I took my 2000 Volvo to a shop that has a dyno to get the engine checked out. I just bought the truck for a good price, but want to know the condition of the engine better, before putting any money into the truck. The shop informed me they cannot dyno it because it does not have a locking differential. I have confirmed there are no switches for locking the differential or to lock the front axle of the tandem pair. Are all dynos reliant on being able to lock the differential? Don't some dynos have a single roller across both sets of tires, so the differential can be left "open" for testing? I'm in the Rochester, MN area at present. Pete
"Don't some dynos have a single roller across both sets of tires, so the differential can be left "open" for testing?" Yes, they do exist, but I don't know where they have one in US. The one in the picture is in England.
Turns out I misunderstood my local shop. They showed me the dyno. What needs to be locked up is the inter-axle differential. The mid axle rides on a pair of free-wheeling rollers, while the rear axle rides against the dyno's main drive roller. So without locking the inter-axle diff, the mid axle would tend to spin at twice the speedometer speed, while the rear axle would torque against the dyno roller, similar to what happens when the mid axle is on ice. After further inspecting my axle, the service manager found the air-operated actuator cylinder for the diff locker, which was not connected (and there are no switches for it in the cab). I guess it may have been disconnected by a fleet manager sometime in its former life. He thinks they can connect shop air to activate it while on the dyno. I should find out if that worked this morning.
My truck got tested on the dyno this morning. Results were 320-355 HP and 2.3 to 3.8 inches WC for blowby. The Detroit 12.7 engine is rated at 430/470 HP; the service manager said it is currently programmed for 430. So the dyno HP readings are 74 to 82% of 430 HP, which is the range I've been told is normal for a chassis dyno. Also the blowby limit I've seen is 4 inches WC for this engine, so mine is just under that. Looks like my engine is healthy and I'm a happy camper. As a bonus, the shop connected the inter-axle locker actuator to a spare switch on my dash, so now I can control it if necessary (though I don't expect to ever again be on snow or ice!).
