You've obviously got a better handle on things than I originally gave you credit for. How heavy is your friend's car? With 347 RWHP he's doing fantastic to get down to 11.30's. I made 325RWHP and only managed to get mine to 11.99 at 3200# weight. Of course that's on an 8.5" slick.
Watch your cam. P/S has a lift limit of 0.500" at the retainer. These N/A cars are really dependent on a good cam matched to the rest of the system.
Stick with the 28x10.5" ET Drags and go with a minimum of a 4.30 gear. You should be able to leave at no less than 5500rpm with short times right around 1.50 on those tires. The ET Streets won't cut the mustard in P/S.
Good luck.
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Jeff Chambers
T/S #3
11.97 Seconds/114.5 MPH
Chambers Racing Team