The Ford Barn

satelite · 10-02-2012, 01:40 PM

Does anyone have the compression ratios for the various later model flat head V8 heads ? I know the EAB heads were the highest stock one available (I believe 7.5:1). I thought the 8RT heads were also 7.5:1. Anyone out there know for sure ?
Thanks Don in SC

Ol' Ron · 10-02-2012, 02:25 PM

The 8RT are among the Lowest. There is a chart someone will probably post, but you must check the CC's of your head to match those in the chart. I have found them to be all over theplace

Walt Dupont--Me. · 10-02-2012, 02:33 PM

Quote:

Originally Posted by satelite

Does anyone have the compression ratios for the various later model flat head V8 heads ? I know the EAB heads were the highest stock one available (I believe 7.5:1). I thought the 8RT heads were also 7.5:1. Anyone out there know for sure ?
Thanks Don in SC

I think you'll find that with the EAB heads with .125 overbore+3-5/16 and the 4in. crank = 276 CI you'll have more than 7.5:1 They usually don't take much milling to get .040-.050 clearance over the pistons. Walt

jimTN · 10-02-2012, 03:48 PM

There is a chart in the Ford Svc Bul that covers 8BA and prior heads. 8BA heads were rated at 6.8, 8CM at 7.8 and 59A heads at 6.75.

51 MERC-CT · 10-02-2012, 04:23 PM

Try this.

51 MERC-CT · 10-02-2012, 04:43 PM

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Quote:

Originally Posted by jimTN

There is a chart in the Ford Svc Bul that covers 8BA and prior heads. 8BA heads were rated at 6.8, 8CM at 7.8 and 59A heads at 6.75.

I wish 8CM's were really rated at 7.8

rotorwrench · 10-02-2012, 06:01 PM

The only combinations that get the 8CM heads in a decent ball park is with modified strokes and max bore sizes.

I remember when I was a kid, a stock 51 Merc would beat a stock 51 Ford but mostly due to the overdrive. The slightly bigger stroke makes a bit of difference and the larger Holly 885 with the 8CM cam made it come to life even more. The old turds ran pretty good when they were new even with that low compression. It just shows how they breath can make a difference even if only slightly. The only thing that will really get them to breath is a blower. Those low compression heads might come in handy with big bore + big stroke + a roots type blower.

Dick Webber · 10-02-2012, 08:10 PM

I always understood 8CM to be 6.8-1. And I've owned a 49 Mercurys for 27 years.

Dick

Ol' Ron · 10-02-2012, 08:17 PM

Unfortunately when I wrote my book I ckecked a dozen or so heads and founf some to have as much as 112cc's chambers. SSSOOOO Like I said measure them.

satelite · 10-02-2012, 09:07 PM

Thanks - great charts

10-02-2012, 01:40 PM	#1
satelite Senior Member Join Date: May 2010 Location: Greenville, SC Posts: 145	V8 head compression ratios Does anyone have the compression ratios for the various later model flat head V8 heads ? I know the EAB heads were the highest stock one available (I believe 7.5:1). I thought the 8RT heads were also 7.5:1. Anyone out there know for sure ? Thanks Don in SC

10-02-2012, 02:25 PM	#2
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,860	Re: V8 head compression ratios The 8RT are among the Lowest. There is a chart someone will probably post, but you must check the CC's of your head to match those in the chart. I have found them to be all over theplace

10-02-2012, 03:48 PM	#4
jimTN Senior Member Join Date: May 2010 Location: Powell, TN Posts: 2,509	Re: V8 head compression ratios There is a chart in the Ford Svc Bul that covers 8BA and prior heads. 8BA heads were rated at 6.8, 8CM at 7.8 and 59A heads at 6.75.

10-02-2012, 06:01 PM	#7
rotorwrench Senior Member Join Date: Jun 2010 Location: San Antonio, Texas Posts: 16,436	Re: V8 head compression ratios The only combinations that get the 8CM heads in a decent ball park is with modified strokes and max bore sizes. I remember when I was a kid, a stock 51 Merc would beat a stock 51 Ford but mostly due to the overdrive. The slightly bigger stroke makes a bit of difference and the larger Holly 885 with the 8CM cam made it come to life even more. The old turds ran pretty good when they were new even with that low compression. It just shows how they breath can make a difference even if only slightly. The only thing that will really get them to breath is a blower. Those low compression heads might come in handy with big bore + big stroke + a roots type blower.

10-02-2012, 08:10 PM	#8
Dick Webber Senior Member Join Date: May 2010 Location: Bowling Green KY Posts: 337	Re: V8 head compression ratios I always understood 8CM to be 6.8-1. And I've owned a 49 Mercurys for 27 years. Dick

10-02-2012, 08:17 PM	#9
Ol' Ron Senior Member Join Date: May 2010 Location: Chester Vt Posts: 8,860	Re: V8 head compression ratios Unfortunately when I wrote my book I ckecked a dozen or so heads and founf some to have as much as 112cc's chambers. SSSOOOO Like I said measure them.

10-02-2012, 09:07 PM	#10
satelite Senior Member Join Date: May 2010 Location: Greenville, SC Posts: 145	Re: V8 head compression ratios Thanks - great charts