i need some advice. i am putting together a quick engine, sort of a test mule. the bottom end is a 1.8. 66mm stroke 93mm bore with flat top pistons. i have a cherry set of 2.0 3 bolt heads for it.

i just completed the short block and did a deck height check. the deck height is .022. and according the porsche repair manual it gives 58.7-60.2cc for combustion chamber volume.

when i plug the numbers into the cb engine calculator it comes up with a compression ratio of 8.1

is this going to be ok? these numbers are obtained with no barrel shims or the head shims.

it seams like i read in various threads that i want between .040-.060 for a deck height. but im not sure this pertains to my build. i think they were big engine builds where i read that.

this engine will be carburated with dual idf 40's and running 92 octane fuel. timed to probly 28 degrees full advance. and using tangerine racings horizontal cooling system, and kerry hunter headers.

do you guys see a problem with the deck height? or do i need to shim it to .040-.060?

any info would be great, so i can keep moving forward on this project.


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You should measure your combustion chambers, because if you assume wrong, it could be unpleasant. It's not hard.

Once you get up around 9:1 you start getting close to detonation territory. 8.1:1 is no problem.

But check that head.

thanks mark....

You need to cc the heads so you know exactly what numbers you are dealing with. Mine came out at 8.4 to 1 without shims. Runs great with good power.

Don't run less than .035 deck. At .020 the pistons will rock enough to hit the heads.
Mock up the engine and check for piston-valve clearance by using light (I use rocker shaft springs) springs instead of valve springs.

your going to damage those heads/valves

you need to clay it and check
but I think you really want to increase that deck height
brant

ok, i have two set of .008 shims. if i use 2 shims per cylinder, that will give me .016 plus my .022 with a new deck height of .038.

this will knock my compression ratio down to 7.8

of course im guessing on the combustion chamber volume, i am going off worsrt case scenario.

Your CR calculation is meaningless w/o CCing the heads. Little changes make a big difference here.

I did not see, but are you using a head gasket? You can lower deck height and raise your CR a little by leaving out the head gasket. It also remove a possible head leak source. Of course, some will tell you its the best thing ever, and some will tell you it will kill your motor - with experienced people in both camps.

Zach