BHP- V -Torque

[Guest]

I've come to a conclusion on this subject as related to towing, not solo where I've got a somewhat different view?!
My towing view is based on several 2000cc petrol Fords, replaced with a 2500 V6 auto Ford, laterly replaced with a 2200 Diesel Ford, all bar one Mondeo's, and mostly towing the same 1300kg van.
While torque/bhp figures vary quite considerable, towing at cruising speeds in 5/6th is what it boils down too, all won't tow at 50mph in top, the big V6 and 2.2 deisel are no better than the 2 litre petrols, these latter two though have just enough 'umph' at a little over 60mph to maintain top without too regularly dropping down a gear, but for me, a little too fast for relaxed towing
So the real problem is not the power of the engine, no, it's how the cars geared and their geared to cruise with effortless ease at motorway speed in top gear. More bhp/touque it has the higher the top gear will be, this cancels out any hoped for improvement while towing, esentially then, there all the same when it comes to towing and that's not very good in top!
Note, above refers to cars, not 4x4's, no experience of nor the desire to find out about them

As for Solo, the other day, my mate chucked me the keys to his, towbar not allowed, Mondeo ST220, ( 220BHP), well forget the talks, bhp is king when it comes to out and out.... delight!!

 

[seth1]

Got to agree with you Gary.All the car makers seem to do it.Increase the output of the engine but then also increase the overall gearing.Maybe with the output increase they expect the engine to be able to "pull" the increased gearing which they normally do until we put a box on wheels on the back.I find this very annoying which i have noted on here before.We have gone from a vehicle producing 228lbs ft of torque to one producing 350lbs ft of torque,the only benifit ive seen is 60mph is now attained at 1300rpm instead of 1800rpm.If however the gearing had been left the same it would have been very impressive.Instead im left disapointed.

 

[JTQ]

The high gearing trend we see is surely there to achieve good solo running fuel economy?
The higher gears also give the ability, within the available power to go faster though I don’t personally understand the rationale in making cars that achieve much higher speed than the legal limit. That must be some sort of “Top Gear” mentality on motoring, way off reality for most I suggest.
When towing I cant understand why some feel that they should achieve it in top gear. Is it not more logical to settle for a lower gear where at the power level towing requires the engine is operating most efficiently? This is exactly what the ‘intelligent’ ZF auto box in my vehicle does, in my case it rarely gets into 6th towing unless on very free rolling motorways etc. Now with the auto boxes featuring 8 gears we surely will not be expecting these to routinely get into top towing at <60 mph?

 

[RogerL]

When towing I cant understand why some feel that they should achieve it in top gear. Is it not more logical to settle for a lower gear where at the power level towing requires the engine is operating most efficiently?

You got it in one - any engine, ie petrol/lpg/diesel, high/low torque or high/low power will run most efficiently (ie most economically) at the revs where maximum torque occurs - in the case of an engine with a flat torque "curve" (electronically clipped torque down to a limited value) the natural peak torque occurs nearer the bottom end of the flat than the top.
So, towing needs a gear that gives the optimum point at 60mph or below - but solo needs a gear that gives the optimum point at 70 (or possibly above when national limits allow). If top gear is geared properly for solo running, it won't be the best gear for towing.
Problem is that caravan magazines and club magazines criticise tow cars that aren't optimised for towing in top because they don't understand how engines and gears work.

 

[WatsonJohnG]

Couldn't agree more
We had 4 X Trails and the first 3 were great towing but always to me seemed to need higher gear solo
The last new shape one had a higher 6th gear but was criticised by some in the motoring press for poor towing in top
Towing in 5th and solo in 6th seemed beyond them

 

[Lutz]

Absolutely. I think we're getting a consensus here.

 

[seth1]

Thats right but i still think were autoboxs are concerned it still has something to do with the fear of destroying the dpf due to over fueling when lugging a high gear under load.
In this day and age their is so much more a car manufacturer could do to an engine for say if someone was to buy brand new and spec the vehicle for towing.
It would take nothing to equip the vehicle with two engine maps the second one activated by the towing module once the van has been plugged in.
Fitment of a mechanical engine brake,another simple idea,so effective and improving safety.I just cant understand why they dont fit these,what an advantage that would be from a sales point to the likes of us guys.

 

[otherclive]

I don't know what series Volvo your dealer was talking about but my XC70 will hold 6th gear when towing 1400kg on the level with no trouble. In france this summer when the car was loaded and also the van the car pulled well even in 6th on inclines but I was not happy to see revs below 1500rpm so just nudged the throttle slightly to prompt it to change down a cog. The alternative would have been to shift into servo-manual and drop down a cog. I'd rather see an engine spinning than labouring.

 

[xtrailman]

I found the T30 xtrail perfectly geared for towing in 6th gear, with just 134 bhp and 231 pd/ft of torque.
While the 171 bhp is slightly higher geared, at 60mph its only around 200rpm lower.
Its the characteristic of the engine more than the gearing, that stunts the towing performance, even towing at max torque 2K revs, any slight incline and the pulling power falls away, and that's with 266 lb/ft of torque, 90% which is available allegedly from 1750 rpm .
My dealer told me that Volvo drivers had complained about the same thing, blaming the emission controls.
But the result is I'm towing most of the time in 5th gear.
That's why i considering buying my next car with a gear box holding 8 gears.
Or am i just getting old.
Finally i always thought a engine performed at its best when the torque curve meet the power curve?
I certainly notice a power surge at over 3500 rpm.

 

[seth1]

But isnt that the idea of todays crop of engines."To labour"?

 

[JTQ]

But isnt that the idea of todays crop of engines."To labour"?

No, the engine needs reasonable revs for the turbo to reach to or close to its optimum mass flow.
Anything less and its not going to be at peak efficiency.

 

[RogerL]

But isnt that the idea of todays crop of engines."To labour"?

No - to repeat myself - any engine, ie petrol/lpg/diesel, high/low torque or high/low power will run most efficiently (ie most economically) at the revs where maximum torque occurs - in the case of an engine with a flat torque "curve" (electronically clipped torque down to a limited value) the natural peak torque occurs nearer the bottom end of the flat than the top.

Regardless of the transmission, drivers have absolute control over which gear is selected and the engine revs.

 

[seth1]

But that is the idea of todays electronic engines,let them "lug" right down and let them "come back",keep the engine speed low.
To back this idea up go on any driver training courses for HGV and this is what is taught.
This is the idea behind a flat torque curve.It really is not a curve as in progressive torque curve but a straight line that is stepped up from say 1000 rpm to a max of 2500rpm and flat.Ok im using a slightly larger engine as an example were engine speed is concerned.
No matter where you are in the curve the torque stays the same.

 

[Guest]

And I have to agree with you Seth!, tried the lower gear stuff and it does not give better ecomomy where modern injected engines are concerned. It goes against the grain, but today it's 'let it labour'
Totally the opposite to old fashioned engines with carbs, here you would get a lot better ecomomy in a lower gear and the engine 'on top of the job'
So I'm sticking

 

[xtrailman]

No i don't agree, labouring a engine is the worst treatment you can give it, if the engine doesn't pick up and accelerate immediately you press the accelerator, then you're in too high a gear, change down.
OK i do find myself in too high a gear, sometimes, and the engine does pick up albeit slowly, but you're doing the engine, and transmission no favours.
The latest xtrail needs revs to make it go, it doesn't have a flat torque curve,( unlike the petrol turbo engine i once had.)
It likes to be revved like a petrol engine, and is more economical when running around 2K revs at max torque.

 

[seth1]

Yes Ray thats correct if it doesnt have a flat torque curve its known as a progressive curve.German diesels were renowned for using them.All revs and no go.In fairness they were in what i call the interim period i.e were waiting for technology to move on a bit so stuck with an old idea and improved it a bit.If thats the design of the engine you have no choice but to rev it.But im refering to flat torque curve engines,these are designed to be laboured it is not bad for them.They are like this to save fuel,in some instances it is pointless spining them up to high speed because there is no gain to be had,instead select a higher gear.Quite surprising the amount of people who still rev the guts out of modern diesels and actually waste fuel needlessly.

 

[otherclive]

I feel the comparison with an HGV powertrain is not really valid as such vehicles are designed to run at max load, albeit governed, when the normal car is really designed for solo operation. With modern car gearboxes (auto-torque convertor) the quantity of fluid has been reduced significantly. My last car ( 2004 model) was 5 speed Aisin gearbox with 11 litres of fluid requiring a change every 6 years or 60k miles. The current car is Aisin 6 speed with 6 litres of fluid which if used for towing should be changed every two years. I know that there are degrees of towing such as van weight and miles covered per year and also terrain and environment. But I would not want to have an engine labouring when towing as the torque on the transmission components is higher leading to more rapid fluid degradation and higher tooth and bearing loads. I generally try and manage the revs so that when towing I am in the band 1700-2000 rpm, but I would hardly call that revving the guts out of the engine. In most cases the auto box looks after the revs all by itself, but there are instances when it is not inclined to drop down a gear and would trundle on at 1250-1300rpm that is when I let it know whose in charge!

 

[xtrailman]

Yes Ray thats correct if it doesnt have a flat torque curve its known as a progressive curve.German diesels were renowned for using them.All revs and no go.In fairness they were in what i call the interim period i.e were waiting for technology to move on a bit so stuck with an old idea and improved it a bit.If thats the design of the engine you have no choice but to rev it.But im refering to flat torque curve engines,these are designed to be laboured it is not bad for them.They are like this to save fuel,in some instances it is pointless spining them up to high speed because there is no gain to be had,instead select a higher gear.Quite surprising the amount of people who still rev the guts out of modern diesels and actually waste fuel needlessly.

Again i disagree.
I have towed with a flat torque curve engine, max torque from 1950 rpm up to 4500 rpm.
I always ensured the car was run in the power band 2k to 4.5K That was a Audi.
Never labouring outside it.
The T30 would happily tow below 2K revs, even though max torque was at 2K, but that was the tractor like characteristic of the engine, and again had the progressive torque curve as you describe it.

 

[seth1]

To clarify a few things,Excluding the transmission of the modern day passenger car diesel engine and hgv engine,besides the physical size difference they differ very little in other respects,even to the point that on certain makes the same fuel systems are used.Turbochargers are the same besides size.Transmissions are really of no interest to me.My references are purely towards the engine.To me if a transmission is happy to trundle along at 1300rpm with 1400kgs behind it,it is fine.Dont forget all modern day autoboxs utilise a control unit which is on CAN with the EDC control unit and many others within the car..The EDC control unit is monitoring torque demand constantly on the engine.If its not happy it instructs the autobox to change gear accordingly.Its the EDC which determens when to change gear.
Ray when i refer to lugging down i dont mean outside the lowest point of the torque curve.If a torque ramps up at 1500rpm from tickover whats the matter with letting it lug down to 1500rpm,its still within the minimum?