Mikesprojects

From reading posts here, I was under the impression that the 243 heads had better valves and springs than the 799 heads. I know that both have larger valves than the 706 heads but through my research online, I can't seem to find any difference whatsoever between the 799's and 243's. Can anyone shed some light or is there no difference to speak of?

Darkman

iTrader: (2)

Some 243s, the ones on LS6s, came with hollow intake valves and sodium-filled exhaust valves, both of which are lighter than the ones found in non-LS6 243s and 799s. The oem valve springs for with the 243 or 799 would have application specific but for replacement purposes were interchangable.

96capricemgr

iTrader: (1)

Just to make that clearer a FEW 243s had lighter valves, but most had the same valves as the 799s.

PREDATOR-Z

That is not clearer (lol),
243 LS6 motor = lighter valves and also taller at stem.
243 all other applications= stock stainless 2.00/1.55 valves.
799 same as above.

A.R. Shale Targa

iTrader: (2)

added info

codyseals

http://houstonperformancetrucks.com/showthread.php?12544-GM-Head-Casting-Info-with-flow-numbers

Mikesprojects

I will not be replacing my LM7 cam, can anyone recommend a manufacturer and also know the part numbers for the push rods necessary for the 243/799 Heads, which I assume would be the same?

96capricemgr

iTrader: (1)

The numbers seem to be from multiple sources making them even more useless than flow numbers from a single source. Flow numbers don't tell anywhere near as much of the story as most folks want them too.

The 317s are down on flow a fair amount based on that thread but they have the same ports as the 243/799 heads, they just have a big open low compression chamber to keep compression down on the 6.0l trucks.

Mikesprojects

I will not be replacing my LM7 cam, can anyone recommend a manufacturer and also know the part numbers for the push rods necessary for the 243/799 Heads, which I assume would be the same?

96capricemgr

iTrader: (1)

If not willing to replace the cam don't bother with the heads either.

Mikesprojects

So 96capricemgr, based on your comment, what I understand you are saying is that without replacing the cams, I will not see any performance gains by swapping out 706 heads with P&P'd 243/799 heads despite the Port and Polish and the increased valve size???
Also- in the event that I DID replace the cams, there would be no LOSS of fuel efficiency right???

Mikesprojects

Is it true that without replacing the cams, I would not see any performance gains by swapping out 706 heads with P&P'd 243/799 heads despite the Port and Polish and the increased valve size???
Also- in the event that I DID replace the cams, there would be no LOSS of fuel efficiency right???

96capricemgr

iTrader: (1)

I am not saying there will be no gain but they will be minimal.

The HP gain the 5.3l saw from the LM7 to the 2008 models was what 15-20hp. The 799/243 heads were PART of that gain PART, the updated intake with larger TB was also PART of that. I believe there was also a compression bump. Not sure about cams but really doubt the later cam was smaller.

There is a lot of room to upgrade the cam before driveability and mileage are of concern based on my EXPERIENCE.

Far as what mods to to fuel economy, you wouldn't believe the truth with proof. At one point I had a Wagons(had a few over the years) and the Caprice sedan. The Wagons had 2.56 or 2.93 depending on options, 260hp 1400stall 191/195 .418/.430 111lsa and admittedly about 400lbs heavier than the sedan. Screwy thing is they only got 2-3mpg better mileage than the sedan with nearly twice the HP 3800stall, 4.10s and 228/234 .608/.608 108lsa cam.


How on earth is the mileage difference so minimal with such a large cam, so much gear, so much stall, so much HP?

The wagons were heavier but also wore more fuel friendly tires.

I am sure that if someone asked you what the mileage difference would be between two such similar but different cars would be you would have predicted something drastic.

People who report drastic mileage changes after mods are probably putting their foot in the throttle more enjoying those mods.

2001WS6-DJP

only the later 405 hp ls6 heads have light valves and longer valve stems the earlyer 385 hp ls6's has the regular valves