There’s not been much activity in the turbocharger selection area recently, but that has changed with the receipt of this data showing a F21 equipped B5 S4 operating with E85 fuel and measured on a Dynapack dynamometer.

It’s good to see a F21 car operating the turbocharger at a boost level consistent with what I believe they are capable of, steady 23-24 psi out to redline.

Details about the car: 2001 Audi B5 S4 on Stock Engine, FrankenTurbo F21 turbochargers, 72 lb injectors, 85mm MAF and intake, 2.5″ catless downpipes, Silly Rabbit Motorsport Intercoolers, tuned by Epic Tuning Group on AU Tuning’s Dyno.

And some results of the F21’s on 91 octane fuel.

In terms of selection criteria these results show that F21’s are going to be able to push the edge of my comfort zone with the stock motor.  With 93 octane instead of 91 I’d expect the horsepower and torque to nudge up another 15-20.

The contenders still are:

• Borg-Warner K04
• FrankenTurbo F21
• Project B5 RS6-X