the dwell just has one position and 3 scales, but i can make my own scale to read in GPH. the tach has three positions of course. the dwell of the injector pulse is directly related to fuel flow per unit time. Dwell is not directly related to RPM, that fooled me for a while. when i am stationary this KEL mileage computer reads in GPH. and i can set no load idle at 1k, 2k ,3k, 4k, RPM for example and the injector dwell tracks with the GPH not with the RPM. If i had an extra injector hooked to the fuel line and squirting in a graduated cylinder and wired up to one injector. And i ran my engine for 6 minutes at a constant dwell. Then i could calculate my fuel usage per hour at that dwell. And then when i'm out driving at that dwell number i would still be using that amount of fuel per hour. Amount of fuel sprayed in 6 minutes at steady speed X 10 X the number of injectors=fuel per hour. If i'm driving at 60 miles per hour then i'm going one mile a minute. From the previous sentence GPH / 60 = GPM. At 60 miles per hour, that gives me gallons per mile. Invert that and i have miles per gallon. i can figure it out once make up table to hang on the dash. does not matter what gear or RPM's. my dig is my meter has a small face and i can't see small changes. i am going to look at bigger meters and the digital duty cycle meters some more, but the least expensive digital i saw with a quick google was $60. my DVM doesn't have duty cycle. actually my dwell meter just happens to be 1 milliamp. full scale so i could tap into that and read thousands of an amp. on my DVM. i got to take the wire off one side of the milliamp meter and connect the DVM in series with it.
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