Diesel or Petrol power - which is best?

[Chicken Drumstick]

Just for a bit of fun, how do we all feel about petrol vs diesel as the chosen power plant for a Land Rover?

For arguments sake, lets assume the vehicles in question are used for off roading a lot, recreational use on road (holidays, fun, touring, weekends) and if used for commuting, it's a distance that wouldn't be completely insane to consider lower mpg options.

So in terms of pros and cons. Does diesel offer anything other than an mpg increase and availability?

Would you rather a chipped TD5 or a tweaked megasquirted 4.0 V8?

2.0MPi over a 2.5TD?

Or is Chevy V8 power better than a modern V6 diesel or a Puma?

[Adam001]

Worth bearing in mind that Rover / Chevy V8 options don't really give petrol any credibility, lets be honest they are old!

If you consider say a german or Japanese lump in comparison then it's a much better argument, especially if you compare them to a TD5 (Price for price).

I've just gone Petrol from Diesel in mine and I won't be going back. You still need a reasonably large petrol though, anything under 2.5L is going to struggle at low RPM unless it's got a turbo attached to it.

Oh and cost wise, I'm currently equaling the TDI on MPG, so it's actually costing me less to run.

[Chicken Drumstick]

Worth bearing in mind that Rover / Chevy V8 options don't really give petrol any credibility, lets be honest they are old!

If you consider say a german or Japanese lump in comparison then it's a much better argument

What's old about a Chevy engine?

[Josh NZ]

Wow, a real can opener!

I'll throw a vote in for diesel power. If I had endless money, I would drop one of the V8 common rail turbo diesel motors from the new Landcruisers into a 110 truck cab. Dream machine!

[FridgeFreezer]

This is just going to descend into a massive argument, it's not like there's a "right" answer.

[simonr]

Please Sir, can I put in a vote for Electric?

Si

[Adam001]

Can-of-worms ...... OPENED

What's old about a Chevy engine?

Presuming by 'Chevy' we are talking the older generation iron block 4.0" bore engines, these were designed in what...1970....that's old, and not a fair comparison. For a all rounder car I'm sorry to say but without a LPG conversion a single cam V8 by any manufacturer is never going to be reasonable to run!

If we are talking LS engines then they may have lots of power but they are both horrendously priced and still pitiful MPG.

Either way, these engines have their place, but not what I would call a fair example in a petrol vs diesel debate.

[Quagmire]

Dons flame suit...

[Quagmire]

Ha! Adam beat me! I only read the bottom of the post

[Tanuki]

Must admit, I've always had a weakness for revvy small(ish) short-stroke petrol-engines with lots-of-cylinders.

I'm not really a fan of the RV8 either in its original Buick-castoff form or the later revisions. Mazda, Toyota and Nissan get the V6 and the V8 right: 3.5-4.0-litre, quad overhead-cams, 4 valves per cylinder. See this: http://en.wikipedia.org/wiki/Nissan_VQ_engine#VQ37VHR

Alternatively, go German with a BMW 3-litre straight-six. Not a lot can beat them for smoothness or sound.

Diesels can be OK provided they've got enough cylinders/valves, and a turbo or two - I really don't like the ever-escalating torques/powers being squeezed out of 4-cylinder 2.0-2.5L Diesels - they become nasty, juddery things when idling and vibrate like an out-of-balance spin-drier at high RPM even when the manufacturers do their best to mask the roughness with DMFs and balance-shafts.

[Why am I now pondering a 3.5-litre V8 version of the JLR TDV6, optimised for smoothness/quietness, free-revving and broader power-delivery across the rev-range rather than out-and-out low speed torque?]

[Chicken Drumstick]

Can-of-worms ...... OPENED

Presuming by 'Chevy' we are talking the older generation iron block 4.0" bore engines, these were designed in what...1970....that's old, and not a fair comparison. For a all rounder car I'm sorry to say but without a LPG conversion a single cam V8 by any manufacturer is never going to be reasonable to run!

If we are talking LS engines then they may have lots of power but they are both horrendously priced and still pitiful MPG.

Either way, these engines have their place, but not what I would call a fair example in a petrol vs diesel debate.

I suppose we can all have our favourites, and I'm a fan of anything fun and powerful. I do think it's unfair to tarnish Chevy V8's in this way though.

The LS was a clean sheet design for 1997. So ok a few years old now, but has been continually evolved. And they offer high power for a small package and IMO usually offer better mpg than Jap/German engines.

For instance, the EPA rating on a 430hp V8 Camaro 5th gen, is about the same as a BMW 335i Turbo, that not only is lighter, but makes 100hp less.

As a trend most Jap/German Vee engines are longer, taller, heavier, wider and have a higher centre of gravity combined with more complexity.

They do offer higher specific output in stock form, although the only real important numbers are total outputs at the end of the day.

The biggest advantage to DOHC setups is valve curtain area, which allows you to maintain torque at higher engine speeds without sacrificing low end emissions, output and driveability. But the reality is, high rpm operation isn't ideal for everything.

[Chicken Drumstick]

Please Sir, can I put in a vote for Electric?

Si

Yes if it's viable to actually achieve

In fairness I think electric power offers a lot of potential for some activities, but is not yet really mature enough in design or technology.

[simonr]

Yes if it's viable to actually achieve

It has nearly 100 years of catching up to do - but it's coming on very fast!

Notwithstanding battery technology, electric has the advantage of max torque at zero rpm and a truly flat power curve.

With an appropriate power source (which I don't yet have), my Siemens electric motor is capable of generating 450Nm torque at 0 rpm and over 400 bhp. Even with my 200Nm / 200bhp - I had to carefully tune the acceleration map not to spin the wheels all the time!

I agree that on an overall system level, it doesn't stack up particularly well against liquid fuels - but perhaps 20 years in to the future, liquid fuel will look like solid fuel (steam) does now!

Si

[Chicken Drumstick]

It has nearly 100 years of catching up to do - but it's coming on very fast!

Notwithstanding battery technology, electric has the advantage of max torque at zero rpm and a truly flat power curve.

With an appropriate power source (which I don't yet have), my Siemens electric motor is capable of generating 450Nm torque at 0 rpm and over 400 bhp. Even with my 200Nm / 200bhp - I had to carefully tune the acceleration map not to spin the wheels all the time!

I agree that on an overall system level, it doesn't stack up particularly well against liquid fuels - but perhaps 20 years in to the future, liquid fuel will look like solid fuel (steam) does now!

Si

I've often wondered how HP is really rated for electric motors.

Bhp is a calculated value:

HP = torque x rpm / 5252

So without rpm you will not see any Bhp.

And as electric motors can vary rpm, even if they maintain torque consistently, their bhp will would still vary.

[FridgeFreezer]

Electric power is brilliant, it's just batteries that suck. An electric-drive Landy with a hub motor at each corner could give amazing capability. I vote portable fusion reactor for the win.

And is this thread the 5 minute argument or the full half-hour?

[FridgeFreezer]

Drumstick - electric motors are measure in watts, 746 watts = 1 HP.

[discomikey]

[Why am I now pondering a 3.5-litre V8 version of the JLR TDV6, optimised for smoothness/quietness, free-revving and broader power-delivery across the rev-range rather than out-and-out low speed torque?]

you mean like project iceberg? if it ever became successfull it would have been my dream engine i think!

[TheRecklessEngineer]

Seeing as the question is about the power plant, and not the storage of the power.

Electric. There's no contest.

[discomikey]

Diesel electric. i STILL dont see why a manufacturer hasnt put a single cylinder put put diesel onto a generator running a motor yet for the consumer market!

[Mo Murphy]

What's wrong with steam ?

Mo

[Tanuki]

Diesel electric. i STILL dont see why a manufacturer hasnt put a single cylinder put put diesel onto a generator running a motor yet for the consumer market!

LPG-Electric would be better - a small lightweight high-efficiency LPG-powered engine running at high, constant revs, turning a 'pancake' alternator (using rare-earth magnets and lots of poles so it generates multiphase high-frequency AC).

Could even consider using a gas-turbine for additional lightness/quietness. Look at what aircraft use for their auxiliary power-units - lots of Kilowatts, not many Kilograms.

[dirtyninety]

i have both diesel and petrol engines in various vehicles, I can truly say I have no preference and struggle to have a 'favourite'

black smoke or v8 burble?

[Adam001]

I suppose we can all have our favourites, and I'm a fan of anything fun and powerful. I do think it's unfair to tarnish Chevy V8's in this way though.

The LS was a clean sheet design for 1997. So ok a few years old now, but has been continually evolved. And they offer high power for a small package and IMO usually offer better mpg than Jap/German engines.

For instance, the EPA rating on a 430hp V8 Camaro 5th gen, is about the same as a BMW 335i Turbo, that not only is lighter, but makes 100hp less.

As a trend most Jap/German Vee engines are longer, taller, heavier, wider and have a higher centre of gravity combined with more complexity.

They do offer higher specific output in stock form, although the only real important numbers are total outputs at the end of the day.

The biggest advantage to DOHC setups is valve curtain area, which allows you to maintain torque at higher engine speeds without sacrificing low end emissions, output and driveability. But the reality is, high rpm operation isn't ideal for everything.

No Doubt the LS engines are great for packaging as they are elegantly simple. But I would rather the complexity and challenge of the DOHC engines with VVT and take the benefits from them. I have a little experience of racing LS engines and they are great at it, but mostly because the materials are quite exotic and they can take alot of abuse, but I don't really need that in a road car. Can't say I'm sold on the efficiency side of it, I've been amazed at the economy of the 335 from a drive in one, don't think I've ever seen anything powered by a LS to see anything like it.

Not trying to be anti 'LS' as I think the engine is great, for racing. But there are good reasons why manufacturers left that technology a while ago.

It has nearly 100 years of catching up to do - but it's coming on very fast!

Si

Ferdinand Porsche would disagree

[mad_pete]

First land speed record - 1898 or thereabouts -electric power. Petrol has been doing 150 mph for ages. 100 years of slacking. Get on and sort electric and stop pretending it will take ages.

[Tanuki]

you mean like project iceberg? if it ever became successfull it would have been my dream engine i think!

If they'd done an Iceberg properly - by which I mean fitting 4-valve-per-cylinder heads, quadruple OHC, belt-driven cams - then it could have had a place I guess.

History of "Dieselising" engines originally designed for petrol use doesn't always seem to result in nice outcomes - google "Oldsmobile 350" and read about the issues they had with head-gaskets.

Hmmm... thinking of "Great British Engines that Could have Been" I'm wondering now about a quad-OHC 4-valve-per-cylinder version of the beautiful little 2.5-litre V8 Daimler engine of the 1960s.

Or "Dolomite Sprint" style headgear on a RV8 or the 2.6-litre straight-6 SD1 engine, with decent [bosch] electronic engine management. I reckon 200BHP from the 2.6, 250BHP from the V8. BMW/Mercedes would have been afraid.