LPG fuel has 80-85% of the BTU value when compared to gasoline. The actual difference depends on if the LPG is butane or propan or a mixture of both. Therefore, one can expect a drop of power of 15-20% when converting from gasoline to LPG. CNG has about 80% of the BTU value as propane - one reason CNG is now a fad of the past in the lift truck world.

Most HP & torque ratings on lift truck specification sheets are based on gasoline fuel performance (except Linde) everybody likes to see the big numbers. Strange as in the US about 90% of the units 12K and below operate on LP fuel. The % of solid (or cushion tire) forklifts is about 95%+

A little fact learned from my college days. It takes about 6 HP to maintain a travel speed of 60 MPH in your automobile (assuming a flat road and not running into the winds of Hurricane IKE). This would explain while in the cruise mode equipment will run fine but when you need to accelrate or climb a grade (when higher torque is important) they are a bit doggy