Power & torque & hype

[craig-pd130]

Just reading an Autocar road test of the new Merc C220 diesel.

It's got a four-cylinder motor with 170bhp / 300lb-ft torque, and a six-speed manual box.

Yet despite the big torque figures and relatively short gearing (4th gear is 22mph / 1000rpm, 5th gear is 26mph / 1000rpm), its in-gear figures are very average:

40-60 in 4th is 4.9 seconds
50-70 in 4th is 5.4 seconds
50-70 in 5th is 6.5 seconds

These are no quicker than Autocar test figures for VAG PD130-engined, 6-speed gearbox cars that have similar gearing (Fabia vRS, Passat Sport etc), DESPITE the fact the Merc claims to have over 30% more torque.

Makes me wonder just how conservative the VAG torque figures are for the good old PD motors, and if Mercedes' figures are slightly hyped

 

[sssstew]

yes, i havent compared weights of the two cars though. but VAG have always been conservative with their power ratings, in the past the TDIs have always put out more than they say on the tin, but later ones have been closer to the mark.

 

[muddyboots]

Weight will make a big difference.

My Passat has the same engine as my Ibiza, remapped to about the same figures, and has shorter gearing - but it doesn't accelerate anywhere near as quickly as the Ibiza did.

 

[craig-pd130]

I wouldn't have thought weight would be a big factor when the car's rolling ...?

There'll be a bit of extra inertia, sure, but you'd think 30% extra torque would overcome that.

Out of curiosity, a B5.5 Passat is about 1350kg, what does a Beeza weigh?

 

[muddyboots]

I wouldn't have thought weight would be a big factor when the car's rolling ...?

There'll be a bit of extra inertia, sure, but you'd think 30% extra torque would overcome that.

Out of curiosity, a B5.5 Passat is about 1350kg, what does a Beeza weigh?

My Passat weighs 1435kg, plus the weight of whatever options are fitted, so probably getting towards 1500kg.

I remember on the way to the last Awesome RR day, Ed Butler was following me in his Ibiza (similar power output). We came off a roundabout, I gave it full beans but he closed down on me in no time at all....and that was effectively a rolling start.

 

[muddyboots]

The other thing to remember is what part of the engine's torque curve is used at those speeds & gears.
It could be that when doing 50-70 in 5th, one particular car could be right on boost, whereas another car could be floundering waiting for the turbo.

It would be interesting to compare the power/torque curves of the MB & VAG engines, they might have quite different characteristics...