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A12 race motor with 10.56 to 1 compression
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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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jpg  P1040116.JPG (145.50 KB)
3475_5dbf5764b61be.jpg 640X480 px

jpg  P1040117.JPG (150.00 KB)
3475_5dbf577799ec5.jpg 640X480 px

Posted on: 11/3 22:51
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Re: A12 race motor with 10.56 to 1 compression
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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!!

Posted on: 11/3 22:54
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Re: A12 race motor with 10.56 to 1 compression
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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?

Posted on: 11/3 23:12
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Re: A12 race motor with 10.56 to 1 compression
No life (a.k.a. DattoMaster)
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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

Posted on: 11/4 11:37
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Re: A12 race motor with 10.56 to 1 compression
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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!

Posted on: 11/5 6:16
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Re: A12 race motor with 10.56 to 1 compression
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My daily driver has a 4.4 final drive. Yes it revs up fast, which is why the car accelerates quickly. I love it

Posted on: 11/5 7:51
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