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Electronically Limited Top Speed

Where did the Torque figures go? don't you put that into account? Also wheel size can effect the top end speed? etc..

My 2004 320 Cdi has 267bhp and 410ibft and weighs about 1730Kg, Height 1450mm so what's the top speed of that?

The influence of torque is limited only to power being a function of torque. Therefore if the power is known, then the torque is not used in the calculation.

Yes, wheel size can affect top speed. Lots of things can. It can affect both gearing, drag and rolling resistance.

I noticed that the drag coefficient of the skinny tyred E240 was 0.26 whereas other models with wider tyres were 0.27 - see second link below.

Sources:
Mercedes-Benz E W211-E 320 CDI
Mercedes-Benz E-class W211

transmission losses 18%
engine power (at the flywheel) 267 BHP
engine power (at the wheels) 219 BHP
engine power (at the wheels) 163 kW
vehicle track 1.577 m
vehicle height 1.452 m
maximum vehicle cross section 2.06 m*m
vehicle mass (weight) (kg) 1735 kg
air density 1.202 kg/(m*m*m)
drag coefficient 0.27

Theoretical top speed of W211 E320 CDi with modified engine is 164 mph.

With 221 bhp, top speed is 152 mph.
 
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Got a few bits of data from the interweb. Can anyone help me fill in the blanks ?

W220

transmission losses :dk: ?18%
engine power (at the flywheel) 306BHP
engine power (at the wheels) :dk: 251 BHP @ 18% loss
vehicle track 1574mm
vehicle height 1444mm
maximum vehicle cross section :dk:
vehicle mass (weight) (kg) 1855kg
drag coefficient 0.26

Using the information provided above

transmission losses 18%
engine power (at the flywheel) 306 BHP
engine power (at the wheels) 251 BHP
engine power (at the wheels) 187 kW
vehicle track 1.574 m
vehicle height 1.444 m
maximum vehicle cross section 2.05 m*m
vehicle mass (weight) (kg) 1855 kg
air density 1.202 kg/(m*m*m)
drag coefficient 0.26

The theoretical top speed of the W220 S500L (306) is 174 mph.
 
Good job indeed - that 1mph could be the death of me! :D

Thanks for working it out though - much appreciated.

It does beg the question, what's the point limiting it, and if they are doing it for safety reasons (or to show they are "doing their bit") then why not limit it to something much closer to the speed limit?

You're very welcome. Getting the information is what takes the time - typing it in takes only seconds.

As I think has been suggested, it originates from a gentlemens agreement between several German car manufacturers and the German Government. It was generally in the interests of safety, and I believe it was one of the factors in the Government continuing to allow a more liberal speed limit than other countries.

Of course it has practical and marketing benefits too. It enables cars with fairly modest top speeds by modern standards to be grouped with much more exotic machinery. It also means that tyres with a lower speed rating can be fitted, which reduces costs for the manufacturer - only a little per unit, but they sell lots of units!!

If the electronic limiter was reduced by much then most cars above city run abouts and eco cars would be limited!!
 
Is it a diesel thing to struggle top end?

The torque and power delivery characteristics of a turbo diesel engine means that they give their best in the mid-range. Torque falls off rapidly at higher RPMs, which is exactly where you'll be in the rev range towards the end of a high-speed run. Couple this with the aerodynamic drag at those speeds and not much happens in terms of acceleration!!

Hence why a diesel engined car might feel like it's struggling more at very high speed than say a peaky petrol engine, which in contrast is giving it's best at high revs. That said, ask someone with a Mazda rotary, Honda V-TEC, E36/E46 M3 what happens when they floor it at 35 mph without dropping a gear - they're struggling, but a turbo diesel would be kicking you in the back!!
 
Although I am extremely interested surely no one is going to give an accurate answer here? :(
Maybe you could work out a rough estimate by hitting the rev limiter in 6th?

Depends what you call accurate. Based upon the values used for the calculation it's absolutely accurate. Based upon top speed publoshed by the manufacturer or claimed by owners/drivers...

If any theoretical calculations were given, it would be nice to "calibrate" those against the E250CDI that has a 149 mph top speed, likely the car with the max speed closest to 250 km/h and not limited.

A good idea. A current model and so the Mercedes website contains some useful information.

Unfortunately Mercedes do not provide details of transmission losses, or power at the wheels and so I've used the same 18% approximation that I usually do in the calculations below.

I'm also unable to find the official published cross sectional area and so again I'll use the same approximation based upon widest track and height as I usually do.

transmission losses 18%
engine power (at the flywheel) 204 BHP
engine power (at the wheels) 167 BHP
engine power (at the wheels) 125 kW
vehicle track 1.604 m
vehicle height 1.471 m
maximum vehicle cross section 2.12 m*m
vehicle mass (weight) (kg) 1735 kg
air density 1.202 kg/(m*m*m)
drag coefficient 0.26

The theoretical top speed of the E250 CDi BlueEfficiency is 148 mph.

Mercedes published top speed is 149 mph. Sadly my approximation for two very significant variables mentioned in the post limits accuracy, as does assuming the rolling resistance coefficient of the road surface.

I can live with a delta of 1 mph though. ;)

Although I am extremely interested surely no one is going to give an accurate answer here? :(
Maybe you could work out a rough estimate by hitting the rev limiter in 6th?

If you tested the top speed of two identical cars taken straight from the production line, the actual top speed achieved for each would vary between the two and the published figure.
 
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Using the information provided above

transmission losses 18%
engine power (at the flywheel) 306 BHP
engine power (at the wheels) 251 BHP
engine power (at the wheels) 187 kW
vehicle track 1.574 m
vehicle height 1.444 m
maximum vehicle cross section 2.05 m*m
vehicle mass (weight) (kg) 1855 kg
air density 1.202 kg/(m*m*m)
drag coefficient 0.26

The theoretical top speed of the W220 S500L (306) is 174 mph.

Right Steve

When are you getting it de-restricted and if you are, can I get a lift to the next meet :thumb::thumb:
 
If you tested the top speed of two identical cars taken straight from the production line, the actual top speed achieved for each would vary between the two and the published figure.

I heard (and may be wrong) that for top speed, the Italians test eg 50 cars and use the highest figure seen, the German test 50 cars and publish the lowest and the British publish the average?
 
I heard (and may be wrong) that for top speed, the Italians test eg 50 cars and use the highest figure seen, the German test 50 cars and publish the lowest and the British publish the average?

Do Italians "by accident" let one Ferrari slip in the group of 50 cars? :rolleyes:
 
I heard (and may be wrong) that for top speed, the Italians test eg 50 cars and use the highest figure seen, the German test 50 cars and publish the lowest and the British publish the average?

I have a feeling that statement may not have too much substance behind it. There is no national preference as far as I'm aware.

There really is no need to test top speed - it is known (calculated) from the design requirements. Manufacturers may test it to make sure the car can do it, but the test will really be about the dynamics at speed, not the actual top speed.
 

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