[Gary H]

Originally Posted by steve25

Do you have any stock assembled rods and pistons to see what you have now?
Most 389 and 400s I have worked on check in at .023” to .026”.
421s. 428s and 455s are more like .019, so between all the motors where not talking a big difference.
With a 4.150” bore and a .021” deck your looking at 4.65 CCs or like a 1/4 point change in compression.

I'm not talking about one specific block per se. I'm talking about the deck height in general on an uncut Pontiac block. Icon pistons assume 10.225", DSS uses 10.210", Autotech uses, I think, 10.230". It's all over the place. I'm trying to get a general consensus so I can convince DSS to use a different number for their off the shelf pistons. I like their pistons but 10.210" is too low. I don't want to deck the block that much each time if not needed.

[JLMounce]

Originally Posted by Gary H

I'm not talking about one specific block per se. I'm talking about the deck height in general on an uncut Pontiac block. Icon pistons assume 10.225", DSS uses 10.210", Autotech uses, I think, 10.230". It's all over the place. I'm trying to get a general consensus so I can convince DSS to use a different number for their off the shelf pistons. I like their pistons but 10.210" is too low. I don't want to deck the block that much each time if not needed.

Your initial calculation is probably pretty close nominally.

The pistons I took out of my engine where the old TRW L2359 which had a compression height of 1.497. When I did the top end on the previous short block, My pistons ranged from .005 to .007 in the hole, with the deck being taller towards the back of the engine vs the front. This led me to speculate that the engine had not yet been decked on it's first rebuild.

2.105 + 6.625 + 1.497 is a compression height of 10.227". If we nominally add another .006, that would put my likely original deck surface height at 10.233"

I do believe that many of these piston manufacturers like DSS, Icon, Ross etc. will anticipate that the engine will have a surface done on it and build their pistons accordingly. Your cheaper off the shelf stuff like the Speed Pro and KB hypers may assume a more budget friendly rebuild approach and may engineer the piston CH based off of that. Speculation on my part obviously.

For what it's worth, it cost me $250.00 to have my block decked with a BHJ fixture. That cost would likely be absorbed by having a piston with an altered CH built. It probably washes out either way. I also get that what you're trying to accomplish is having a company that supplies a quality forged piston that utilizes a modern ring pack, metallurgy and technology without the need to spend extra to deck the block according to its construction.

I believe the problem then becomes in situations where a block must be decked, that shelf piston may no longer be a good choice. You can run an engine with the piston in the hole easier than you can run it with the piston out of the hole. That would mean the manufacturer would need two skews and that adds cost.