TDIs and bhp question?

[Davidp]

Here’s a question for TDI geeks.

The TDI 2.0 litre 140bhp engine in the Leon has a faster 0-60 time that the same engine in the Altea. Obviously the Altea is heavier and taller so you would expect it to be a bit slower. Thing is though the 140 bhp is measured at the brake so does it not take into account the weight of the vehicle.

In other words to achieve 140bhp in an Altea (or a heavier car than the Leon) the engine would have to be remapped to produce more power to achieve the 140 bhp at the wheels.

Have I got this wrong, is it just the same engine plonked into each car with no retuning or remapping.

A VW dealer explained to me that if I drove a 140bhp Golf it would be exactly the same acceleration as a 140bhp engine in the heavier Passat as the engine is retuned to give the same power at the wheels. The 0-60 figures don’t bear this out so I find it hard to believe.

So I’m confused!

 

[redcupratdi]

A VW dealer explained to me that if I drove a 140bhp Golf it would be exactly the same acceleration as a 140bhp engine in the heavier Passat as the engine is retuned to give the same power at the wheels. The 0-60 figures don’t bear this out so I find it hard to believe.

So I’m confused!

no acceleration is to do with bhp/tonne so no the 140bhp in the passat would be slower than in the golf

also the 140bhp is the manufactures quote at the flywheel not the wheels

so transmissons losses are whatever it the drive train is less effiecent in the passat then it would have even less power at the wheels than the golf.

the 140 2.0 has the same power whatever car it is in the heavier the car the slower the acceleration!

 

[Davidp]

thanks for the info thats great.

if the bhp is measured at the flywheel why is it called 'brake horse power'.

if you get your car remapped (say revo) dont they measure the bhp under load on a test rig so if its in the car how can they measure it at the flywheel, surely the car weight has something to do with it if its on a rig.

cheers

 

[Fluke]

Firstly, it's call 'brake horse power' because it is measured by the power needed to brake the engine to a halt.

Secondly, power measured at the flywheel or the wheels or wherever has nothing to do with the weight of the vehicle.

Thirdly, the dealer lied. If the heavier Passat want to get to 60 as quick as the Golf, it needs more power. That could be done by tuning it to deliver more power through the rev range, without affecting the peak power figure, but in that case why not put that more flexible engine in the Golf to begin with?

 

[sssstew]

typical dealer comment! (rolls eyes!)

 

[OLDOILER]

Here’s a question for TDI geeks.

The TDI 2.0 litre 140bhp engine in the Leon has a faster 0-60 time that the same engine in the Altea. Obviously the Altea is heavier and taller so you would expect it to be a bit slower. Thing is though the 140 bhp is measured at the brake so does it not take into account the weight of the vehicle.

In other words to achieve 140bhp in an Altea (or a heavier car than the Leon) the engine would have to be remapped to produce more power to achieve the 140 bhp at the wheels.

Have I got this wrong, is it just the same engine plonked into each car with no retuning or remapping.

A VW dealer explained to me that if I drove a 140bhp Golf it would be exactly the same acceleration as a 140bhp engine in the heavier Passat as the engine is retuned to give the same power at the wheels. The 0-60 figures don’t bear this out so I find it hard to believe.

The power/weight/cd/gearing/trans type ALL have an effect, the heavy car will lose out to the lightweight car - (if the eng/trans are the same).

To get 140 at the wheels you'l probable need an extra 25/30bhp - this is a very coarse assumption hope this helps

 

[Davidp]

Thanks Guys
questions answered and understood.
Cheers

 

[muddyboots]

You have to take account of different gear ratios too. You could put a lower-power engine in the Passat and it could still accelerate faster than the Golf if the gearing was suitable (but would have no top-end speed).

 

[basstard]

then it's not only a maximum power output issue either [as fluke partly explained],,, if you take a high revving jap that has, say 200hp at say 6500rpm, it might have much lesser hp figures at lower revs,,, on the other side, you could take a petrol turbo with, say 180hp, but with a much flatter torque curve, well spread along the rev range and if you do the integral of the power and torque curves of both engines, it could quite easily happen that the area under the curves is bigger on the turbo engine graph,,,

I don't know if I have been clear,,,

 

[Davidp]

then it's not only a maximum power output issue either [as fluke partly explained],,, if you take a high revving jap that has, say 200hp at say 6500rpm, it might have much lesser hp figures at lower revs,,, on the other side, you could take a petrol turbo with, say 180hp, but with a much flatter torque curve, well spread along the rev range and if you do the integral of the power and torque curves of both engines, it could quite easily happen that the area under the curves is bigger on the turbo engine graph,,,

I don't know if I have been clear,,,

I think what you are saying is that you can have a very powerful engine but with only a tiny power band.
My 150bhp 1.9 tdi has a great power band once you get over 2000rpm so I suppose its all down to having the right amount of power in a usable rev range.
Cheers.

 

[basstard]

Yes, 450Nm over a 1000rpm range
380Nm from 2500 to 6500 rpm