The Ford Barn

Nosetime · 10-18-2017, 12:54 PM

Hi, I have an aftermarket head in mind, but the seller is unsure of the compression ratio. He said, it is within 2cc volume of an original head, I assume less volume= higher compression, but any way to know if its a super high or lower end HC head? I probably need to pull the trigger or it will be gone, Thanks.

Charlie Stephens · 10-18-2017, 01:14 PM

A picture would be nice. If it is within 2cc the volume of an original head it doesn't sound very high. Other than that you will need to measure the volume of the combustion chamber (or have a machine shop do it).

Charlie Stephens

BRENT in 10-uh-C · 10-18-2017, 01:18 PM

Charlie is correct, 2cc difference is negligible, and likely there will be that much variance between chambers on an older aftermarket head. Also, you cannot just use water to measure volume. Find a local race engine builder and he will have the proper equipment to check it for you.

Nosetime · 10-18-2017, 01:57 PM

Thanks to both of you, that is exactly what I was thinking, it would be a long distance transaction, so not worth the gamble. I did remember, I think.. Boyles law about volume and pressure from college 35 years ago, but knew that was not much help! I will just wait for a Winfield. Regards, Greg.

Bob Bidonde · 10-19-2017, 06:29 AM

A compression test will tip you if the cylinder head has a higher than stock compression ratio. Pressures with a stock head will range up to 75 psig.

Nosetime · 10-19-2017, 09:51 AM

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The head is not on an engine, thats the problem.

Jim Brierley · 10-19-2017, 10:32 AM

I wouldn't spend much money on a head that is that close to the stock compression ratio unless you really need a head.

Nosetime · 10-19-2017, 02:26 PM

Thanks Jim. Exactly what I was thinking!

10-18-2017, 12:54 PM	#1
Nosetime Senior Member Join Date: May 2017 Location: Huntington Beach, Calif Posts: 330	Determine Compression ratio of an unknown head? Hi, I have an aftermarket head in mind, but the seller is unsure of the compression ratio. He said, it is within 2cc volume of an original head, I assume less volume= higher compression, but any way to know if its a super high or lower end HC head? I probably need to pull the trigger or it will be gone, Thanks. Last edited by Nosetime; 10-18-2017 at 12:55 PM. Reason: sp

10-18-2017, 01:14 PM	#2
Charlie Stephens Senior Member Join Date: May 2010 Location: Southern California Posts: 7,039	Re: Determine Compression ratio of an unknown head? A picture would be nice. If it is within 2cc the volume of an original head it doesn't sound very high. Other than that you will need to measure the volume of the combustion chamber (or have a machine shop do it). Charlie Stephens

10-18-2017, 01:18 PM	#3
BRENT in 10-uh-C Senior Member Join Date: May 2010 Location: Eastern Tennessee Posts: 11,534	Re: Determine Compression ratio of an unknown head? Charlie is correct, 2cc difference is negligible, and likely there will be that much variance between chambers on an older aftermarket head. Also, you cannot just use water to measure volume. Find a local race engine builder and he will have the proper equipment to check it for you. __________________ . BRENT in 10-uh-C . www.model-a-ford.com ...(...Finally Updated!! ) .

10-18-2017, 01:57 PM	#4
Nosetime Senior Member Join Date: May 2017 Location: Huntington Beach, Calif Posts: 330	Re: Determine Compression ratio of an unknown head? Thanks to both of you, that is exactly what I was thinking, it would be a long distance transaction, so not worth the gamble. I did remember, I think.. Boyles law about volume and pressure from college 35 years ago, but knew that was not much help! I will just wait for a Winfield. Regards, Greg. Last edited by Nosetime; 10-18-2017 at 01:59 PM. Reason: sp

10-19-2017, 06:29 AM	#5
Bob Bidonde Senior Member Join Date: May 2010 Location: Long Island, NY Posts: 3,486	Re: Determine Compression ratio of an unknown head? A compression test will tip you if the cylinder head has a higher than stock compression ratio. Pressures with a stock head will range up to 75 psig. __________________ Bob Bidonde

10-19-2017, 09:51 AM	#6
Nosetime Senior Member Join Date: May 2017 Location: Huntington Beach, Calif Posts: 330	Re: Determine Compression ratio of an unknown head? Sponsored Links (Register now to hide all advertisements) The head is not on an engine, thats the problem.

10-19-2017, 10:32 AM	#7
Jim Brierley Senior Member Join Date: Jun 2010 Location: Temecula, CA Posts: 4,095	Re: Determine Compression ratio of an unknown head? I wouldn't spend much money on a head that is that close to the stock compression ratio unless you really need a head.

10-19-2017, 02:26 PM	#8
Nosetime Senior Member Join Date: May 2017 Location: Huntington Beach, Calif Posts: 330	Re: Determine Compression ratio of an unknown head? Thanks Jim. Exactly what I was thinking!