Topic: Digital Gauge Conversion Hack?

[SOHCiro]

I was looking at trail tech gauges with digital tach&speedo.
So sohcs have analog tach&speedo cables, and lots of fellas say that you need to wire digital techs to coils or wrap em around spark plugs, which still won't guarantee smooth operation.
But then today I found this interesting product.
https://www.dimecitycycles.com/acewell-digital-speedometer-conversion-cable-for-honda-cb-cl-yamaha.html

It's a digital speedo conversion cable for classic Honda/Yamaha bikes, meant to be put into the front hub speedo drive slot. Simple plug and play type of thing.
Since both speedo and tach cables use the same ends, it seems possible to simply plug this into the tach drive hole, hook up the wires to digital tach. From what I understand, these digital cables just make binary signals from the number of revolutions.

Maybe somebody with more knowledge can correct me if I'm wrong, but if this were true I think it'd save tremendous amount of time and effort for DIYers around here who want to go digital.

[calj737]

Let me make sure I understand what you're proposing:

You want to use this type of cable for the stock tach gear to feed the digital tach?

If so, I am dubious of the fitment. It is super easy to get the digital tach to register an accurate signal from the coils. And you have no cable length issue to address. It would also be necessary to verify that the cable is capable of converting the input signal to the "speed" seen at the tach gear versus the front wheel. You're talking 4,000-9,500 RPMs versus 70-80MPH. Do that math, but I think the speedo conversion is much lower. Not saying it won't, just saying you'd better be sure so Acewell doesn't tell you to take flier when you call up to return it or get help with it.

[DaveBarbier]

Seems like if this was possible, the engineers who designed it would know this and the marketing team would want to advertise it as a speedo/tach digital cable replacement.

[Bodi]

I don't see the point in adding a drive cable and electromechanical device to generate tach pulses, the pulses are already freely available at the coils. Electronic tachs with a coil connection have always been accurate for me - as accurate as the tach can be, at least. Wrapping a pickup wire around a spark plug wire is bogus, I suppose that would be used if you have a CDI system with no easy connection elsewhere?

[evanphi]

Yeah don't plug that SPEEDO cable into the tach plug hole. The ratios are different. Your conversion factor for the tach would not be possible to set on an electronic tach.

Tach 4:1
Speedo 2240:60

Use that cable for your speedo, and check out the link in my sig to get the correct input circumference.


For the tach, just plug your tach lead wire into the connection just before the coils.

[slikwilli420]

Scitsu tachs wrap a pickup wire around one wire from each coil. Its a high quality and very accurate piece and easy to hide under the tank so no wiring is visible.

[American Locomotive]

While it's a cool product, tach conversions are really easy. I think this product would just complicate it if anything. I've never really heard of a good, name-brand tach having an issue with inductive pickup or being tapped into a coil wire.

[SOHCiro]

Thanks everyone!
Learning something new everyday:D
I know that some digital techs have the ability to select the number of cylinders/coils, but for those that don't,
should you split the tach wires into two and tap them to each coils for the actual readings?
In that case, would that require diodes or anything like that?

[American Locomotive]

No, because that would tie the two ignition coils together. Just buy a tach capable of handling 1 pulse/rev of the engine, or 2 pulses per complete cycle.

[SOHCiro]

I've been searching around lately for the result of Trailtech conversion, so far have only come across those that fail to display correct steady rpm. I have yet to see a video of a perfectly working digital tach on a SOHC cb750.

I'd really appreciate it if anybody wrote their very own REAL success story here, with exactly how they proceeded through the conversion, before I throw away my hard earned $130 !!
I don't wish to hear theories that explain how easy it is, or somebody else's story, although a link to another post would be awesome.

Sucks the search function is dead
Huge thanks in advance!!

[calj737]

I’ve installed and use digital gauges (other brands) commonly. The tach signal is dirt easy and dead reliable. As for the Speedo, you need a sensor, and then all it takes is calculating the diameter of the wheel/tire to calibrate the gauge. The brand gauges I use allow 5mm increments on wheel size, so precision is a breeze.

I’m still confused if you are uncomfortable with digital gauges, or your issue is uncertainty with the brand you’ve listed.  If the latter, I thought we already cleared up you can’t use it for a Speedo since the ratio is all wrong.

[American Locomotive]

There are plenty of videos of trailtech vapors working just fine on vintage bikes. I've used my Trailtech on everything from a Briggs and Stratton lawnmower to my CRF450. Works fine.

[SOHCiro]

Thanks for the replies!
calj737, I saw your build and it's magnificent! I see that you went along with the +$500 tach/speedo, which is no wonder why it works excellent, but my wallet isn't deep enough unfortunately.

Vapor is one of the best looking+function for the price range I'm looking at.

Thank you American Locomotive, yes I am fully aware of trailtech products working beautifully on single cylinder bikes.
But for the 4 cylinder sohc's, somehow the rpm seems to jump around quite a bit.
Apparently, multi cylinders produce "dirty pulses" or "wasted sparks", and maybe the Vapor isn't too good at handling them.

Here's some of the findings
http://forums.sohc4.net/index.php/topic,17620.25.html

In this 11y/o video, the tach manages to work decently, with "resisted tach wires". I have no idea what or how resisted wires are different from regular ones. Thinner diameter wires for more resistance?

[American Locomotive]

My CRF450 runs wasted spark, as does the Briggs and Stratton, and every other engine I've used my TrailTech on. There are many ways you can hook the trailtech tach up. You can hook it to the points, you can wrap it around wire. Make sure you wrap the tach signal wire as far as you can away from other plug wires.

"Resistance wires" are spark plug wires made out of a carbon filament with a high resistance to reduce EMI. Just buy the vapor or whatever on Amazon. Worst comes to worse just return it.

[evanphi]

My digital tach came with a resistor for managing the wasted spark. The resistor will basically smooth out the signal so only the big bumps trigger the tach. Also you should be able to set which type of firing you have on your tach.

[SOHCiro]

Cool! Do you happen to know how many Ohms the resistor is?

[evanphi]

1MΩ, I believe. It is covered in shrink wrap now so I can't go check.

EDIT: But I just looked up the Acewell 2853 documentation and it says 1MΩ, so I was right I guess.

[piefairy]

I was looking into this same Acewell system when I was starting my build. I'm not sure on the cross comparability of the cables between manufacturers. I had run into a few forums and eventually a website selling a product to specifically correct issues with the Acewell cable. I stopped at this point mostly because I was looking more into the speedo conversion rather than the tach. I ended up going with another gauge that wired to my coils. Seems to read pretty damn accurate.