Milling P51 Heads

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Milling P51 Heads

Post  quikmule84 on July 7th 2015, 12:56 pm

Have a 501 BBF with @ 12:5 compression, race only. Would like to increase compression while motor is out. How much do the heads (P51's) need to be cut to pick up 1 point of compression? Would like to end up between 13.5 to 14.5 comp. Pistons in the hole .005. How far can I go before getting into intake alignment issues?

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Re: Milling P51 Heads

Post  dfree383 on July 7th 2015, 2:35 pm

At .030 it's going start affecting bolt holes on the intake.

I've ha CJ heads decked to 62cc and slotted intake holes and made intakes work with out milling them.
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Re: Milling P51 Heads

Post  supervel45 on July 7th 2015, 5:31 pm

http://wallaceracing.com/cr_test2.php If he has 72 cc's now and goes to 62 cc's he should be in the low 14/1 range with flattops and 0ne 3cc valve relief.

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Re: Milling P51 Heads

Post  IDT-572 on July 8th 2015, 10:33 pm

What ever you mill the deck just cut the intake face half that and the intake will bolt right up.
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Re: Milling P51 Heads

Post  quikmule84 on July 9th 2015, 1:13 am

Ok. Thanks for all the advice. Also, generally speaking, how far can I mill the heads before having to change pushrod lengths.

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Re: Milling P51 Heads

Post  IDT-572 on July 9th 2015, 9:00 am

quikmule84 wrote:Ok. Thanks for all the advice. Also, generally speaking, how far can I mill the heads before having to change pushrod lengths.

.050 makes a difference in your rocker geometry. but you need to see how it looks now before you start.
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Re: Milling P51 Heads

Post  wayney on July 9th 2015, 6:27 pm

is there a specific amount to mill per CC of chamber reduction? ex. .005 per CC?

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Re: Milling P51 Heads

Post  supervel45 on July 9th 2015, 7:16 pm

http://www.wallaceracing.com/millcalc.php You could run the numbers through here.

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Re: Milling P51 Heads

Post  IDT-572 on July 9th 2015, 7:30 pm

If I remember right it's about .0055 to .006 per 1 cc
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Re: Milling P51 Heads

Post  supervel45 on July 9th 2015, 7:31 pm

For what it's worth that calculator comes up with .2 points of compression increase with a 4.15 stroke crank and .005 removed, with a 12.5C/R as a start. It mentions Pontiac so be aware of that.

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