looking for info on SBC Pistons
 

A friend wants to build a SBC using a 6" rod and a 3.78 crank,Who makes a 13.1 piston for this? If he were using a 4" crank it would be no problem but its an oval track motor so hes limited on CI..

I am going to assume you mean 3.75" stroke. Howard sells one it is #HRC4584, made by Ross pistons.

http://kmjperformance.com/sbc-383-13...-hrc-4584.html

Also, the 3.875" stroke SBC crank is also common.