the s trim compressor wheel, has smaller fins, and different compressor tips, thus changing the amount of boost with it.
i think from memory, the s trim runs up to 56,000rpm, and 20 psi
the t trim has larger fins, better, tip angle, and is more efficeint in what it does.
the t trim from memory, supplys 28 psi at 58,000rpm
with the s trim supplying 540hp of air and the t trim 680hp.
all numbers are just off the top of my head, its been 3 years since i last looked at them
this is an aussie site, but its got some good info.
www.cappa.com.au
cheers.joe.