65 to 68 'B' block variations?

Okay, so I checked with a local machine shop (guy does mostly heavy equipment but does all things well), about a basic rebuild on my 65 383. He calls his parts supplier who proceeds to tell him that they only stock engine kits for 68 and up 383's. I can't recall any significant differences between the pre/post 68 383's especially on the short block side, am I forgetting something here? Why wouldn't a post 68 overhaul kit work on a pre 68??? (Not talking the 59 RB 383's here.)

Several things I can think of off the top of my head is the 67 and older had engine had a different lifter and pushrod than the more common later style big block setup, the 68 and newer had the same size pushrod ends which i believe both were 5/16 where the 67 and older had two different size pushrod ends one being 1/4 and the other is 5/16. The older motors can be easily updated to the newer set up if needed.

Also 67 and older motors had closed combustion chamber heads where as the 68 and newer used an open combustion chamber head, I believe the piston compression heights are different.

Okay, I had forgotten the lifter differences with the pre 68 having the smaller bottom ends. The 516 closed chamber heads I didn't think would have a major impact on the bottom end. I mean the lifters/cam are typically serviced separately, aren't they?

Lifter and cam diffs ?????

The only thing I’m aware of is the CD of the early and later pistons.

If you use the 68 + pistons ... you will get a much better compression ratio ... which should still be ok with regular gas of today

You’ll just need to be careful about piston choices. I’ve been going through the same thing selecting pistons. The blocks are the same. It’s the pistons and heads that were different. Don’t think you can even buy the early lifters. Just get later pushrods. Don’t get the cheap ones with the balls welded on the end. My customer had one break off and cause catastrophe failure. My build is using later open chambered heads and seal power forged pistons with the higher compression height. They make cast pistons with a lower compression height. I don’t use the KB hyperutectic. I’m out of town visiting with the kids but I can dig out my measurements by tomorrow morning and post them. It should help you out.

See my post below. I had some time to kill and had my infor with me.

That would be handy info to have.

On my buddies ‘66 383 4-bbl motor, we are just using the later low compression 2 bbl pistons. It’s a stock rebuild, so they are cast, compression ht was very close if I remember correctly. Stuff will be back from machine shop Friday nite, I can compare them again. Jim.

What Heads are you using? The 516 I have at the shop had 79cc for chamber volume. I’m pretty sure they were factory untouched.

My suggestion is for you to use the tutorial on the JE piston website and figure your compression ratio with long math and not an online calculator. You can more easily see what changes make the difference in CR.
My KB 162 has a deck height of .031 below the deck with a stock block, unmilled. Yours could be a little different. They have a published compression height of 1.908. They have big(8cc) valve reliefs.
The L 2315F has a compression height of 1.920 and no valve reliefs.
Another cast stock type Sealed power piston has a lower CH. It’s 1.848. It’s part no 366AP.
I’m using 87 cc 452 heads.
Stock shim steel head gaskets were .023 and the felpro blue is .039.
Like I mention earlier, 516 closed chamber heads should be around 80 cc.
Good luck.

Yes, pre-'68 pushrod has a smaller ball lower tip and in '68 cam lobe profile changed.

Now THAT slipped my mind but I kind of read that initial post as the later model cam and lifters not fitting into a 65 block ...

So I stated it poorly, John showed exactly what I meant to say. :-P

No easy answers, huh?? Really it just means I have to get it all torn down so I can start with some known values - I did rebuild it once already, but I looked up the paperwork today and it's not much help as most of the part numbers have changed since 1983 and my memory isn't that precise.
Thanks, I think I'll give up on the shortcuts................

Yes, we are using stock 516 head, I had bought the pistons from the machinist. We just compared CH rather crudely by shoving a pin thru both pistons. Now I’m curious how accurate that was. Guess I’ll know tomorrow nite when he brings stuff over. Jim