[scott70]

Originally Posted by Formulajones

Yes, a factory engine (all of them I've dealt with) will have the pistons down in the hole .020-.025"
But we don't want to rebuild them that way. It doesn't cost anymore to correct the problem, you should be decking the block anyway, and custom pin heights don't break the bank. So lets get it to zero deck for better quench and octane tolerance.
For starters, the factory engines don't have their advertised compression ratios, so this is one way to correct that. Plus you are going to need an overbore, which increases compression too, so the rules allow a 1.5 compression bump, which makes sense. I've had engines where the compression was different in different cylinders, with the deck lopsided and a crank that's a few thou short on stroke the pistons varied in deck height from hole to hole. What a mess.

Is it absolutely true to stock form? No but you aren't going to find absolutely true to stock form cars that are 50+ years old unless it's a survivor, and those types of owners in most cases don't want to race those cars, hell they rarely even drive them.

So the rules keep the spirit of stock at bay with a few small variances that allow us to rebuild these things and keep them running, and have a little fun in the process, both for owners and the fans.

Also as far as how much power difference there is between an original verse one that is rebuilt properly??

By the time you correct the compression issue, index the crank and grind it with proper stroke, degree a camshaft for proper valve events, a good valve job on a set of unported heads........
I'd guess easily as much as 30hp and even more on certain engines.

Thats what I did,,,the pistons I had were 1.47 CH and were .035ish in the hole. Ordered custom autotech pistons with a 1.5 CH and with a cometic .036 head gasket now Im .around 040 quench. Thought it was better than milling the block that much. Pistons didnt take that long to get and werent crazy money.