randall 32

iTrader: (3)

A friend bought a motor from a salvage yard that has 5.3/4.8 on the back of the block with 243 heads and a 5.7 head gasket. If you run 243's on a 5.3 do you run a 5.7 head gasket or is this motor possibly been punched out to a 5.7.

garygnu

some 5.3 came with 243s.

remauto1187

iTrader: (1)

Any idea the year of the motor? They started putting the 243's on the truck 5.3L's in 2007. Measure the bore to see if that engine has been bored to 5.7L specs.

Im having a 5.3L bored to 5.7L. This engine had 255K on the clock so it needed rebuilt anyway. I wanted the extra cubes to work with.

randall 32

iTrader: (3)

Thanks, I think it is a 07 or 08. So are there any difference than the zo6 243's.

jsteele90

iTrader: (13)

just the valves.

remauto1187

iTrader: (1)

Z06 243's have sodium filled exhaust valves (in the stem) and the intake valve stems are hollow. Otherwise the valve diameters are the same between the 2 versions.

LS-240

wait, am i reading this incorrectly? according to this, you make it sound as tho the z06 243 heads have a 5.7L bore whereas the heads the OP is talking about, which are 243 castings, have a 5.3L bore.

i was pretty sure all BARE 243 heads are exactly the same. i mean, thats why they have the same part number, right?

i'm bout to pick up a set of 243 heads from an 07 5.3 DOD truck (i dont know what a DOD is).

edit - nevermind, i guess you were addressing his 5.7 head gasket question.

BlueBird346

iTrader: (13)

Theyre all the same.

remauto1187

iTrader: (1)

He said in the first post that the block had 4.8/5.3l cast into the rear. The 5.7L have 5.7l cast in the rear. If the engine was a pre 2007 then it would have to be a 4.8/5.3l block that had been bored to a 5.7l and someone would have had to swapped the 243 heads onto that 4.8/5.3l block. If that was the scenario then they would have bored to the 5.7l and had to mill the heck out of the heads to bring compression back up because of the larger combustion chambers of the 243 heads.

But since its a 2007 then it could go either way since GM put 243's on the 5.3l engines.

Great find!

DUSTYWS6

I've got a 2006 Grandprix GXP, it has the LS4 motor (5.3L with 243 heads). The latest Monte Carlo SS has the same engine.

SOMbitch

iTrader: (8)

yep and when choosing a HG always match to the larger diameter between the bore and chamber... That explains the 5.7 HG on that motor.....

remauto1187

iTrader: (1)

We are talking about truck/rwd car engines here. I think the 2007 year for 243 heads is strictly for trucks.

Is the grand prix FWD or RWD? Im not up on the newer ones considering the last one i had was a 1981 RWD. If its a FWD then that engine is useless for a RWD application.

Do the car heads have a different bolt pattern for accessory mounts? If so then that would also be a problem for a truck application.

DUSTYWS6

Unfortunately the Grandprix is a FWD, but the GXP model uses the same 5.3L truck engine. I've really enjoyed the motor, it's got a good amount of torque so it's pretty fun on the street. As far as accessories, I'm not sure if it's same as the truck engine, but I imagine it is. I don't see GM spending a ton of money retooling the 5.3L just so that it will fit in a limited production of Grandprixs, especially when they were getting ready to kill the grandprix in a couple of years.

Bo185

The Gen III L33 aluminum block 5.3L has 243/799 heads. It had the 4.8L flat tops to boost CR because of the larger chamber of the 243. It was the high output motor. None of the iron truck motors had the 243/799 heads stock.

All 2007 and up Gen IV 4.8/5.3 use flat tops and the 243/799 heads.