Full-Force

iTrader: (11)

I was just peeking at my Dads new Avalanche and it has 243 heads. Why are they running those heads on the 5.3? It obviously lowered the compression from the old 5.3 heads. I did notice that 87 octane is recommended in his truck. Maybe the idea was to use the 243 head to lower compression so you could run regular unleaded while maintaining power with the better flow of the 243 head.

5.3LJimmy

iTrader: (10)

The older 5.3's had dished pistons and 62cc heads, all the new ones have flat top pistons and 64cc chambers. Which I think is really good b/c the cost of the 243 casting should drop with the huge production numbers of 5.3 engines. LS6 heads cheaper than 5.3's sounding good to anyone else?

ae13291

iTrader: (8)

so if i slap on a pair of 5.3 heads compared to the 243 ls6 heads, which one will make more power??

Tainted

iTrader: (9)

depends on how much each one has been milled and ported

Stangkilr

iTrader: (47)

LS6 heads are on all 07+ GM trucks/suv's.

ae13291

iTrader: (8)

i see alot of people using the 5.3 heads! but what does everybody do with them?? like are they ported? or are they just used for more compression? i know the 5.3 has smaller valves but if its only bout compression, my dads a machinist and he can mill my stock heads, wont that be better??

quiet_storm98

iTrader: (48)

yes the 5.3's people use are ported..the main reason people use them over ls1 heads is because you can have a smaller combustion chamber with them without having to mill them. For instance most of the ones that are ported have a 62 or 63cc combustion chamber without milling so therefore you wouldn't have to worry about ptv clearance (depending on the size of the cam) and you would still have the higher compression

cdoggy81

iTrader: (6)

...& smaller runner size to keep the velocity up esp. down low.

ssheets

iTrader: (1)

Remember the old 5.3 heads have smaller intake valves 1.9???. I assume the 243's have 2.00" intakes.

Most people use 5.3 heads and then have new (larger) valves put in and porting done.

I like the idea of cheap 243s...I'm already itching for head and cam swap part deux

ssheets

iTrader: (1)

This is not entirely true. 5.3 heads have a .035" valve drop from 241 castings. In effect, you're milling your 241 heads .035" with respect to PtoV. The upside is your valvetrain geometry is not effected like it is when you mill your heads and neither is the intake manifold to heads mating surface.

Full-Force

iTrader: (11)

Well bottom line, there are gazillions of Avalanches, Tahoes, and Suburbans on the road, not to mention the pickups.

No reason the 243 heads should not come on down in price some more.

litle88

iTrader: (20)

I also found out from gunnar and froma GM engineer on the corvette forums that the new 243 casting numbers are 799's, some vettes after 06 and even some TBSS's have 1 243 on one side and a 799 on the other side. Just a li FYI.

ae13291

iTrader: (8)

thanks 4 the info guys!! (=