After running several different setups over the years and spending hours on the dyno I am just curious as to where the most TRUE signal comes from. I have run everything from the Stock tach to AutoMeter off a MSD Dig6 signal to a Pivot off a coil signal. When I dyno I hook a clip lead to the plug wire. As I have seen 1st hand the stock tach is a joke. Right now its off by 500rpms at 4500rpms compared to my Pivot.
How do stock tach signals compare to the clip on Dyno type as I have never paid attention to it.
Im just trying to figure shift points based on powerband and Im trying to do it as efficiently as possible.
Thanks
-Clint

 

Anyone?

 

i have mine ran off my msd dizzy.

 

I have the helms manual for the civic, was curious about the rpm signal a while ago (something unrelated)

The RPM signal comes straight from the igniter unit, every time theres a spark theres an output. The signal itself should be more accurate than the "inductive pickup" that the dyno uses, but we all know how inaccurate the stock dash is..

I have a fancy multimeter- when i hook that up and set it up right, i get the correct rpm- and there is a significant error all the way up the revs- that gets seemingly worse towards the top of the power band.

Hope that helped...

 

So the closer to the dizzy the more true the signal? I'm running mine off the coil right now so thats probably why its so low compared to the stocker. Even when it was hooked up to the MSD box it was reading a little higher than it does now. Difference's were more like 3oorpms not 500.
Thanks!

 

straight to the ecu is the place place imo..

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by onepoint6i &raquo;</TD></TR><TR><TD CLASS="quote">straight to the ecu is the place place imo..</TD></TR></TABLE>
Isn't that where the stock tach gets its signal from though? And do you think its moreso the tach or the signal that causes the horribly false readings?
If Im getting -500@4000-4500rpms I know the coil signal is great....but Im also using a nice tach.

 

when i had a vafc it was directly to the ecu and read 500 lower than the factory tach, actually currently i have a defi HUD and it reads lower than the factory tach its not the signal thats off; its the factory tach itself...they engineered them purposely like that..

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by onepoint6i &raquo;</TD></TR><TR><TD CLASS="quote">when i had a vafc it was directly to the ecu and read 500 lower than the factory tach, actually currently i have a defi HUD and it reads lower than the factory tach its not the signal thats off; its the factory tach itself...they engineered them purposely like that..</TD></TR></TABLE>

Hahaha....I make things so hard.....I will check my vafc in my DD compared to the stock tach today.
Thanks again!

 

let us know your results

 

Through the EMS (if applicable in your case).

Jason

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by onepoint6i &raquo;</TD></TR><TR><TD CLASS="quote">straight to the ecu is the place place imo..</TD></TR></TABLE>

That makes no difference.

The problem, clint, is that the way the ICM indicates RPM is the same way the coil ground tach works.

All the ICM does is give the coil ground when it needs to spark, and so the tach signal will look like a sqare wave on the signal wire, the circuit in the tach that converts that square wave to an rpm reading has trouble always getting an accurate reading because the rising and falling edges on the signal aren't as sharp as they should be.

You'll get this with any system, all tachs work this way AFAIK, some are just better than others.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mgags7 &raquo;</TD></TR><TR><TD CLASS="quote">
The problem, clint, is that the way the ICM indicates RPM is the same way the coil ground tach works.

All the ICM does is give the coil ground when it needs to spark, and so the tach signal will look like a sqare wave on the signal wire, the circuit in the tach that converts that square wave to an rpm reading has trouble always getting an accurate reading because the rising and falling edges on the signal aren't as sharp as they should be.

You'll get this with any system, all tachs work this way AFAIK, some are just better than others.</TD></TR></TABLE>

Whoa....
Someone knows something about electrical engineering....

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SFWD 1934 &raquo;</TD></TR><TR><TD CLASS="quote">Through the EMS (if applicable in your case).

Jason</TD></TR></TABLE>
I would have thought that to be true but its not. When I was on the dyno, I was making power to ~8200rpms on the Dyno Tach. I in turn set the rev limiter to ~8250rpms on the S300, and when I drove it, the rev-limiter hit at ~8000rpms on the Pivot tach.

Well, I am going to do some testing.
So far:

4000 Stock Tach
3750-3800 VAFC2

4500 Stock Tach
4000 Pivot tach-coil signal

5000 Stock Tach
4700 Monster Tach-MSD Dig6 signal

8250 Hondata S300
8000 Pivot Tach-coil signal

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by mgags7 &raquo;</TD></TR><TR><TD CLASS="quote">

That makes no difference.

</TD></TR></TABLE>

it does make a difference, its easier to run it to the ecu...thats the difference...i never said it was a better signal or anything of that sort..