The 4.9L engine in my 1986 F150 rarely experiences greater than 2500 RPMs, due to my relaxed driving style [economy minded]. With the factory 6000 RPM tachometer, the needle hardly moved. I replaced it with a tachometer from a 1981 or 1982 F600 with a 370 gasoline engine. It works beautifully!


Look at page #1 of this link: https://www.ford-trucks.com/forums/1...a-chapter.html

 

That's awesome!!

I've seen those lower RPM tachometers, but they were always for diesels. I didn't know they made one that would fit our gas trucks. That's very cool.

Putting a tachometer in my truck is probably one of the best things I've done for it. I can't believe it didn't come with one. (However, I do take it over 4000 semi-regularly, so I need the full 6k. )

 

The diesel ones I looked at were 3500 and 4500 RPM units. The 4500 RPM ones from F250 and F350 trucks have marked yellow and red zones. The 4500 RPM unit from larger trucks has no designated zones. The 3500 RPM unit from a larger truck also had no designated zones.

On the back of the tachometers, the poles for the wiring and the printed circuit looks the same as for the gasoline versions, but if on the left side, it is marked with S+ and S-, the tachometer is for diesel and will not work [as is] for the gasoline engines.

Fellow forum member, Ford F834, found this particular 4000 RPM tachometer.

 

Will those tachs read accurately for a six cylinder engine? Aftermarket tachs usually have a provision to change from an 8 to a six or four - dip switch / cut wire shunt / etc.

 

Yes sir! I marvel at how Ford handled this through the wiring harness enabling the use of the same tachometer [6000 RPM] for our beloved 6 cylinder as well as V8s. On the back of the tachometer are 4 electrical contact points. One goes to a 12V power source, one goes to the coil, the other two are grounds. The six cylinder application requires only one ground and both grounds are used for V8 applications.

With the original 6000 RPM tachometer, @ 70 mph, the tachometer indicated 2000 RPMs [3.08 rear gears and O.D. transmission]. The 4000 RPM tach shows closer to 1950 RPMs. I imagine that the 4000 RPM tachometer is closer to being accurate at that range since one can see more accurately the increments due to the wider sweep of the needle.

The engine idles @ 650-700 RPMs. If I "gun" it, it quickly revs to 2000 RPMs. With the original tachometer, the needle seemed to barely move... now, it is as though it has a much lighter flywheel, in that the same action causes the needle to quickly sweep to 1/2 of its range.

 

Very nice!