BHP per Tonne vs Torque
 

Hi all

I read in Chris's book and other books about the minimum BHP per tonne required for a good overlander, but this figure does not consider torque?

I am restoring a 1963 FC Land Rover and it is fitted with a 4236 Perkins. Looking at the bhp figure for this engine it is under powered, but when testing the engine in a RR it pulled like a train. We loaded it up, added a fully loaded car transporter and it still pulled like a train?? Which raise the following questions:

Why is torque not considered in these calculation? Have Turbo engines made everyone think about revs and bhp? Which is better for desert driving, high torque at low revs or as on modern turbo engines, torque higher up the rev range? Do Jap turbo diesel engines suffer from reduced power before the turbo cuts in???

I know the limitations of the vehicle I am restoring and am only using it as an example. I am a big fan of simplicity and would like you views on the questions above bases on your experiences in the desert. I, unfortunatly have no expectence on driving on sand, unless driving on Ainsdale beach, nr. Southport counts?

Cheers Mick

Broadly speaking power is speed, torque is pulling power. Sometimes, for example you need to build up speed to climb dunes or accelerate through soft sand, that's why overlanders need 50-70 bhp per gross ton. On the flat - power - or the lack of it is not so important. The 4236 as I recall was used in 7.5 ton trucks and with suitable gearing pushed them along at over 70 mph even in the early sixties. Don't know what version you have but it would probably eat the transmission in any overland or enthusiastic driving situation.

Andrew.

[This message has been edited by Andrew Baker (edited 11 February 2005).]

Hi Andrew

thanks for your reply. It does not answer the questions, but does highlight why I asked it. The 4236 vehicle engine has a max 60bhp and it was fitted in 7.5 Tonne truck, which is 8bhp per tonne. Torque is far more important in these slow reving engines, but never discused???

Is speed the best aproach to accend dunes? or is slow and steady better?

Cheers Mick

Mick,
It's not about charging at speed but building up momentum. Imagine a vehicle with standard tyres, unlimited torque and momentum going uphill in soft sand at a speed equal to the vector of gravity. How far would it be able to travel before sinking down?


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Roman (UK)
www.overlandcruiser.info

Hi Mick,

Gnerally it's good idea to tackle obstacles slowly to limit damage to vehicle and to maintain good control. These are both very good reasons, but it's actually kinder to your vehicle to go as FAST as you can, providing you don't risk losing control or doing damage. Momentum is like a free ride for the transmission.

Sand is perhaps the best example of where faster is better, subject to maintaining good control. If you go too slowly through a soft or steep patch, you will sink further into the sand, and the engine and transmission have to do ALL the work of ploughing you through.

Regarding torque vs power: Torque is what pulls you up the hills; power is how fast the torque can do it. A lack of torque can be fixed by lower gearing, but there is no solution for a lack of power. (Power = torque x revs, so an engine that delivers high torque at high revs is by definition a high powered engine).

A high, wide torque output is important only because you need not change gears as often, for a given power. (That is to say, a 100kW engine with 300Nm of torque over most of its rev range can stay in a higher gear than a 100kW engine that delivers only 200Nm). The challenge facing a low-power vehicle is that if he starts in a low gear, he can't build up much speed; if he starts in a higher gear, he runs out of steam halfway up.

The reason that torque is an important consideration for a 4x4 is that high powered engines for road cars often deliver their torque at high revs only. Since P = T x r, when revs decrease, T decreases also, so P falls pretty dramatically - a sort of double whammy.

Off-road, you want an engine with a nice flat torque curve - your revs will be changing all the time to suit the terrain, and you want the power to fluctuate as little as possible, especially at low revs. The actual maximum torque figure is not that vital, so long as the curve is flat, the gearing is well matched, and the power output is adequate.

HTH,

Michael...
www.expeditionoverland.com

Is speed important to ascend dunes - yes - and therefore you need power.

An observation - new 300 Tdi 110 bhp vs 15 year old Land Cruiser both on 7.50x16's attempting steep dune climbs over 500 mile stretch. The LC beat the Tdi every time - same peak power, but the bigger engine had more of it available even at lower revs. So you don't actually need loads of power, but what you have you need available at modest revs, which the large capacity Land Cruiser engine delivers.

Andrew.

I've read this through a few time and I understand what you are saying, but which engines give a good flat power curve? Are diesels better than petrols? are N/A engines better than turbo engines? or is it down to CC ? Where can you find this sort of data?

I should explain why I am so interested. I have drivern Land Rovers all my life and eventually had a 300tdi Defender 90 which I thought superior to the previous vehicles. Then I got promoted and ended up with a Vectra. so out i went an bought a 2a Diesel, fixed the suspension and found out that the old diesel 2a can dig its way out of situation the defender would never get out of. Hence my interest in engines and how they effect the offroad performance of vehicles.

Jabbawocky,

Your dream machine should have a 1HD-T or 1HD-FT engine. It will give you all the torque and power you will ever need - without electronic engine control, oil leaks and the legendary LR reliability problems ;-)

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Roman (UK)
www.overlandcruiser.info

Jabbawocky, can you give me an example of where the 2A beats the 90 ? interesting
I spent many years driving 101's

Some of it - on sand is down to tyre size - if you are running 9.00x16 the taller tyre works much better than a 7.50x16 and you get more ground clearance.
The 2A has much deeper gearing which is also a help, and IMHO a vehicle with a 100 inch wheelbase (ish) is the best length - 90 bit too short, - 110 bit too long.
Thats why a FC101, Classic Range Rover and Discovery are so good off road.
Tyre Tread pattern and pressure make a huge difference. -obviously
Also vehicle weight - it makes an enormous difference if you keep the weight down

If youve driven a (200/300) LR you know that when you hit some soft sand you have to be in the correct gear to keep the turbo spinning - if you loose it you go back down through the box and loose your momentum - which makes the engine work even harder to regain momentum.

If you have a large capacity engine it does not rely on the turbo for peak torque/power so it is easier to drive - however you generally get poor fuel consumption.

The best combination is to have a larger capacity engine with a Turbo charger - best of both worlds - and a little economy , this is why a TLC is generally better than a LR in Sand.

However my 90 is kept very light and I have put it in places (in Mauritania on the PD Route) where a TLC on 7.50 XS could not go - I was on BFG Mud Terrains !!!
A lot of it is how you Drive/Ride
.....Forward Obsevation, Correct Gear/Momentum and Route Selection etc etc.

Cheers
Grif

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Ex RAF Regt, Ex Dragoman, LRE Instructor,
LR 90 300 Tdi Overlander
Suzuki DR650 Overlander
..and Bloody Nice Bloke!

I struggle to think of any reason a diesel 2A might outperform a 300TDi Ninety in any situation.

Series LR fans might argue that it has the advantage of simplicity, but in terms of "getting out of situations", the Ninety has similar dimensions and mass, better articulation, more power, more torque at all revs, better visibility and controls, and it's an easier drive. The 2A has lower diff ratios, but overall gearing on the Ninety is amply low (as low or lower than on a 2A).

I'd go along with Grif - a big diesel has oodles of low-down torque, but tends to run of revs too soon. A turbocharger complements this perfectly, doing nothing at the low end, but boosting performance at higher revs.

Rgds,

Michael
www.expeditionoverland.com

Well it's almost all been said. If you want to keep the grunty great Cummins you have to accept a certain amount of leg and arm work to keep the thing in the right gear. IMHO you won't enjoy dunes like that.
You could of course stick in an auto box. Always in the right gear, continuous transmission instead of hurried gearchanges.
I would imagine that one of those huge-engined low-revving American heaps would have a box that could survive the load. Avoid ones with electronics for all the normal reasons.
Good luck with the conversion/renovation whatever you decide.
L

Final Drive Ratios:
Land Rover 90 - 43.38
FC 2A - 49.40
FC 101 - 55.32

The FC deeper ratos offset by 9.00x16 tyres.

I always Remember driving a 101 and thinking it was awesome - even with 2 tonnes behind it in a peat bog ! - I'll have one on coils with a GMC 6.6 Turbo Diesel, Auto and that lovely PTO winch.
However Cresting steep Dunes in a FC is not for the fainthearted........

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Ex RAF Regt, Ex Dragoman, LRE Instructor,
LR 90 300 Tdi Overlander
Suzuki DR650 Overlander
..and Bloody Nice Bloke!

[This message has been edited by Gipper (edited 02 March 2005).]

Thanks chaps for the replys. I though that might get you talking. I am a self confessed Series fan without a doubt, but I do believe the statement above.
Here are few pictures to prove that 2 1/4 diesels do have their uses.
http://img.villagephotos.com/p/2004-...71/2bvs101.jpg
http://img.villagephotos.com/p/2004-...110caravan.jpg
http://img.villagephotos.com/p/2004-...owingDisco.jpg
http://img.villagephotos.com/p/2004-...onDefender.jpg

What was that about 101's

Cheers Mick

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The Simpler, the Better!

[This message has been edited by Jabbawocky (edited 02 March 2005).]

[This message has been edited by Jabbawocky (edited 02 March 2005).]

[This message has been edited by Jabbawocky (edited 02 March 2005).]

That is down to the tyres - Bar grips are Useless - and the rest are on road bias.
Grif


[This message has been edited by Gipper (edited 02 March 2005).]

Yeah, but by Christ they're ugly...

Sam.


That should get a response!!! http://www.horizonsunlimited.com/ubb/wink.gif

Beauty is in the eye of the beholder

The expedition defender was on MTs as far as I can remember.

I just need to find a turbo 4236

As has been correctly deduced - a big-capacity turbo diesel engine with low-reving characteristics - what we rightly or wrongly call call 'torquey' , is well suited to power-sapping desert conditions. Let alone experience, techinque, etc.

I was also attracted to Series simplicity once. Finding the regular diesel engine nice and gruntly but slow (and all the rest), I got another one with a 3-litre, 4 cyl Perkins (dont know the numbers).
Before I even left the country it had shagged the transmission and I realised it would shag it again because they were not complimentary - hence the box on p.84.
I guess its OK running around the UK with a Perked-up Series, but in the desert the first deep bogging or heavy dunes would ping the axles (if your lucky). You don't just need power or torque out there, you need a whole package that is built for the conditions.

A tractor has a lot of torque, I would guess, plus big tall tyres, great visibility and a natty raised air intake! It does not make it a good desert overlander.

Chris S

Hi Chris

Sorry this thread degenerated. My interest is in your BHP per tonne figure. The figure seams to suit the revier petrol engines, more than torquey diesel engines, especially on comercial vehicles.

As a kid I had to just take things apart to see how they worked. I do not beleive that cars are made out of the best bits. I beleive they are built out of what can be modified to last just long enough to get the customer to buy a replacement vehicle. Maybe I have been around Land Rovers to long??

My ultimate aim would be to build a unique overlander out of all the best bits out there, but that goes against everthing you wrote in your book. As you know I am on with building the 2a FC into a camper overland using the best Series/RR bits Land Rover made. Unfortunatly they never built (except in Lofty) a diesel engine powerfull enough to push a loaded FC along, so going for the Perkins.

Will give you a call from the desert to tell you, you were right all along, next year.

With the money I have spent, I could have gone out and bought a toyota, but anyone can do that these days and where's the chalenge in that?

Thanks to everyone that replied.

Mick

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The Simpler, the Better!


[This message has been edited by Jabbawocky (edited 04 March 2005).]

There really is something strange about some LR fans, It's almost more important to fiddle about with the mechanicals of a vehicle which, according to their actions, wasn't strong enough in the first place than to go out and enjoy the places you intend to visit.
I like the idea of a vehicle without a snout (FC) but consider why LR discontinued the 101 and stopped development on the Lama.
There just isn't enough of a market for a vehicle that's too cumbersome to be a car and too fragile to be a truck.
The load bay is so high that it might as well be a lorry but it has neither the carrying capacity nor the width to be proportional once you put a standing height camper box on the back.
It's tricky keeping an overland equipped vehicle, let alone a camper, under 3.5 tonnes; surely it's more practical to just buy a 7.5 tonne lorry? British licences allow it. It's forward control, the transmission, chassis and suspension are designed for the load, you get bigger tyres which is always a plus in the sand, and if it's not loaded to capacity there's a comfortable margin of security in all the working parts.
And you can put a bed across it instead of along, a great saving of living space.

Just a thought, obviously if, like me, you've only got 35 days holiday a year you need to have something to do for all the other weekends... you could concentrate on the camper box.
I'm sorry if I've offended any LR FC enthusiasts, I can see how once you've put personal time into a vehicle a fondness can develop (for the comfort of the overalls and the weight of the toolbox too ;-)))

Enjoy your preparations
Luke
Coolmatic CF 80
a lot of cold drinks
and an annoying habit of listing useless ans pretentious things after his name...

Mick,
I wouldn't read to much into the figures, Especially for commercial vehicles, Ive driven trucks that on paper should be great - but were absolute dogs in sand - as you can have loads of torque and still have the worlds worst overlander with the wrong gearing - that is what counts - get you gearing correct for the engine torque and power and you will be fine - if you can keep the engine revs at the sweet spot while accelerating and doing all those gear changes with very little momentum all is well.
Your FC has good gearing and torque for its laden weight - just keep it as light as you can and you should be fine.

Luke
Yes, us Land Rover Anoraks are a strange bunch aren't we ?
They stopped development of the Llama, as LR knew it was not going to beat the Pinzgaur in the Procurement tests- The Pinzgaur too - is too small to be a truck, to big to be a car and has a high load area - and over the last 20 years has sold thousands of units around the world.

Sounds nice the 7.5 ton -however it would probably be the worst thing going - underpowered, completely overgeared, still heavy - bad fuel cosumption - 4 or 5 k/pl, and an undriven axle with a heavy block over it - not a good idea really is it ?

The FC like anything is a compromise - but at least its proved itself with sterling service to the forces in its day and did the first ever self sufficient West-East Trans Sahara Crossing. (Tom Sheppard)
As for strength, Ive seen quite a few FC's air dropped at the wrong height out the back of Hercules and still drive off the parachute platforms afterwards...
Cheers
Grif

Sorry mate - does the use of my long signature offend you ?
I just like to keep in touch with other Rockapes, Overland Drivers, People who Drive 90s or Ride DR650s - which has just been stolen - so I will shorten it just for you....

[This message has been edited by Gipper (edited 07 March 2005).]

Sorry to hear about your loss, especially as you were keen on switching to two wheels which has its merits (fewer arguments with the passenger cos there isn't one http://www.horizonsunlimited.com/ubb/wink.gif
When I wrote lorry I neglected to specify that I meant a 4WD truck of course; although I'm tickled to see an advocate of 101s talk about fuel economy...
Pinzis are almost as thirsty, and a super vehicle.
At the risk of reoffending, one of the reasons the Pinzis were guaranteed to win contracts is their legendary reliability. How many accounts of repairs and bodges necessary to get home do we see on the web? Perhaps it's because there are so many of them out there but the (I have to admit) easily repairable Landy features quite a lot.
It's clear your experience shows, your 90 was very lightly laden when we crossed paths in Ghana - which is the best way to make any vehicle last. I should try and put my Iveco on a diet, it's also a surprisingly capable old heap.
Happy trails
Luke

Luke,
Yes Fuel Cosumption and FC arent 2 words that spring to mind together are they ?
A nice grumbly Diesel will sort that out a bit though. Those V8s sound lovely though....

With Trucks, the middle sized ones never were much good - Unimog was ok but tyre size always too small for sand - The Steyr S21 was about the only good medium sized 4x4 truck in sand - much better to go big straight off - MAN 8x8 much better capability and capacity and 1 k/pl YIKES !

If you go down to Arborfield where they repair the majority of Military vehicles and talk to the REME and Civvi mechanics, it is not all sweetness and light with Pinzgaur, they spend a bit of time off road - in workshops - but they certainly cut the mustard when they are working off road and the latest TD's appear to be the Dogs Maracas..especially that 6x6....

Yes bit of a blow with the DR, Lifes a Bitch etc.....but it goes on - gives me a good excuse to blow some Insurance dosh on a second hand KTM Adventure - another machine that is horribly unreliable - but has an amazing following because of its capability when it works.
Sounds like Land Rover......

No Offence Taken, Cheers Mate
Grif

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Ex Rockape, Ex Drago,
LR 90 300 Tdi Overlander - Lighter than CF 80 Fridge
Ex Suzuki DR650 Overlander *Stolen - L185 KDA *
..and Bloody Nice Bloke!

Then ... if you want diesel and factory-like reliability in your FC , you could fit an entire "Santana 6 cyl" drivetrain.

It is based in the old diesel series engine , but -litterally- adding two cylinders more .Othre than the obvious It shares most parts with the standard 4 cyl one.

It is a perfect fit on the tranny -literally bolt-on , althought you could go also for the Santana box , which apparently is a heavier duty version of the series one.

Then you could have a 95 HP -SAE- forward control , so you at least , got a chance in the sand , althought If I were You Id go for a 101 FC , or as someone said , a medium sized truck (4-6 Ton) . The fact that you can put a bed/matress sideways is indeed a good point , as is being able to stand up in the box.Also the bigger loading capacity gives peace of mind .

Good luck !! .
JAvier.

What about the Perkins Phazer engines - available from old dodges or ex mil rb44's.

I have a friend with one of these in his 101 and its great - it would haul up hills in Iceland with low revs and had plenty of grunt to deal with the sand. It is basically the turbo versio of your engine i believe

A good engine as long as you mate it to the right (ie. strong) gearbox



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Rich
LR101 300Tdi Ambi 'Tiggurr'