tacho calibration?
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tacho calibration?
Hi All , my truck is a 83 f100 bullnose with retrofitted 6.9/c6/3,55.
It used to have a 250 ci six cylinder petrol engine , and my question is if the tacho is capable of being recalibrated to show the diesel rpms accurately. At our legal open road speed of 100 km/hr or about 62 mph the tach is showing something like 3100 rpm 3.55 ratio and 31/10.5/15 tyre.I'm guessing it should be somewhere in the order of 2400 rpm. Wrong?
It used to have a 250 ci six cylinder petrol engine , and my question is if the tacho is capable of being recalibrated to show the diesel rpms accurately. At our legal open road speed of 100 km/hr or about 62 mph the tach is showing something like 3100 rpm 3.55 ratio and 31/10.5/15 tyre.I'm guessing it should be somewhere in the order of 2400 rpm. Wrong?
Lead Driver
Joined: Oct 2003
Posts: 8,476
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From: Madison, WI
It's not a diesel vs. gas issue, it's a 6-cylinder vs. 8-cylinder issue. Multiply 3100 by 3/4, and you get 2325, which is probably about right for 100 km/h, 3.55s. The tach circuit is fairly simple; sensor, wires, tach head. It could be simply that a tach head from an 8-cylinder (gas or diesel) engine truck will solve the problem for you.
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very likely
Now that it has been stated it seems obvious. Thanks for that pearl. If I can't find one i'm certainly capable of the arithmetic. This is a very helpful forum, especially considering that there maybe 2 or 3 of these beasts in a 300 mile circle down here
Logistics Pro
Joined: Sep 2007
Posts: 3,737
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From: Western Mass
It's not a diesel vs. gas issue, it's a 6-cylinder vs. 8-cylinder issue. Multiply 3100 by 3/4, and you get 2325, which is probably about right for 100 km/h, 3.55s. The tach circuit is fairly simple; sensor, wires, tach head. It could be simply that a tach head from an 8-cylinder (gas or diesel) engine truck will solve the problem for you.
A diesel tach might solve your issue, but not knowing the wiring differences between the two setups, I can't much more. What I mean is, are the wiring harnesses setup so that if engines are swapped, the tach signal still goes to the same place? Its possible the person that did the swap had to change some other things around to get the tach to function at all.
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