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Discussion Starter #1 (Edited)
Singh's Grooves in Ported & Milled vortec heads on stock 350

I am porting a set of 062 Vortec heads for an otherwise stock (including fuel injection) 97’ 350 in a 4 wheel drive pick-up. I will be milling the heads to assure the surface is true.

My question is can I mill the heads to raise the compression to further improve performance with out detonation? If so what’s a safe amount to mill?





 

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Vortec heads are very thin GM castings and I will not mill them more than .010 which is approx 1.5 cc from the combustion chamber. I have seen them milled .020 or more. They tend to crack across the center deck.
 

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Discussion Starter #4
Thanks,
I measured the head deck thickness to be 0.275", this appears to be thick enough to allow milling.

I’m interested in raising the compression with in the detonation limits; I can’t find specifications on the engine’s stock compression ratio or camshaft specs to calculate dynamic compression ratio.
 

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Discussion Starter #6 (Edited)
The engine is still running so I estimated some of the numbers to come up with this:

Cylinder Head Volume (cc) 64
Piston Head Volume (cc) 10
Gasket Thickness (in.) 0.026
Gasket Bore (in.) 4.166
Cylinder Bore Diameter (in.) 4.0
Deck Clearance (in.) 0.030
Stroke (in.) 3.48
STATIC COMPRESSION RATIO 9.3:1

You think I can bump it up to 10:1 with the stock camshaft?

With a 0.040" mill at 1.5 cc per 0.010"

Cylinder Head Volume (cc) 58
Piston Head Volume (cc) 10
Gasket Thickness (in.) 0.026
Gasket Bore (in.) 4.166
Cylinder Bore Diameter (in.) 4.0
Deck Clearance (in.) 0.030
Stroke (in.) 3.48
STATIC COMPRESSION RATIO 9.96:1
 

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your asking the wrong guy about that. i have a vortech blower on mine, so i don't need any more static compression. do you plan to use 93 octane ?
 

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Then don't raise it. Its on the edge as it is using the stock knock sensors and EFI. I'd not raise it unless you plan on more octane. The polished chambers will help, but not much more than .1 or .2 additional.

Polished chambers might have added a cc or two and a clean up milling will probably take you back to stock CR. Sounds good to me.
 

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If I were you I'd cc each chamber to make sure its 64cc. I had my vortecs decked .010 and they measured 65.5cc. also I'd cc the pistons as well. I wouldnt mill the heads any more than I absolutly had to. The 062 casting is better than the 906 casting but they still crack easily. I would have the block zero decked or at least decked enough to make up the difference in compression.
I used a set of KB 120 KiethBlack pistons 7cc 2vr
the heads measured 65.5cc
deck ht is .015
4.30 bore
headgasket thickness .015 with a 4.100 bore felpro embossed shim
this gave me a static compression of 10.22
 

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Discussion Starter #11
I haven’t CCed the heads but I will do so before and after milling. The short block is not coming out. During the holidays it just a head swap. I can adjust piston to head clearance with gasket thickness.

Yours does OK at 10.2:1? What camshaft and fuel?
 

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Discussion Starter #12
curtis73 said:
Then don't raise it. Its on the edge as it is using the stock knock sensors and EFI. I'd not raise it unless you plan on more octane. The polished chambers will help, but not much more than .1 or .2 additional.

Polished chambers might have added a cc or two and a clean up milling will probably take you back to stock CR. Sounds good to me.
Your thinking maybe 9.4:1 maybe 9.5:1 max. I supose I could put it on a scan gauge and check for knock retard before I cut anything.
 

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My 906 Vortecs (uncut) are advertised at 64, but actually measured out to 62.5 or so. Tolerances from what I understand range from 61 to 66. Measure twice, cut once :)
 

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If I were you I would step the compression up to about 9.5:1 and run high ratio rockers and consider a more agressive cam. It looks like you did a fairly good job of porting, but its all in vain without lift numbers to match.
 

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Discussion Starter #16
I'm a bit surprised, with the improved combustion of the fast burn chamber, I thought I could get away with 10:1 compression.

I know increased cylinder pressure improves power and efficiency, with the cost of high grade fuel it's not a good trade off.
 

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Improved combustion(faster flame front) ment less timing was needed and increased effiency. 32 timing not 36 like most wedge chambered head.
 

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You can get away with more these days... just 30 years ago in the same exact engine architecture, they had 8:1 compression and even that could have some ping to it on 87 on "good" gas. As shortly as 10 years ago, everyone's rule of thumb was to multiply CR by 10 to get your octane requirement, so 87 octane would work fine in 8.7. Now we're seeing some factory setups running high compression with 87 octane. My 96 Impala SS is a good example of that. It was advertised at 10.5:1 but its actually 10.25:1. The reverse flow cooling is what saves it. You have a normally-cooled engine so keep I suggest keeping it to stock CR.
 

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Discussion Starter #19
Thanks for the input. I’m a bit hard headed; if it were my engine I would mill the heads to 10:1 and deal with it. Not that I don’t trust the advice, that’s just the way I am. The truck belongs to a local collage student and I don’t want to force him to buy premium fuel so I’ll continue to study my options. He’s looking for power; I’m convinced we can find power with efficiency.
 
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