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Author
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Topic: 351C - FLAT TOP VS DISHED COMPRESS
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MOSS
Gearhead Posts: 100
From: Arlington, Tx, U.S.
Registered: Dec 2004
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posted 01-23-2005 10:11 PM
   
I pulled the heads on my 70 351c 2barrel engine and noticed that not only do I have the expected big combustion chambers but the pistons are dished as well. I am putting aussie heads back on. What approx compression will I have.
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f100cleveland
Gearhead Posts: 328
From: St. James, MN
Registered: Sep 2004
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posted 01-23-2005 11:08 PM
If I remember correctly, the Aussie 2v heads are around 62cc's. And if you use those heads with a flat top that has 2cc's for valve reliefs, you'll yield about 11.1:1 compression and if you are using the stock type pistons, it will be around 9.8:1 compression. It might not be totally right, but it will get you close.------------------
1982 Ford F100 2wd Shortbox. Powered by a 357 Cleveland w/ closed chamber 4v's and a Funnelweb. Full Roller c-6 trans with Gear Vendors Overdrive and 4.86 geared Detroit Locker equipped 9" rear. 1982 F100 351c 4v 1977 F150 460 Burnout Truck
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kid vishus
Gearhead Posts: 6220
From: middle of NC
Registered: Oct 2000
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posted 01-24-2005 07:32 AM
I think most of the stock aussie heads are 58-60 cc's. Has the motor been rebuilt? Or was it originally a 4v motor that someone stuck 2v heads. I've never seen a '70 2v motor with dished pistons. All of the early year motors I have seen, both 2v and 4v, all had factory flat tops in them.
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MOSS
Gearhead Posts: 100
From: Arlington, Tx, U.S.
Registered: Dec 2004
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posted 01-24-2005 10:43 AM
Its been rebuilt and .30 over. It looks like around 10:1 for my compression with the dished pistons. Is that correct?
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RonnieT
Gearhead Posts: 835
From: Port Allen, La. 70767
Registered: Jun 99
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posted 01-26-2005 09:36 PM
Moss, There is no way to figure your compression without some info on the pistons. Dished pistons can be as much as -24cc volume. How far the piston is down in the bore also plays a factor. If you figure 60cc heads, the pistons down in the bore .025, -14cc dished pistons, and a .039 head gasket get a cr of 9.35. If the pistons are -24 then the cr is 8.5. To get a CR of 10 with -14cc dished pistons the block will need to be "0" decked. ------------------
Ronnie
69 mach1 351W-4V engineless at the time!
70 Torino GT 351C-4v with a "shaker"
Mustangs and More Member #23
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