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straight at T
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2,472 Posts
>Does anyone have reasonable guesstimates regarding the
>horsepower and hp/weight ratios of Thumper's Open and Stig's
>GroupN cars? What about gearing differences? Do they both
>run the same size restrictor?

The open class cars are running a 34mm restrictor, while the N cars run a 32. For the thermodynamically inclined, that means that the open cars can get 12-13% more air at the limit.

>I ***think*** I read somewhere that Thumper beat some stage
>records, but can't find that info again. True/false? Who set
>the previous records? Were they using restrictors?

The previous records were, I believe, all set by Open cars with 40mm restrictors (the SCCA limit since at least 1997).

Adrian
 

·
straight at T
Joined
·
2,472 Posts
>>The open class cars are running a 34mm restrictor, while the
>N
>>cars run a 32. For the thermodynamically inclined, that
>means
>>that the open cars can get 12-13% more air at the limit.
>
>I get about 11.5%, based on area alone. I did a quick
>spreadsheet as I was curious as to what exactly was
>theoretical.... I assumed the following:

>Anybody up for checking my numbers?

It's not quite based on area alone. The limit comes when the flow is choked (i.e. has a standing shock wave at the throat of the restrictor).

The choked flow through the restrictor (i.e. the maximum possible airflow) is approximately:
40mm = 514 cfm
34mm = 371 cfm
32mm = 329 cfm

which is where I came up with 12-13%
these assume standard atmosphere and my vaguely remembered gasdynamics...

Adrian
 
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