petrol/diesl torque /bhp

[robert_374565247]

which is considered better for towing

2.5L petrol giving 174 BHP or 3.0L diesel giving a similar BHP?

How does torque fit into the equation what is more important BHP or Torque, indeed is there a difference or are the two directly proportional?

 

[Mikey_74]

Torque is more important and more useable, my choice without a 2nd thought would be the diesel, and with one that size you really wouldn't know a caravan was on the back

 

[Guest]

Engine pulling power is all about Torque, BHP is a measurement of work rate based upon the torque an engine has.

For towing there is no question a diesel has more torque low-down, which aids towing, obviously.

but Petrol engined cars are quite capable of doing a good job too.

 

[Philspadders]

Diesel.

Torque is the "pulling power" the engine develops.

On Diesels this gives maximum "pulling power" at very low rpms when compared to a petrol engine.

A diesel usually achieves max torque at around 2500 rpm,where as a petrol would be up at around 3500 to 4000 rpm.

Thats one of the reasons heavy goods vehicles use diesel engines and not petrol.

What it really means is that you dont need to rev its nuts off to get going ,especially on hill. However you may not accelerate as fast and may go down the gear box a bit on hills when compared to a petrol.

For example i can climb a 10% gradient with a 2.0l diesel in 1st with the van on the back in slow moving traffic and my feet on the dash board with the engine doing 1400 rpm.

To do the same with a petrol engine i would need a lot more rpms and would probably have to keep slipping the clutch... and we dont want that.

 

[otherclive]

Go for the diesel for the far better pulling capability. Doesn't the diesel that you are looking at show better mpg than the equivalent petrol, I would be very surprised if that were not the case. Also a diesel of teh type you are thinking of would be a real belter when overtaking solo or when towing....is it an Audi or BMW?

 

[Sproket]

I have a 3.0 ltr diesel auto, which gives max torque at 1800rpm, i use cruise control when ever possible @ 60mph which is equivalent to 1900rpm ( 1500rpm = about 50mph ) on the newer engine the max tourqe is now at 2000rpm.

When fully laden towing our 1600kg van, we weigh in at about 4.25 to 4.5 tons & get about 23-25mpg @ 60mph whilst towing.

You can't go wrong with a big lazy diesel.......

 

[Garfield]

Power = force X velocity

which is the same as saying

BHP = torque X RPM

You can put a sanner on a driveshaft and exert torque, but if the brake is on, nothing moves and no power is produced so torque on its own gets you nowhere, it is power (bhp) that determines how well an engine pulls.

you can double the torque an engine produces by attaching a 2:1 reduction gearbox but the power stays the same as the rpm is halved (ignoring friction losses)

Hence a 1200cc motorbike engine with 160bhp @ ~12000rpm / 90lbft torque will outperform a 115bhp @4000rpm / 236lbft torque in a vehicle of identical weight, by using lower gears, but it will be screaming away to do this, if both vehicles were in an appropriate gear to be both doing 40mph at 2000rpm and you floored the accelerator, the diesel would leave the bike engine for dead, as the diesel would be producing about 70bhp @2000rpm but the bike engine would be producing about 20bhp @2000rpm

In the real world of car engines the 2.0 tdci S-max produces 71.2kw @2000rpm but the petrol 2.0 only produces about 39kw @2000rpm, the 2.5 petrol turbo has the same max torque as the 2.0 diesel turbo but because it can produce torque at much higher revs, it has more power.

Confused yet????.

Contrary to another post, the turbo diesel will need to change down less on hills (the non turbo diesel is a gutless heap of junk that is not worth mentioning!).

Another aspect is that the modern diesel can be quieter than a petrol when towing because it needs far fewer revs to produce an equivalent power.

 

[xtrailman]

The original post gives insufficient data to enable any accurate recommendation.

Are they turbo engines?

Are they pulling the same car?

What is the gearing/ number of gears?

 

[robert_374565247]

The question was a hyperthetical one I am currently using my nissan x trail 2.5 sve petrol auto to tow my abbey expression. I considered a 2,5 petrol to have a similar BHP to a 3.0 diesel. I have been scanning other cars wondering if another combination would be better. reading the spec lists it struck me that these two ratings, to me, were unclear and which was more important.

My thanks to the respondants

 

[xtrailman]

I have towed 1333kg with three different tow cars.

1/ A4 1.8 Turbo Quattro Avant petrol 0/60 in 8.5 secs, 145mph, 180bhp/171 lbft

torque max from 1950 to 4500rpm.

Towing 23/25, solo max 33mpg.

Kerb around 1550kg if i recall correctly speed.

2/ xtrail 2004 2.2 diesel turbo, 0/60 in 12.5 secs, 120mph approx. 134bhp/231 lbft, torque max at 2000rpm.

This car is almost perfectly geared for towing, 6 speed gives around 60 mph at 2000rpm max torque, kerb around 1650kg SVE. Towing around 30mpg. Solo around 40mpg.

3/ present car xtrail Aventura explorer 2009.0/60 9.5 sec, around 127mph.

171bhp/266 lbft max torque at 2000 rpm.

Kerb around 1720kg.

6 gear is too high for towing at 60mph, except on the flat. requires a down change on long up hill gradiats, but has become noticeable more flexible with mileage, will tow happily now at 1500rpm on the flat.

Towing around 30 mpg.

Engine is a renault, revs like a petrol car, is very quite for a diesel, performance is excellent, but the engine does not feel as toquey as the previous xtrail. solo economy is just as good at around 40mpg.

4/ All these cars are good tow cars, really not just saying that, the low profile tyres of the audi are to be avoided, tramling with the 225/45 profile was uncomfortable on the lorry ruts, will never have a car with low profile tyres again, had 3 tyre blebs on the side walls over 4.5 years, resulting in the tyres being scrapped, not suitable for uk roads.

5/ Whatever you go for get a turbo engine, 2 litre min, or a great big lump 3 litre plus.