The Ford Barn

paleot · 11-06-2013, 11:00 PM

I just bought a set of offy heads stamped 375 anyone have any Idea what the compression ratio may be?
Tony

jr9162 · 11-07-2013, 01:14 AM

The heads have 57 cc combustion chambers. Used on a stock 239 w/no relief the CR will be ~8.41:1, with a relief ~8.09:1. The CR will increase as the bore size increases. In a 255 (Merc) you're looking at ~8.90:1 with no relief, and ~8.56:1 with a relief. The reliefs quoted above would be .0100" and gaskets above would be at 0.057" thick. John

Ol' Ron · 11-07-2013, 08:42 AM

Best to measure them, the casting can be all over the place. The 375was for Valve lift, but this didn't clear the Max #1 in most cases with out some clearancing.

paleot · 11-07-2013, 09:27 PM

Thanks John and Ol' Ron info will be a big help. Ron I am planning on running a Winfeild ¾ Cam do you think I will have valve clearance problems?

Ol' Ron · 11-07-2013, 09:35 PM

That's impossable to answer. Depending on the net lift and if the heads have ever been milled. are they new or used.

paleot · 11-08-2013, 10:17 PM

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Used, but they don't look to be milled at all. I will fit up a couple of valves and guides and check my clearance what is safe?

Ol' Ron · 11-08-2013, 11:25 PM

.050" over pistons and the valves should clear, for a street engine the valve clearance isn't that important. the closer the higher the CR

paleot · 11-08-2013, 11:35 PM

Thanks a bunch Ron I will mock it up and check in the morning.
Tony

11-07-2013, 01:14 AM	#2
jr9162 Junior Member Join Date: Sep 2013 Posts: 14	Re: Offenhauser Heads The heads have 57 cc combustion chambers. Used on a stock 239 w/no relief the CR will be ~8.41:1, with a relief ~8.09:1. The CR will increase as the bore size increases. In a 255 (Merc) you're looking at ~8.90:1 with no relief, and ~8.56:1 with a relief. The reliefs quoted above would be .0100" and gaskets above would be at 0.057" thick. John

11-07-2013, 08:42 AM	#3
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,859	Re: Offenhauser Heads Best to measure them, the casting can be all over the place. The 375was for Valve lift, but this didn't clear the Max #1 in most cases with out some clearancing.

11-07-2013, 09:27 PM	#4
paleot Senior Member Join Date: Jan 2012 Location: s/w Louisiana Posts: 119	Re: Offenhauser Heads Thanks John and Ol' Ron info will be a big help. Ron I am planning on running a Winfeild ¾ Cam do you think I will have valve clearance problems?

11-07-2013, 09:35 PM	#5
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,859	Re: Offenhauser Heads That's impossable to answer. Depending on the net lift and if the heads have ever been milled. are they new or used.

11-08-2013, 10:17 PM	#6
paleot Senior Member Join Date: Jan 2012 Location: s/w Louisiana Posts: 119	Re: Offenhauser Heads Sponsored Links (Register now to hide all advertisements) Used, but they don't look to be milled at all. I will fit up a couple of valves and guides and check my clearance what is safe?

11-06-2013, 11:00 PM	#1
paleot Senior Member Join Date: Jan 2012 Location: s/w Louisiana Posts: 119	Offenhauser Heads I just bought a set of offy heads stamped 375 anyone have any Idea what the compression ratio may be? Tony

11-08-2013, 11:25 PM	#7
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,859	Re: Offenhauser Heads .050" over pistons and the valves should clear, for a street engine the valve clearance isn't that important. the closer the higher the CR

11-08-2013, 11:35 PM	#8
paleot Senior Member Join Date: Jan 2012 Location: s/w Louisiana Posts: 119	Re: Offenhauser Heads Thanks a bunch Ron I will mock it up and check in the morning. Tony