I have a .30 0ver 225. Flat-top pistons, .180 in the hole. I have no idea what cc the head is, but it's a 1964 vintage milled .100 and a fel-pro .40 head gasket. Could someone please make a educated guess at what my compression ratio should end up being. Thank you for your time.

9.05 STATIC C/R
7.985 DCR with a 50 degree ABDC Intake Close

Doc, I would like to figure this math and see if I can understand how to do it. What cc did you figure the original 1964 vintage head would be before I shaved it .100? Thank you.

Educated guess at 56cc to start... that could be a bit more.
Figure a 1cc drop for every .007 of milling.
DD

I'm not sure what you mean by .180 in the hole.

But with a 3.43" bore, 0cc piston volume, 40cc head volume (a guess), 0.0315" thick head gasket (0.8mm), and 50 degree intake valve closing angle, I get

10.18 static CR
8.54 dynamic CR

1 cc for every 0.007" milled off subtracted from ~56cc = 56-14.28 = 41.62cc

using that number I get 9.97 Static CR, and 8.37 dynamic CR

_________________
Dan H
Dudes Ex Machina

This is the depth piston is below or recessed from deck at TDC, in other words, when piston is at its highest point in cylinder bore, it is the measured distance between top of piston and deck surface of block.

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

I don't get this. I have .040 over, .1875 in the hole, and a cut in the head at .093, and he gets over 9, and maybe 10, but I get 8:15. What do I not get here?

He obviously is missing some numbers from his formula, since he was unsure what .180 in the hole meant. But given you have that much deck clearance, it just isn't realistic you'll any more than what you have, regardless of how much the head has been cut.

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There's no such thing as too much cam....only not enough engine!

I have my own Excel spreadsheet which I built. It uses the bore, crank stroke, rod length, piston height, block height to calculate the CR. I built this for my Datsun 510 engine calculations so its in metric. It might be a little off for Head volume, head gasket thickness, and piston dish volume.

It gives me the clearance to the top of the block, and also to the head (so you could change to a different thickness head gasket if needed for CR change or height change). It was built that way to warn if the pistons would hit the gasket or the head. The Datsun guys have figured out how to make a bunch of interesting motors using junkyard engine parts from other Datsun motors. Like a low comp engine for turbo 1.6L or 2.0L, a long rod high rev-ing 2.1L. A bored out 2.0L block with pistons from a V6 (VG30) to get to a 2.3l. This spreadsheet allows me to analyze KA24 pistons in a 280Z block with a Diesel crank from a 280 block from a Nissan Maxima, which gives a 3.1-3.2L stroker engine, with a ~2mm thick head gasket to get the CR in a suitable range

Did you use 0 cuin (cc) for the flat top pistons?
Do you guys account for the head gasket thickness? what thickness?

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Dan H
Dudes Ex Machina

Deck height piston down .180

Other numbers should be:

.039 for comp head gasket height with a 3.5 bore (at best)

0cc for flat top pistons

stock early 60's heads weigh in somewhere in the 60+ cc range (I've seen 64-68 on truck heads from 1963), so 56 would be the guess on the stock head after the cut, if he cuts again then he'd be at about 41 (.0066 per 1cc assuming that the head still has cylindrical chamber lip on it and the cut isn't deep enough to start on the 'shelf' in the chamber...typically you start in on that section if you cut enough to be in the 40-42cc range)...

FYI,

-D.Idiot