What is DJHP?

One abbreviation you may see in dyno readouts is DJHP corrected. This stands for DynoJet Horsepower corrected.

There is a long story behind this, but basically when Mark Dobeck first built the cheap and cheerful DynoJet dynamometer the automotive industry was rife with over-egged claims of exaggerated bhp figures. 

Dobeck started selling carburettor jet kits but found a problem of proving the jet kit’s performance.  He also found that mechanics didn’t have a proper way to tune the engines to take full advantage of his kits.  He researched and developed a dynamometer.  The dynamometer was basically like any other dyno and used the Torque x RPM / 5252 formula.  He decided to test a motorcycle that advertised the most horsepower available in 1985.  That bike was the Yamaha V Max and was advertised to have 145 horsepower.  The chassis dyno only showed around 120 hp.  The dyno engineers double checked to find out why the readings differed.  The dynamometer was correct, which meant that the advertised HP was fudged.  Instead of sticking with the SAE formula, he told his engineers to fudge on the formula to make the dyno read what the advertised HP was.  Basically they changed the formula to read: ‘Torque multiplied by RPM divided by 5252 multiplied by 1.20’.  This formula configuration is still used today on Dynojet dynamometers.  

So when newer more accurate dynos were developed, they were given the option of showing the power calculation as DJHP corrected, or in other words, falsely inflated to massage the egos of scooter owners who are used to hearing higher figures from their engines.