Hank, I believe a "S" trim wheel is the largest wheel available for a T4 frame turbo, I have only used a "Q" trim wheel and never had a problem with spool. but I run a 292 ci.
I think a 250 could easly use a "Q" trim.
Last year I was having problems and found it was my turbine had melted away, this was after the season was over. I switched to a "S" Trim and tried it in my driveway (I can make a 60ft pass on my driveway) and it had no spool problem at all.
With the "Q" Trim 28# boost 55# turbine (2x's) BAD
"S" Trim 40# boost 60# turbine (1/2 x's) BETTER
Can't wait to try it ! When I get it together again.
Beware: like I said in a previous post the nomenclature for these trims are different depending on the manufacture one "Q" or "R" or "S" from one is different than another even the number of fins can be different. that is why I measure everything.
All Co. make a form of all trims.
Harry
