DIY dyno idea.. would this work

[MWP]

You are after somthing like this:

http://www.tweecer.com/StreetDyno/

Can be quite accurate if you can find a good road and give it the correct car values.

Even when its not chassis-dyno accurate, its still good for comparing engine mods, etc.

 

[SCV8]

I've toyed with the idea of a dyno built into the floor of my home garage(every home should have one right?), using a large daimeter steel pipe and an auto type water pump and a strain guage against the pressure.
We had a torque measuring device that worked like this for testing industrial valve actuators at one of the shops.