Restrictor Plate Diameter Tolerance

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Supercharged111
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Restrictor Plate Diameter Tolerance

Postby Supercharged111 » Fri Oct 02, 2015 9:43 pm

I never ran this by Al, just throwing it up here as I've busted the 1 Oct deadline and it may be too late. We have tolerances for fuel pressure and ignition timing, I think we need to specify our tolerance for restrictor plates but I don't know what's reasonable.

3.11.1 Fuel Pressure Tolerance shall be +/- 2psi for EFI cars. Carbureted cars are not subject to a fuel
pressure tolerance.
3.11.2 Timing tolerance shall be +/- 1 degree

What do you guys think?
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BADVENM
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Postby BADVENM » Fri Oct 02, 2015 9:52 pm

Here is the rule currently:

7.21.4 All Cars may install a restrictor between the air filter and intake manifold to reduce horsepower and torque. The diameter and thickness of the restrictor plate orifice(s) shall be noted on the Dyno Sheet and must match at all times. Carbureted cars may install a mechanical throttle stop on the carburetor linkage for the same purpose. Throttle stop dimensions must be noted on the Dyno Sheet for inspection purposes and must match at all times.
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Supercharged111
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Joined: Sun Jul 28, 2013 9:18 am
Location: Colorado Springs, CO

Postby Supercharged111 » Sat Oct 03, 2015 8:12 am

Yes, but there's no +/-, I was thinking maybe .1mm? Just something to account for a different caliper being used to measure at the track vs in your garage.
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mach1
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Postby mach1 » Sat Oct 03, 2015 8:18 am

.1mm is pretty tight, i'd say .5mm

Supercharged111
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Location: Colorado Springs, CO

Postby Supercharged111 » Sat Oct 03, 2015 8:26 am

That may very well be the case if I'm reading the rules right, thanks to Glenn for pointing out the uber obvious.

3.11 Tolerances
Unless otherwise specified, all published measurements infer a tolerance of +/- one-half of the last specified
decimal place. All rounding will be done to the nearest decimal place that is specified in these rules. In a
case where a measurement falls exactly on the halfway mark it shall be rounded up or down in favor of the
competitor.

7.21.4 All Cars may install a restrictor between the air filter and intake manifold to reduce horsepower and
torque. The diameter and thickness of the restrictor plate orifice(s) shall be noted on the Dyno Sheet and
must match at all times. Carbureted cars may install a mechanical throttle stop on the carburetor linkage for
the same purpose. Throttle stop dimensions must be noted on the Dyno Sheet for inspection purposes and
must match at all times.

Below from the dyno sheet:

Restrictor size, # of orifices, diameters, thickness:

The rules don't specify how accurately the restrictor plate's diameter must be annotated on the dyno sheet. If specifying within 1mm is OK, then I'm seeing a +/- .5mm tolerance which ought to be enough to account for variances in calipers. I've had this come up already and didn't know the answer, shame on me.
Rocky Mountain CMC Director
#45 Camaro Challenge Race Car

mach1
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Joined: Tue May 08, 2012 11:11 am

Postby mach1 » Sat Oct 03, 2015 1:32 pm

On my sheet I just put "Medium" on the diameter, I hope thats ok!


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