[coyled]

They both do the same thing. But, the engine dyno has less mass to turn so the flywheel, drive train, tires, how well the dyno is tied down, etc. There are just a lot more variables with a chassis dyno, different types of chassis dyno's, hence more variances.. An engine dyno is used for race classes and tend to be more accurate. The reason is that if a team gets a motor from you producing xx hp, they will know on the track if the hp is fudged when some other same class racer walks away from them on the straight. I also think the chassis dyno is more for tuning the motor than anything else. The hp loss is only a guess on a chassis dyno. But, comparing your cobra to somebody elses cobra of the same weight on the same dyno, will tell you who has more rear wheel hp. Scott