I hope to eventually buy new heads for my ls1. My understanding is that aftermarket castings have more power-potential, but that ls6 heads are lighter. Does anyone know the exact weight difference between the two?

 

It won't be more than a few pounds, mostly due to thicker decks and possibly port walls on the aftermarket heads, all in the interest of strength.
What are the goals for your engine? You would be surprised at how good a well-ported set of 243/799 can make power, for less than the cost of new castings.

 

The car is my DD and currently has most of the major bolt-ons, 3.42's, a 3400 stall converter and a Tick Performance SNS Stage 2 cam: (227/235; 0.618"/0.605", 110+3). I'm not on a mission to set any records, just like to have fun on the street, the occasional impromptu race, and maybe take it to a strip just to see what happens.

 

Find a good pair of 243/799 heads. Even untouched they will outperform 241's handily
BTW, 799's are identical to 243's. Both came on all Gen IV 4.8/5.3 truck engines, and are not hard to find.
You will gain a bit of compression with the 2cc smaller combustion chamber,

 

so, stock heads, A, have power potential X and weigh Y pounds. If aftermarket casting B has a power potential of X+10 hp, But weights Y+10 lbs...

take out 10 lbs from your car, and you won't notice it.

add 10 hp, and you will.

the only real consideration is overall cost., and whether you will realize the potential of the heads or not.

 

And consider here as well that a good set of aftermarket dual valve springs will easily add a couple pounds to the equation, vs. Oem beehives.

 

i think you have to take into consideration if you will need to go with aftermarket rockers with the aftermarket casting heads, as well. more $$$ and also more weight over the stock rocker setup.

 

I expected the weight difference would be small, but since that extra weight would go up front where I'd least want it I thought it would be worth finding out.

Dreadpirateroberts, when you estimate a difference of 10 hp are you referring to as-cast aftermarket heads or their cnc-ported variants?

 

You'd never feel the weight difference. I'd run duals just for the peace of mind.