[Plums]

The quickest unopened LS1's use 1 3/4" or 1 7/8" four into one headers. My ute uses 1 3/4" four into one Pacemakers (mine is the fourth quickest in the country I think).

On the Dyno, I've found that 1 3/4" pipes only lose a small amount of torque compared to smaller pipes, but gain that back at the top-end. The larger 1 7/8" pipes demonstrate similar loses/gains but on a larger scale, (though the loss is proportionaly more than the gain). The 1 7/8" pipes start to come to life on head and cam (aggressive cam) cars.

For general street use and to retain maximum low-down torque, you can't go past 1 5/8" tri-y's, though this will present problems with sidepipes.

For the person that wants to go racing occasionally, I highly recommend the four into one, 1 3/4" pipes.

I will be running 1 7/8" pipes on my Cobra.

Just remember that a good tune/tuner can get back some of that lost torque and magnify the gains up top too.......

Geez, that was a long spiel to say not much!