Max Hp w/GT42/74
 

well Am putting the S88 away for now and stepping back to a GT42 74 mm for now because i want it to spool a little faster for now (need my converter re-stalled) also i am getting alot of surging @ low boost (11psi and lower) and 12 psi and 2600lbs on the street is too much with the S88. so i have a brand new Gt42 74mm with 1.15 ex that will bolt up for now till i can get a custom 80mm built.. how many have gone over 650RWHP with a turbo like this? i will prob run a max of 18-22 psi just looking for some real data with a gt42 turbo..
348ci

We have maxed them out around 700-750rwhp. Also check with some members here. They have ran them and maxed them out as well.

Well got it on and all i can say is insta boost..... have a 7 lb spring now and it is at full boost as soon as yo floor it LOL.. 10-20 psi to come later this week...

Yes, instaspool for sure. Problem is back pressure will be HIGH if you plan to try to push it. Check to make sure you don't start pushing water.