SIR (or TIR) and weight questions

[CRallo]

To what tolerance are SIR's and TIR's measured? and with what tool?

The second tier of my inquiry is less IT related, but I know we have some good rules guys here including a couple ST guys...

And how is the size of the SIR/TIR and weight of the vehicle decided? Especially for something like all the GT2 vehicles like GT3 Cup cars, Ferrari Challenge, Audi R8 and many of the STO implants where the prep level of the engine is limited compared to the rest of the class.

TIA!

[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.

[Ron Earp]

To what tolerance are SIR's and TIR's measured? and with what tool?!

The practical answer is any amount you want to fudge it AND go undetected won't help you. So make it the correct bore size.

[CRallo]

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

I see... part of that is what I was afraid of. that and who's favor this fudge factor is swinging in.


Good to know about the measuring. must be special caliper though!



^^^ I'm with Chip.

Since when did you go with the flow? :p


The practical answer is any amount you want to fudge it AND go undetected won't help you. So make it the correct bore size.

Not trying to fudge anything. Considering a letter or two, but I need to know more about how the currently implemented numbers were arrived at.

[Chip42]

regular caliper works well for a SIR of the type used on an SM.

TIRs and other long throated designs could make use of a caliper on the backside in some cases, or a bore gauge. I suppose you could make certified lollipop checkers for the more common sizes but then you actually have a fudge factor.