I was just wondering how accurate the stock tachometer is ? I've been told by numerous people that it isnt accurate and gets less accurate the higher the rev is. The number I was given was that it was off by about 500 rpm.

I just recently made a video of me hitting the redline like 5 times in a short cruise just to show what my car sounds like and how well it accelerates. I hit 7500 rpm once or twice , hit 7200 rpm or so once , and hit 7600 rpm on a miss shift (only time i ever done this in the rx7).


So according to this if its 500 rpms off I could of been shifting at 8000rpm and not actually 7500rpm ? Also when I hit 7600 during the missshift that could actually be 8100 rpm ?

Sorry this just all seems weird, makes me feel like im redlining my car way higher than I would think I am if the gauge is reading 500 rpms lower than it should be and I dont want to be revving higher than what I think I am.

Whats the best solution to get 100% accurate tach reading ? Get a tach with shift light from autometer and/or get an safc that gives the tach reading. (the person that told me the tach is off was going by his safc rpm readings and comparing to the stock tach)

edit - I wouldnt think me redlining my car is bad, but I do think it would be bad to be revving the car higher than 7500 rpm (thats the highest I want to go). So if that other guy is right, then Id have to be shifting at only 7000rpm to ensure Im not actually hitting over 7500 rpm (incase the tach is off by 500rpm), it just seems crazy to think the tach is that far off.

Link to the video I made - http://youtube.com/watch?v=9HLUQxFr700

 

My stock tach is pretty far off.

It is off by a percentage like a speedo would be, so it isn't much at idle and a lot more at redline.

I check it against the Haltech display and its data logs.

From what I remember, mine is about 50-100rpm off at idle and 200 rpm off by 3,000rpm.

 

based on my SAFC, i'd say my tach is off by around 200rpm by redline (7000 rpm)

 

So I guess I could be at higher rpm than I think I actually am, I think getting a autometer tach and safc wouldnt be a bad idea for the future.

I'd like to see how far off mine is and actually know the real rpm the engine is at so I can shift where I really want to.

 

The stock tach is about 270 off according to the Haltech, stock reads 3K, haltech says 2730 or so-mine is always off by this amount, pretty minor IMO

 

Well if you are redlining the car I wouldnt think its minor, because if youre over revving the car past where the ecu would normally limit (8000rpm) , that could be bad in my opinion. I dont think revving up to 8000 is a good thing but you can be and not even know it if your tach is off that much, and if you actually goto where 8000 is then cant you actually be going beyond 8000 is the tach is reading lower ? Or will it cut out at 7700rpm if the tach is off by 300 rpm ? Because if you can get to 8000 and youre actually at 8300rpm, i wouldnt think that is good for the motor.

 

You can adjust it to be quite accurate at one point if you have haltech or some other accurate external tach.

I adjusted mine to match haltech at 6000 rpm, it seems to hold in the low rpms as well.

 

What do you mean adjust it ? How do you do that ?

I have no external tach , or safc or anything that lists rpm other than my stock tach for now.

 

Well once you figure out thats its off by 300, 8000 rpms is 7700, pretty easy to remember, I dont rev that high, too much money spent to risk extreme revs-If your anywhere in the 8000 range, I doubt 300 rpms will be what killed it, its the 8000 rpms your turning

 

you have to pull apart the instrument cluster, and take out the tach. There are a couple potentiometers on the back of it. Yours most likely have some glue on them from the factory to keep them from moving, so that has to be removed.

Then, what I did was reassemble everything, but keep it loose so icould adjust the pots. THen i started the car and revved to 6K on the haltech, then turned the pot till tach read 6k right on.

 

Interesting, sounds like something I might mess up on doing though..I'm not one to mess with taking apart electronics. I would probably rather go with an aftermarket tach but if i could get the stock tach 100% accurate according to an safc or something that would be pretty nice.

 

So my JDM Rx7 has this Tech-o-meter in it. Would this be more accurate than stock?



BTW, anybody know if FEED has a site. I havent being able to find anything.

Ben

 

I want that dash so bad.

 

mine is as just like everyone else, i am also about 200-300rpm off.

 

The tach and the ECU are completely unrelated. The ECU gets accurate engine speed info from the CAS, so it doesn't matter what the tach says, the ECU's limiter will always work at the right time.

 

Thanks for clearing that up, is the stock rev limit on s4 na 8000rpm or is it 7800 ?

 

Answer is accurate enough...

 

S4 fuel cut is 7,800 rpm

 

Well i must have not ever hit it yet because ive hit 7500 rpm shifting when i redline and 7600rpm once misshifting and it never seemed to hit any limiter maybe my tach isnt very far off

 

I run an RE-amemiya 10K tach, it looks very similar. I guess i will spill their beans and tell you guys these are just stock tachs with a faceplate and the electronics readjusted to match the new faceplate. The electronics on the RE one is IDENTICAL to the stock, just they dont have glue on the pots you need to adjust.

Again, can be accurate if calibrated. When i got my RE it was way off, like 1000 rpm off. Now its dead on.