[Nonfractal]

I am in the market for a tachometer that I can sit the car on, turn the tachometer on and it provides me with the motor RPM's ..

I've seen one that you need to remove the motor and place on the machine... if the motor is glued in and meshed nicely.

I have that same small digital meter as Alan mentioned  ...not liking the half arsed setup and use

Johnno,
Once the motor is in the car your pure rpm measurements go out of the window.
So many other factors come into play: gearing, transmission efficiency, weight, tyres etc

Perfectly correct to say that once your motor is in the car, it is best not to be pulling the motor out just to take measurements. 

My solution is the rolling road. 
With a unit like this, you get numbers that reflect the whole performance of the car including transmission.
You can then compare cars on a "metres per second" basis and optimise gearing to match other cars that run well.

Unfortunately, at this time  there appear to be no commercially available units so this is a unit I designed and built for my own use.
All of the components are "off the shelf" items and the most difficult part of the build was installing and balancing the roller.

   

Link to design including a full components list and sketch of the wiring here: https://ibb.co/album/7NR8c9

Alan Wilkinson