Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[cem_devecioglu]

 
 
last week we tested a friends auto omega 2.5 (year 2000) on a dyno.. the car had inconsistent results..
 
first measure was around 231 cv     later we changed to another roller.. this time measured 207.5 cv on the second run and last time 199 cv.. any opinions 
 
 

[05omegav6]

Clutches slipping as it gets hot due a fluid change perhaps...

[Entwood]

Auto's on dyno's are always "difficult" as the gearbox does odd things to the readings on rundown, which is when the "system losses" are calculated. Very hard, if not impossible, to get accurate readings.

[cem_devecioglu]

Clutches slipping as it gets hot due a fluid change perhaps...

but how can be a stock 2.5 this much powerful ? 

[Marks DTM Calib]

I seem to recall seeing something in TIS about locking up the torque converter with Tech 2 when doing a dyno run.

[cem_devecioglu]

Auto's on dyno's are always "difficult" as the gearbox does odd things to the readings on rundown, which is when the "system losses" are calculated. Very hard, if not impossible, to get accurate readings.

you may have right Entwood.. a stock 2.5 is around 170 hp .. those figures are too high

[cem_devecioglu]

I seem to recall seeing something in TIS about locking up the torque converter with Tech 2 when doing a dyno run.

thanks Mr DTM.. 
 
we were very surprised and baffled with the results.. obviously the dyno shop had no idea about Tech 2

[Entwood]

If memory serves me from way way back ... Dyno test is done (on a manual) up to WOT in the gear that best approximates to 1:1 ratio ... then the throttle is released, neutral selected and the system coasts to a halt, during which time the losses (drag from gearbox/diff) are calculated.

With an auto it is very difficult to get "lockup" at WOT as the system goes to "sports mode" (kick down) by default and will keep trying to change gear (down) as the dyno load increases, - on the Omega if the road wheels drop below 40mph (ish) then the torque convertor unlocks as well !

As soon as the throttle is released from WOT the gearbox will change UP the gears - very quickly - which throws the calculations of drag out, and selecting neutral is not good for the system. Either way the calculations see a very large amount of "drag" and so falsely UP the power achieved by the engine ....

Power of engine = power developed during run + power lost to drag

So a high false reading occurs...

Now all that is dragged from memory cells that have slept many times since I last used a dyno.... and may well be out-of-date for modern dynos and gearboxes ..... 

[Kevin Wood]

The autobox is creating more drag during the coastdown, where the system calculates the losses, than on the acceleration phase, probably because the energy is going into drag in the clutches in the box. 

This gives you an unrealistic figure. Do you have the plot and the losses calculated?

A dyno needs to be well calibrated and the run executed with skill to get consistent figures even before you throw in an automatic box IME.

[Entwood]

Had another thought to add to the above .... if neutral is NOT selected, and the engine is a DBW, then the ECU will switch off the injectors to give maximum engine braking on the coast down, so the "drag" will be even higher as the rollers are actually driving the engine !!

[Kevin Wood]

You have to select neutral to get any sort of meaningful coastdown. Otherwise, you will get loads of engine braking.

To be honest, it's probably better just to skip the coastdown and use figures at the wheels, although they'll be horribly inconsistent too, it's the best of a bad job.

[Marks DTM Calib]

Had another thought to add to the above .... if neutral is NOT selected, and the engine is a DBW, then the ECU will switch off the injectors to give maximum engine braking on the coast down, so the "drag" will be even higher as the rollers are actually driving the engine !!

Not just DBW, true of all the Omega engines

[cem_devecioglu]

If memory serves me from way way back ... Dyno test is done (on a manual) up to WOT in the gear that best approximates to 1:1 ratio ... then the throttle is released, neutral selected and the system coasts to a halt, during which time the losses (drag from gearbox/diff) are calculated.

With an auto it is very difficult to get "lockup" at WOT as the system goes to "sports mode" (kick down) by default and will keep trying to change gear (down) as the dyno load increases, - on the Omega if the road wheels drop below 40mph (ish) then the torque convertor unlocks as well !

As soon as the throttle is released from WOT the gearbox will change UP the gears - very quickly - which throws the calculations of drag out, and selecting neutral is not good for the system. Either way the calculations see a very large amount of "drag" and so falsely UP the power achieved by the engine ....

Power of engine = power developed during run + power lost to drag

So a high false reading occurs...

Now all that is dragged from memory cells that have slept many times since I last used a dyno.... and may well be out-of-date for modern dynos and gearboxes ..... 

phew.. to much info

[cem_devecioglu]

The autobox is creating more drag during the coastdown, where the system calculates the losses, than on the acceleration phase, probably because the energy is going into drag in the clutches in the box. 

This gives you an unrealistic figure. Do you have the plot and the losses calculated?

A dyno needs to be well calibrated and the run executed with skill to get consistent figures even before you throw in an automatic box IME.

nope.. the owner took the papers and from that time the question was both on our heads