Question: Different racers get different boost readings (more…)

In our drag racing, we did use air to fuel ratio as a controlled value to get the engine into a linear range. That task is an extensive explanation through out writings. The linear range is where the engine is completely predictable. We achieved that very well in our racing. (more…)

Congrats to Scott Williamson for great result reported as follows:

“… I raced last weekend at the Jegs Cajun Sports Nationals (more…)

A blown nitro ford combo was reviewed that was run for a year with no breakage, no burned pistons, and no other problems associated with nitro. An extensive analysis tech info may follow if there is interest. Let us know.

Message: in your fuel injection book, you show a vacuum gauge with a telltale,
do you know where to obtain one of these gauges? KS

It is not a vacuum gage but a pressure gage. You probably
want a 0-200 psi, liquid filled, tattle tale gage. (more…)

Question: Effect of lowering blower overdrive?? More or less power?
Bob?s answer: A trend now is gearing the blower to the racetrack. That is done with rear end gearing, tire size, shift point, and blower overdrive. Adjustment of any of those will change the speed attained by the blower at the end of the drag race or the straightaway.
(more…)

Question: Fuel injection adjustment with launch controls for a torque converter racecar

Answer: When a mechanical fuel injection throttle is part open, such as in preparation for launching from the starting line using throttle control setups, the air to fuel ratio is dependent on that throttle position at the time just before the launch. (more…)

Question: Can we put an 8-71 blower on a high output, normally aspirated Big Block V-8 with very high compression ratio (15 to 1)?
Answer: The detonation can be controlled with enrichment and air to fuel ratio control, theoretically regardless of the compression ratio. However, I am not sure about the mechanical strength of the components.? With that real high compression using a blower and a wedge head, the power stroke starts on one side of the dome. If you are using short skirt pistons or pistons that are not full circumference at or below the wrist pin (typical of normally aspirated high output engines), you may have a problem with skirt deflection, breaking a piston, or galling it. An 8-71 Roots blower, at 10% overdrive, theoretically pumps the same amount of air as an engine approaching 900 cubic inches. The math for that is in Fuel Injection Racing Secrets. Stuffing that amount of air into your BB engine gets a lot of boost and loading. FYI; Our book 5000 Horsepower on Methanol provides information about actual compression ratio with supercharging including simple math on how to determine it.

Question: How did you dial in your mechanical fuel injection setup for bracket racing?
Answer: Our tune-up is set up to be in a linear range. That is when we increase the shift point, our ET is proportionately lower. When we lower our shift point, our ET is proportionately higher.? That is a result of many characteristics from our combination, some intentional and some accidental.

I recall a setup many years ago that was not linear. If you raised the shift point beyond a certain point, you slowed down. The cylinder heads were small and acted as the limiting factor in the combination.

The subject of linear is an extensive one. Keeping everything moderate is a good step in that direction: moderate timing, launch point, shift point, and fuel enrichment. In our case, we know what our air to fuel ratio is from jet area and air calculations from Fuel Injection Racing Secrets. We know our rich air to fuel ratio limit and our lean air to fuel ratio limit and we keep in the middle. It is difficult to get there without record keeping and some calculations or data measurements. And we found that method to be very repeatable year after year after year. And once we found it, we race in that range and never had to recalculate or find it again.

Question: How do you get consistency in an ET bracket drag racer with fuel injection?
Answer: A consistent racecar setup is probably as difficult to do as other performance goals such as all out performance in open ended racing classses. In our ET bracket case, we worked towards a LINEAR setup. That result is one in which the shift point determined the ET. A higher shift point results in a faster ET, and a lower shift point results in a slower ET, and in a relatively proportional manner. With this setup, our life became simple. That is not always the case in many combinations. Many are not linear. I often see race vehicles where the shift point is not known or it is changed with unpredictable ET results. In our case, our fuel injection high speed bypass opening was conflicting with our shift point. Changing only the main bypass jet caused a whole lot of changes to the setup: different air to fuel ratio, different system pressure, different high speed opening point, different ET, etc. Fuel Injection Racing Secrets describes a lot of what we did to sort out those variables. And that is where tuning fuel injection got to be a lot of fun. With that knowledge, it becomes interesting and customized to the individual tuner and race vehicle as well.

FOOTNOTE: A linear setup involves building and engine that does not push the design limit of its components. Fore example, the intake and exhaust flow are not pushed to the limit. When either one is at the limit, pushing the engine power further up with engine speed often becomes non-linear. That is it noses over at higher speeds. Modulating the ET with engine speed becomes difficult.