Re: Compression questions

[trnsfrma@ix.netcom.com (Shawn C. Meze)]

At 10:40 PM 5/27/97 +0000, you wrote:
>OK I know that the 84 JH has 8-5-1 compression and the 1.8 16v has 
>10-?-1 compression but what do the three numbers stand for?

First, your not reading 3 numbers, you should be reading just 2. Like 
10-1 or 8.5-1 or 8-1. get it?

The "Compression Ratio" is the comparison of the total volume of the 
cylinder with the piston at BDC and the piston at TDC.


>When you compression test an engine it has been said that a 84 JH is 
>good if each cylinder is between 135 and 150 PSI(i think its psi).  
>Is this pressure in any relation to the 8-5-1?  

Absolutely!

>What happens when you put on a high compression head gasket?  I know 
>it bumps the JH to 9-5-1 but would there then, be more pressure in 
>the cylinders? 

I actually makes the volume of the chamber smaller. Forces the piston to 
compress the air/fuel mixture even more. Increasing the CR. Increasing 
the CR = POWER!!
The VW motorsports head gasket is 1.4mm thick. The stock head gasket is 
2.8mm. The increase in CR using the Vw motorsports is only .4 to .6 
increase in compression. So your only looking at a net increase in 
compression to about 8.9-1 to 9.1-1. 
Now, if you were to shave the head .40 then you would gain another .6-.7 
CR. Combine the head gasket with the head work and you could have from 
9.5-1 to 9.8-1 CR! Not bad eh? Now do the exhaust work, cam, intake, 
knock sensor and P/P the head and you've got something like 11-1 CR and 
about 145hp. 
(Is that what the Pottermans rocket is putting out to the crank?) Either 
way, a very fun car to drive!


> I understand all the other aspects of the engine but 
>this stuff confuses me.
>
>                                      Jay


Probably because its math!  J/K!!   :-P


Shawn
<recently educated in basic engine math 101>
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