Getting heads rebuilt after overheat, my 5.3 has 706 heads I was thinking port and polish . The mechanic has offered me his 317 off his 6.0 . He’s selling them to me for 250 and my 706 heads . Don’t know if he’s helping me out or helping himself out . Should I keep my 706 or take his 317 ? Pls help

 

Here's some info on the two stock casting heads in question:

Casting Number 706 and 862
Head: 1999+ 4.8L / 5.3 Liter Truck
Material: Aluminum
Part Number:
12559862
12561706
Combustion Chamber Volume: 61.15cc
Compression Ratio: 9.5:1
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


Casting Number 317, 035
Head: 2001+ LQ4 and LQ9 6.0 Liter Truck
Material: Aluminum
Part Number:
12562317 -LQ4
12572317 -LQ9
12572035 -LQ9
Combustion Chamber Volume: 71.06cc
Compression Ratio: 10:1 LQ9 Flat top pistons
Compression Ratio: 9.6:1 LQ4 Dish piston
Intake Port Volume: 210cc
Exhaust Port Volume: 75cc
Intake Valve Diameter: 2.00 inches
Exhaust Valve Diameter: 1.55 inches

Stock Head Flow Numbers
Chamber 71.06cc----0.100---0.200--0.300--0.400--0.500--0.550--0.600
Intake 210cc-----------66-----142-----196---228----236---238-----240
Exhaust 75cc----------59-----104-----137---155----167---173-----177


The main concern here in my opinion would be the combustion chamber volume. The 317 heads have 71cc combustion chambers and the 706 heads have 61cc chambers. If you were to leave the combustion chamber volumes as is, the 317 heads would lower your compression ratio drastically and ultimately hurt performance, regardless of having bigger intake valves and larger intake & exhaust ports. The 317 heads would need to be milled right about 0.050" to achieve 61cc-62cc chambers. I'm not certain if it's ok to mill that much but thinner head gaskets is also another option to help lower compression.
Also, if you get the 706 heads ported, it maybe a good idea to replace the stock 1.89" intake valves with 2.00" intake valves. I believe this is ok even with the 5.3L's 3.78" bore, be good to make sure though. But I don't think it would be ideal to go larger than 2.00" intake valve with that smaller bore. Should do some research on that.
CNC porting service (to any gen3 casting aluminum LS head) usually costs around $750-$1100 depending on what you have done (install new valves, new springs, etc).

Edit: after thinking about it and did a quick search, using 2.00" intake valves on a 5.3L 3.78" bore will likely cause valve shrouding issues and hurt performance. It would be about the equivalent of putting 2.12" intake valves on a 3.9" bore LS1. Not so good. The 317 heads may not be a good way to go.
Do the math.
2.00" int valve + 1.55" exh valve = 3.55". 5.3L bore 3.78" - 3.55" = 0.23"
2.12" int valve + 1.55" exh valve = 3.67". LS1 bore 3.9" - 3.67" = 0.23"

 

You’ll lose a bunch of compression and might not even be able to Mill them enough to get back to stock

 

Don't do it!

 

Those heads won't do you favors in a NA setup. Keep your 706s.

http://www.superchevy.com/how-to/eng...der-head-test/

 

^^^+1

 

706s all day long! port and polish them If u want, cant hurt!