BrianE
12-20-2009, 01:03 AM
From time to time the subject of whether a dynamometer test would be a good idea when going through the pre-buy stages of purchasing a Prevost. While I've never spoken to anyone who has actually done this, I've always been curious about the validity of the procedure. It turned out, with the proper equipment, a trained technician, and thanks to DDEC and a good computer program, the test should be very accurate.
When our new to us Royale had just turned 100K miles I contacted the previous owner and learned the bus had never had a valve adjustment. Since we were having the rear closet re-carpeted anyway and would soon be leaving for the Oklahoma rally, it was a good time to get the job done. All well and good however during the trip it seemed we had lost some power as a result of the adjustment. Add to that the fact that Mango's Mothership easily out climbed our bus on the trip to California Coach, I decided a trip to the dyno shop would be in order.
Last week I made an appointment at Pacific Power Products (a large west coast DD-Allison dealer) in Eugene, OR and had the job done on Thursday. PPP was very cooperative when I explained I'd like to take some photos for a show and tell and the tech was also enthusiastic when he learned that some Prevost owners are actually interested in the greasy stuff.
In the first 2 photos you can see the rear of the bus is restrained by a large chain shackled to the frame, the purpose of this chain is to keep the rear of the bus straight. The front chains actually keep the bus from charging ahead off the roller.
The drive wheels are shown on the dyno roller in the third photo. This dyno is normally used to test tandem axle trucks, hence the two rollers. The rollers are approximately 6' in diameter and are 15' long. Water is pumped into the rollers to create the rolling resistance. This particular machine was rated at 800 horsepower, a fact I wasn't made aware of until we ran the test. More on this later.
The 4th photo shows the tech holding a specialized DDEC reader. He will control engine throttle position directly from the reader, manual application of throttle is not necessary. Shift selection however is made on the shifter keypad. There is a laptop computer sitting on the dash behind the right windshield.
The 5th photo is a laptop page showing the engine configuration and basic parameters.
Ran out of photo space, continued on next post.
When our new to us Royale had just turned 100K miles I contacted the previous owner and learned the bus had never had a valve adjustment. Since we were having the rear closet re-carpeted anyway and would soon be leaving for the Oklahoma rally, it was a good time to get the job done. All well and good however during the trip it seemed we had lost some power as a result of the adjustment. Add to that the fact that Mango's Mothership easily out climbed our bus on the trip to California Coach, I decided a trip to the dyno shop would be in order.
Last week I made an appointment at Pacific Power Products (a large west coast DD-Allison dealer) in Eugene, OR and had the job done on Thursday. PPP was very cooperative when I explained I'd like to take some photos for a show and tell and the tech was also enthusiastic when he learned that some Prevost owners are actually interested in the greasy stuff.
In the first 2 photos you can see the rear of the bus is restrained by a large chain shackled to the frame, the purpose of this chain is to keep the rear of the bus straight. The front chains actually keep the bus from charging ahead off the roller.
The drive wheels are shown on the dyno roller in the third photo. This dyno is normally used to test tandem axle trucks, hence the two rollers. The rollers are approximately 6' in diameter and are 15' long. Water is pumped into the rollers to create the rolling resistance. This particular machine was rated at 800 horsepower, a fact I wasn't made aware of until we ran the test. More on this later.
The 4th photo shows the tech holding a specialized DDEC reader. He will control engine throttle position directly from the reader, manual application of throttle is not necessary. Shift selection however is made on the shifter keypad. There is a laptop computer sitting on the dash behind the right windshield.
The 5th photo is a laptop page showing the engine configuration and basic parameters.
Ran out of photo space, continued on next post.