Manual Vs Automatic transmission losses

[Gazwould]

That's thick stuff compared to the 236.15 fluid .

 

[BTB 500]

For information - my manual W124 has transmission losses of 17.9% through a 270cdi box with Millers CRX 75w90NT+ in the box and diff. Accurate MAHA dyno on a warm 22c day to DIN70020.

The old set up was in BHP -
456 Flywheel
369 Wheel
82 Losses

How do you measure flywheel bhp without taking the engine out of the car and putting it on a test stand (engine dyno)??

 

[maxypriest]

How do you measure flywheel bhp without taking the engine out of the car and putting it on a test stand (engine dyno)??

The dyno uses the freewheel cycle (many other dynos do the same) after the power run to accurately measure the parasitic losses from the ENTIRE transmission to the rollers (from the input shaft to the edge of the tyre). The MAHA ones are often used in official automotive test houses and are very accurate. Some dynos are not… and are best used for comparative data! (…and pub chat).

 

[190]

For information - my manual W124 has transmission losses of 17.9% through a 270cdi box with Millers CRX 75w90NT+ in the box and diff. Accurate MAHA dyno on a warm 22c day to DIN70020.

The old set up was in BHP -
456 Flywheel
369 Wheel
82 Losses

82 BHP losses is 61kW. That's a lot of heat to get rid of. Any idea how that breaks down across the box, diff and wheels. Presumably you would need a cooler on the diff as well as the box.

 

[BTB 500]

The dyno uses the freewheel cycle (many other dynos do the same) after the power run to accurately measure the parasitic losses from the ENTIRE transmission to the rollers (from the input shaft to the edge of the tyre).

I think this is still an estimate though, rather than an accurate measure. For one thing the rolling resistance of the tyres will be different between max. power/speed and coasting, due to deformation etc.?

 

[popuptoaster]

I think this is still an estimate though, rather than an accurate measure. For one thing the rolling resistance of the tyres will be different between max. power/speed and coasting, due to deformation etc.?

The dyno can tell exactly how much drag is on it as it slows down so it will give an accurate measure of the losses rather than an estimate. You are right though it can be effected by lots of things, even down to tyre type but that's where experienced dyno operators come into it, power results are usually corrected for temperature, humidity and air pressure but given a decent dyno and a good operator you will get figures close enough to manufacturers specs to be accurate enough for all practical purposes.

 

[popuptoaster]

82 BHP losses is 61kW. That's a lot of heat to get rid of. Any idea how that breaks down across the box, diff and wheels. Presumably you would need a cooler on the diff as well as the box.

Drivetrain losses (efficiency) – x-engineer.org

 

[190]

That article calculates 15.9% losses which is still a lot of heat but makes the point that the losses are variable with some dependency on temperature. This would explain MB's move to thinner oils. Diffs now use 75W85 which is similar in viscosity to a 5W30 engine oil and manual transmissions use 75W MT fluid which is very thin indeed and thinner than a 0W20 engine oil.

 

[BTB 500]

The dyno can tell exactly how much drag is on it as it slows down so it will give an accurate measure of the losses rather than an estimate.

The point though is that the rolling resistance of the tyres on rundown (just coasting) is not the same as when running at full power (when they deform more). So any estimate of flywheel bhp on the power cycle using that figure will be out. The only thing that can actually be measured is the power being given at the rollers. A hub dyno is more accurate than a rolling road one because the tyres are removed from the equation, but the only way to get an accurate flywheel bhp figure (if this is really needed) is to take the engine out and run it on a test stand.

 

[popuptoaster]

The point though is that the rolling resistance of the tyres on rundown (just coasting) is not the same as when running at full power (when they deform more). So any estimate of flywheel bhp on the power cycle using that figure will be out. The only thing that can actually be measured is the power being given at the rollers. A hub dyno is more accurate than a rolling road one because the tyres are removed from the equation, but the only way to get an accurate flywheel bhp figure (if this is really needed) is to take the engine out and run it on a test stand.

As I said, a good dyno and operator will get you figures close enough to be good enough for all practical purposes, I've had an engine that was built and engine dynoed by HT racing and then was rolling roaded in the car at Track'n'Road and the figures were spot on. I'm guessing no one is going to be able to convince you otherwise but that's just the way it is.

Question 1.) So, how accurate is this dyno then ?


It is incredibly accurate and consistent.
It is simply the closest thing one is ever going to get without using an Engine Dyno.

So far, we have performed well over 9,000 dyno runs (in words: nine-thousand !) and from
those which we could directly compare against engine dyno data of the exact same engine
we have never been out by more than 1,5% which in any book is a most respectable figure.
(1,5% difference on a 200hp engine for example means 3hp - this would be the absolute difference,

not the difference between runs. The difference between runs is far less)

Source: TRACK 'n' ROAD and TAT Rolling Road / TAT Chassis Dyno

 

[Justintyme]

If I'm not mistaken, the VAG DSG automatic transmission was a development from their racing car box.

 

[AllPow]

If I'm not mistaken, the VAG DSG automatic transmission was a development from their racing car box.

I think you’re right. It’s an awesome bit of kit untill it breaks!!