Tachometer conversion to 4K for low-RPM engines

I've always wanted a tachometer that was suited to my work-truck's low-end cam, automatic transmission, and mizerly driving habits. My interest is more in tuning, and getting the most out of my fuel money.

Racing tachometer are pretty silly for my needs, and most of the instrument sweep is wasted. Since most tach's have a switch on the back for 4,6 or 8 cylinders, I decided to set it on the 4-cylinder position, and change the numbers on the face. Also, I don't like a bunch of gibberish detracting from a clean, and informative look.

I had a challenge or two. Finding a Black-out marker/paint, and adding new letters.

Here's the album:
Tachometer 4K Conversion by 1972-34ton | Ford-Trucks.com



Tachometer with 8K face modified with new numbers and blacked-out 'junk'. I like the cleaner look, and more realistic values of engine rotation shown.



On the other hand, I did not get the background blackout just right. My first try with a normal fine Sharpie was a little on the shiny side. Coverage was adequate, but not ideal. My S.O. was great and suggested this marker, but we thought in some light it looked rough.



The black-out ink used is OK, but there are better alternatives. Your light angle and source may make a difference. This is just a work truck, so I didn't worry too much.




Our local art store was very handy with markers, and suggested some better alternatives to the Sharpie.




The Montana marker was the best match, as it had some sheen to it. A flatter and denser mark was made by the Sharpie poster paint.
See this link for the Montana marker: https://www.artsupplywarehouse.com/p...l.php?id=53879 (2015-10-27)




By all accounts, these stick-on letters are the easiest way to get good numbers on the face. The adhesive is aggressive, and it is a one-shot deal to align the letters.

I will update this with results after installation.

Luck.

 

Interesting mod!


For the blackest of black, consider using india black which is an ink used in artist/architectural renderings.

 

How would I make a 6K tach for my 300 IL 6?
Baja

 

It depends how many rpm your tach will measure now. If you have an 8k tach and switch it from 6 cylinder mode to 4 cylinder mode, it will now read 8k rpm when the engine is at 5,333 rpm. Meaning when you painted the new gauge it would go from 0 to 5300 rpm. it changes based on what rpm the tach is capable of to begin with.

I did a quick calculation on a bathroom break




Someone please correct me if I made a mistake lol

 

I wonder if there is a 12K tach that has a three-cylinder setting?

Getting the index marking to be correct would probably require printing up a new face plate. Not a bad option. You can produce one with backlight show-through, but the technique is beyond me. I see directions on the internet, and services that do the custom work. The price is not too crazy. Check the farm tractor restoration sites, I saw something there. You will need a graphics buddy to assist.
Let us know what you find.
Kevin

 

I currently have a '70's era Sun Super tach, that has a 6K faceplate, but it finally quit after 46 years... Hey, stuff just doesn't last any more... (humor, hope you see the funny part), anyway, some months ago, I purchased a newer Sun Super tach, with a 8K faceplate.

I am thinking that if I can open the new tach, can I just switch faceplates? On the "6" setting, all should be well...?? Hope so, and thoughts??

Baja

 

Me LIKEY.

Good job.

 

Some of the beginners might be getting confused by this conversation.

This particular tachometer only has a 4-6-8 cylinder switch on the back.
The long-stoke, work-truck engines won't use half the tachometer 'sweep' of an 8K meter. We only turn the stock engine to maybe 4K (4,000 Revolutions Per Minute).

There are tachometers available that can be set for any number of cylinders. 1-2-4-6-8-10-12 are common. (Some expensive ones can even be tuned and adjusted to whatever strange pulse might be available.)

Fortunately, our original trucks are the simple old coil-type, with a negative coil terminal supplying the 'pulse'. For 8-cyl engines, choosing the setting on the back of the tach to 4-cylinder, will double the reading on the tachometer face. If you don't mind the 'lie', you can get twice the movement from the needle. 2,000 RPM would show up as 4,000 RPM. The whole meter face provides information this way.

In the case of a 6-cylinder engine and this kind of tach, just changing the face (numbers, index, .etc) won't change the needle action proportionately. In a relative way, it doesn't matter. Higher is faster RPM. You can get a sense of what-is-what by comparing to another tach source, such as your tune-up device. Most people wouldn't know the difference, but you would, and you can use the information knowing it is a relative measurement.

In the case of a 6-cylinder engine, I believe that a 12-cylinder setting, on the appropriate tachometer movement, could be set to 6-cylinders. Then changing the numbers like I did would work fine. Black-out the old numbers, and re-number it skipping over every other major index mark.

I have seen older tachometers on Eb*y that are 4K or 6K RPM. So that might be the simple way to go. Caution: some are fed by the alternator (?), or require an odd electric sensor to be used. These are usually for boats and diesels. You don't want them for a gas engine. Look for the automotive coil-hookup style.

 

Thanks '72, very good explanation for those of us that may be "Tricklicity" challenged. My word, but you get the idea.. Mostly I used the old 6K tack in my truck, to maximize fuel economy. Any more, its just another toy to fill a hole in the instrument panel.
I have a newer Sun 8 or 10K and can probably put it on 4 cyl, and do the math conversion. Getting the tach open is tricky, at lest it was for my old one.. The chrome rim is crimped on, and then the face was crimped also, and made of very thin steel.. Some dental tools were handy, but I still cobbled it a bit, and not sure how the factory ever opens them? Any shop tricks you know, will be greatly appreciated if you can pass them on.. Thanks

Baja

 

Baja, this model has a twist-off plastic ring around the face, and plastic shell housing.

And the original face looked like this:


Original

Kevin

 

That's handy, do you know if they make one with a chrome ring, as all the other gauges have the chrome ring.. My instrument panel and gauges are from a '68 F 600, so I have the 'In Dash' style, missing only the vacuum gauge. The old 3- 3/8" Sun Super tach fit right in where the factory Diesel tach would have been.. I like the old school look, with that aircraft style from WWII.

BTW, my father-in-law was a flier in WWII, and was shot down 3 times in the Pacific. He flew a Gruman Avenger, and once he landed with just over 400 holes in his plane. The crew worked all night, and he flew it the very next day, with over 400 patches.. and that was before duct tape.. We've got the book, with the photos, even some of his crew doing the patch job.. It's called "Clear the Decks"..

Those were real men, with 'Basket *****'

Baja

 

Hi 1972-34ton,

I got your message through email about the air cleaner assembly on a 1980 f150... I couldn't respond through the forum messaging system hence this message.

To answer your question:

I don't see why it wouldn't work. I beleive the diameter of the opening on the 2100 car is the same as the 2150 carb, so it should drop right on top.

The only peripherals that are needed are a tube leading from the snorkel down to the exhaust manifold shroud (warm air supply when the engine is cold) and a vacuum port stemming from the manifold to create pressure in the system.

Let me know if you have any questions.

 

I received your second email...

Yes, there is a thermostatic strip on the top of the air cleaner...mine is rusted but the fillament looks ok. When I have a chance over the weekend, I will try to take some pics and grab part identification.