There is one question that I think is very important when evaluating the
different methods of fueling a motor at Bonneville.
Does the density of the air coming into the system change during a run?
Mechanical injection and fixed venturi carbs work best if the answer is no.
If the answer is yes, then modern variable venturi motorcycle carbs or EFI
will do a much better job. Especially with gas.
The variable venturi carbs will compensate for some changes in air density
which is needed on modern street/race bikes that have very efficient ram
air pressure recovery systems. In low gear at 10,000 RPM the air delivery
system is actually restrictive but at 180+ MPH produces several thousand
feet of positive air density recovery. As the new aero designs have improved,
the air density compensation design limits of V.V. carbs have been reached
and they are being forced to use EFI.
Howard had a real problem with his new air scoop last year. The excellent
pressure recovery kept causing the motor to go lean at the top end.
He ended up with the smallest pill is his box on the last run. It was very,
very fat at the bottom end (<150 MPH) and STILL lean at the top (>275).
Running gas would not have been possible. (at least for more than one run)
If you look at a picture of a pre EFI Indy car, you will see that the engine
air intake is placed where it always sees static air pressure and is pulling in
boundary layer air.
For those planning to experiment with scoops who don't use EFI, remember
the Keith Turk law .. plugs are easier to replace than pistons.
Bryan
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