On the Dyno

After a winter's rest, I've been driving the 914 a bit. I finally had an opportunity to put the thing on the dyno and see how it's running from an empirical standpoint. It's fun on the road with a bit of torque - I love hustling it through the gears - but, because I'm an engineer, I want to see some numbers.

Here it is on a Dynojet mobile dynometer, a device that uses a car's wheels to turn large metal drums. A computer monitors the speed of the drums over time, and the amount of energy needed to spin them can be calculated. This amount of energy translate into torque (foot pounds) and power (horse power).

Porsche 914 on a Dynojet mobile chassis dynometer


Once it's strapped down and hooked up to a computer, it's time to drive! It's a curious feeling accelerating and shifting gears while standing still. The idea is to get the drums rolling and get the car to a medium high gear - I used 4th - then, when the computer is recording data, step on the gas and run it up to red-line.


I did a bunch of runs, trying out different carburetor jets and adjustments - each run was a learning experience and a way to collect data. Here's a graph that shows the results from one run. Torque and HP are graphed on the top and the air-fuel ratio (measured by the exhaust gas) is graphed at the bottom:

Dyno chart of Van's Porsche 914


One of the big things to note is the air-fuel ratio dip around 3,000 RPM. This means the engine is running rich and, consequently, builds more power once it goes back to the proper fuel mixture. Can it be corrected? Probably, but I need a few more jets to try and need to focus on the ignition timing.

Ever wonder what a carburetor looks like when it's working? I did - so I rigged my camera to film a carb for a run:


And, finally, my car had it's public debut at my town's Memorial Day parade:

Porsche 914 decorated for a parade


All pictures and text copyright 2008