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 Post subject: Milling Heads
 Post Posted: Sun May 07, 2006 6:48 am 
 
Ok so I need new heads and am planning on using AFR.

Question is, how much will I raise compression if I mill .125 off the heads?

Pistons are a forged flat top at 9.5:1

AFR states I can mill .125 safely and up to .200 with care, but don't really want to go over the safe point.

TIA


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 Post Posted: Sun May 07, 2006 7:13 am 
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depends on size of combustion chamber. one of the head guy's that are here from time to time may know from previous work they have done. \:D/

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 Post Posted: Sun May 07, 2006 7:23 am 
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be sure to check your valve to piston clearance if you do...we had a set of bowtie heads done once .125 angel mill and had to fly cut the pistons


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 Post subject:
 Post Posted: Sun May 07, 2006 7:34 am 
 
Thanks for the info, the combustion chambers's are 68cc. They are the 195cc heads.

With the flat tops I am hoping clearence will be a non-issue....


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 Post Posted: Sun May 07, 2006 7:45 am 
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edit:
If this is more of a daily driver than a racer you'll need to limit the CR to around 10-1 anyways. I would save milling the heads for when it needs it. Especially when your taking about .125" or more


Last edited by DCarr on Sun May 07, 2006 7:58 am, edited 1 time in total.

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 Post Posted: Sun May 07, 2006 7:58 am 
 
Good point Duane.

I am just hoping not to have to pull the bottom end apart and save a little $$$$ if I can.

Slapping the heads on right out of the box should raise my C/R to about 9.8-9.9:1 but am hoping for about 10.1-10.2:1 with 93 octane gas, avaiation fuel on race days.


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 Post Posted: Sun May 07, 2006 1:39 pm 
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A good ballpark for a sbc is mill .006" per cc of chamber volume you want removed.

Of course it varies some depending on the area of the chamber at the deck. If you measure the sq. in area at the deck and multiply that by the amount you're milling, it will tell you the volume it will remove in cubic inches. Convert ci's to cc's by multiplying by 16.387.

Rick


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 Post subject:
 Post Posted: Sun May 07, 2006 3:03 pm 
 
Thanks all!!!!!

So, if I angle milled from 68 to 62 cc I would have to take off about .036, is that correct?

That would be a do able number in my mind.(better than .125)

That should also give me the 10.1-10.2:1 C/R I would like without changing pistons and without going to thin on the heads.

How much will that affect the lift of the cam as far as valve clearence?
Cam is the voodoo 60103 (268/276 .489"/.504") but plan on using a 1.6 rocker to increase lift to about .540".


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 Post Posted: Sun May 07, 2006 6:00 pm 
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That .006 number rick used is for flat mill it would be closer to .0075 for angle. When you angle mill it will always take more.

If you are only going from 68 cc to 62 cc flat mill them.

When you angle mill you have to re-correct the intake side and all the bolt hole pads.

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 Post Posted: Sun May 07, 2006 10:28 pm 
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Yes carl, that is correct. .036" would remove approx 6cc's when flat milling. .045" if angle milling would remove 6cc's per Mike's .0075"/cc number.

I agree with Mike on flat milling them too. Angle milling is for major chamber reduction.

Rick


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 Post Posted: Mon May 08, 2006 7:19 am 
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Hey rick i don,t know if you or Curtis have notice this but on some heads where the chamber flares out or big at the gasket surface it takes more then .006 and then after some it takes less the .006.

Have you guys run into this the Pro Toplines are like that.

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 Post Posted: Mon May 08, 2006 7:23 am 
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Mike Rogers wrote:
Hey rick i don,t know if you or Curtis have notice this but on some heads where the chamber flares out or big at the gasket surface it takes more then .006 and then after some it takes less the .006.

Have you guys run into this the Pro Toplines are like that.
i have run into that. that is why i mentioned the size of comb chamber. i knew some of you would know this and remember what chambers were diffrent. i would like to here from curtis and rick for their input. \:D/ i am making notes lol.

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 Post Posted: Mon May 08, 2006 10:38 pm 
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Mike Rogers wrote:
Hey rick i don,t know if you or Curtis have notice this but on some heads where the chamber flares out or big at the gasket surface it takes more then .006 and then after some it takes less the .006.

Have you guys run into this the Pro Toplines are like that.


The angle the chamber approaches and meets the deck will determine how much difference there is from the first .010" milled to the last .010" of material. When the chamber meets the deck at a very shallow angle, the area where material is removed changes quickly making the volume removed vary more also. When the chamber is more bathtub shaped and sides meet the deck at steep angles almost straight in, the difference will be almost nothing.

Nothing can be done about it and it can be almost impossible to calculate exactly how much to remove to get a specific chamber volume. Measuring the actual area of the chamber opening will get you right on for the first bit of material removed, then the more you mill off the farther from your measured numbers you can be based on the angle of the material that was just removed.

I have a computer program I wrote to measure CSA of port openings, it would work good for chamber shapes too. You trace around a shape onto paper, scan that shape into your computer, do a small amount of editing with Paint and the program tells you exactly what the CSA of that shape is. It beats counting squares on graph paper, thats for sure.

Rick


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 Post Posted: Mon May 08, 2006 11:55 pm 
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Mike Rogers wrote:
Hey rick i don,t know if you or Curtis have notice this but on some heads where the chamber flares out or big at the gasket surface it takes more then .006 and then after some it takes less the .006.

Have you guys run into this the Pro Toplines are like that.


Yea I've seen that, ..

we calculate what to mill to get close then CC the chambers while in the
mill, .. PIA but it get's it right.

Rick, .. I still count squares sometimes, .. but now the CnC software just
tells me CSA where ever I want. =D>

Curtis

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