The Ford Barn

JayJay · 10-02-2022, 10:08 PM

I appear to have a non-stock cylinder head on my '31 Town Sedan, possibly high compression of some sort. The biggest flag is the words "Model A" on the outside of the water channel. There is also a small boss between the #2 spark plug and the distributor, maybe it says "A-5" (I can't tell the first for sure, the second is pretty sure a 5). I'm thinking it might be a high compression head because

Previous owner (that I bought it from) had a record of a compression test in the high 80's psi, which is a bit much for stock; and

Traveling on the freeway at 55+ mph it feels like there is plenty left, which is not my experience with a stock motor.

Do any of you recognize this head? It likely dates from the original restoration in the 1970's or early 1980's, as the previous owner didn't say anything about it to me when I asked him what he'd done to the car since he'd owned it.

Thanks a million.

JayJay

Jim Brierley · 10-03-2022, 11:10 AM

It is undoubtedly an aftermarket head. The best way to determine the compression ratio is to measure the volume of the combustion chambers and do the math.

Benson · 10-03-2022, 11:22 AM

I have one of these and over the years have seen many of them in Model A parts stashes.

They are an after market copy of the 1930 Ford 5.2 to one Police head with the heart shaped combustion chambers (v.s 4.2 on stock head).

Bob C · 10-03-2022, 11:39 AM

Vince's site shows it as a copy of the Police Head like Benson said. https://www.fordgarage.com/pages/hea...ssionratio.htm
I have one and the combustion chamber looks just like a stock head.

JayJay · 10-03-2022, 12:11 PM

Thanks, all. No plans at present to pull the head, so I'll go with the 5.2 "Police" head copy for now.

Great to have all these resources handy!

Anteek29 · 10-03-2022, 08:57 PM

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Previous owner (that I bought it from) had a record of a compression test in the high 80's psi, which is a bit much for stock; and

5.2 Comp. Ratio X 14.7 lbs. Atmosphere = 84 psi. Sounds about right for Police Head. I do believe that is what you have.

Jim Brierley · 10-04-2022, 11:43 AM

Quote:

Originally Posted by Anteek29

Previous owner (that I bought it from) had a record of a compression test in the high 80's psi, which is a bit much for stock; and

5.2 Comp. Ratio X 14.7 lbs. Atmosphere = 84 psi. Sounds about right for Police Head. I do believe that is what you have.

This is a good rule of thumb to remember!!!

10-03-2022, 11:22 AM	#3
Benson Senior Member Join Date: May 2010 Posts: 2,599	Re: What cylinder head is this? I have one of these and over the years have seen many of them in Model A parts stashes. They are an after market copy of the 1930 Ford 5.2 to one Police head with the heart shaped combustion chambers (v.s 4.2 on stock head). Last edited by Benson; 10-03-2022 at 11:31 AM.

10-03-2022, 11:39 AM	#4
Bob C Senior Member Join Date: May 2010 Location: So Cal Posts: 8,755	Re: What cylinder head is this? Vince's site shows it as a copy of the Police Head like Benson said. https://www.fordgarage.com/pages/hea...ssionratio.htm I have one and the combustion chamber looks just like a stock head.

10-03-2022, 12:11 PM	#5
JayJay Senior Member Join Date: Jan 2020 Location: SF Bay Area Posts: 1,077	Re: What cylinder head is this? Thanks, all. No plans at present to pull the head, so I'll go with the 5.2 "Police" head copy for now. Great to have all these resources handy! __________________ JayJay San Francisco Bay Area ------------------------ 1930 Murray Town Sedan 1931 Briggs S/W Town Sedan

10-03-2022, 08:57 PM	#6
Anteek29 Senior Member Join Date: Dec 2014 Location: Santa Maria, CA Posts: 985	Re: What cylinder head is this? Sponsored Links (Register now to hide all advertisements) Previous owner (that I bought it from) had a record of a compression test in the high 80's psi, which is a bit much for stock; and 5.2 Comp. Ratio X 14.7 lbs. Atmosphere = 84 psi. Sounds about right for Police Head. I do believe that is what you have. __________________ Alan 1929 Special Coupe 1941 Pick-Up 1955 Victoria

10-03-2022, 11:10 AM	#2
Jim Brierley Senior Member Join Date: Jun 2010 Location: Temecula, CA Posts: 4,091	Re: What cylinder head is this? It is undoubtedly an aftermarket head. The best way to determine the compression ratio is to measure the volume of the combustion chambers and do the math.