243 Heads

[Tonyrodz]

Just curious : my buddy has some 243 heads that are on a 5.3 motor from an 08. He was told they're basically LS6 castings. Is that true?

 

[iamdub]

Kinda. But, there is no "LS6 casting". I have these on my '08 5.3. There were a couple different casting plants for 243s in the earlier years. IIRC, the "better" ones had triangle marks cast into them. Being from an '08, there's no danger of getting the lesser-quality castings since they were kicked out of production well before '08. Identical heads would be the 799s. They don't have the cult following of the 243s, so they're often found cheaper but they're the same head, just cast at a different plant. The only difference in the "regular" 243 from the LS6 243 is that the LS6 version had lightweight valves and special springs. The intake valve is hollow and the exhaust valve is sodium-filled. Also, the valve stems were a little longer to make up for the LS6 cam's smaller base circle. They're all the same bare castings, though.

I have a set of these heads, slightly worked over with mild hand-porting (really just smoothing and they were flowbenched before and after), resurfaced, Comp rocker trunnion upgrade and Comp dual springs. They were left over from my LQ9 build and will be going in my Tahoe when I swap the cam and lifters to delete the AFM.


***Edit: I realize I was kinda all over the place in that reply. But, the info's there. Lol

Cliff notes:

243 bare castings are all the same, aside from the lower-quality castings in some older versions
LS6 version just had different valves and springs
799s are the same and often cheaper

 

[rockola1971]

What Iamdub said. They are great heads and lots of potential. You can still get the LS6 parts and convert your heads to true LS6 heads too.

 

[iamdub]

^^^ Yeah, but not necessary unless you need the valvetrain to be 100% stable at ~6500 RPM. I'd do the trunnion upgrade on anything firmer than stock valve springs. Hell, I'd do it on stock stuff.

When my LS6 heads were delivered, I compared them to some regular 243s at a speed shop and couldn't tell a lick of difference in the castings and I spent some time scouring for the smallest consistent detail. I removed an intake and exhaust valve to weigh them just so I was assured that the guy didn't rip me off. The valves weighed what they were supposed to. Actually, I could hear the sodium moving around inside the exhaust valve if I shook it.

 

[iamdub]

@Tonyrodz , I can't remember- you have an LQ4 or LQ9 in your Tahoe? You looking to swap the heads on it?

 

[Tonyrodz]

I have the LQ4. Me and my friend were talking and he has the motor with those heads on it sitting in the corner. He said something about them being the same as the LS6 castings, so I just got really curious about them. Not looking to swap out for a stock casting head. He also has a motor, 4.8 actually, that has the 862 heads on them. Same as mine. He's gonna scrap that motor, which sux.

 

[iamdub]

I gotcha. I was about to say that it's not worth it if you have an LQ4 with 317s. The 243s and 317s flow the same. The only difference is the 317s have a larger combustion chamber so the compression is lower. You'd gain maybe 5-10 HP/TQ swapping to 243s from the bump in compression and you may feel a little extra snappiness from the extra low-end TQ. Regardless, it's not worth it stock-for-stock. Ported 243s would be much better, but then you're investing into a limited setup and, at that point, should be looking into CNC'ed stockers or aftermarket or switch to an L92/LS3 setup.

It's only money and we're happy to help you spend it.

 

[Tonyrodz]

L92/LS3 stock heads? What did they come on?

 

[iamdub]

 

[Tonyrodz]

Those all have the 243 heads?