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.

Question: We want to race with a Roots blower. There are standard Roots blower bottom openings, and there are smaller ones. Some with a small pie shape towards the front. What is the influence from the size of blower output opening
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In addition to the math in the FI book, a lot of text and editorial are provided about fuel injection. However, the correspondence that follows is from a ‘Fuel Injection Book’ customer. It is a demonstration of the extent that a tuner can get into from the FI book math section. (more…)

Below is an email correspondence I had with Jimmy:

Hi Bob, I talked to you last week through email about doing a MFI Enderle Birdcatcher on gas on the street … I will use your book to set up and tune my system. But i have a question that may not be covered in your book. I hate the way the air filters look for the hats, it hides the butterflies and i want mine to be seen. I talked to a guy that designed an inside air filter and he said it worked good for short while until the cotton between the wire mesh got soaked with fuel then it cut air flow way down. He said even though the blower is sucking air and fuel down you still get fuel bouncing around in the hat. My question is this: they sell all steel air filters for cars now, what if I designed an all steel (stainless) air filter to be mounted right behind the butterflies would you think that might work? That way if fuel did get on it the air flow would keep it blown through. This is a prostreet car I will drive only about twice a month to the local car shows we are talking about only driving in pretty weather and I would take the filter out for the race track. I was just trying to figure a way to run a filter on it without running one of those front mount filters. I also see people running those BDS efi bugcatchers with no air filters, there is a guy running a blown coupe like that and he said he is not worried about running with no air filter no more than he drives it. I’m running a blown BBC with a Littlefied 871, the blower is set up for gas on the street with no teflon strips so its not real tight. I just don’t want to score the inside of my blower and cylinders all up. No more than I drive it on the street it may not be a big concern. Thanks for any advice you can spare…J

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Message: in your 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. I was told McMaster has them. McMaster is a large gage supplier. I did a web search awhile back and was able to locate them. I do not have any further info from that.

In addition, locate the gage connection after the barrel valve to get the injector pressure after the bypasses and the pump relief pressure. You can tie into any extra port in the distribution block or tap into the block if no added ports are available. Many do not firmly connect the gage to the engine. It is left hanging loose so that engine vibrations will not destroy it.

The following comes from JB in the UK:
Just a quick note to say thankyou for producing a fantastic source of information with the Fuel Injection Secrets book. (more…)

After his FIRST season with mechanical fuel injection on a BLOWN GAS bracket dragster, one of our previous Fuel Injection Racing Secrets book customers wrote the following:

“This combination … can be driven to the staging lanes from the pit, shutdown, then restarted by the driver without assistance, (more…)

One of our customers ran 6.8 second quarter mile time in a match race funnycar at a racetrack that was 50′ above sea level (high air density).? Then he towed to a racetrack at 5,500 feet above sea level (low air density).? Using the math in the Fuel Injection Racing Secrets book and the 5000 Horsepower on Methanol book, his setup was computed for the high elevation track with low air density.? The setup from the computation was put into the racecar in preparaion for the high elevation event.? Then, off the trailer, he ran 6.8 seconds and was low qualifier for that match race event.

This illustrates the importance of tuning your car for it’s location. Higher altitudes have less oxygen in the atmosphere so the air-to-fuel ratio needs to be adjusted accordingly. Otherwise the same engine can perform extremely well or bad depending on the atmospheric conditions at the track.