Aftermarket Tacho Settings.

[flamingheads]

I bought a KE70 yesterday, with a worked 4k. It has a monster tacho, which I'm moving to replace the clock in the dash.

On the back of the tacho it has a switch with three setting marked 4 6 8. I assume these are different settings for 4, 6 & 8 cylinder cars. The tacho was set on 6 and if I change it to 4 it seems like the revs it's reading are too high. Also the needle seems pretty jumpy/shaky when it's set on 6.

I know I've read about this somewhere before but couldn't find the info. So what's the right setting for it before I seal it inside the dash?

[philbey]

You definitely need it on 4 if it's a 4 cylinder. When you say too high, what is "too high"

[flamingheads]

When the tacho is set on 4, if I sit in the car and rev it to what sounds like 3-4000 rpm and it says 6000.

When I was driving the car with the tacho was set on 6, it got its power at about 4000 rpm and went up to about 6500rpm. If I set the tacho to 4 it says the revs are higher. That would mean it's getting power at 4500 or so and redlining at 7 or 7500rpm. If I set it on 8 it says the revs are lower.

The engine is a 4K and mods I know of are: a cam, the engine has been bored an unknown amount, I think it has a 3K head, 4 to 1 extractors & exhaust.

[jono1986]

What brand is the tacho, cause the $40 one that i have for my car jumps up and down about 150 rpm and also revs 200rpm higher than it really is.

[flamingheads]

The only writing I can find is NEO. I used to have a $40 tacho that worked fine.

 

Could it be loose wires or something?

Edited April 20, 2010 by flamingheads

[flamingheads]

What speeds should I be doing in different gears eg. 60kpm in 4th = 3000rpm etc. so I can figure it out by driving?

[towe001]

How about at idle ? Whats it sitting at ?

I'm pretty sure i had a link for something else but

http://www.locost7.info/gearcalc.php

Its download program about 516k

You just plug in your

>tire diameter

>gearbox ratios - http://www.rollaclub.com/faq/index.php?title=Manual_Gearbox

>Final (diff) ratio - find the code on the build plate in the engine bay and look here http://www.rollaclub.com/faq/index.php?tit...ferential_Gears for the ratio. Unless the diff has been screwed with....

 

and it'll spit back what the road speed is for each gear

 

Either that or find one (tacho) that's tested.

 

EDit - just a little house work

Edited April 20, 2010 by towe001

[Taz_Rx]

If your points are open up enough that can cause the needle to jump around a bit.

[philbey]

Electronic dizzy (hall effect) will also mess with the signal causing it to jump around.

 

If it's worth the effort, I would use towe001's method to check it. Your ear probably hasn't been calibrated for rpm.

 

If it does have elec dizzy etc, you can usually muck around with a resistor in the circuit to modify the signal and prevent the jumping around. Google it.

[flamingheads]

Thanks for the info.

 

Towe that's some good info but I couldn't find the diff code in the engine bay. I'm sure I'm just not seeing it but it doesn't seem to be on either of the plates on the firewall.

 

I think I'll just live with a jumpy tacho for now and check it out later if its too much of a pain.

 

At idle, when the tacho is set on 4 it says about 1200rpm, 6 says 1000 8 says 800.

 

I'm putting the dash back together so I'll set it on 4 and assume it's right and worry about how high I'm revving the car. With the mods done it shouldn't change the redline at all should it? Unless it has a wild cam that gives it power at like 5000rpm.

 

Sorry for the stupid questions and thanks for the help so far guys.

[greenmac80]

i had a cheap one as well a type r and it did the exact same thing. set it to 8 cyl and you'll find that its correct.

[flamingheads]

8 kind of seemed more right.

Why is 8 right?

[towe001]

:dance: yeah good question. Always thought that being set on the 8 cylinder the tacho would be reading 8 pulses from the coil whereas on the 4 cylinder setting its reading only the 4 pulses.

 

Thats it the build plate. It'll tell you what the motor that should be in the car, frame number, colour/trim, trans/axle <- and this what you'll be after (axle code last three digits and possibly a letter (more then likely the letter "U") before the three numbers).

[flamingheads]

I looked at that plate and it didn't have a code or anything after trans/axle. Just the colour/trim code and whatever the bottom one was.

[towe001]

Well that sucks

 

Another way to figure out the diff ratio - apart from pulling it apart and counting teeth and dividing them is to place chocks at the front wheels so the car doesn't roll, jack a back corner up, have the transmission in neutral, stick a length of string to the prop shaft, spin the lifted wheel one complete revolution and count the number of times the string went past the spot where it was stuck to the shaft. Its rough but it works.

 

The bottom one is Plant/GVW - where the car was built / Gross Vehicle Weight