The Ford Barn

1929 · 10-23-2016, 04:15 PM

did a compression test on my one year old motor, and all cylinders were at 95, a long time Model A Club member said that was to high for my engine. Is that true?

Y-Blockhead · 10-23-2016, 04:28 PM

Do you have a High Compression Head? I believe "Normal" is ~75 psig.

1929 · 10-23-2016, 04:35 PM

Quote:

Originally Posted by Y-Blockhead

Do you have a High Compression Head? I believe "Normal" is ~75 psig.

6-1 head.

Y-Blockhead · 10-23-2016, 05:12 PM

Quote:

Originally Posted by 1929

6-1 head.

I'm guessing that would be about right. Stock is 4.2:1.

I don't understand what he means by "too high"?

Synchro909 · 10-23-2016, 05:33 PM

I've done tens of thousands of miles with a compression reading of between 95 and 99 but I run an inserted bottom end and counterweights crank shaft. I don't think I would have gone so far on a standard bottom end.
What sort of bearings are you using? I think your reading would be OK on a standard bottom end but you are at about the max.

tbirdtbird · 10-23-2016, 06:31 PM

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you do not have a problem

Tom Wesenberg · 10-23-2016, 07:29 PM

No matter what head you use, adding counterweights is the first thing I'd do to improve an engine. A higher compression head is next. Actually I'd do both at the same time.

Other modifications like porting, larger valves, larger carb, and high lift cam will give you gain at the top end, and how often do you drive with the throttle to the floor?

1929 · 10-23-2016, 09:46 PM

Quote:

Originally Posted by Synchro909

I've done tens of thousands of miles with a compression reading of between 95 and 99 but I run an inserted bottom end and counterweights crank shaft. I don't think I would have gone so far on a standard bottom end.
What sort of bearings are you using? I think your reading would be OK on a standard bottom end but you are at about the max.

I have inserts and a counterbalanced crankshaft.`

denis4x4 · 10-23-2016, 11:35 PM

I have a Brunfield Superhead, inserts and a counterweight crank.. Compression is 115 pounds.

updraught · 10-24-2016, 12:28 AM

Quote:

Originally Posted by Tom Wesenberg

Other modifications like porting, larger valves, larger carb, and high lift cam will give you gain at the top end, and how often do you drive with the throttle to the floor?

These together sound OK.

I'd be concerned about a longer duration cam tho.
It could push the power band up to where it cannot be used on a slow revving engine. The high compression head will help push the exhaust out.

harleynut · 10-24-2016, 10:24 AM

I have two As....one with a Snyders HC head. Compression is 95..... the one without is 65. The only difference I notice if the HC head has a little more power on the hills.

V4F · 10-24-2016, 10:35 AM

my car has 126# per cyl

10-23-2016, 04:15 PM	#1
1929 Senior Member Join Date: Jan 2015 Location: New York Posts: 943	Compression test? did a compression test on my one year old motor, and all cylinders were at 95, a long time Model A Club member said that was to high for my engine. Is that true?

10-23-2016, 04:28 PM	#2
Y-Blockhead Senior Member Join Date: Jul 2011 Location: Redondo Beach, CA Posts: 5,849	Re: Compression test? Do you have a High Compression Head? I believe "Normal" is ~75 psig.

10-23-2016, 05:33 PM	#5
Synchro909 Senior Member Join Date: Jun 2014 Location: Melbourne, Australia Posts: 7,496	Re: Compression test? I've done tens of thousands of miles with a compression reading of between 95 and 99 but I run an inserted bottom end and counterweights crank shaft. I don't think I would have gone so far on a standard bottom end. What sort of bearings are you using? I think your reading would be OK on a standard bottom end but you are at about the max. __________________ I'm part of the only ever generation with an analogue childhood and a digital adulthood.

10-23-2016, 06:31 PM	#6
tbirdtbird BANNED Join Date: May 2012 Location: inside your RAM Posts: 3,134	Re: Compression test? Sponsored Links (Register now to hide all advertisements) you do not have a problem __________________ '31 180A

10-23-2016, 07:29 PM	#7
Tom Wesenberg Senior Member Join Date: May 2010 Location: Mpls, MN Posts: 27,582	Re: Compression test? No matter what head you use, adding counterweights is the first thing I'd do to improve an engine. A higher compression head is next. Actually I'd do both at the same time. Other modifications like porting, larger valves, larger carb, and high lift cam will give you gain at the top end, and how often do you drive with the throttle to the floor?

10-23-2016, 11:35 PM	#9
denis4x4 Senior Member Join Date: May 2010 Location: Durango CO Posts: 1,309	Re: Compression test? I have a Brunfield Superhead, inserts and a counterweight crank.. Compression is 115 pounds. __________________ No restorable Model A's were harmed in the building of this truck!

10-24-2016, 10:24 AM	#11
harleynut Senior Member Join Date: Jun 2013 Location: Pittsburgh Pa Posts: 279	Re: Compression test? I have two As....one with a Snyders HC head. Compression is 95..... the one without is 65. The only difference I notice if the HC head has a little more power on the hills.

10-24-2016, 10:35 AM	#12
V4F Senior Member Join Date: May 2010 Location: ca. Posts: 2,522	Re: Compression test? my car has 126# per cyl __________________ V4f