HOW ACCURATE ARE THE FACTORY TACHS

Thinking of finding & putting in a factory tach in my 67 barracuda. How accurate are they ?

Anything that uses a mechanical meter is subject to a fair amount of inaccuracy, especially as old as these are. There are LOTS of room for error, including temperature and humidity changes, variations in the circuit components, as well as changes in the circuit components do to aging, temperature, etc. And the meter itself. Just static electricity on the face can give problems. Should I bother to mention these get beat to $hxt with bumps and the rest of it? Some? Many? newer tachs like autometer do not use the same kind of meter movement as "in the old days." I would guess Autometer uses a stepper motor movement, as when you shut them off, they "stick" at whatever RPM the engine was turning.

For what it worth, on restore I went back to my factory tach with the RTE upgrade board. It seems just as good as the Super Sun II on the column I dished. My standards may be lower but sure seems to be fine! If using a factory piece make sure you make it compatible to the ignition used!

I was looking at the replacement tach at Classic industries that has modern internals. I understand they are more accurate than the original and look the same. I don't have a factory tach option.

B'cuda said:

I was looking at the replacement tach at Classic industries that has modern internals. I understand they are more accurate than the original and look the same.

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I don’t know about the originals, but the reproduction tach I had was terrible in both accuracy and quality. I pulled it and replaced it with a modified SW tach.

B'cuda said:

I was looking at the replacement tach at Classic industries that has modern internals. I understand they are more accurate than the original and look the same.

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Get the board and do it yourself. Fairly easy deal. What they sell is basically a stock unit with the upgraded internals. The font may not match, depending on year!

I run an original tach works fine. I also have the a new classic repop one that I just cant get myself to install in one of my cars, going to sell it. I rather just but an old school one in that spot.

a lot of racers will tell you any electrical tach sucks for accuracy, so use what you like

kursplat said:

a lot of racers will tell you any electrical tach sucks for accuracy, so use what you like

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Agree, but the purpose?

1969383S said:

Agree, but the purpose?

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of my post? just to say run what make him happy and don't worry about it. unless he has another one to hook up to that he knows is correct, he might never know the one he uses isn't.

The rt-eng.com tach board has a built in calibrator at 1,000 and 4,000 rpm. I've compared my factory tach with the rt-eng.com to my friends timing light tach at idle and rev to about 2,000 and it seems accurate.

I'm a stickler for originality, I would buy the upgraded board and install it. But depends on type of ignition you are going to run.
Fyi not sure if you have a 67 tach or not, but 67 is one year only. The insides are a little different then 68/9 as well.

IMO
for a streeter;
never mind the accuracy,the factory location is terrible.
To see it, you have to take your eyes off the road, and re-focus, and your eyes have to readjust to the different lighting.
Then, you look back to see where you are going, and your eyes have to readjust again.As your eyes get older, it takes longer for them to do this.
Top of second gear might be 90 mph, and you are moving at 132 feet per second. Even with young eyes, this business might take .25 second/33ft, to .5 second/66 feet. A two-lane hiway is 24 ft wide,36 with graveled shoulders up here in Manitoba.How do you feel about that?
IMO
the tach should be on top of the dash, in or nearly in, your line of sight. and with a shift light, so you never have to focus on it. And if you're buying new, I recommend a 3.75 inch 270* sweep, with rpm suited to your redline. THat way you get the best resolution. Those big racing tachs are mostly 11,000 or 8000 rpm jobs; and street-engines are mostly 5000 to 6000, occasionally 6500
But for a streeter, it doesn't have to be particularly accurate, cause you probably don't have a dyno chart anyway, so you are just guessing about when to shift. And even if you knew where the power plateau was, it can be 300/400 rpm wide, which at the top of second gear might be 6 to 8 mph wide........ so, then, you might as well just mark the speed-O meter,lol, and use it.
Honestly; I rarely look at my tach. I just floor it and let her buck. Somewhere between 5 and 6 seconds later, the car is getting close to speeding, so I shift into second and shut down.
My cheap tach has a rev-limiter in it, that I find very useful as a cruise control. I set it to whatever rpm gets me 100kph/62 mph and that eliminates the possibility of me getting a speeding ticket. Well it outta.... and it must be working, cuz that car has never since it first rolled out in 1999,got me a speeding ticket.
It has a tiny adjustable shift light too, which I mostly ignore and drive right on thru; it seems like I got some of my Momma's rebelliousness in me.
Nice tach, but mostly jewelry.

B'cuda said:

I was looking at the replacement tach at Classic industries that has modern internals. I understand they are more accurate than the original and look the same. I don't have a factory tach option.

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I put one of the Classic Industries reproduction tach in my 68 Barracuda. I had seen some online comments that they were jumpy and not accurate. However mine works fine. The response is smooth and the rpm matches to my shift light. The part has a one year warranty so if it is bad out of the box or in use you have some coverage.

im going to be running all MSD ignition the barracuda is a 67 just thought it would be nice to have some sort of tach better than nothing id prefer an aftermarket tach but I don't want to put any holes in my dash I don't have a tach so ill have to buy one let me ask this is it possible to buy a "factory" tach install the upgrade board & add a shift light ? Put the light off to the side alittle so I see the light come on & not have to keep looking at the tach no its not a race car but I do run my cars hard at times that's what they are built for

Here is my solution, hard used and still ticking. Clearly I subscribe to AJs explanation.

my68barracuda said:

I put one of the Classic Industries reproduction tach in my 68 Barracuda. I had seen some online comments that they were jumpy and not accurate. However mine works fine. The response is smooth and the rpm matches to my shift light. The part has a one year warranty so if it is bad out of the box or in use you have some coverage.

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The re-pop I had in my duster worked fine for awhile too, then started bouncing all over the place after a year or so. It was never particularly accurate though.

This is what I did with mine, it works far better than the repop ever did and doesn’t really look out of place in the original spot. The font and printing of the face on the repop wasn’t an exact match either.

Want to put and aftermarket tach in a rallye dash

1969383S said:

For what it worth, on restore I went back to my factory tach with the RTE upgrade board. It seems just as good as the Super Sun II on the column I dished. My standards may be lower but sure seems to be fine! If using a factory piece make sure you make it compatible to the ignition used!

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I used the RTE upgrade as well. It works and moves the needle, probably not all that accurate but I don't really care. I'm happy just to see the thing somewhat functional.

I think most folks would be shocked to know their tach’s are not correct, at probably several different RPM ranges.

I have a tach in the shop that is off almost 200 RPM at 1100 RPM. It’s caught up at 1500 and stays that way until 8k. That’s an Autometer monster tach.

Had another Autometer in my race car, and it was off at idle by 100 RPM and about 300-400 at 8500. These aren’t cheap tachs.

I can now test a tach when I test an ignition with the tach on my distributor machine. Some of my digital Mallory ignition boxes have a tach test feature as well.

It’s another thing that should be tested, because if the tach is wrong, it changes things.