Head ?
The 243 heads are off the LS6 and LS2. The have a better short turn to them so they have been able to make more power than the LS1 heads.
The 317 heads were from LQ9/LQ4 engines. They had the better port like the 243 heads, but larger chambers which are ideal for low compression.
Then there are the 4.8/5.3 heads. The port isn't that great, but they have smaller chambers for a bump in compression.





