Belly Tank Build Diary

[Jack Gifford]

... I really like Hall Effect sensors...I am using a reverse biased gear tooth sensor...

Gear tooth sensors generally have only two wires. Hall effect transistors require three wires (as do all transistors). And Hall effect transistors respond to a magnetic field, not to ferrous metal. So- how do these "gear tooth sensors" function?

[Mike Brown]

... I really like Hall Effect sensors...I am using a reverse biased gear tooth sensor...

Gear tooth sensors generally have only two wires. Hall effect transistors require three wires (as do all transistors). And Hall effect transistors respond to a magnetic field, not to ferrous metal. So- how do these "gear tooth sensors" function?

Jack, I believe the two wire gear tooth sensors that you are referring to are simply coils of wire called Variable Reluctance sensors.  The target is magnetic and as it moves past the sensor an AC signal is created.  They are very rugged and the least expensive of the sensors.  There are problems with VR signals as I see them.  The signal is a slowly rising and falling AC output so the input typically has a comparator to help shape the signal.  The VR output is also a linear AC alternator, the faster the target moves the larger the signal and conversely no movement equals no signal.  The sensors that I like use Hall Effect elements that do detect a magnetic field however in this particular sensor there is a magnet opposite the actual sensing element so as a ferrous target passes by the sensing element it detects the change in the magnetic field.  It is three wire as it requires 5-24Vdc power for operation.  The output is open collector in that it acts like a switch contact to the negative lead.  The output requires a "pull up" resistor.  In my case I use a 2.2k Ohm resistor to +12V.  This gives me a 0V output when the target is detected and +12V with no target present.  The output is an almost perfect square wave and works with no movement.  This is helpful when setting up.  I use a LED on the output that will illuminate when the target is in range.  It is a good idea to use an oscilloscope to set up a VR sensor in a new application.  I hope that this helps. 

[Mike Brown]

A photo of the sensor for the rear tire speed mounted on the back of the transmission.  I was lucky enough to snap a photo on my phone as it gets more and more difficult to stuff things inside the belly tank body, not much room. 

[SPDRACR]

Looks like the pickup sensor
on my MSD crank trigger

[Jack Gifford]

Thanks Mike for the info. Who is the manufacturer of the sensors you use?

[Mike Brown]

Thanks Mike for the info. Who is the manufacturer of the sensors you use?

I used a version from Microswitch for many years, it is now very pricey.  I have been purchasing this sensor from Ebay.  It is reasonably priced and works well. 

[Mike Brown]

I replaced the coil springs on the rear of the car with the original rubber springs.  When doing calculations, I noticed that the compressed height of the rubber springs was shorter than it should have been for the weight.  My best estimate is that the original spring perches were too small which prevented all of the rubber spring from being utilized.  So, when I reinstalled the rubber springs I added 4" diameter 1/4" thick aluminum plates to the perches.  The compressed height was then much closer to the calculations.  It will be back to the 1/4 mile for test & tune to see how these changes affect performance. 

Of note I did drive the car for a car show a short distance at slow speeds and the wheel speed sensors and calculations worked spot on. 

[ronnieroadster]

Were you able to determine fuel economy on the drive to the show?

[Mike Brown]

Were you able to determine fuel economy on the drive to the show?

Ron, the drive was only from the trailer unloading area to the car show that was on the main street of Morrow Ohio so I did not calculate the fuel economy.  Historically it takes a gallon of VP MS109 for a mile run.  I guess that like the F1 guys I could look at the data log to see what percentage the fuel injectors were operating at and calculate that with the injector capacity (1050cc) versus the revolutions traveled to come up with a fuel economy.  Next weekend I was invited to show the car at the Cincinnati Concours de Elegance (they always need some "filler" cars to make the real show cars look good).  That will be a longer drive from the trailer lot so hopefully I get out of first gear and can get you some better fuel economy data. 

[Stainless1]

Mike, your ECU data probably has a fuel used burried in it  ... although I don't know anyone that looks at MPG on their Bonneville car... but I know Bockscar gets about 5MPG with the 1 liter.... E85 is about 4