearings better lubrication. I do know that some of the 4.25" bore Gen VI's have provisions for the mechanical fuel pump - I have two of them.

If you're going to build them, my guess is you'll be going to aftermarket lifters anyway. My preference would be the mark IV bowtie blocks. Stock bore is 4.470 not 4.5

If you choose to use a gen6 block keep in mind that they don't have allot of meat in the cylinder walls. They are only recommended to be bored to .30 over. I have a procharged 502 at .60 over and it's been fine but it is the weakest part of my build. I would suggest sonic testing the cylinder walls if you choose to go with a gen6 if you're punching it out above .30 over. It's money well spent. Maine motors definitely have a harder life than street or even quarter mile race motors. They need to be built with the fact that that run for miles at a time at high rpms. Valvetrain, oil system, etc. .. all come into play brother.

save your money and use a dart big m block, they are way stronger ,higher nickel and they don't flex like a gm block..

Also, try to find a closed cooling or automotive used block as they will not have all the scale in the water jackets that a marine used engine with lake water in the jackets will have.

I have a gen 6 gm casting (the latest one) with a mechanical fuel pump boss on it.

I appreciate all the info. I fully understand the differences in marine and automotive. I know a dart block is much better than gm. That's why I said without dart block. I was mostly interested in the differences between 4,5 and 6. Thank you all. My brain is just working all angles and figuring out what to do.