20-06-2012, 04:20 PM
No dyno is ever "right" as it depends on to many things...
But the thing most likely to be right / close is the torque reading, not so much in line with the rpms on graph, but just the peak torque / delivery of torque in some way... That only depends on the dyno load sensor being calibrated correctly, which in most cases shouldnt be far out, unless there playing silly with your money..
HP is obviously directly calculated from the rpms the motor is dong, now 99% of dynos, just nick this straight from your car tacho, so they bring your car up to say 3krpm, look at your tacho, tell the computer its doing x rpm there, and the computer can then calcuate the gear ratio to know what rpm its dong at any point in that gear during the pull....So instantly if your car tacho is out (which often is) the hp reading / grash will be skewed totally, and as Ruan pointed out, 250-500rpm out, can make a big different to the output... You can buy laser rpm meters from china for like 11 quid delivered, so worth getting one and revving car thro each 1k mark on your tacho, and looking to see how far out it is, because you will be quite suprised when you do this!
The next issue for diesels is dyno operator....alot of the bigger power 11mm cars, dont have very effective fuel control at all, hence the smoke...this creates chronic ammounts of bogging resulting in the turbo coming in much later than it would normally have, therefore ruining your normally driveable car and producing a graph that looks like shite...
Then obviously on top of that, you have all the other varibles like weather / temperature, lack of fans giving as much cooling as you have normally on the road etc....
In other words, dynos are never that reliable, just a usefull tool to give you a rough idea of the power, and for comparing cars directly one after another, or modifications if done at the same dyno...
Not to say your shouldnt read much into the results, as on a decent hard standing calibrated dyno, the results should be pretty good, but id only trust a dyno up to 10/20% as they read so much pants at times...
But the thing most likely to be right / close is the torque reading, not so much in line with the rpms on graph, but just the peak torque / delivery of torque in some way... That only depends on the dyno load sensor being calibrated correctly, which in most cases shouldnt be far out, unless there playing silly with your money..
HP is obviously directly calculated from the rpms the motor is dong, now 99% of dynos, just nick this straight from your car tacho, so they bring your car up to say 3krpm, look at your tacho, tell the computer its doing x rpm there, and the computer can then calcuate the gear ratio to know what rpm its dong at any point in that gear during the pull....So instantly if your car tacho is out (which often is) the hp reading / grash will be skewed totally, and as Ruan pointed out, 250-500rpm out, can make a big different to the output... You can buy laser rpm meters from china for like 11 quid delivered, so worth getting one and revving car thro each 1k mark on your tacho, and looking to see how far out it is, because you will be quite suprised when you do this!
The next issue for diesels is dyno operator....alot of the bigger power 11mm cars, dont have very effective fuel control at all, hence the smoke...this creates chronic ammounts of bogging resulting in the turbo coming in much later than it would normally have, therefore ruining your normally driveable car and producing a graph that looks like shite...
Then obviously on top of that, you have all the other varibles like weather / temperature, lack of fans giving as much cooling as you have normally on the road etc....
In other words, dynos are never that reliable, just a usefull tool to give you a rough idea of the power, and for comparing cars directly one after another, or modifications if done at the same dyno...
Not to say your shouldnt read much into the results, as on a decent hard standing calibrated dyno, the results should be pretty good, but id only trust a dyno up to 10/20% as they read so much pants at times...
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