Well, well, the meters look nice. I entered the site and couldn't find information about mechanic method of the flow meters.
Good of using this meters (I have to use two for my diesel) is you measure real fuel flow, instead of estimating it.
I already used a couple of meters once, but they dind't last enough as to calibrate my Arduino board: before I ended both stuck with debris of oil, despite each one has a special filter, in addition to the car fuel filters.
Short afterwards, both flow meters begun to leak and I had to remove them and replace the fuel hoses I cut before.
In my experience, the only reliable fuel flow meters I know, so far, are these:
Differential fuel flow meter DF
These are heavy duty fuel flow sensors that will last enough to take advantage of them. Plastic fuel flow meters based on turbines are many, all of them very fragile.
Look one that is a lot cheaper:
Flow Sensor
There are these also:
Buy Flow Controllers RS 0.05 to 10L/min Cable Pulse Flow Controller, 4.5 to 24V dc RS 800-226 online from RS for next day delivery.
In my experience, you can find good and reliable and durable flow meters which are very expensive, or, you can find cheap flow meters that will not last for long.
Besides, as you need two and you need to calculate the difference, you need a programmable board to make the calculations.
And, you need to cut whatever mean of fuel transport you have, hose or pipes.
Anyway, if the guys that sell the 13mm flow meters can guarantee durability and resistance and robustness of the meters, and they have a solution to calculate the difference between two meters flows, I would try both, the meters and the digital display. Will investigate more.
The meters look robust, let see how they really are.
There is the posible fuel leaks I know well and the space issue too, you must arrange them and the hoses in little room, but if they work well, I would do the effort.
On the other hand, the rpm and tps method is less precise, but a lot less invasive in the car, you will never have fuel leaks this way.
My objective to retrofit such a device in the car (whichever) is not to know exactly how much fuel the car is spending, but to have a real time and objective COMPARISON instrument. For what? For knowing mechanic mods, tire pressure, driving habits, "fuel economizers", aero mods, etc. real effect in fuel economy.
Knowing exactly fuel economy of my car is as easy as to divide all miles driven with a tank for the gallons of fuel I spent.
Thanks for the info, I will investigate it more.
Oldbeaver