Re: How much to mill stock hemi heads to gain half a point?
[Re: domingo]
#981386
04/27/11 01:27 PM
04/27/11 01:27 PM
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Joined: Dec 2005
Posts: 293
Kansas City Metro
mbogina
enthusiast
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enthusiast
Joined: Dec 2005
Posts: 293
Kansas City Metro
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3 basic variables to work with, Volume of cylinder (Vcyl), volume of everything above that (Vtdc), and Compression ratio (CR). Example: for a 4.31 bore, 4.15 stroke, 10.0 comp ratio, Vcyl= 992cc, the unknown variable is Vtdc, the general equation reduces to 992= 9.0 x Vtdc; so Vtdc= 110.2. To increase the comp ration by .5, the equation changes to 992=9.5 x Vtdc, so Vtdc= 104.4, a reduction of 5.8cc. Milling a hemi chamber is about .0041"/cc, so 5.8 x .0041= .024".
All hemi heads have a register on the deck near the exh face at the center of head (about .5" x .5"), once the register is gone, that is the factory safety limit for milling (usually about .080 deep when untouched.)
Be a Rebel- Break the Laws of Physics!
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Re: How much to mill stock hemi heads to gain half a point?
[Re: mbogina]
#981388
04/27/11 09:27 PM
04/27/11 09:27 PM
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Joined: Jan 2003
Posts: 9,670
Lima, Peru
domingo
OP
EL Master
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OP
EL Master
Joined: Jan 2003
Posts: 9,670
Lima, Peru
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Quote:
3 basic variables to work with, Volume of cylinder (Vcyl), volume of everything above that (Vtdc), and Compression ratio (CR). Example: for a 4.31 bore, 4.15 stroke, 10.0 comp ratio, Vcyl= 992cc, the unknown variable is Vtdc, the general equation reduces to 992= 9.0 x Vtdc; so Vtdc= 110.2. To increase the comp ration by .5, the equation changes to 992=9.5 x Vtdc, so Vtdc= 104.4, a reduction of 5.8cc. Milling a hemi chamber is about .0041"/cc, so 5.8 x .0041= .024".
All hemi heads have a register on the deck near the exh face at the center of head (about .5" x .5"), once the register is gone, that is the factory safety limit for milling (usually about .080 deep when untouched.)
This is a 4,15" stroke engine. 4,28" bore
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Re: How much to mill stock hemi heads to gain half a point?
[Re: racingblues1426]
#981389
04/27/11 09:28 PM
04/27/11 09:28 PM
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Joined: Jan 2003
Posts: 9,670
Lima, Peru
domingo
OP
EL Master
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OP
EL Master
Joined: Jan 2003
Posts: 9,670
Lima, Peru
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Quote:
From past experience I would never remove anything more than necessary to true the hemi head. Alignment issuses are a huge problem once you start milling the heads.
You have a point there.
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Re: How much to mill stock hemi heads to gain half a point?
[Re: RUNCHARGER]
#981391
04/28/11 10:12 AM
04/28/11 10:12 AM
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Joined: Dec 2005
Posts: 293
Kansas City Metro
mbogina
enthusiast
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enthusiast
Joined: Dec 2005
Posts: 293
Kansas City Metro
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at 4.15 Stroke, 4.28 bore, Vcyl= 978cc, reduction needed is 5.7cc for 0.5 CR increase (-.023"). Minor amounts of milling such as this will not cause other alignment problems. Our SS hemi's are decked about -.500", the heads another .040 to .065"- combine that with angle milling and milling the intake face- THEN you have some engineering to work through.
Be a Rebel- Break the Laws of Physics!
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