would puting ported 241 heads on 5.3 block be good ive herd it will lower compression

 

I don't know much about the LS series, but any thing that lowers compression does not benefit an engine unless it is boosted. That is the only circumstance in which you'd want lower compression.

 

Not worth it unless you are boosting it. The 241 heads flow better than the stock 5.3 heads however its going to drop your compression A LOT. The 241 heads have 66ish cc chambers compared to 61 on the LM7. I am not going to do the math on it right now but its going to drop you probably below 9.0 CR. This would be great if you planed on pushing 18 pounds of boost into it but its going to hurt you other wise.