How Can Whp Vary From Dyno To Dyno?

[sharkster]

I've been reading through power losses from crank to wheel of a bone stock EVO and it seems that one dyno reads a loss of 13% and another reads a loss of 22.5%...how can u trust a chassis dyno if thats the case?

[noaim]

Shak, bro read this thru. Hope it helps.

http://www.sdsefi.com/techdyno.htm

[MrCat]

I was jus wondering, are there any dynos here in Sri-Lanka..?? Has anyone tested his car on one..?? Normally there are small dynos which can read the power output at the flywheel and also there are larger dynos to measure the power output on wheels right..??

[Thusha]

  MrCat said:

I was jus wondering, are there any dynos here in Sri-Lanka..?? Has anyone tested his car on one..?? Normally there are small dynos which can read the power output at the flywheel and also there are larger dynos to measure the power output on wheels right..??

obviously no dynos 4 that ... in here

[Overdrive]

  Thusha said:

obviously no dynos 4 that ... in here

Your right. There are no dyno's in SL. They cost a bundle. and don't think they can cover the cost as we don't have that many modifying their cars for MAX power.

[MrCat]

  Overdrive said:

Your right. There are no dyno's in SL. They cost a bundle. and don't think they can cover the cost as we don't have that many modifying their cars for MAX power.

Guess u r right... So it must be a gud drag for us ppl to test da power of da machines.. Finding things out da hard way...

[isurujosh]

  MrCat said:

Guess u r right... So it must be a gud drag for us ppl to test da power of da machines.. Finding things out da hard way...

yah but in drags, the driver skills play an important role too

[Pericles]

  isurujosh said:

yah but in drags, the driver skills play an important role too

Apparently, not in SL. Driver error seems to be a reason to call off the run and re run.

[MrCat]

  Pericles said:

Apparently, not in SL. Driver error seems to be a reason to call off the run and re run.

So tru..

This reminds me of some past threads...

[Mean Green z28]

  monamonu said:

Shak, bro read this thru. Hope it helps.

http://www.sdsefi.com/techdyno.htm

pretty good read and answers a few questions but his judgement on the Innertia load/eddy current dyno is half educated. The innertia load/eddy current dyno is possibly the best chassis dyno you can get. You get the most accurate readings from this type of dyno. Ofcourse since it's more accurate, you're probably gonna see a bit less on the HP numbers but it's not like that's the only thing that gets you to the end of the track. We have cars putting down 400HP at the wheels but running numbers at the track that suggest over 500HP because of drivetrain, etc. An automatic car is gonna show less than a manual car 'cos of the higher losses in the driveline due to the torque convertor, etc. A auto car with a hight stall convertor is gonna show even more less ... but that doesn't mean it's not producing the power. We had an engine put out about 950HP on an engine dyno, but when installed in the car and dynoed, put out only 640HP at the wheels ... but it covered the 1/4mile in 9.3 seconds (pretty damn good for only 640HP right?)

There's two types of chassis dynos. The constant load dyno and the innertial load dyno. Constant load dynos have a drum of predetermined weight (usually 2000-4000lbs) and the computer calculates the power of the car by measuring the amount of time it takes the car to spin the drum. Innertia load dynos go one step further and put an additional load on the drum through means of an eddy current load cell and calculate a more accurate number depending on the weight of the car and load. Example - rather than just spinning a 2000lb drum (assuming your car weighs 3500lbs), the dyno will add 1500lbs of load to the drum (for a total of 3500lbs.) and run though the test procedure, thereby giving you a more accurate reading. As always, the run should be conducted at a 1:1 gearing for proper calculation (usually 4th gear). Any other gear would give slightly offset numbers (since a lower gear has more trq. etc.).

The weight he's talking about is probably the weight of the roller/drum used. By altering the value of the weight, the software is going to calculate the power according to the weight given. Yes, altering it will change the values, but that is why the unit is calibrated when built. I work with a innertia load dyno and it's so much better than a constant load dyno because you can actually simulate actual on-road driving by increasing the load/etc.. You can even simulate a full 1/4mile drag race (with the lights and everything!) and it's accurate to about 2-3 tenths in most cases. Ofcourse, you need to know about the car ... weight, wind resistance due to frontal area, etc. 'cos it takes all that into account when it calculates and loads the dyno accordingly. The guy from the dyno company probably didn't reply to him 'cos he was such an ignorant boob.