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post #1 of 8 (permalink) Old 10-07-2011, 10:38 PM Thread Starter
 
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head milling

Does this sound right? Has any one had success with this

Heads can also be milled to increase the compression ratio. Generally, uncut Pontiac heads can be milled at least 0.040 inch; each 0.005 inch removed from the cylinder head deck surface decreases the chamber volume about 1 cc on '67-and-later open chamber heads.



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post #2 of 8 (permalink) Old 10-07-2011, 10:44 PM
 
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Originally Posted by SDGoat619 View Post
Does this sound right? Has any one had success with this

Heads can also be milled to increase the compression ratio. Generally, uncut Pontiac heads can be milled at least 0.040 inch; each 0.005 inch removed from the cylinder head deck surface decreases the chamber volume about 1 cc on '67-and-later open chamber heads.



Read more: Spirolock Tool & 421 Pontiac Combo - Hot Rod Magazine
yes but why. most people have too much compression for pump gas now days.
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post #3 of 8 (permalink) Old 10-07-2011, 11:02 PM Thread Starter
 
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I have a 72/73 455 with 4x-1h heads and from all my research this heads are less attractive than the 6x or 7k3 heads for my year. I think that the more compression that I can pull out of my heads the better. Also I need to match the cam to whatever heads I choose to use. I would like to use the 4x-1h as they are in good shape.

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post #4 of 8 (permalink) Old 10-07-2011, 11:17 PM
 
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Once you start cutting down heads a lot, you run into having to cut down the intake. If you are willing to cut .040 out of a head, why not get more dome pistons. KB pistons are around $350. For me if your going to cross 10:1 you might as well go 12:1 and get the most out of 100 octane. Of couse cam and valve slap play a roll.

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post #5 of 8 (permalink) Old 10-08-2011, 12:29 AM
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Hold on there, Kemosabe... before you start cutting on anything make sure you actually measure those chambers yourself. Pontiac heads fairly often vary in chamber volume from the published factory specs, occasionally significantly. Those 4x-1h's spec at 114 cc's, but can you be certain that's what they really are or that they haven't already been "worked" by a previous owner? On a standard bore 455, if you also zero-deck the block and run "standard" gaskets, 114 cc's puts you at 8.217:1. 97 cc's puts you at 9.309:1 If those 4x-1h's really are "nominal" then you'd be looking at shaving them by about .035 to get into the ballpark. That's not going to leave much meat on the heads for any future cleanup, if you're planning on keeping this engine awhile, plus you'll wind up having to mill the intake too in order to get everything to line up.

Alternatively, cutting the heads by .025 and running .030 (compressed) head gaskets would put you in the same ballpark on compression but with better "quench" and more meat left on the heads. (I'm assuming flat top pistons with 6 cc's worth of valve relief in both cases). If you've got your heart set on running those heads, I'd probably go that route instead.

Let me say it again though - don't cut anything until you measure them first.

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post #6 of 8 (permalink) Old 10-08-2011, 10:31 AM Thread Starter
 
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Thanks bear, I am still trying to figure out my game plan with my engine. It drives well enough now, however i want to start game planning for my ultimate goal of putting a procharger on it. So I am sold, as of now, on a top end rebuild, new cam, work the heads, maybe go with aftermarket heads if I can't find a better option. I would like to be at around 400 HP all motor. Before I think about putting on something as expensive as a procharger and have the motor strong enough to handle that power output. Procharger claims 50-85% power gain. I think 600 HP would be well enough for me.

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post #7 of 8 (permalink) Old 10-08-2011, 10:51 AM
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Using a good set of properly prepared aftermarket aluminum heads along with the right cam and rest of the flow path designed to work together, 600 HP -naturally aspirated- is easily attainable. You don't need boost to get to that point.

I'm right at 500 HP right now with iron heads, a moderate cam, QJet/factory intake, and headers. I know I'm leaving quite a bit on the table due to what I had to do to get my compression where it needed to be, and even though they're ported Ram Air IV's my heads "only" flow 282/212 cfm @ .600 lift. Getting a set of Edelbrock round ports up into the mid 300's or better is easy for someone who knows how, like Dave at CVMS.

You still sure you want to "mess with" a 'charger?

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post #8 of 8 (permalink) Old 10-08-2011, 09:58 PM
 
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if you are thinking of running a supercharger you definitely dont need to be trying to raise your compression.


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