blueovalz Posted December 23, 2003 Share Posted December 23, 2003 One measure of energy or losses expended is heat. How much heat is the transmission and differential (along with wheel bearings, joints, and yes tires that are aligned incorrectly) producing. I've never done a run on a dyno, but just curious, how does the operator isolate the torque effected by gear ratio or transmission gear ratio. I'd think that my 4:11 rear end would skew the numbers verses a 3.54 rear end. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted December 23, 2003 Share Posted December 23, 2003 I've never done a run on a dyno' date=' but just curious, how does the operator isolate the torque effected by gear ratio or transmission gear ratio. I'd think that my 4:11 rear end would skew the numbers verses a 3.54 rear end.[/quote'] EXACTLY!!! I suggested this the other day and kinda got shot down... it seems to me that a higher numerical diff or higher geared tranny or combination of both would definately result in higher torque numbers... I mean think about it... a car with a 4.11 definately pulls harder and will accelerate faster in a given gear than a car with a 3.54. Figure a car also accelerates faster in a lower gear... which should/could skew the numbers too... I know some dynos have dynoed my car in 3rd gear, and some have done it in 4th. Quote Link to comment Share on other sites More sharing options...
TimZ Posted December 23, 2003 Share Posted December 23, 2003 I've never done a run on a dyno, but just curious, how does the operator isolate the torque effected by gear ratio or transmission gear ratio. I'd think that my 4:11 rear end would skew the numbers verses a 3.54 rear end. Well, yes and no. An inertia dyno measures the acceleration of the roller, whose rotational inertia is known and constant. This is directly proportional to the torque being applied to the roller, but it is not the value that gets reported as the engine's torque, for exactly the reasons that you mentioned above. Instead, the power being delivered to the roller is calculated from the acceleration of the roller (i.e., torque to the roller) and the speed of the roller. This way, no other inputs are needed to get the power figure. Because of this, the gear ratio issue goes away - the torque to the roller is higher, but the speed of the roller is proportionally lower, so the effect is cancelled out. Perhaps you've noticed that they can still give you an accurate power graph, even if they can't get your rpm signal - this is why. The torque value that is reported is calculated from the power figure generated above, and the engine RPM (torque = HP*5252/RPM). This is why they need a pickup for the engine RPM to give you a torque number. Now, frictional losses are generaly higher for shorter (numerically higher) gearing, so all else equal, shorter gearing will probably net a somewhat lower dyno reading, just not for the reasons you were thinking. Also, because the system works by measuring acceleration rates, taller gearing will tend to give more repeatable results, due to the slower rate of change - it's just less noisy. Quote Link to comment Share on other sites More sharing options...
blueovalz Posted December 23, 2003 Share Posted December 23, 2003 Sounds good to me. What I glean from this then is a chassis dyno is fine for power while an engine dyno works well for both torque and power when it comes to what's at the flywheel. The enertia of the drum seems to be the key then in measuring all this. Thanks. Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted December 23, 2003 Share Posted December 23, 2003 TimZ, that is an excellent explanation. Makes sense to me, I was curious that my dyno chart was taken in third gear - I thought my 419 torque was high as a result - but now I know it's REAL! (unless they screwed up the rpm readings...possible ) Quote Link to comment Share on other sites More sharing options...
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