Manual Vs Automatic transmission losses

Gazwould

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204 HP C250 CDI's can't have the same power and torque manual and auto as surely there are transmission losses with the auto ?

I presume a bit of 'marketing' involved quoting manual figures for auto .
 

BTB 500

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They are surely quoting engine power and torque, rather than what's available at the wheels. So the type of transmission wouldn't matter.
 

rf065

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A lot of modern autos accelerate as quick or quicker than the manual versions nowadays, so very unlikely that they are down on power at the wheels.
 

BTB 500

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Modern auto gearboxes are pretty good. Hard to make a direct comparison on acceleration though as they normally have different ratios (and often more gears) than a manual.
 

Martin 1

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The VW DSG fitted cars are faster to 60 than the manuals, I don't believe that MB can't do the same.
 
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Gazwould

Gazwould

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I ask as the auto is on a dyno , a 'heartbreaker' Dyno - Dyno Dynamics, and it's down ( *Flywheel 182 HP & 340+ ftlb ) , however it flagged a fault prior which was cleared and has come back .

2018-11-27 13.44.17.jpg

What is it ?
 

st13phil

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Modern auto 'boxes pretty much all have torque converter lock up so their is no additional loss over a manual 'box.

For acceleration performance the 0-60mph / 0-100kph benchmark is often used. For a manual transmission car this can be heavily skewed by the choice of gearing which will decide if the upper speed needs one or two gear changes to reach it, while an auto is less affected as the gear changes are quicker.
 

BTB 500

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I ask as the auto is on a dyno , a 'heartbreaker' Dyno - Dyno Dynamics, and it's down ( *Flywheel 182 HP & 340+ ftlb )
A car dyno can only measure power at the wheels. The flywheel figure is just an estimate based on that and an assumed transmission loss, which may not be accurate/correct.
 

190

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I'll admit that modern Auto's are vastly better than the old 4 speed with no lock up in my 190e.

A simple answer to the original question might be which gets hotter. Any losses in a transmission component whether frictional or oil churning will be turned into heat. So which gets hotter, a manual box or an auto box. If auto boxes still need and have oil coolers I would suspect that vastly improved as they are, they may still be slightly less efficient than a manual box which needs no cooler.

Modern manual boxes have reduced losses too and now use very thin 75W oil the same viscosity as ATF.
 

Martin 1

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Look 6 posts up ! modern tech is cleverer than you think !
 

mercmancdi

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The VW DSG fitted cars are faster to 60 than the manuals, I don't believe that MB can't do the same.
I have a new vw Tiguan sel 170 bhp dsg , worst auto ever the lag when you tramp the pedal is terrible I fact it’s so bad I am taking it in for a check up,
There’s now 4000 mls on it I am sick waiting on it to improve , the last Tiguan I had 140 bhp dsg took the throttle twice as fast.
 
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Gazwould

Gazwould

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I vaguely remember 158 on one of the 3 early runs before the screen changed to flywheel figures .
 

thebiglad

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I ask as the auto is on a dyno , a 'heartbreaker' Dyno - Dyno Dynamics, and it's down ( *Flywheel 182 HP & 340+ ftlb ) , however it flagged a fault prior which was cleared and has come back .

View attachment 81563

What is it ?
If you compare dyno runs to factory figures you're not comparing apples with apples. Also if you flit from one dyno to another you'll get different figures because they may be set up differently.

The best way to get value form dyno runs is 1. establish a baseline figure on a std. engine; then do whatever modifications you plan to do. Now run again on the same dyno and get a second set of figures which shows the difference or impact of the modifications.

Also note well an important point that was mentioned earlier is to be clear about whether the results are measured at the wheels or calculated to be at the crankshaft. Just for your info the difference between the two can be as much as 20% - eg 200bhp at the crankshaft and about 160 bhp at the driving wheels. This is due to the frictional losses inherent in all drive trains.
 
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Gazwould

Gazwould

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And also the final result of tuning isn't the final result in terms of smooth curves and outputs as the ecu relearns some values .
 

190

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75w Very thin...???? o_O
Yes it really is very thin !!!

Gear oil and engine oil are not measured on the same scale. It's like comparing apples and oranges.

MB's MTF 75W gear oil is approx. 30 cSt at 40 Deg C and 6 cSt at 100 Deg C. That's thinner than even 0W20 engine oil.
 
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popuptoaster

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A good dyno with a good operator can get very close to the true transmission loss figures, they do it by letting the car slow the dyno down after the power run, there are, however, a lot of things that can effect your results, including such simple things as tyre pressures. The one I've always used make a point of having a "test" car on hand for when we do dyno days, usually something as new as possible that gets run and compared to the manufactures power figures they have, I've not seen it more than a couple of percent off and the one engine I had on and engine dyno at the engine builder and then on the chassis dyno matched up perfectly and that one was running through an old Ford Sierra 4 speed auto box

Their website appears to have died but they are on FB.

Track 'n' Road

Nope, it's working now, maybe was my connection.

TRACK 'n' ROAD and TAT Rolling Road / TAT Chassis Dyno
 
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maxypriest

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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
 
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