Just did a test for you since I'm sitting in a 94 na8. They do not register speed in reverse.

Thanks. I wasn't sure and my car is apart right now. that narrows the potential parts list.

I wonder if this is something that could be created and 3d printed. Not sure how well the plastic from 3d printing would hold up, but could be a possible option.

I have several 3d plastic printers at work. I've considered it.

My research seems to indicate that M501-17-341A is the 7 tooth version of the M503-17-341A 6tooth drive gear that is use in the Miata. It is pared on an automatic 929 that also uses the same 20T drive gear M503-17-441 driven gear that I have been using with my 3.636 rear end so I think it will mesh with Miata compatible speedo gears and I’m hoping it is in fact 7 tooth. It is also used on a Mazda E2000 which is sort of a small delivery truck/van only sold in Asia where it gets pared with the 4.778 ring and pinion.

7 tooth drive gear. M501-17-341A
22 tooth driven gear M510-17-441A when using 4.778
18 tooth driven gear 3902-17-441A when using 3.909

I hope that’s what works. The M501-17-341A is on backorder however might take a while to get from Japan and of the three 18 tooth driven gear part numbers I found that is the only one that worked with Mazda motorsports parts list I hope it has the correct direction it is found on some b series trucks that use M part number drive gears. I’m hoping the M in the part number means the Miata direction but I am not sure of that even. its not too terribly expensive to find out the parts run between $13-$15. Way cheaper than gage faces or added electronics.

I like my indiglow gage faces with shiny polished button covers and orange painted needle backs.

Because its still a $129 "solution" (unless you bought just the speedo)
Because you would need 2 clusters and 2 sets of gauge faces, one to match each diff you plan to run
Because it can't be changed as easily as a sender...

No, you do not have to change anything.
See how it says Km/h and MPH on the dial?
It will say 3.909 and 4.778 instead.
Simple. Clean. Elegant. Clever.

NO ONE (but godless commie) IS LISTENING TO ME

Holiday party and I'm drunkposting on my phone. :dealwithit:

THANK YOU FOR EXPLAINING IT IN A WAY US THICK HEADED CAVEMEN CAN UNDERSTAND

I'm guessing Rev already has the scaling for the various popular gear ratios? Its not something I've ever looked into as I'm happy with the stock gauge faces. It IS a simple and elegant solution.

Sorry Bob, I'll get the fuck out of your thread now. Thanks again for loaning Gesso the bolt so he could limp the Exocet home. :bowdown:

I read your o.g. post and thought to myself "damn. that is an elegant solution"

Then lol'd at everyone still stumbling over senders and swapping things.

Well played Curly! :rofl:

Dakota Digital I believe makes boxes that can do exactly what you want. Not exactly cheap solution.

ECD-100

Pretty sure Rev keeps completely stock locations for MPH and kph, so you would have to tell him what indicated speeds equals what actual speeds using one of many free GPS apps.

Cheap NB speed sensor, electronically-controlled motor hooked to speedo cable, Ardunio and some custom software that reads the NB speed and drives the speedo cable at the right speed?

--Ian

Cause that's easier than a gauge face.

But nowhere close to Rube Goldberg-y enough!

--Ian

Did some research because this is interesting and found this document if it helps at all.

http://fm.no-ip.com/Car/sgpartno.txt

A bit helpful thanks.

I discovered an error in my calculation. I laid out my xl spread sheet then typed in the formula wrong and got multiply and divide swapped doh. Actually need a 5 tooth drive gear not a 7. But I think the 929/E2000 one M501-17-341A may in fact be the 5 tooth I need anyway that can swap with the Miata M503-17-341A 6 tooth and still will give me what I need I’m hoping.

Unfortunately that listing doesn't give the tooth counts for everything. Another piece of information that is always missing is whether the helix angle is to the right or left on any of them. Everything I have found is incomplete so it's still a crap shoot, order parts and see if they will work together or if they are what you think they are.

Has anyone used one of the NB speed sensors? I assume it just outputs a square wave? If so it looks like a way better solution than a hall effect sensor/magnet for my data system.

Nope, the speed sensor outputs a nasty sawtooth signal.
See more in this thread.

Wow, that's quite the signal. Thanks for the information (and the lead on a pretty nice looking little 'scope). Looks like a place to start at least, just a little conditioning to do.