Highlights
Specifications
- Keihin carburetor with accelerator pump
- Air-fuel ratio approx. 10.5:1 (WOT)
- VP-C23 gasoline (123 octane)
Modifications
- Custom needle jet & additional fuel jet for high-RPM
- Anti-detonation injection (ADI) system for additional water/methanol
It’s critical that supercharged engines never run lean of fuel.
Carburetor
The Red Baron uses a Keihin carburetor with a custom jet needle and additional high-power fuel circuit at high-RPM (more below). The Keihin carburetor has a large enough diameter to supply fuel for 80-90 HP, yet small enough to create fuel atomization with high velocity air flow. It also has an accelerator pump which is critical during sudden throttle openings to maintain the rich air-fuel mixture.
The fuel pump supplies fuel to the carburetor at 3 – 4 psi at all times. The air-fuel ratio sits between 10:1 and 10.5:1 at full-throttle with VP- C23 leaded race gasoline (123 octane). The Red Baron runs rich for power, to cool the supercharger, and to cool the compression-heated intake air charge which reduces detonation frequency and intensity (more below).
High-Power Fuel Circuit
The Red Baron has a fuel pump to the carburetor which also has an additional high-power jet, both to ensure the supercharged engine never runs lean.
Brake-specific fuel consumption (BSFC) is a measure of the rate of fuel consumption divided by the power produced. The BSFC “rule of thumb” for air-cooled, two valve, spark ignition engines is 0.5 pounds of fuel per horsepower per hour (lb/hp/hr). With the high-power fuel circuit, The Red Baron runs 0.55 – 0.60 lb/hp/hr, which is in line with accepted supercharged engine practice.
Anti-Detonation Injection
First used at Bonneville, the anti-detonation injection (ADI) system injects water and/or methanol into the intake air and fuel stream (post-carburetor, Fig. 2).
The additional water/methanol is really a thermal control modification rather than a power modification. Water and methanol both have high latent heat of vaporization (i.e., it requires a lot of energy to evaporate). The water/methanol injection counteracts intake compression heating caused by the supercharger by absorbing the additional thermal energy during evaporation.
Fig. 2. Connection from carburetor to supercharger with ADI nozzle installed