Aussie Heads and compression ???????????????
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New User
Joined: May 2002
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Aussie Heads and compression ???????????????
Well, I rebuilt my 400m using Aussie heads I spent too much money on it- Balanced , Forged pistons, Roller rockers ,headers, MSD Ignition ect. I built it for toque instead of HP. But it seams to have both.I had custom pistons made for the quench effect. Started it on 104 octane -no knocks. Added 50/50 premium pump gas - no knocks. this should be about 97 oct. How ever i am going to run it on Propane and yes I used the right valves. As ya'll know propane is high in octane. Anyway I checked compression and the guage read 185-187. My Question is there a formula to figure if this is 11 to 1, 10 to 1, 12 to 1? I was shooting for 11 to 1 but doin't know how to convert.Thanks
Posting Legend
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Aussie Heads and compression ???????????????
Conversion is not possible due to a number of variables.
Use the compression calculator formula in the back of the Ford Racing catalog.
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Use the compression calculator formula in the back of the Ford Racing catalog.
Thanks for using FTE!
[font color=red]As a Moderator I do not "Subscribe" to most topics,
please send email/pm if you need a reply -Thanks![/font]
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Junior User
Joined: Nov 2002
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From: Connecticut
Aussie Heads and compression ???????????????
I am currently looking at installing Australian heads on my 400m and the calculated compression ratio would be roughly 9.4:1 (62cc chamber). This modification would be done with stock crank, rods and pistons. If i was to use the technique mentioned here:
https://www.ford-trucks.com/dcforum/DCForumID12/1068.html
(This is I6 rods, custom pistons and a ground crank under the aussie heads of course)
I get a compression ratio of 10.0:1 with a 24cc relief in the pistons
I guess my real question is that if i was to mirror the head chamber shape on the piston, would it be possible to run the engine on pump gas 87-93? What causes question is when i read specs of stock engines built in the mid 1960s boasting 10.5:1 compression. I have heard greater than 9.5 leads to pre-detonation, but all factors involved, how high is too high?
https://www.ford-trucks.com/dcforum/DCForumID12/1068.html
(This is I6 rods, custom pistons and a ground crank under the aussie heads of course)
I get a compression ratio of 10.0:1 with a 24cc relief in the pistons
I guess my real question is that if i was to mirror the head chamber shape on the piston, would it be possible to run the engine on pump gas 87-93? What causes question is when i read specs of stock engines built in the mid 1960s boasting 10.5:1 compression. I have heard greater than 9.5 leads to pre-detonation, but all factors involved, how high is too high?
Posting Guru
Joined: Jun 2002
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Aussie Heads and compression ???????????????
Hey that thread looks familiar. The only problem is with the 24cc dish. The pistons were custom but reasonably priced because it was a common application.
I believe they were only made in a flat top version. Custom pistons with the 24cc dish may cost considerably more than the KBs. Keep the piston pin diameter in mind. Customs are usually made with a .927" pin vs the I6 .912" pin.
ACL also makes a similar piston that may work in this application. 351C with 6.0 con rod. I'm not sure how to order, but their catalog is available here.
http://www.acl.com.au/web/aclwebsite.nsf/8df7d3f7b605537a4a2569660082eda8/f7914230e2e6c7cc4a256967000e22bb/$FILE/PP99-1.pdf
I believe they were only made in a flat top version. Custom pistons with the 24cc dish may cost considerably more than the KBs. Keep the piston pin diameter in mind. Customs are usually made with a .927" pin vs the I6 .912" pin.
ACL also makes a similar piston that may work in this application. 351C with 6.0 con rod. I'm not sure how to order, but their catalog is available here.
http://www.acl.com.au/web/aclwebsite.nsf/8df7d3f7b605537a4a2569660082eda8/f7914230e2e6c7cc4a256967000e22bb/$FILE/PP99-1.pdf
Junior User
Joined: Nov 2002
Posts: 98
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From: Connecticut
Aussie Heads and compression ???????????????
thanks for the catalog, it will surely come in handy, but cant the 24 cc dish be made with a lathe or milling machine into that flat top piston?
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Posting Guru
Joined: Jun 2002
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Aussie Heads and compression ???????????????
Check with the Cleveland board. They have been talking about the same pistons and where to get info.
http://www.network54.com/Hide/Forum/119419
Ideally, the only dish piston that will compliment the Quench chamber is the D-shape. The depth is around .150" for 22cc. There may not be enough thickness to go that deep without weakening the piston. Check with KB.
A round dish is fairly easy to cut on a lathe, but you may as well use open chamber heads.
The D shape chamber can be done on a milling machine but involves more set up time and labor cost from a machine shop.
http://www.network54.com/Hide/Forum/119419
Ideally, the only dish piston that will compliment the Quench chamber is the D-shape. The depth is around .150" for 22cc. There may not be enough thickness to go that deep without weakening the piston. Check with KB.
A round dish is fairly easy to cut on a lathe, but you may as well use open chamber heads.
The D shape chamber can be done on a milling machine but involves more set up time and labor cost from a machine shop.
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