Mychron xg log questions

[Robber98]

Hey all happy new year. I am installing a mychron xg log and I'm trying to find out how to hook up the tach on a vee and which wire to use. Instructions are a bit vague. Also how to install the magnetic speed sensor and the best way to do it. Thanks for any input. Rob Murray

[David Ferguson]

I would start with using the 4-50 volt input (blue wire) attached to the negative side of the coil. You may find that signal is noisy (resulting in a non-steady tach signal when on track), and if so, the solution normally is an AIM Coil RPM filter.

If that still fails to produce a steady tach signal (which sometimes happens when using the pertronix points-replacement -- not sure if that's legal/used in Vees), then we have a solution that allows you to connect a magnetic or proximity type wheel speed sensor -- you'll have to find a way to mount a trigger of some type on the front pulley.

Hope that helps. Feel free to call us if you need parts, or need more details.

David Ferguson
Veracity Racing Data
805-238-1699

[Mark Filip]

David is great to deal with and has tons of knowledge on data. Much thanks to all the help you gave helping with my set up.

Support the vendors that support us!

[Diamond Level Motorsports]

The Pertronix points replacement is legal in FV. Strangely enough one Vee I had needed the RPM filter and one didn't.

The front brake drum seems to be the most popular place to install the wheel speed sensor. I drill a hole in my backing plate and mount a magnet against the wheel bearing boss near the seal. It's hard to describe so I will try to find a picture. Put the magnet on the drum if you can rather then the wheel.

As mentioned above, David is a great source of data accessories and knowledge. Also Jim at SR Racing.

[Rick Kirchner]

The only thing I'd add is go ahead and use the amp regardless. I went without one for a couple years and eventually the tach input degraded until it burned out.

One more thing - protect the amp. I had two amp failures in quick succession. If the input voltage falls too low when receiving the signal off the points, the op-amp will fail. All it takes is cranking a really cold motor on a flat battery once - sort of a $80 fuse.......

I put a diode in line with the power supply, and a big-ass capacitor (can't remember the value, something like 250,0000uf) and if you wait just a second or two after turning on master power, the cap will charge and has enough energy to power the amp until cranking is over and the battery recovers from lack of load.

If you want to be really anal about it, switch on the power and select the battery voltage display before cranking. Even with amp protection, if it's below 10V don't hit the starter.

The op amps are $.89 each from digikey, but the pin spacing is so small that it takes a microscope equipped soldering station and a special iron to fix. I've thought about reverse engineering it and building it with full-size components instead of surface mount - wouldn't take any more room and would be repairable.

[Diamond Level Motorsports]

I use a separate switch that powers the data system. That way you can turn on the data system once the motor is running.

[Mark Filip]

I use a separate switch that powers the data system. That way you can turn on the data system once the motor is running.

How do you read oil pressure before you start the engine?

[Diamond Level Motorsports]

How do you read oil pressure before you start the engine?

Mark,

Not sure I understand your question. If you mean checking oil pressure while the engine is cranking I have never checked that or worried about it. Maybe I should be, I don't know.

[KevinFirlein]

I have never installed an AIM system and not needed the filter for a clean signal. Its a cheap and easy install , I'd say just go ahead and do it and be done with it.

Veracity are good people.

[Mark Filip]

Mark,

Not sure I understand your question. If you mean checking oil pressure while the engine is cranking I have never checked that or worried about it. Maybe I should be, I don't know.

Yes that's what I mean. I crank the engine until it builds oil pressure then I have ignition on a separate switch to allow the engine to run this way the engine will not start until I know there is oil pressure.

[sracing]

The only thing I'd add is go ahead and use the amp regardless. I went without one for a couple years and eventually the tach input degraded until it burned out.

One more thing - protect the amp. I had two amp failures in quick succession. If the input voltage falls too low when receiving the signal off the points, the op-amp will fail. All it takes is cranking a really cold motor on a flat battery once - sort of a $80 fuse........

What "amp" or op amp are you talking about?

[sracing]

I have never installed an AIM system and not needed the filter for a clean signal. Its a cheap and easy install , I'd say just go ahead and do it and be done with it.

We have installed dozens of them and have our 4 rentals (w/Pertonics) using them and none have the filter. Of the dozens I have sold mail order, I think I have only heard back from maybe 3 that needed the filter. A dirty ignition signal to the AIM is normally bad points, condensor, or poor wiring practices. I admit that there are a few ignition systems that can generate lots of electrical noise that an AIM, or any d/a system could pickup.

[sracing]

Yes that's what I mean. I crank the engine until it builds oil pressure then I have ignition on a separate switch to allow the engine to run this way the engine will not start until I know there is oil pressure.

Mark, not a bad idea, but probably overkill. Cold cranking with the plugs in, still generates lots of bearing load, so you aren't saving much. Assuming your oil system is working and plumbed in a normal way, you will get oil pressure instantly. You probably start your street car everyday without any concerns and no pre-cranking?

[Mark Filip]

Mark, not a bad idea, but probably overkill. Cold cranking with the plugs in, still generates lots of bearing load, so you aren't saving much. Assuming your oil system is working and plumbed in a normal way, you will get oil pressure instantly. You probably start your street car everyday without any concerns and no pre-cranking?

It can't hurt.

Depending on the oil cooler set up oil can drain out of the cooler and takes some cranking to fill. I was really surprised the first time I checked it took a lot longer than I thought it would to build pressure.

[Rick Kirchner]

What "amp" or op amp are you talking about?

the "filter" is actually an active device - an op amp with a few resistors and capacitors here and there to produce the proper frequency response.

here's a pic of the filter with the shrink wrap peeled off. If not protected, the solder corrodes easily - the shrink tubing isn't enough.

12 resistors, 5 caps, 4 diodes, and an op amp.

[sracing]

It is actually a Low Pass Filter. (Not really an amplifier, allthough an op amp is a part of the active filtering)

There is no reason why one would fail with a low supply voltage (or low input voltages).

[Rick Kirchner]

Data speaks louder than words. No filter = potential to burn out the tach input. I had two filters fail in quick succession, replaced the amp on each, and added the protection. no failures since.

That's the difference between theory and practice. It really doesn't matter if it's bad points or a bad condenser if $5 parts take out $800 parts.

The chance of damaging the filter with low cranking voltage was told to me by MyChron Mike when I sent my dash in for repair. I didn't pay attention to the warning twice.......

[sracing]

Data speaks louder than words. No filter = potential to burn out the tach input. I had two filters fail in quick succession, replaced the amp on each, and added the protection. no failures since.

On the input to the Dash internally there are already a zenor and 2 additional diodes back to back limiting input to the internal filters. Of course if you attach the low voltage (12V) RPM input incorrectly (instead of the HV one) to the coil or points primary circuit you COULD blow a diode. (although I have not even seen that.)

That's the difference between theory and practice. It really doesn't matter if it's bad points or a bad condenser if $5 parts take out $800 parts.

My data, practice (and theory) of using Op Amps (and AIM stuff) in hundreds of applications would indicate otherwise. But, if it works for you do it.

The chance of damaging the filter with low cranking voltage was told to me by MyChron Mike when I sent my dash in for repair. I didn't pay attention to the warning twice.......

Mike is a good guy but the distributor. I am not sure of his EE knowledge. Again, if you feel better, do it. The capacitor idea is not a bad one, since it can keep the display from freezing temporailly on startup during the voltage drop to ~8V which is typical.