Horsepower vs Torque (2.5T/T5)

Can anyone explain how the torque figures are so close on the 2.5T and T5
engines (236 vs 243), while the horsepower numbers are so different (208 vs
247)?

2.5T T5
HP 208 @ 5,000 rpm 247 @ 5,200 rpm
Torque 236 @ 1,500 - 4,500 rpm 243 @ 2,400 - 5,200 rpm


If HP and torque are related by the formula
Horsepower = torque * RPM * 1/5252
how can this be explained?


What are the driving and/or performance implications of having similar
torque but different HP ratings? Is there any way of telling how much
torque the T5 would have at 1,500 RPM?

Thanks in advance......

 

Well, just looking at the numbers you give, above, the 2.5T
shows the torque from 1,500-4,500 rpm but supplies the HP at
5,000 rpm, which isn't in that range...


Cheers,
-+JLS

 

The 2.5T obviously starts delivering torque at lower rpm's. Or it is
just defined at that rpm. It is never flat over a range of 1500-4500
rpm.

This is only valid at one rpm. This does not explain the bandwidth.
Power = torque * conversionfactor (read: gearing).

Look at the motor data.

high torque advantages: A motor that has a high torque at lower rpm
makes driving easier and less nervous. You do not have to change gear
often, it drives easier in the mountains, and it can pull heavy
weights - diesels are like this. The mileage is probably good too.

high power advantages: when you want to drive in a 'sportive' way. At
the high revs you have more power.

I personally would go for torque.
We drive a Volvo 440 1.8i, and an old Peugeot 1.9 Diesel. The Volvo is
much faster, much more acceleration, much better road behaviour, more
comfort etc. But when I must pull a caravan, I take the Peugot for its
torque.

Regards,

Pieter Hoeben
http://www.hoeben.com

 

Because power is the product of speed and torque, you get higher powers when
the max torque occurs at a higher speed. For example, diesel engines have
very high torque at low speed, but relatively low max power because they do
not operate at high engine speeds.

To fully understand the examples you have given, you need to plot the
figures on a graph. Tabulate the published torque figures at various engine
speeds and calculate the power in each case, using the formula which you
have quoted. The torque on the 2.5T falls off after 4500rpm - so the power
doesn't go on rising so steeply as it does on the T5 - which holds its
torque right up to 5200rpm (if we believe the figures!).

Cheers,
SS

 

Following what has already been said, hp quoted is at a single
operating point. So for a 2.5T delivering 208 hp at 5000 rpm, the
torque is 218 ft*lbf. For the T5 delivering 247 hp at 5200 rpm, the
torque is 249 ft*lbf.

It is useful to compare hp at consistent rpms where torques are
provided, for example:

at 2,400 rpm: 2.5T T5
Torque 236 243
hp 108 111

at 3,000 rpm: 2.5T T5
Torque 236 243
hp 135 139

at 3,500 rpm: 2.5T T5
Torque 236 243
hp 157 162

at 4,000 rpm: 2.5T T5
Torque 236 243
hp 180 185

at 4,500 rpm: 2.5T T5
Torque 236 243
hp 202 208

at 5,000 rpm: 2.5T T5
Torque 218 208
hp 243 231

Between 2,400 and 4,500 rpm, the torque characteristics of these
engines are very similiar, thus the hp output is also very similar.
At 5,000 rpm the torque on the 2.5T starts to fall off while the T5 is
still flat. This is where the hp starts to change drastically between
the two engines.

 

From a technical point of view the 2.5T is a longer stroke slower revving
unit than the 2.3 T5 which immediately gives it potentially better torque
lower down the rev range. Plus the port sizes are smaller, and cam timing
such to allow it to breath well at lower rpm.

The main reason however is that the 2.5T uses quite a small low inertia
turbo which can deliver boost from very low engine revs where the T5 uses a
larger one which doesnt spool up quite so soon, but can flow alot more air.

Throw in some cunning software in the ECU and the result is as you see in
the figures. The 2.5T is able to generate maximum boost of ~0.6bar from
about 1500rpm, but at higher revs the engine just cannot breath so runs out
of puff early. Torque however is strong and linear right through low to
medimum revs....

Tim..

 

Does anyone have specs on the 2.5T turbocharger (only) and a picture
or drawing of the unit? I've got a non-Volvo project that I'm trying
to find a small turbo for, and so far, I'm not happy with the size
and/or exhaust configuration for my project.
you can e-mail them to

Thanks!

Ron/Champ 6

1963 8E5 Champ (Champ 6)
1962 Lark Daytona Convertible (Boomerang)
1995 VW Passat (Vanilla..yuk)
1994 Volvo 850 (Tilley)