compression calculation

i guess the stock deck hight in LT1 block is 9.037", is that correct?. when piston reaches TDC in LT1 how much of an inch is the piston below the deck?

Small block chevy deck height from the factory is 9.025" Which is usually milled down to 9.000"

Your perfect setup would be a zero deck block. I can't say where the stock engine sits stock, but that's the deck height 9.025"

Bret

thanks but you didn't specify the distance between the the top of the piston at TDC and the deck? i need to know this distance so that i can calculate compression of some pistons? anyone can help?.

i can remember the LT1 has 9.037" deck hight. and also i can remeber the other SBC's have deck hight of 9.025".

Originally posted by Abdullah
thanks but you didn't specify the distance between the the top of the piston at TDC and the deck? i need to know this distance so that i can calculate compression of some pistons? anyone can help?.

i can remember the LT1 has 9.037" deck hight. and also i can remeber the other SBC's have deck hight of 9.025".


Abdullah,

For the most part, a untouched LT1 should have a stock deck height of 9.025. Now, due to core shift and stackable tolerances, it is possible (although unlikely) that a LT1 block could have a deck height of 9.037". This would be a rare case IMHO.

The only way to know for sure would be to take the block in question and have a machine shop measure the distance from crank centerline to the top of the deck. Once you know what that distance is, you can then have them machine the top of the deck surface down, so that you will have a 9.000" deck height. This is an optimum height for good "quench" in the combustion chambers. Ultimately, you would want to have your whole rotating assembly and assemble it in the block. Then measure the distance from the top of the deck, to the piston crown on each cylinder to find out which one is the "tallest" (or the smallest number) and that would be the amount you'd want to mill the top of the deck surface. The actual distance from the top of the piston crown to the surface of the cylinder head will then be determined by your compressed gasket thickness.

If you are trying to figure out a certain compression ratio, just use a 9.000" deck height, enter a compressed gasket thickness and order custom pistons to get the compression ratio you want.

Hope that helps you out a little.

Mike

Originally posted by Mikey 97Z M6
For the most part, a untouched LT1 should have a stock deck height of 9.025. Now, due to core shift and stackable tolerances, it is possible (although unlikely) that a LT1 block could have a deck height of 9.037". This would be a rare case IMHO.

Why would you say that? GM doesn't take the block to 9.025" anymore than they machine heads to the blueprint cc spec. They, by design, machine the deck surfaces, (heads and block) conservatively. It is more likely that the block is 9.037", than it would be 9.025". That is also why heads cc out to 57-58, in lieu of 54-54 1/2. (.015-.020") BTW, nothin' to due with core shift. Deck machining is tied into other machining operations.

i found in some engine compression calculator webpage that the LT1 has a deck hight of 9.035" and they consider 0.035" to calculate the compression. and i'm sure that i read that the LT1 has a stock deck hight of 9.037" meaning that i need to consider 0.037" to calculate the compression. 0.037" is the distance between the top of the piston at TDC and the block deck :D i found it :D . decking a block to zero deck hight will increase the compression considerably.

Originally posted by arnie
Why would you say that? GM doesn't take the block to 9.025" anymore than they machine heads to the blueprint cc spec. They, by design, machine the deck surfaces, (heads and block) conservatively. It is more likely that the block is 9.037", than it would be 9.025". That is also why heads cc out to 57-58, in lieu of 54-54 1/2. (.015-.020") BTW, nothin' to due with core shift. Deck machining is tied into other machining operations.

So you work for GM then?

Well, I was only speaking from my personal experience, hence the "IMHO". I have personal experience with 3 LT1 blocks, and they were all within 9.022", and 9.027" and I've never even heard of any being over 9.030". So I guess it must just be a coincidence?

9.025" is a target number, but I'd tend to say a stock LT1 block would be closer to that number, than 9.037". JMHO though.

Mike

Originally posted by Mikey 97Z M6
I have personal experience with 3 LT1 blocks, and they were all within 9.022", and 9.027" and I've never even heard of any being over 9.030". So I guess it must just be a coincidence?

9.025" is a target number, but I'd tend to say a stock LT1 block would be closer to that number, than 9.037".

Mike, I've even seen 'em under 9.015". Considering various years, sounds like they vary quite a bit. :)

When they true-decked my block they had to take off .040" to even one side of the block..Came from the factory like that..

Cody

I heard it was 8.99 inches. That would make sense since that would mean the piston would come up dead even with the top of the block. 3.48 inch stroke/2 + 5.7 + 1.55 = 8.99 I made my own compression calculator on microsoft excel and I think it came out to 10.4 with the piston dead even with the deck of the block. I would have to check and I could be wrong.... where did you find this stuff?

Originally posted by 97 RedSS
When they true-decked my block they had to take off .040" to even one side of the block..

DAMN! That is a lot!

Well, that would certainly explain why some LT1's run so much harder than others. This could make quite a difference when comparing relatively stock cars IMO.

Mike