The racer is one step closer to setting up a tuning plan for density altitude like we wrote about throughout our technical manuals; the racer can log onto www.airdensityonline.com and get current air density and density altitude for many race sites throughout the US; (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…)
QUESTION: Do any of your books help in areas of tuning with using O2 sensors? I am needing some what of a baseline for a good tuneup using the correct nozzles, pills to help with getting the most or should I say most consistent in drag race ET’s. Of course everything being the same.
Thanks for replying, R. in Texas
Hi R in Texas,
Thanks for your inquiry. Our Jetting for Racing Mechanical Fuel Injection … book has info on O2 sensors including accuracy limits.
REPEATABILITY VS ACCURACY: O2 sensors are a great tool, however, the accuracy (especially for methanol or ethanol) and repeatability may be issues. Accuracy is less of an issue if they are repeatable. (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.
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.
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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.
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
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.