Attached are the compression worksheets I created. This is the engine in previous posts with the Arias forged pistons, shaved crank, originally had a F10 flywheel & clutch , I'd already stole the Cannon single sidedraught manifold for the A15 in the car, H72 match ported head, etc...

I'm wondering if anyone has ran a similar setup w/a real worked up ratio ? I cc-ed the combustion chamber, piston volume, negative deck clearance volume, calc-ed the head gasket (Felpro Printoseal) managed to buy another NOS one - all metal gasket @ .041 compressed thickness. I've clearanced the pistons and head with clay so I know what all those numbers are now.

Have to talk to Delta Cam as its a fine line between grinds for above 10.5:1 and below.

Interested in how this will run. Obviously it'll need as high an octane as I can get but I think pump gas will be fine. Lookin for real world experience , thoughts anyone?

thanks,
evan

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One other thing - the posted H72 cylinder head combustion chamber volumes for aq stock head are totally wrong. The Wiki says 29 to 31 cc's, I have a brand new NOS H72 head, never milled, installed, etc.. and it cc's at 41 for the chamber volume.

Wiki be wrong!!

Premium pump gasoline is fine for 11:1

And the cam doesn't matter as much as they will lead u to belive back in the day we put "high compression" cams in 8.5:1 engines and got very good results the fear is that high-overlap cams will bleed off too much compression at low RPMs but who cares about that just fit a higher ratio rear gear such as 4.62 instead of the stock 3.90

The H72 is just a casting number and the actual heads using that casting are many different part numbers, could be open chamber or semi-open with air injection or without etc depends on how the haed was machined at the factory. which part number is your head?

Now work out your dynamic compression ratio
My static was about 12.9 but dynamic was closer to 10

https://www.enginebasics.com/Advanced% ... tatic%20vs%20Dynamic.html

I’ll have to look at the casting #. either way mines at 41cc so the data is really far off, thought it was worth noting for others.

As far as “just fitting” a 4.6 ratio ring / pinion setup- those are like unobtainium & besides that who’d want a street car with that setup. I sold a 4:10 setup to a dude in England for like $400 about 8 years ago, he was ecstatic to pay that cuz he couldn’t find one.

When I get the motor back together I’ll check the dynamic compression #’s with the cam in , I can use the timing wheel for that, it’d be interesting to see what that works out to.

Thx all!

My daily driver has a 4.4 final drive. Yes it revs up fast, which is why the car accelerates quickly. I love it