hi, i'm a newbie to Nissan. I have a quick question. what's the difference between the red top SR20DETs and the black top ones?

 

difference is i have a blacktop and i dont have a redtop

J/K your best bet is to search, you'll find this answer right away..
blacktop is newer 94-98
redtop is older
im not sure if there are any power differences, ive read many different articles saying yes and no..so i dont know.

 

There is no power differnce at all..search and u will find deeper differnces..but there really arent many

 

What about the internals? like the pistons, block and the head?

 

we have covered the same topic before..search around for it and u will find it bro

 

trust me, search ,you'll find more than enough info about this all of the other motors.also try and memorize the faq