G-Tech meter

[Shaun Brady]

I don't have any experience with the G-tech meter, but...

Lotsa experience with accelerometers, racing, & motors, soo...

Yep, the garden variety accelerometer is a mass on top of a piezoelectric
crystal with a charge amp, and thus measures acceleration in an inertial
reference frame.  It works just as well in space as in your car.

A single integration yields velocity (I've used velocity transducers that
were accelerometers with built in integrators), a second integration yields
distance.  Integration is a good thing to do to electrical signals, it is an
extremely effective filter.  Differentiation is a particularly effective
noise amplifier, and therefor intrinsically evil

The velocity and distance are along the axis of the sensor, multi axial
accelerometers are available, but I doubt that is what we are talking about.
It will not sense changes in elevation, but it could.  It will not sense
cornering loads, but it could.

The hills will affect the estimated HP and 1/4 mile times because lifting
the car vertically takes power.  If the road is sloped down, the car gets
faster.  A standard 1/4 drag strip is flat.

Driving with or against the wind takes power, and also affects the
acceleration, and thus the 1/4 mile time and HP estimate.  Top speed trials
generally require a 2 way run for a record.

The HP estimate will be no better than the weight input, but who cares?  In
real performance applications you are after relative changes in output as
you tune your combination, and not a single number corrected into
insignificance that you use to pander parts to an ignorant crowd of
wannabes.  In roadracing, the acceleration coming out of a given corner
would be very useful even if the HP estimate was junk.

Atmospheric conditions affect HP and are generally corrected to standard
conditions when a dyno is used.  No atmospheric inputs, no atmospheric
corrections.

On the other hand, an engine dyno can't calibrate or account for underhood
conditions at speed, traction improvements, or a host of other things.

"Turbochargers" by Hugh MacInnes ISBN 0-89586-135-6 contains a similar
tirade against stationary dyno numbers, a method for obtaining road HP by
hand, and all the equations you need to automate the process.

I'm supprised products like this havn't appeared earlier and think its one
of those things where mother nature is working for you every step of the
way, and is an ideal sort of project for the DIYer.

Shaun Brady