My heads were milled-effect on compression ratio?

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OL DODGE

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My heads were milled-what effect on the compression ratio would it be-they are the proverbial "x" heads and this is the first time they were cleaned up with .031" taken off both. I understand there are variables involved here and have seen where machine shops can "cc" the heads but didn't have that done. I plan on using the good Fel Pro blue head gaskets(Perma Torque) because I've never had trouble with them . I believe they are .040" or so, and don't recall what factory steel shim style ones are, to throw that into the equation.
 
The .030 milling will make up for the difference between the steel shim's and the Fel Pro's. I don't have the specs of each but I would say it's a wash. Gain in compression by milling and loose compression by using thicker head gaskets.
 
The original shims were about .022" IIRC.... Permatorques are around .051" so you are pretty much dead even.

If you used Mr Gasket 1121G's at around .028" thickness, then you will have eliminated approximately a bit over 4 cc's of chamber volume. Not sure what engine you have, but if a 340 or 360, that would gain somewhere around 0.4 points in static CR.
 
"Around" .070" on the open chamber small block head equals 1 compression point. That means .031" is less than half of a compression point.
 
Original 340 head gaskets were composition about .028 of an inch. There was a .022 shim gasket, but the 340 did not come with them. I'd run the Fel-Pro gaskets myself, for the same reason.
 
I just had .040" taken off a set of 318 heads to accommodate the FelPro blues. Machine shop said .040" off will not do much and intake bolts will still match up. I port matched the heads to the intake and it was off height wise just a tad from before the head cutting. I tried to find a set of steel shims but they are hard to find.

Good luck and keep us posted.
 
Well, thank you to all you guys for the input,and so quick too! I did some digging today and found according to Larry Shepard in the Mopar Performance engine book the following info "The production 318-340-360 head gaskets were around .035"......." so with that in mind, went to Fel Pro to ask what their 8553PT head gaskets were thickness -wise and they say .039" . Not sure if that is compressed or not on either measurement but heck it's something more to ponder.........if they are both say for the sake of argument-compressed ,then I have gained .004" over a stock gasket but lost .031" in the milling process..........oh mathematics-my long time nemesis.......
 
Does anyone have a compressed set of the Fel-Pro blue gaskets that are used so we can measure the thickness ?
They are great gaskets but are thicker than factory ones for sure.
 
Syleng1 said:
Does anyone have a compressed set of the Fel-Pro blue gaskets that are used so we can measure the thickness ?
They are great gaskets but are thicker than factory ones for sure.
Click to expand...
I have old used 8553PT ones here. .050" @ the fire ring and .047" in the blue.
 
IQ52 said:
I have old used 8553PT ones here. .050" @ the fire ring and .047" in the blue.
Click to expand...


If you wanted a "thinner" head gasket- what options are out there for raising compression?
Copper gaskets?
Joe
 
You can buy a cheap cc kit at Summit and find out the cc of your chambers. Then use a online compression calculator and figure out your compression. You'll have to know deck height, and other info however.
 
Sorry OL DODGE - I did not want to steal this post on you.
Good information. - I can use but again sorry if it looks like I'm taking the thread in a different direction.

Joe
 
Syleng1 said:
If you wanted a "thinner" head gasket- what options are out there for raising compression?
Copper gaskets?
Joe
Click to expand...
Felpro 1008: .039"
Mr Gasket 1121G: .028"
Cometic: .027". 030" and on up in steps of .005" (About $100 per EACH head gasket BTW)
 
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