Looking at this:



Does it calculate mpg using the rate of fuel flow and somehow getting an output from the speedo? I'm a little confused as to how it works.

The main unit is a de-luxe calculator.

There's a fuel flow meter that installs in the fuel line that spins around and give a pulse signal for the rate of fuel flowing.

There's a set of magnets which are wired round a driveshaft coupling and a pick-up that is fixed near them, so it gets a pulse signal for the speed of car.

I can't remember which model it is, but it's a re-badged Zemco unit from memory. I had a similar unit - a Zemco ZT4, re-badged for Unipart - in an Austin Maxi I had. Still got it somewhere (I think).

I've not seen one for a fuel injection model, but I'd assume it would have a different fuel flow metering arrangement?

A non-Volvo one might be easier to find. There were various ones around back in the day:
Zemco did a ZT3 & ZT4 amongst others.
Mobelec did one called a Maximiser (and Maximiser II). There was also a Mobelec GasFax. Both were similar to the
Smiths one.
Sparkrite did one Voyager, with "ICE WARNING DETECTOR"

any more variations on the above were probably just clones.

Thanks, I'll keep an eye out for those. Surely to tell the speed it would have to be 300 specific though (for the exact diameter of the shaft). I'll take a look.

No it's universal, as when first fitted, you calibrate it.

Yup, FI has a different wotsit, instead of a whirry thing in the fuel line it has electrics that piggy back the duty cycle of the injectors.

I have an injecty thing here I've been meaning to make some copies of as there was some interest a while back, but standard Chris timescales apply. These as ever can be sped up by someone fixing Fake for me