5.5 or 6.0 head?

Ayers1

Ayers1

Well-known member
Hi everyone, a while back i remember a thread was going about the difference between a 5.5 head and a 6. I have searched but can't find the one I'm looking for. People said the 5.5 combustion chamber looked stock but the 6 had heart shaped chambers. I picked up a head that was sold as a 5.5 at a flea market this year. When I compared the old with the new they look very different. Could I have gotten the higher compression head?

Thanks,
 

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The one on the left is higher compression ratio. Put a plug in one of the locations and fill up the combustion chamber with a light oil, carefully measuring the amount it takes to fill it up. Then divide that into the displacement of one cylinder, 50.25 cubic inches. That will give you the compression ratio. The head gasket will lower the ratio slightly but the amount the piston sticks up above the block will raise it, so the measurement should be pretty close.

For instance if you measure 8.375 cubic inches, or .58 cup, or 4.65 fluid ounces, then 50.25/8.375 = 6:1. There are online calculators to convert any fluid measurement to cubic inches.
 
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nkaminar said:
The one on the left is higher compression ratio. Put a plug in one of the locations and fill up the combustion chamber with a light oil, carefully measuring the amount it takes to fill it up. Then divide that into the displacement of one cylinder, 50.25 cubic inches. That will give you the compression ratio. The head gasket will lower the ratio slightly but the amount the piston sticks up above the block will raise it, so the measurement should be pretty close.

For instance if you measure 8.375 cubic inches, or .58 cup, or 4.65 fluid ounces, then 50.25/8.375 = 6:1. There are online calculators to convert any fluid measurement to cubic inches.
Click to expand...


Thanks nkaminar, I didn't realize you could do that!
 
Steve, There is a Model A tour coming up that will go through your neighborhood. We will be driving down Skyline Drive from Front Royal and continuing on the Blue Ridge Parkway. We will leave Front Royal on the morning of Sunday, October 18. At last count there were 7 cars.

Sorry for hijacking the thread. If anyone would like more information about the tour, please send me a personal message.
 
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thanks Neil. if your club doesnt mind I'll let my club know that you're coming through. Waynesboro is about 5 miles from the entrance to the Parkway. A few may be interested in joining you guys. What time do you think you'll be getting in this area?
 
I sent you a personal message (PM) with the tour notice. It has some contact information for Wayne who is leading the group. It is about 105 miles from Front Royal to Waynesboro. So assuming we leave at 8 and travel an average of 25 mph, we should be in Waynesboro about noon. We should be looking for lunch about then. But who knows exactly what time we get to Wayne's Boro.

I am sure Wayne would like anyone to join in and travel as many miles as they wish. Just let him know what the plans are via his email or cell phone. Wayne may want to hook up for lunch. On the day of travel you could call Wayne on his cell to check on the progress.
 
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got it, thanks! I'll share and there may be a couple of members that would like to meet up with you guys for a while.
 
Vince compares well over a dozen HC heads, including aftermarkets at his site.

https://www.fordgarage.com/pages/headcompressionratio.htm

Nice he's straightened out the "referencing issues" allowing access without having to utilize Archive.com.

I was just at the Epping, NH Antique Auto Flea Market where a seller was selling (claimed) "Model B Police Head." One could tell by the shape of the combustion chamber this was not an ordinary B head? Marked "C" on top.

Good buy but...

Looking now I see it was an ordinary Model B head B-6050. Not so good a buy. I did well to hold back.

Joe K
 
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There are other considerations in flathead head design besides the compression ratio. The air/fuel has to flow from the Intake valve down into the cylinder, the exhaust has to leave, and the squish area has to impart turbulence to the combustion process. The best flathead designs have been heads for Harley Davidson racing motorcycles, see photo below. The valves are not crowded, there is good flow down into the cylinder, and the squish area imparts turbulence. In my opinion the heart shaped (triangular) combustion chambers in most after market heads are not ideal. I am talking about the combustion chamber in the left hand head shown by Steve in Post #1.

Notice in the HD design that the full width of the cylinder is available for air flow down into the cylinder and that there is a slope to deflect the flow down (a curve would be better). The squish area is across the width of the piston and it pushes air straight into the combustion chamber. The intake valve is not crowded (spark plug side) and neither is the smaller exhaust valve.
 

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Briggs & Straton also did a lot of development work for their karting race engines.
The Brierley head is 7.0:1 and has a lot of the newer developments that occurred since the early 50s when most of the Model A flathead development stopped.
 

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On my supercharged flathead V8 dragster engine I used a rosebud cutter and radius the cylinder head wall around the intake valve area this improves flow substantially in a flathead combustion chamber!!!! Ssshssssss!!!!!
 
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