Performance measurement using Racelogic Driftbox - October 2008

Click here to jump straight to the figures

I am often asked about the performance of the Mojo, usually the typical 0 - 60mph and top speed questions.  I don't see top speed as particularly relevant for a kit car; cars like the Mojo are really most at home on smooth winding B roads where top speed is not really important.  I do know that when I was let loose on the proving ground at Gaydon, I bottled at a speedo indicated 127mph (probably below 120mph actual, knowing my speedo over reads) when my sidescreens started to fold inwards!

0 - 60mph, however, is a useful measure of acceleration from rest, giving a good indication of power and traction.  Based on the power to weight ratio of the Mojo, I have always hoped that it would be somewhere in the 5sec region for this measure.  When presented with an opportunity to borrow a nifty bit of kit called a Driftbox for the weekend, I could hardly say 'no' could I?

The Driftbox is a GPS based performance meter that also has some other sensors lurking inside to enable measurement of speed, distance, longitudinal and lateral acceleration, yaw rate and sideslip (or drift) angle, amongst other things.  It is based on Racelogic's VBOX, which is a piece of equipment used widely within the Motor Industry for performance measurement, and is also used by magazines such as Autocar for all their published performance figures.  It is therefore a fairly well respected bit of kit.

It is installed using a windscreen suction cup mount mount and plugged in via a 12V socket.  Inserting an SD card logs all data to enable transfer to a PC.  Here it is installed in the Mojo:

CIMG0588.JPG (89095 bytes)

I then drove to a specially selected bit of road with a suitable layby for lying in wait for a traffic free acceleration run.  I only did about 4 runs as I wanted to be as mechanically sympathetic as possible, and my 2 fastest runs were within a tenth of each other.  So, the important figures are shown below:

Accel increment Time (s)
0 - 10 0.51
0 - 20 1.11
0 - 30 1.77
0 - 40 2.81
0 - 50 3.71
0 - 60 4.66
0 - 70 6.31
30 - 50 1.81
50 - 70 2.55
30 - 70 4.36
0 - 64 feet 2.25

The speed data for the best 2 runs is shown in the plot below:

The gearing is pretty much spot on for a 0 - 60 run, with only one gearchange required - this interrupts the acceleration for 0.3s.  The 0 - 64 feet time also seems reasonable when compared with Matt Bearshaw's Mojo K-series with 176bhp - his latest sprint at Curborough had a best of 2.31s for this interval.

I think that the 0 - 60 acceleration time could be improved a little further with more practice, warm tyres, smoother road etc, but I think somewhere in the 4.5 -  4.6 seconds bracket would be the most I could expect.  I'm happy enough with the best timed result of 4.66 to not dish out any more pain to the Mojo in pursuit of the last tenth or so!  

One final interesting exercise was to do 3 or 4 laps of a large, quiet roundabout to see what kind of levels of lateral acceleration the Mojo was able to generate.  This was done with fairly cool tyres, running the 185/60 R14 Yokohama A539s that have been on the car for the previous 20,000 miles.  The plots below show the results:

Click for larger version

G-circle shows main cluster of points at 0.8-0.9g,and some points at or slightly above 1g.

GPS position data for the oval roundabout

Speed and lateral acceleration time history

For a car running 185 section tyres, I think 1g lateral acceleration is fairly reasonable!