Well just got my truck back on the road after swapping a tbss intake and ported 0.30 milled 816 heads. Needs a retune bad can't get on it hardly at all without it stumbling, so taking it easy till the retune. How much should these help my et? Truck in sig has 3.42s ran a 15.3 with a 2.56 60ft at 92.85 mph. I know my gears are killing me, thoughts? thanks.

 

I'd say it'd be worth 2-3 tenths.

 

816? What these heads come off of?

 

Think it's 816 correct me if wrong, but I was told there 5.3 heads.

 

862 or 706 heads if they are from a 5.3l

 

IMO Them heads or going to kill your performance. Milled 243's or 317's

 

Why would the kill my performance?

 

I agree with scooter. Those will choke it down. If you want compression get 243's or mill some 317's. Hell mill the 243's, but those heads will hurt the performance. In terms of the intake, that is probably a step in the right direction, but not with those heads.

 

They flow much less, on the intake and exhaust ports, I also believe they have smaller valves.

 

Gen.III, aluminum 4.8/5.3L

http://www.enginebuildermag.com/Cont...0000001259.pdf

"4.8L/5.3L Trucks
Both of these engines share a common aluminum head with 61cc chambers.. The 12559862 casting was used from '99-'04, but the 12561706 showed up on some engines in '04, too. The 862 casting came with and without the recess on the edge of the deck surface, so rebuilders need to make sure they use the right head gasket when installing one of these heads."

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


What you need to know:
These small combustion chamber truck heads offer no advantage over an LS1 head except the smaller combustion chamber. This along with milling of the deck surface will allow a slightly higher compression ratio to be achieved. Because of the smaller intake valve installed in these heads a valve upgrade is practically mandatory.

Id say your compression is going to be way high. 12+ or so.