Tach conversion for aftermarket EFI

[Britain Smith]

Are there any OEM 911 tach's that are compatible with aftermarket EFI systems (i.e. Electromotive TEC-3) or do I have to send mine into one of the speedo shops and have it converted? Is there anyone other cost effective solution?

-Britain

[Britain Smith]

Anyone?

[dean]

My stock tach works fine with my DTA EFI

Dean

[Britain Smith]

What year?

[atlporsche]

been thinking about this a lot recently...

there's a couple of things I've been thinking about...

1. I've got a 912, subaru powered...no tach yet...I got an autometer tach adapter, and can run an autometer tach, been thinking about refacing one of those and it would work fine.

2. hacking the tach. basically all meters are ammeters...they read a mA signal. I've confirmed that a mA signal exists in the tach adapter I have, I just need to modify the signal to meet the calibration needs of the tach. I can't just plug it in the back and have it work because it expects the noisy signal from coil neg. side...

3. replication of the coil signal...not gonna happen...the subaru engine has a twin coil setup....

sjd

[beepbeep]

Most tachs are running off low-voltage ignition signal and all EFI's can supply that so I don't think it's a problem unless you are using wastefire EFI which is doubles the frequency of pulses, but there are circuits to solve that.

[dean]

Mine is an 81 and mine is also wasted spark. I just hooked the wire from the ECU marked tach to the tach. And it worked

Dean

[Britain Smith]

It was my understanding that you have to convert your tach to electronic for electromotive TEC-3 EFI...is this true? Has anyone done it for this system?

-Britain

[beepbeep]

Originally posted by dean
Mine is an 81 and mine is also wasted spark. I just hooked the wire from the ECU marked tach to the tach. And it worked

Dean

Most EFI's (especially more expensive ones) have separate tach-driver signal outputs with correct pulse frequency.

Tachs take square-signal from ECU and convert it internally to voltage that is dependent on frequency, which in turn drives the indicator needle. So they are not voltage-driven but frequency driven.

if you can get ignition trigger signal from your engine you can hook it to your tach.

[Early_S_Man]

Britain,

There have been a couple of 'horror stories' about Hollywood Speedo on the board lately, so my confidence in their capability to help you is ZILCH! Their techs are apparently in the mode of making excuses and badmouthing the Bosch CDI for SCs and Turbos as being unreliable, so any information you get from them could be pure BS!

There are many resources and sources for tach circuits that could be used to drive the 912 meter movement. You would, of course, need to calibrate the 'updated' tach ... but that isn't very difficult.

Do you have a specific EFI system in mind, or are you just 'testing the waters' for a possible solution?

[Britain Smith]

I have the electromotive TEC-3 system to run my new engine (turbo type-4). I currently have two tach's to use...one with a boost gauge that I will probably convert to something else. Both of these tach's however were originally from a 6-cylinder car and I need them to work with my 4-cylinder and EFI. What are your thoughts about Palo Alto Speedo?

-Britain

[briankeithsmith]

Britain:

I used my stock tach with my TEC3 system and wired it to the brown wire coming out of the TEC3 harness.

No issues. Then I bought a mechanical boost gauge from NH Speedo and replaced my clock instead of using the stock boost guage that is built into the tach.

Brian

[Britain Smith]

OK, great. That is what I wanted to hear.

On the stock boost gauge, I thought that the one in the speedo was mechanical with a vaccum line input in the back.

-Britain

[beepbeep]

Originally posted by Britain Smith
OK, great. That is what I wanted to hear.

On the stock boost gauge, I thought that the one in the speedo was mechanical with a vaccum line input in the back.

-Britain

Nope. It's electrical and is running off the sender in intermediate throttle body.