Piston To Deck Hieght

[fmster]

Can any one show me pics of your short block at TDC,so I can see the distance and or give messurements please. Thanks

 

[Jerryl]

Try this thread.
http://www.turbobuick.com/forums/general-turbo-buick-tech/267505-stock-block-deck-height.html

 

[fmster]

.010 thats almost flush to the deck.

 

[bison]

Mine are about .007-.008 out of the hole on the current build. Compression is calculated to be about 9.3:1.

 

[charlief1]

.010 thats almost flush to the deck.

You want it for the "squish" effect to help create turbulance in the combustion chamber. You need to know the crushed thickness of the gasket you're using. No more than .025 total and you should be good.

 

[Lee Thompson]

I believe factory specs were

86-87 eng. ---.060 head gasket thickness compressed.
Pistons were .010 down in the hole which gave an 8.0 CR
All eng. assemble I do I order pistons with the deminsions to be .010 recessed.

 

[fmster]

Pics Any one!!!!!! Please.

 

[bison]

I just checked the 149k one ive got and the pistons appear to be about .045 in the hole with the piston at TDC. I didnt have a really good straight edge to measure with so im sure im off a few thousandths. I believe stock dish is about 23cc. Someone else can confirm this.

 

[bison]

86-87 eng. ---.060 head gasket thickness compressed.
Pistons were .010 down in the hole which gave an 8.0 CR
All eng. assemble I do I order pistons with the deminsions to be .010 recessed.

What dish volume do you order?

 

[bison]

On the compression calculator a stock engine came out to 7.9:1 using .060 compressed gasket, 49cc chamber, 23cc dish and .045 in the hole. Changing the piston height to .010 in the hole raised it to over 8.4:1.

 

[fmster]

On the compression calculator a stock engine came out to 7.9:1 using .060 compressed gasket, 49cc chamber, 23cc dish and .045 in the hole. Changing the piston height to .010 in the hole raised it to over 8.4:1.

Thanks, mine is 045 in the hole,I thought maybe that was to much.

 

[bison]

Thanks, mine is 045 in the hole,I thought maybe that was to much.

It would depend on how many cc's the dish on the piston is. Mine are 27cc with the 3.820 JE's. If they are stock they should be about 23cc's. If yours are 27 you compression ratio will be about 7.5:1.

 

[fmster]

It would depend on how many cc's the dish on the piston is. Mine are 27cc with the 3.820 JE's. If they are stock they should be about 23cc's. If yours are 27 you compression ratio will be about 7.5:1.

That's not too good.Is it? Thanks

 

[fmster]

It would depend on how many cc's the dish on the piston is. Mine are 27cc with the 3.820 JE's. If they are stock they should be about 23cc's. If yours are 27 you compression ratio will be about 7.5:1.

That's not too good.Is it? 7.5 They are stock piston

 

[bison]

That's not too good.Is it? 7.5 They are stock piston

I dont see how they could be stock since it says .040 over in your sig. You will have to cc them to find out for sure. It will tolerate more boost with lower comporession but will take more boost to make the same power as a setup like mine where its about 9.3:1. I run a minimum of 110 octane though.

 

[fmster]

I dont see how they could be stock since it says .040 over in your sig. You will have to cc them to find out for sure. It will tolerate more boost with lower comporession but will take more boost to make the same power as a setup like mine where its about 9.3:1. I run a minimum of 110 octane though.

How can you check the compression ratio,not the psi with the motor asembled.?

 

[charlief1]

How can you check the compression ratio,not the psi with the motor asembled.?

Compression ratio is calculated as distance piston is at its lowest point to its highest poin but you have to know cc of the head, cc of the head gasket, how far down the piston is in the cylinder, both ways, and how much dish the piston has. It has to be done before the engine is assembled.
This is a simplified version and I'm sure someone will give you a complete method of calculation to do it.

 

[rmar]

RSR Static Compression Ratio Calculator


Have fun.