Electronic rev counter...

[Douglas Alderson]

Smiths / MGB rev counter swap the bezel for one off an older warn out speedo or clock. Replace the face with an aluminium disc and print off a new face on slip transfer, I also added the speed in 4th to the face. If you are lucky you can find a smith rev counter which is both 6v and 12v (adjustment on back).
   

[Bob Culver]

Useful for trails and racing but for most cars things happen realtively slowly. In a road Seven seldom any confusion about which gera in.It is not difficult to remember the mph speeds corres any arbitrary rev limit.

[Colin Morgan]

Hi,

Curious about revs so bought one of the cheap induction tachometers mentioned above from Amazon.  Just measured the revs as follows (figures in brackets were not achieved - extrapolated instead - as were some intermediate speeds.):

Look reasonable?  This standard 3-bearing Ruby engine also seemed happiest up to about 3000rpm.

Colin

[Oxford Jack]

Not quite along the lines of the previous correspondence but closely related. I have a Durite 52mm electronic rev counter in my trials car, the gauge reads 0-8,000 rpm. On the back of the instrument there is a switch for 4-6-8 cylinder use.
My question/s: if I change the switch to 8 cylinder, will it read at 50% of the revs? or is there a tech savvy reader who knows how to make the full scale read up to 4000 rpm, so that it suits the engine speed rather better than at present?
I could then remove the front and pointer, print a new face reading 0-4,000 rpm and have a more suitable instrument for my purpose.
Here is hoping!

[John Cornforth]

Hi

If you use the 8 cylinder setting, at any given RPM reading the instrument "expects" to see twice the rate of impulses compared to 4 cylinders. The scale will therefore be 0 to 16000 RPM when used on a 4 cylinder, which isn't very helpful.

There may be a way of modifying the internals but unfortunately I have no details of the inner workings of the Durite gauge.

When I needed a tachometer I used a secondhand Durite instrument scaled 0-4000 RPM. This was the sort aimed at the marine market, and is normally driven from the alternator as there are no igniton pulses available. The only workaround I found to this was to build a small driver circuit and use this to drive the meter movement directly, the original circuit being bypassed. I can give you a copy of the circuit if you PM me.

[Oxford Jack]

Thank you John, I realised shortly after writing that my first suggestion was bonkers! I will pm now
Thanks Jack

[Colin Morgan]

After changing to Longstone 400/425 x 17 tyres on my late Ruby, the engine revs for a given speed seem a bit higher than with the previous 450s, so I measured the RPM v speedo speed again with an electronic rev counter:


  EYV 20 Revs v Speedo Speed 2024.jpg (Size: 89.49 KB / Downloads: 230)

Figures are rounded to the nearest 50rpm.  

In top gear, 1900rpm at 30mph and 2500rpm at 40mph seem reasonable.  In third, 30mpg is now 3150 rpm - with the larger tyres it was lower at about 3000rpm.  The big difference in ratios between third and top in the standard gearbox is now even more noticeable.

[Tony Press]

This exchange reminds me- still no word from our New Zealand cousins about Bob Culver ?

[Nick Lettington]

After changing to Longstone 400/425 x 17 tyres on my late Ruby, the engine revs for a given speed seem a bit higher than with the previous 450s, so I measured the RPM v speedo speed again with an electronic rev counter:



Figures are rounded to the nearest 50rpm.  

In top gear, 1900rpm at 30mph and 2500rpm at 40mph seem reasonable.  In third, 30mpg is now 3150 rpm - with the larger tyres it was lower at about 3000rpm.  The big difference in ratios between third and top in the standard gearbox is now even more noticeable.

Did you push a little harder or is the extra 5mph due to the slightly lower gearing?

[Colin Morgan]

The lower gearing no doubt helps, but the engine has also been changed in the interim.