Pontiacg5

iTrader: (3)

I have a 5.3, supposed to have 130K. My 5.3 has 706's and I'd like to get rid of them before they crack and start leaking.

I have a pair of 853's from a LS1 I'd like to put on the 5.3. I know I'll loose some compression, but I can have the heads milled for free.

How much would I need to take off of these heads to get back to stock 9.5:1? Could I take a little more off and get 10:1? I'm worried about bending valves if I ever decide to swap cams. My 5.3 has dished pistons.

I read somewhere that you need to mill around .005 to get 1cc back, so from my logic I'd need to mill .040 off to get back to 9.5:1. Is that anywhere near right?

Thanks for the help guys!

dgcustomz

iTrader: (127)

853's=66.67
706's=61.15

5.52cc difference.

5.52x.007"=.03864cc

So about .039" milled will get you back to a 706 head compression.

dgcustomz

iTrader: (127)

853 specs
Combustion Chamber Volume: 66.67cc
Intake Port Volume: 200cc
Exhaust Port Volume: 70cc
Intake Valve Diameter: 2.00 inches
Exhaust Valve Diameter: 1.55 inches

Stock Head Flow Numbers
Chamber 66.67 cc------0.100--0.200---0.300---0.400---0.500---0.550--0.600
Intake 200 cc------------67----122-----178-----215-----219-----223---227
Exhaust 70 cc------------52-----97-----133-----156-----170-----76----180

706 Specs
Combustion Chamber Volume: 61.15cc
Intake Port Volume: 200cc
Exhaust Port Volume: 70cc
Intake Valve Diameter: 1.89 inches
Exhaust Valve Diameter: 1.55 inches

Stock Head Flow Numbers
Chamber 61.15 cc----0.100--0.200--0.300-- 0.400--0.500---0.550---0.600
Intake 200 cc----------63 ---128----179-----210----218----221-----226
Exhaust 70 cc----------54 -- 93 ----121----145-----163----168----174

Intake valve is the only thing that is different on the heads other than the cc's, you can see the small increase in flow from the bigger intake valve on the 853.

bww3588

iTrader: (49)

also, keep in mind, dished pistons have nothing to do with PTV clearance.

Pontiacg5

iTrader: (3)

Hey, I was closer than I expected on how much I needed to mill!

I wasn't expecting much of a gain with the heads alone, but I figure if I get them ported the larger valve would be an extra bonus. I wouldn't have to worry about cracking castecks either...

Would I have PTV problems milling .039 with something like a .600 lift?

Thanks for the help guys!

chrisfrost

iTrader: (8)

Generally large duration is where You have ptv issues but there is only 1 way to be sure and that is to measure with the correct type of clay .

Pontiacg5

iTrader: (3)

Dang, so I would have to buy a cam and try it to see if it would work? Seems expensive and time consuming, more work than these 853's are worth lol I guess I'll hold off on a cam till I can afford nice ported 5.3 heads.

Has anyone ever milled 853's 40 thou for a stock 5.3? Surly I won't have PTV clearance there right?

I've tried searching for this stuff, but all I seem to find is 5.3 heads replacing 853's on an ls1. Not sure how to word my search different to find what I'm looking for. Someone has to of tried this before!