Compression Ratio Woes

Howdy guys,

So my 2V 1980 head just finished at the shop. It's got the VI port flow stainless valves, 1973 302 exhaust valve springs, new hardened seats, new guides, new seals, larger exhaust valve to 1.5", and he gave a light pass on the exhaust port side as well as took off .010" on the chamber side. I didn't want him to cut the chamber side till I got it back so I could CC it but it't too late now.

After running my calculations, I'm assuming stock bore/stroke/piston/deck height b/c I have no idea until I take the head off the car, I'm running a 8.789 comp ratio with a 50cc head. That's terrible. I'm planning on running at least in the 9's as it will compliment my 256H Schneider cam nicely. Here are my calculations: (all in inches and inches^3)

bore=3.68;
stroke=3.126;
gasBore=3.81;
gasThick=.044; Victor
chamber=16.387^-1*50; conversion from cc to in^3
piston=16.387^-1*6.5; conversion from cc to in^3
deck=.030;

cylinder=pi/4*bore^2*stroke;
gasVol=pi/4*gasBore^2*gasThick;
heightVol=pi/4*bore^2*deck;

VTDC=gasVol+heightVol+piston+chamber;
VBDC=VTDC+cylinder;

CompRatio=VBDC/VTDC

=8.789

The only way to get it where I want it looks like I need a FOMOCO gasket with a crush and bore of .024" and 3.75", respectively. With that gasket it gets me to 9.246, but I still have to shave the head to 50cc. Which I can live with. With this setup and my Schneider 256H cam, I'll have a 8.39 DCR. I think this will be alright with 92 octane, but what do you all think? Is 8.39 too high for a DD on 92 octane without worrying about heating issues or anything? If I change the chamber to 52cc, it puts me in the 9:1 SCR and 8.17 DCR. What is my best choice here?

I guess my final question now is, does anyone know of where I can get or have an old 200 FOMOCO gasket?

Thanks,
Ryan

"..get or have an old 200 FOMOCO gasket?"
by chance on flee-bay, they do come up.
OR
custom...
but let's wait till a lill further on the initial Qs U just posted...

Good luck getting the old steel shim gaskets. They are not easily found and are a limited commodity. I have a 0.035" FoMoCo gasket. I've bought a few more of the valve grind gaskets I bought to get this one, but they've all ended up being thicker (0.045"-0.050" range). They can be found, but it's going to start getting harder and harder to acquire.

Steel shim gaskets for 3.50" 144/170 bore are fairly available and often sold as suitable for 200/250. The 3.68 200/250 bore steel shim gaskets (AFAIK) are unobtainable except for rare appearances on Interweb' sales sites.

Original STEEL shim gaskets with 3.50 bore : FELPRO 7915





I run a steel shim gasket with a D7 head cut to 48cc's BUT on a 170 (71 Maverick C9xx block) with the 3.50 bore. With 48cc chambers and steel gasket the 170 is close to 9.5:1 CR. Runs great for @ 10 years on HiTest ...

have fun

Yeah. The smaller bore ones are regularly available. 90% of the time that I think I've found one for the 200, I find out it's the small bore

Howdy again guys,

So i got decent news. I was able to find one of the 1969 FOMOCO gaskets C9. It has a 3.81" bore and it should have a .035" crush. This works if I shave the head to 49cc. This leaves me with a 9.1:1 static and 8.25 dynamic. I think this is a good settlement. THANK YOU EBAY!

Ryan

Good Find !
check it close. Unknown entities @ flee-bay.
(arms length purchases)
I'd attempt one if it fit the 250 (got 2 of'em)...

Can I ask you how much did it cost? If so how much?
A ford shim should be about .025 or so when compressed...There is a thinner one and a little thicker one, but both are about ..025 or thinner.

drag-200stang":1os9tt86 said:

Can I ask you how much did it cost? If so how much?
A ford shim should be about .025 or so when compressed...There is a thinner one and a little thicker one, but both are about ..025 or thinner.

Click to expand...

Yeah it was $30. According to the handbook, Ford had a steel shim which compressed to .025 and they had a composite that compressed to .035. The steel shim is part number D2xxx, the composite is C9xxx. I got the C9. If this compresses to .025 that's great, but I don't believe it is supposed to.

Here's a picture of it. Our site ain't letting me post pictures here anymore so here's a google drive.

https://drive.google.com/file/d/1VDS6ND ... sp=sharing

I thought that you were buying a shim and not a replacement composite gasket, my mistake.
That gasket should be about .035.

drag-200stang":sazp7lvt said:

I thought that you were buying a shim and not a replacement composite gasket, my mistake.
That gasket should be about .035.

Click to expand...

I wanted a shim gasket but apparently they are rarer than I thought. I saw this one and figured it was as close as I'm gonna get to what I need. I just gave a call to a special NOS parts place that has helped me out before. I'll let you all know if they have any

Did you happen to measure the thickness of that gasket to confirm that it is an 0.035"?

cr_bobcat":1494er98 said:

Did you happen to measure the thickness of that gasket to confirm that it is an 0.035"?

Click to expand...

No not yet. I need to get a micrometer. It is the same part number as the one that was mentioned in the book. I might borrow one from school.

geta cheep venier caliper style, save the bx it came in, throw them in ur tool bx @ home.
Use one myself several timesa wk. Lost my micromiter I use it so lill. VC can measure inside, out side,
and depth. Now have'em w/a 100th (or is it 1000?) ona lill dial (not mine), or 1 that is i.finger-operated & all electronic

Have you pulled the head yet? Measured the deck height and seen what gasket is in there now? Don't put the cart before the horse.

Econoline":jamsqvqb said:

Have you pulled the head yet? Measured the deck height and seen what gasket is in there now? Don't put the cart before the horse.

Click to expand...

No i haven't yanked my head b/c its my daily. I need to have everything ready to swap it in before I do anything.
Yes after measuring everything when I yank my head and putting all the measurements into my program, I'll know exactly what kind of compression ratio to expect. Currently I'm assuming everythjng is stock measurements to get a rough idea, but I will be measuring everything when the head does come off.

That will likely go on about April time during spring break

Better get the Stud going, then