SIR (or TIR) and weight questions

[Chip42]

I don't know in all cases how the S/TIR to weight is calculated, I think STU relies at least in part on data collected by the FIA, I believe the same which is used for world rally. some might be POOMA or "eductated guess", more might be base don actual dyno evaluation.

as for the measurement, all restrictors and throttle body dims specified are absolute maximum values for the bore of said device. they are usually measured with a caliper, and there is usually a NIST standard block available to demonstrate at least some accuracy in the tool. see GCR Appendix G, section 2.6

[Greg Amy]

^^^ I'm with Chip.