78 head on 66 block, how much to mill ?
- Thread starter Bort62
- Start date
8) go to http://falconperformance.sundog.net and check out the compression calculator there. it seems to me the falcon performance handbook says .060, which leaves about .030 for future clean up cuts as needed.
A
Anonymous
Guest
Hey, Bort;
Check the deck height (from the top of the piston to the top of the block) before milling that head. In the 60s engines, this varied from .040" up to over .100". If you have one that's at .040" and you mill .060" from the head, you'll be in the stratosphere with the CR. Also, if you have a 1978-1979 head, the cc volume is between 55cc-58cc, and the stock bore of 3.680" at 3.910" stroke gives you 41.587 cu. in. (681.5cc).
Turn the engine until #1 cylinder is at TDC. Then, scrape ALL the carbon off of the top outside edge of the piston (the highest part), but gently - don't scratch it up. A little dab of kerosene will help loosen it up. Then, set a flat piece of steel across the bore, over the clean spot. Start stacking feeler gauges between the steel flat and the piston crown until you think you've got it pretty snug. That's your deck height number. Mine, just for reference, was .046" on #1 and .050" on #3, so they are not necessarily all the same.
The volume of this deck height area, plus the volume of the "hole" of the head gasket, plus the combustion chamber volume, together equal your compressed volume. Add to this number the volume of your full stroke for your uncompressed volume. Then divide the big number by the littler one, that's your COMPRESSION RATIO (presuming a more-or-less stock cam).
Just in case you don't know it, the 'volume' of a hole is:
(Diameter/2) x (Diameter/2) x 3.14159 x Height (cubic inches)
or, in English, "radius squared times pi times height".
To convert this to cc values (cubic centimeters), multiply the cubic inches by 16.3871 .
(Not trying to be uppity, it's just that a lot of guys don't know these formulas.
).
The steel head gaskets compress to about .020" at 60 ft-lbs, .018" at 70 ft-lbs head torque. The NAPA/Victor brand go down to about .045" at 70 ft-lbs torque and the Fel-Pro gaskets go to about .055" at 70 ft-lbs (I only know because I spent lots of money to try all 3 out).
Hope this helps.
Check the deck height (from the top of the piston to the top of the block) before milling that head. In the 60s engines, this varied from .040" up to over .100". If you have one that's at .040" and you mill .060" from the head, you'll be in the stratosphere with the CR. Also, if you have a 1978-1979 head, the cc volume is between 55cc-58cc, and the stock bore of 3.680" at 3.910" stroke gives you 41.587 cu. in. (681.5cc).
Turn the engine until #1 cylinder is at TDC. Then, scrape ALL the carbon off of the top outside edge of the piston (the highest part), but gently - don't scratch it up. A little dab of kerosene will help loosen it up. Then, set a flat piece of steel across the bore, over the clean spot. Start stacking feeler gauges between the steel flat and the piston crown until you think you've got it pretty snug. That's your deck height number. Mine, just for reference, was .046" on #1 and .050" on #3, so they are not necessarily all the same.
The volume of this deck height area, plus the volume of the "hole" of the head gasket, plus the combustion chamber volume, together equal your compressed volume. Add to this number the volume of your full stroke for your uncompressed volume. Then divide the big number by the littler one, that's your COMPRESSION RATIO (presuming a more-or-less stock cam).
Just in case you don't know it, the 'volume' of a hole is:
(Diameter/2) x (Diameter/2) x 3.14159 x Height (cubic inches)
or, in English, "radius squared times pi times height".
To convert this to cc values (cubic centimeters), multiply the cubic inches by 16.3871 .
(Not trying to be uppity, it's just that a lot of guys don't know these formulas.
).The steel head gaskets compress to about .020" at 60 ft-lbs, .018" at 70 ft-lbs head torque. The NAPA/Victor brand go down to about .045" at 70 ft-lbs torque and the Fel-Pro gaskets go to about .055" at 70 ft-lbs (I only know because I spent lots of money to try all 3 out).
Hope this helps.
A
Anonymous
Guest
I had only.30 milled off my '78 head, but, it's a '69 250 and a Felpro gasket, that wouldn't be too crazy low would it?, it's already together.
A
Anonymous
Guest
Well, hard to tell without knowing for sure where you started, but...
the .030 mill job would make the FelPros I've seen only raise your head about .005" to .008" over a steel gasket. The FelPro becomes .055" at 70 - 90 ft-lbs head torque (typical Mustangs used only 60-65, according to my books). The Ford steel gasket became .020" at 60 ft-lbs, .018" at 70 ft-lbs.
So, if your original was .020" and the FelPro is .055" and you milled .030" you get (.055"-.020")-.030" = .005" extra height. If you add a few thousandths to the FelPro at 60 ft-lbs, you could be at .007" or so extra height.
That's not much CR difference, but the quench band height with the FelPro will certainly be taller, by exactly the difference between the FelPro and the Ford (.035" added). It's the quench band that gives you the added engine efficiency for better MPG, lower emissions and a little better power. This part can only be restored with the steel gasket or by decking the block itself. Generally speaking, a quench height of more than .040" is like none at all.
The most noticeable difference without quench band activity is carbon buildup on the piston tops over time. While this slightly raises the compression (good thing), it tends to hold heat on top of the piston. This is OK if you drive highway miles, as it improves efficiency. If you drive mostly putsy town miles, put some BG44 in the gas a few times every year to control the carbon buildup.
MarkP
the .030 mill job would make the FelPros I've seen only raise your head about .005" to .008" over a steel gasket. The FelPro becomes .055" at 70 - 90 ft-lbs head torque (typical Mustangs used only 60-65, according to my books). The Ford steel gasket became .020" at 60 ft-lbs, .018" at 70 ft-lbs.
So, if your original was .020" and the FelPro is .055" and you milled .030" you get (.055"-.020")-.030" = .005" extra height. If you add a few thousandths to the FelPro at 60 ft-lbs, you could be at .007" or so extra height.
That's not much CR difference, but the quench band height with the FelPro will certainly be taller, by exactly the difference between the FelPro and the Ford (.035" added). It's the quench band that gives you the added engine efficiency for better MPG, lower emissions and a little better power. This part can only be restored with the steel gasket or by decking the block itself. Generally speaking, a quench height of more than .040" is like none at all.
The most noticeable difference without quench band activity is carbon buildup on the piston tops over time. While this slightly raises the compression (good thing), it tends to hold heat on top of the piston. This is OK if you drive highway miles, as it improves efficiency. If you drive mostly putsy town miles, put some BG44 in the gas a few times every year to control the carbon buildup.
MarkP
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