[Bassman]

Hi all,
I was just wandering if what my dyno guy told me was true regarding dyno figures at sea level Vs altitude such as here in Canberra. He says my AU2 XR8 ute on his dyno was making good power after the Unichip with only 143 rwkw, and reckons this figure on the coast would be closer to 153. Is he right?

 

[ebxr8240]

Yep air is more dence at sea level.Atmospheric presure is less at altitude, there is less atmo pressure to push air into engine....

 

[TIKFD6]

Doesnt sound to bad Bassman, welcome to the forums.

 

[laminge]

arent these factors keyed into the dyno before the run to allow these conditions so regardless of where you are they should be the same?

 

[TIKFD6]

They should be Gaz, depends on the operator.

 

[Noboss]

A mates AU2 XR8 auto did 141 rwkw bog standed, so your sounds about right, I dont know about the hole sea level thing I think it should auto callabrate for that. Hope this helps Cheers

 

[Bassman]

I dont know how good the dyno operator is, after reading about the way some of the others are operated, ie shootout mode, where all the atmospheric conditions are adjusted for, I think I went to the wrong guy, he isnt a registered 'shootout' operator.
Anyway regardless of the figure, at the end of the day its the difference between before and after on the road that really matters, and I am very happy, the ute just revs its t**s off now. And as for air on the coast, I think Ill just have to take a run down the Clyde and see for myself.

 

[fullthrottle]

I got a question for the experienced dyno readers...
Why do people dyno kws against km/h?

Isn't it more useful to get kw vs RPM?
Then you know where peak torque and power is...?

 

[Bassman]

I hear ya, I had to ask for different print outs on my run so I could actually read the thing and work out at what revs my biggest gain in power was.

 

[Noboss]

Yer I cant work out why some use hp instead of kw's we've been using kw for years now ! so why some keep going back to hp is a bit strange dont ya think? We've had kw & nm for years.....

 

[fullthrottle]

no i was referring to the X axis. converting kw to hp is easy so never mind that.

75% of the dyno charts I see show KM/H on the X axis. I can't see how that is of any benefit to the owner. At least with RPM you know your strength/weakness in low end, midrange or top end.

I'm hoping someone can explain )

 

[slipper]

Yer I cant work out why some use hp instead of kw's...

Horsepower is a sexier unit of measurement - Galloping horses are more 'romantic' than fleets of 1000W vacuum cleaners...

 

[laminge]

Horsepower is a sexier unit of measurement - Galloping horses are more 'romantic' than fleets of 1000W vacuum cleaners...

Agree

1000hp does sound much better that 650kws!

 

[WBT56]

no i was referring to the X axis. converting kw to hp is easy so never mind that.

75% of the dyno charts I see show KM/H on the X axis. I can't see how that is of any benefit to the owner. At least with RPM you know your strength/weakness in low end, midrange or top end.

I'm hoping someone can explain )

I had to ask also. The bloke I spoke to said that it may be difficult to get a tach feed signal out of some cars, so to stop confusion among the printouts for those you can and those you can't, you just leave it on km/h instead of RPM?

 

[slipper]

I'm hoping someone can explain )

Dynos measure tractive effort (torque) only and then use a mathematical formula to calculate power:

HP = RPM x T(torque) / 5252

(where torque is measured in ft/lbs)

This formula uses engine RPM so the dyno operator *must* know the RPM of your engine at any point on the power curve. It should be a matter of asking him to change the X-axis values. If he is incapable of doing this, that is a worry.

 

[C0V3R]

They know the rpm of the rollers so I cant see why they'd need to know the rpm of the engine, since the tractive effort is being applied to the rollers anyway. RPM would be nice to know however.

 

[slipper]

They know the rpm of the rollers so I cant see why they'd need to know the rpm of the engine, since the tractive effort is being applied to the rollers anyway. RPM would be nice to know however.

They most certainly do need to know the RPM of the engine - check the formula above.

The RPM of the rollers will differ depending on the size of the roller (may vary between dyno manufacturers) and the gear the car is in. It may be used internally to measure the speed of the car. If you know the speed of the car and details about it's gearing, it is possible to calculate RPM of *the engine*

 

[Soxx]

Agree
1000hp does sound much better that 650kws!

That's cos 1000hp is actually 750kw. :shh:

Rick.

 

[laminge]

sorry

Got my pre and post nos kws mixed with my pre and post HP coversion!