I thought they weighed about 1000 lbs each. I was just wondering because I watched a handful of cars dyno last weekend and they seemed to accelerate the drums pretty good straight from 2000rpms in 4th gear. Is it theoretically like accelerating 2000lbs? The reason I was wondering was because there is no way my Maxima could accelerate like that in 4th gear at 2000 rpms. I could see it if the drum weighed less than the car, but otherwise no. I visualize my car lagging along trying to build up rpm from 2000-3500 rpms....and my car ain't slow by any means.

Dave

 

the the drums do weight around 1000 pounds each or so, but the cars DO NOT start out in 4th gear, they slowly accellerate from 1st, to 2nd then 3rd, then go to 4th then they punch it.

 

It's rotating mass, so you've gotta figure 1000 lbs spread over whatever the radius is, if it's a solid drum. Goes something like 1/2 mass times radius squared...

 

Yeah, they accelerated thru the gears like normal. I was just amazed at how easily a Probe GT was able to spin the rollers from 2000 rpms in 4th.

Another question. Aren't they suppose to let the engine coast down in gear after doing the run? I always thought it was bad on the car to apply the brakes at a high rpm on a dyno because the tires could loose grip and hop horribly on the rollers and possibly break an axle or half shaft.


Dave

 

actually you want to put the car in neutral and use the brake on the dyno roller to slow everything down.

 

A dyno drum weighs 3200 pounds.........

 

I thought that's what I've heard, too.

But to nitpick (sorry), I don't think that the actual weight of the roller is 3200 lbs, but that the acceleration the drums is the equivalent of accelerating a 3200 lb mass (your car). The results of a dynojet dyno test are optimized when the car weight is 3200 lbs (engine has as difficult a time during the test as it does on a flat street). Luckily, that weight nearly matches the weight (w/ driver) of a 4th gen Maxima. But yes, I think I recall hearing 3200 in the past.