Why add a Restrictor to a Car Without Data?
#38566 from Doug Piner · No action required · Minutes (2025-08 Fastrack)
Thank you for your letter. The 2.5L engine in the Z3 and Z4 are nearly identical (bore, stroke, horsepower, torque, manifolds,
etc.) and it is reasonable to expect that their performance potential when prepared to Production specifications will also be
similar. In light of this fact, the use of the same FPR on the 2.5L Z4 as the Z3 is necessary to bring the Z4 into the EP performance
envelope. The Z4 races at a heavier minimum weight than the Z3 due to its improved rear suspension and larger brakes front
and rear. Lastly, "slick" race tires are available for 17” diameter wheels. The letter writer is encouraged to campaign the car so
that further data can be collected and analyzed, in order to help determine if any further adjustments are warranted.