my 853 heads are cracked, but i have a set of 706 heads. what needs to happen to have them match the 853 heads as far as performance?

 

Casting Numbers 241, 806, 853
Head: 1997+ LS1 5.7 Liter Passenger Car
Material: Aluminimum
Part Number:
12559806 (1997-98) Chambers = 69cc
12559853 (1999-00)
12564241 (2000-03)
Combustion Chamber Volume: 66.67cc
Compression Ratio: 10.1:1
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


Casting Number 706 and 862
Head: 1999+ 4.8L / 5.3 Liter Truck
Material: Aluminimum
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

I assume the 853 heads are center bolt. I would have them ported and larger valves installed. Others should chime in and give you some advice.

 

If the 853's are too far gone crack-wise, the 706's can be ported and re-valved to match or surpass the 853's. Plus with the smaller chamber, the compression will be up compared to its use on the original 5.3. TSP does these all the time.

 

Have you looked in buying a used set. I just bought a set of 853s on eBay with 34000 miles on them for $260 shipped from Canada. They arrived today and look great. I have a pair of 241s that need a valve job and the shop wanted $300 with out parts so it was just easier and cheaper to replace them sense they are so plentiful

 

706's are prone to crack also FWIW