Did the SCCA actually test and measure the SIR setup they've mandated for the E36 cars in ITS? I've read that a lot of experience was drawn from cars in GTL -- but was a real BMW used with the restrictor setup and run at a track and timed, or run at a dyno? What were the results?

The stock air intake plumbing has a diameter of 80mm. The throttle body is about 56mm or so, so the 27mm restriction means a huge reduction in air volume. The area of the intake cross section is reduced by 66 percent!

I finally had the time to call a couple of the well-known BMW racing parts suppliers. One said that the SIR can't possibly be the right solution, and that the car won't even run with such a restriction. The other shop said they tried it and it cost them such a substantial amount of horsepower that the car isn't possibly competitive.

Both vendors said that the SCCA hadn't done their homework; that they didn't test the design and just went with a guess. Perhaps more disappointingly, neither vendor is working on a product to solve the problem! They both believe the rule will be corrected, and said they're working with the SCCA to get them to understand the issue.

Are other BMW drivers having better luck in preparing for the season?