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PROPOSED RULE 2015: Change dyno variance to a percentage


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Proposed change

Change from a a fixed dyno variance to a percentage based difference.



The error in a dyno due to calibration, etc. is unlikely to be a fixed number across the entire range of measurement. If the weight of the drum, friction factors, load cell calibration, etc are off, the calculations done by the dyno software will multiplicative in error not additive. By changing to a percentage of error, it should be more accurate to the actual variance experienced by the range of cars.


Looking at the typical HP ranges for GTS1 through GTS5 cars, a 4 hp variance is as much as 2.5% and as little as 0.9% of a declared number. With the fixed 4 hp, drivers at the lower RPM ranges might be incented to push the limit whereas a driver with a high HP car needs to have a larger cushion.


Proposed wording

To allow a small safety margin for dyno variance, the peak HP number (or average of peak HP/TQ for those cars it applies to) will be multiplied by 0.98 (number up for discussion). However, if a car does not meet the minimum weight listed on the certification sheet, the forgiveness cannot be used to arrive at a compliant number.

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Yes, that makes perfect sense.


We should do the same with the various power-to-weight penalties as well. Penalizing a sequential tranny with 0.2 lbs/hp is a 1% penalty in GTS1 and a 2.7% penalty in GTS5, which doesn't make sense. It too should be a percentage.

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Yes. This make sense!

And I think using the .98 as the factor is pretty darn close, but I may like .985 better to keep things a little tighter.

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CARVAL Motorsports

Is this correct:



100hp - 102 good on dyno

200hp - 204 good

300hp - 306 good

400hp - 408 good

500hp - 510 good


I fear that the lower hp cars could fail at the dyno disproportionately to the higher hp cars. Food for thought.

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