Well,
With all do respect to the great reference material given by Bob (right into my
Bookmarks), there are easier to read explanations, but no less correct. And the
correct solution to the given problem.
I did say my answer was quickie estimate and not exact, as I had left out (in
total displacement change) the 10 cc's in the chamber itself.
Tom Hall had it right on the button.
Remember, we were NOT given any engine data. It was 'backed out' from the
original compression ratio and chamber volume.
The correct formula, for that specific instance, is: (from Tom Hall)
54 x 11 = 594 594 + (64 - 54) = 604
604 / 64 = 9.4375
I had left out the (64-54) piece, and he is correct.
the simple description form Tom Monroe is:
Compression Ratio = (Swept Volume/ Clearance Volume) + 1
The "Clearance Volume is not just the Combustion chamber volume, but also
includes
head gasket spacing of the head above the block, the "deck-height" volume, AND
any
piston shape volumes, either concave, or convex.
This is all taken into account in the quoted example, but this just lumps all
those factors into the existing compression ratio/chamber volume given, and
assumes the only change would be the new head chamber volume is correctly known.
Another issue, that is NOT addressed, is where did this 54 cc chamber come from?
The only thing Ford produced that was even close was the 221 CID heads at 54.5
cc,
and the HiPO 49.2 cc and 54.5 cc heads. There was a limited run of 302-4V heads
with 53.5 cc in '68 and the smallest since was 58.2 cc.
Tom Hall correctly points out that milling a head gives insignificant changes to
the combustion chamber volume, in any rational metal removal, so it could not
be a
351 head, with 60.4 cc (early ) to 69 cc heads Maybe a Dart head????
Let me throw another question on the table. (Or in the Punch Bowl)
The 260 is listed as having 54.5 cc chambers and 1.67" Intake and 1.45" exhaust
valves, same as the early 289's. The HiPo's of the same years ('63) were the
same and in '64 went to 1.78 with an increase in chamber volume (49.2 to 54.5)
So, if this is correct, it would seem that the 260 can take the valve increases
popular in the 289's, using Chevy sized stainless valves and get 1.94" intakes
and
1.55 exhaust (with seats) and 1.60" without seats, in stock heads. This would
avoid using the latter 302 non-HiPo heads with compression ratio killing
chambers, or speed shop (64 cc Ford GT-40, 62.5 cc Holley H.O. aluminum, 60 cc
Edelbrock) heads. Worried about hitting 3.8 bore, piston tops with .5 inch lift
cams, Etc. Any hands-on experience available? I've got a set of good early
289's
heads available.
Steve
--
Steve Laifman < Find out what is most >
B9472289 < important in your life >
< and don't let it get away!>
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