Ok, so I'm going a little nuts here... I've checked out an array of calculators on the 'net, and so far, inputting the exact same numbers gets me original CR of anywhere from 6.7 to 7.6, and with my expected changes, anywhere from 10.5 to 9.6 which is quite a range, to say the least.

does anyone have one they know is more accurate?

I have the following:

piston to deck - .210
Head chamber - 61cc's before milling the head.
and it's a 225, and I had a standard composite and will be using a steel shim in the future.
The engine is bored .030 over.

My plan is to mill the head .180 and I expect to end up with a true 10.2 compression ratio when I'm done.

This engine is to run on PROPANE, so octane and pinging aren't an issue ( propane has > 105 R+M/2 octane rating).

Does this all agree with what you experts know, or am I off in left field.

No, it is not possible to deck the block at this time.

Yer numbers seem funny......


I had to do a lot of check and recheck when I built my motor .....eventually it all got consistent and sensible. Keep plugging.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Thanks for the input...

How about you guys who've done this repeatedly.... am I off somewhere?

I think .180 of would be higher comp then that if i remeber correctly my head is cut .100 then i had a clean up pass on it a year later and it's right on the nose of 9.9:1 compression.

Kev

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Depending on the head gasket I get 7.1 compression out of your setup. .210 down in the hole is a lot.


With a steel shim head gasket, and cutting the head till you get a 40cc chamber I get 9.6cr. I dont even know if you can cut the head that far, although it seems I have heard of people getting 35cc chambers with a lot of cutting. Your going to need 35cc to get above 10 to 1 on cr with the piston that far down in the hole.


Jess

Ok...well it always pays to triple check things...

I found some errors...

1. Gasket thickness was wrong, measured to be around .015 metal shim.
2. dial caliper 'tail' not accurate. fixed.
3. slight chamfer on piston edge

so, what I really have is about .193 down the hole...

taking off .180 from the head should get me to 10.5:1 CR @ a chamber size of about 33 or so.

There you go!

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Yeah....Im the one who destroyed this rare, vintage automobile.....

what head casting number was used for the .180 cut? ron

I don't know. It's at the machine shop right now, getting cut .170 and should be done tomorrow.

I believe the engine is a 77 or 78.

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'81 W150 on Propane... Oversize valves, Oregon Camshaft cam, 10:5 static CR, Distributorless ignition, megajolt timing controller, PowerTrax lockers.