You loose about about 6 cc'c for every .010, according to my machinist... When I originally posted to this I didn't know nuttin about it but was asking about computing my hanber size after a mill and a block deck, then he finally told me...
So in order to get yours down you'd need about 20 thousandths taken off according to him.
<font size=-1>[ This Message was edited by: FEandGoingBroke on 11/25/06 7:31am ]</font>
.010 does not take 6ccs off of a 289 head. It's .006 per cc for '65 to '68 289 heads. For 8cc reduction, that's .048. Ford does not recommend more than .050 milled off the heads. Info is coming from Bob Carrolls Ford Stockers Bible.
What 289 heads came with 68cc chambers? Those are big for 289s.
I spoke with my machinist about it and he asked me which heads and I said 289 heads, he said about 6cc per ten thousandths! He does this every day and I will double check with him on monday if this feller chimes in with the year of his heads...
Here's an approximation for a '70 351w head that's 61 cc. The chamber measures 4" x 2.68" at their widest points. I'll approximate the area of the chamber by using a rectangle 3.75 x 2.68 to compensate for curved sides. Converting to cc (2.54cc per in), it takes .006 to take 1cc off of this head...this agrees exactly with Bob Carrolls book for a DOOE head.
If it were .010 for 6 cc, that would mean I have an error factor of nearly 400%...no way.
Think of it intuitively. If it were .010 for 6cc and the chamber is 61cc or 68cc, then the chamber should only be .100 to .110 deep if the sides were straight. Again, no way.
If you mill .048 off the head, you may increase the quench area somewhat where the chamber slopes to meet the flat bottom...generally a good thing. Your also moving the valves a lot closer to the pistons...be careful
Tracy Blackford: Corona, Ca
'65 FB Mustang 331, 282S cam, ported 351W heads. T5z, 3.50 9" posi.
346 [email protected] on a warm spring day (335 RWHP SAE corr.)
<font size=-1>[ This Message was edited by: blkfrd on 11/27/06 1:07pm ]</font>
Uno the best way to have this done is to have the heads CC'd first to get a better more accurate comp ratio to start with using a good COMP CALC like this one ( this has been posted here before). http://www.diamondracing.net/cocalc.htm
Then ask the head shop to get the wanted cc's on the head to make the comp ratio that you want. Thats the most accurate and the most costly (expensive) way to do it on an engine by engine basis IMO. But then youll KNOW what you have regardless of what any book says.
Angle milling gets serious. You start messing with a few more varibles. Id let the head shop talk with you on wether or not thats good for your application.