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How much to mill L92 heads?

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Old Sep 24, 2010 | 07:54 PM
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Default How much to mill L92 heads?

Got a gen III 6.0 iron block with 16cc dished pistons on a 4.005 bore with factory stroke.
With untouched L92's & stock GM gaskets SCR would be roughly ~ 8.8:1
Goal is to get as much compression that I can safely get (supercharger setup).

I'm unsure about the deck height measurement (at XP Racings shop). Any general ideas on how far I can mill L92s to run a 229-236 .590/.600 cam while maintaining a decent ptv clearance? Thanks in advance!
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Old Sep 24, 2010 | 08:57 PM
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how mush boost are u trying to run?
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Old Sep 24, 2010 | 11:24 PM
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14 would be plenty enough. but, it'll be awhile before I get to that, if I even do.
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Old Sep 25, 2010 | 06:31 AM
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The deck height on those heads are pretty thin, add that to them being just a 4 bolt head and the fact you want to put moderate boost thru them I would say not to mill them at. It would be better to make up the CR with pistons.
FWIW, I ran those heads N/A and my motor was 13:1cr and we did not mill the heads.
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Old Oct 7, 2010 | 10:02 PM
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Milling those is not the best thing, they will wake up for you with a light port job on the exhaust side only and a cam swap.. then is your still bent on upping the CR then get the CR up with pistons and rods..

You mentioned you wanted to run a supercharger.. you would think a higher CR and a supercharger would make for even more power.. works more like a bomb.. lol Supercharged motors actually us lower CR and then adjust the other factors involved (fuel, timing and air)

You have to remember that the supercharger is forcing a larger volume of air into the cylinder so getting it out becomes very important, therefor you would need to increase the injector size to add more fuel to the air, port the exhaust side and add a free flowing exhaust to see good power with the CR you have already..
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Old Oct 8, 2010 | 11:42 PM
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twenity to thirty thousandths would put you at about 10:1/1. Goal is to bring the stock l92 head which is 70cc down to 64cc.
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Old Oct 8, 2010 | 11:45 PM
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Originally Posted by LS1MonteSS
Milling those is not the best thing, they will wake up for you with a light port job on the exhaust side only and a cam swap.. then is your still bent on upping the CR then get the CR up with pistons and rods..

You mentioned you wanted to run a supercharger.. you would think a higher CR and a supercharger would make for even more power.. works more like a bomb.. lol Supercharged motors actually us lower CR and then adjust the other factors involved (fuel, timing and air)

You have to remember that the supercharger is forcing a larger volume of air into the cylinder so getting it out becomes very important, therefor you would need to increase the injector size to add more fuel to the air, port the exhaust side and add a free flowing exhaust to see good power with the CR you have already..
Milling is the best thing to do to raise the compression. A porting job does nothing but gain 8hp on a stock bottom end 6.0 because the ports are already large flowing at 320cfm. 1point of compression equals 18hp.
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Old Oct 8, 2010 | 11:55 PM
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The lower the compression the more boost its going totake to make the same number with a higher compression. 11:1/1 is aperfect compression ratio for a supercharger. Only probelm is with the block he is running he can tgo past thirty five thousanths unless he notchs the pistons with that big of a cam. Also the l92 heads like a smaller camshaft because they have larger intake ports so they don't need the valves to stay open for alonger time to fill the cylinder up. Now a turbocharger compression ratio is a whole other story.
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Old Oct 9, 2010 | 11:08 PM
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I think I was thinking about a turbo when I wrote that last thread.. My Bad!
I also think I read the same thing about the piston notching is you shaved the heads...
Not to hijack this thread but my 6.0 L96 only has 2 miles on it and I just changed out the truck intake for a LS3 intake and I noticed this little machining flesh on all the intake ports..
Attached Thumbnails How much to mill L92 heads?-machining-extras.jpg  
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