MTFCA Forum

Hoping someone has a overhead head gasket (that would fit an 8 valve head such as a Fronty or Rajo). I am hoping you can measure the bore size and thickness for me. It really would help if you have a used gasket as it's already squished, but I've got a good idea of what the difference would be if you only have a new one.

Chad what are you up against? Over bored or over size valves?

Hank

I'm just trying to accurately measure for compression ratio. I don't have a head gasket in my possession at this time. This is information I'd like to pass to my camshaft builder doing a custom grind.

I’ve got a handful of new and used flatly gaskets here (steel, copper, and comp)... all start bout .080”-.090”, and crush to bout .050”-.060”

Thats great Kevin! Thank You ----whats the bore diameter on them?

Chad my bores (not crushed) are at 3.850” on a copper gasket.

Hank

Chad,

If you check the Tulsa Model T Ford Club page titled "Head Design" at: http://mtfctulsa.com/Tech/head_design.htm It describes one method of determining the compression ratio of Model T Ford Flat heads.

I'm still a novice at this -- but from memory -- it is not the bore of the head gasket but the bore and stroke of the engine; thickness of the head gasket, and size of the cylinder head chamber that impact the compression ratio. I.e. a stock engine will have a lower compression than if you pull the head bore it .060 over and install the .060 pistons and assemble it back in the same stock configuration otherwise. And yes, if you have a large over bore on the cylinder, you have to have a large enough opening (bore) in the gasket for the piston to clear (in a T where the piston sticks up above the surface of the block).

The Tulsa sight has some other good information on engines see their Tech page at: http://mtfctulsa.com/Tech/index.htm And good luck with your project.

Respectfully submitted,

Hap l9l5 cut off

The head gasket adds volume to the combustion chamber and needs to be accounted for in any CR calculations. A 3.875 bore overhead gasket is about 0.73 cubic inches, while a stock flathead gasket is pretty close to 1.09 cubic inches.
for conversion 1 cubic inch = 16.39cc

Kevin Pharis wrote: ↑

Wed Jun 03, 2020 6:00 pm

I’ve got a handful of new and used flatly gaskets here (steel, copper, and comp)... all start bout .080”-.090”, and crush to bout .050”-.060”

Should say flatty... damn auto correct!

So no diameters from these gaskets

You guys are awesome as usual. That is the info I needed to continue on my calculations. Thank You very much.

Hap, bore and stroke, as well as head chamber size, piston - or + volume, and head gasket volume are all needed to accurately calculate compression. Most are satisfied with assumptions and previous data, but the potential for every engine to be different is there. Especially if you start looking at piston to deck height clearances. It's always nice to know the real numbers...I'm an engine guy so I geek out on info like that.