From the 2020 GCR
9.1.1. Formula 500 (F500) Specifications
14. Snowmobile Derived Engines
A. Carburetors: The induction system is restricted to two (2) 38mm Mikuni VM 38 round slide carburetors (except AMW). No modifications are permitted to the carburetor bodies. The use of any jets or jet needles is permitted.
External carburetor jetting devices such as Mikuni Power Jet, Thunder PowerJet, Dial-A-Jet, IntelAJet, or other similar devices may be used, provided they are plumbed to the float bowl and body of the carburetor for which they are installed. Cockpit adjustment of external jetting devices is prohibited.
From here:
http://thunderproducts.com/product/thunder-powerjet/
Thunder PowerJet $ 64.95 – $ 189.95
The Thunder PowerJet fits any size or brand carburetor. It is exactly what you need to achieve maximum performance with your engine. The TPJ improves performance by precise fuel metering with needle valve adjustment. Fuel distribution is improved by adding fuel through two sources instead of just one. This means more horsepower at any temperature or altitude. The TPJ gives you a range of over 10 to 12 jet sizes with precision external adjustment.
Is anybody using this new jetting stuff?
I am not a EFI expert. But here is some stuff from the GCR concerning 600cc motorcycle engines and the fuel metering system.
15. 600cc Motorcycle Engines
D. The stock ECU shall be used. The ECU fuel and ignition map may be changed.
Devices that modify inputs to or outputs from the ECU (e.g., Power Commander) may be used. Stand-alone after market ECUs are not permitted.
It would appear that the motorcycle engines have an advantage over the snowmobile engines in the fuel metering area. If I understand 15 - D correctly, the ECU is adjusting the fuel into the engine based on inputs in real time.
But looking at 14-A, the adjustment of the jets by the driver, while the car is in motion, is prohibited.
Why not allow driver adjustment of the jets?
Photo of the Thunder Jet
https://www.apexspeed.com/forums/att...id=89494&stc=1
Richard
reddevilsix@msn.com