Smiths RVI tacho & electronic igntion

[abri]

I've got an Accuspark electronic ignition module fitted to my distributor but I would also like to fit a rev counter. I've read in a few places online that the RVI version of the Smiths tacho and electronic ignition don't play nicely together. Does anyone have evidence to the contrary or do I have to make a choice between the two?

Thanks in advance

[JC T ONE]

My car have a RVI revcounter, hooked up to a electronic Metro turbo distributer = works perfect.

Mind you it does have a company sticker from some gauge repair shop in Salisbury, so my guess is that JanSpeed had it "re wired" .

[impala]

Check this out, may be handy:

https://www.spiyda.com
The home of Spiyda Design, as well as the Fuel Gauge Wizard and the RVI to RVC tachometer conversion board.

[Nick W]

Chris (Spyda) did mine , he also does an external small box , to keep the gauge original £40ish


Nick

[dklawson]

I know of only a few people who have had "non-modified" RVI tachs work with electronic ignition. Most find they have to have the RVI tach's converted or choose an RVC tach instead. Spiyda's board is a great product offering to address the problem.

[sclemow]

I had to have mine converted from RVI to work with my lumention ignition.

[mk1]

The Spyder conversion works a treat. If you use an RVI tacho with 99.9% of all the electronic ignitions you will blow them up.

M

[abri]

Thanks for the replies. Looks like it's back to points for me if I want to fit a tacho. I can't see myself forking out over 40 GBP for a non essential with the exchange rate as it is.

[dklawson]

... with the exchange rate as it is.

Which implies you are not in the U.K. If you are in the U.S., follow eBay for used tachs. In addition to the Smiths RVC tachs from MG and Triumph donors, there are lots of aftermarket tachs that will work. I assume you are after a traditional look. If not, there are many generic "modern" tachs that can be had for less than $60.

[wantafaster1]

Please pardon my ignorance, I am not good with electricity!

I don't understand why, if you replace the switch that is the contact breakers, with an Aldon or some other trigger, that the rev counter won't like it? Assuming the coil hasn't changed at least.

[timmy201]

Here's a little article on the difference between the two. I wish I knew about the differences before I bought an RVI tach!
http://www.super7.dk/instruments.html

[mk1]

Abri is in SA where the current exchange rate is 21 Rand to the Pound. Last time I went out there it was Eleven!

makes for a cheap holiday destination from the UK though.

M

[mini129]

Its all about the amplitude of the voltage spike that triggers the tachometer.

[dklawson]

Please pardon my ignorance, I am not good with electricity!

I don't understand why, if you replace the switch that is the contact breakers, with an Aldon or some other trigger, that the rev counter won't like it? Assuming the coil hasn't changed at least.

The RVI tachs are sometimes impulse tachs. They have an induction coil loop (either inside or external to the case). Current flowing through the induction coil creates a pulse inside the tachometer which is "counted" via the tach circuitry. The charge/discharge rate and voltage amplitude of the ignition coil is "different" with points and electronic ignitions. The old impulse tach circuit is not expecting the different pulse profile provided by electronic ignitions and either counts "wrong" or not at all.

The later RVC tachs are more like a modern tach and sense voltage pulses directly via a connection to the coil (-) terminal instead of using the induction loop. Since they are only counting voltage pulses, they are more tolerant of different ignition types.

[abri]

Abri is in SA where the current exchange rate is 21 Rand to the Pound. Last time I went out there it was Eleven!

makes for a cheap holiday destination from the UK though.

M

Yes! Come visit us here and bring us mini parts in your luggage

[abri]

Please pardon my ignorance, I am not good with electricity!

I don't understand why, if you replace the switch that is the contact breakers, with an Aldon or some other trigger, that the rev counter won't like it? Assuming the coil hasn't changed at least.

The RVI tachs are sometimes impulse tachs. They have an induction coil loop (either inside or external to the case). Current flowing through the induction coil creates a pulse inside the tachometer which is "counted" via the tach circuitry. The charge/discharge rate and voltage amplitude of the ignition coil is "different" with points and electronic ignitions. The old impulse tach circuit is not expecting the different pulse profile provided by electronic ignitions and either counts "wrong" or not at all.

The later RVC tachs are more like a modern tach and sense voltage pulses directly via a connection to the coil (-) terminal instead of using the induction loop. Since they are only counting voltage pulses, they are more tolerant of different ignition types.

Thanks a lot for the explanation Doug. My tacho is one of the induction loop types. I'll be searching around for a nice Smiths RVC or Jaeger tacho that can deal with electronic ignition. If that fails I'll swap back to points

[dklawson]

When searching for Jaeger tachs, remember that there is "British Jaeger" (which is Smiths) and there are "Jaeger" tachs (which were primarily French and not at all related to the British models). I have tried to help people with continental Jaeger tachs a few times. I am sure there must be printed information about them but online information is scarce.

Most British Jaeger tachs I have seen were cable driven... such as those used on early MGBs.

[smithyrc30]

Please pardon my ignorance, I am not good with electricity!

I don't understand why, if you replace the switch that is the contact breakers, with an Aldon or some other trigger, that the rev counter won't like it? Assuming the coil hasn't changed at least.

The RVI tachs are sometimes impulse tachs. They have an induction coil loop (either inside or external to the case). Current flowing through the induction coil creates a pulse inside the tachometer which is "counted" via the tach circuitry. The charge/discharge rate and voltage amplitude of the ignition coil is "different" with points and electronic ignitions. The old impulse tach circuit is not expecting the different pulse profile provided by electronic ignitions and either counts "wrong" or not at all.

The later RVC tachs are more like a modern tach and sense voltage pulses directly via a connection to the coil (-) terminal instead of using the induction loop. Since they are only counting voltage pulses, they are more tolerant of different ignition types.

Thanks a lot for the explanation Doug. My tacho is one of the induction loop types. I'll be searching around for a nice Smiths RVC or Jaeger tacho that can deal with electronic ignition. If that fails I'll swap back to points

I would say you still need a little care with electronic systems and RVC tachos. The collapsing voltage in the coil causes a back EMF which goes back to the tacho. The higher performance coil (higher voltages) deliver more back to the tacho and higher engine speeds also increase this. Most electronic systems have an in line resistor between the tacho and the coil. I seem to recall 6k8 ohms was the 'norm'. On the Range Rover it was a plastic encased item with a male and female 1/4" blade on each end.

[mk1]

Not an option for everyone, but can I recommend the superb quality Reproduction Speedwell tachos available from Howard Instruments. These are visually indistinguishable from an original.

http://www.howardinstruments.com.au/pro ... 27dafe7310

These are of superlative quality, all have modern stepper motor movements so actually read accurately & smoothly & are when compared to buying an unknown original brilliant value.

Oh & BTW, Rodger Howard is also a member here too.

MOST HIGHLY RECOMMENDED!

M

[mk1coopers]

Very nice, and there's a 10'000 version too, I wonder if they will work with a CSI dizzy, my Smiths one is a bit erratic