2.5L Diesel vs. 2.5L Petrol

[Thommo55]

My son and I are building a 1973 Series 3, we need to choose the powerhouse, 2.5L Diesel vs. 2.5L Petrol, any thoughts?

[Gazzar]

Both non series motors. Both with different strengths. And weaknesses. Loud and low down torque and somewhat economical, versus quiet at tick over, higher revving and thirsty.

 

[Ex Member]

200TDI......

They are more or less the same (usable) power.  The petrol uses twice as much fuel and is quieter.  Both will require modification to fit in a Series.

[Tanuki]

What will you be using it for?

A few decades back I did a 45-mile-each-way daily commute along M4/A34 in a petrol SIII (with RR 3.54 diffs, the compression raised to 9:1 and a 2-inch SU carb on a homemade manifold). It'd cruise happily at 65-70MPH and I still had functional hearing. I would have hated to have to try the same journey at the same speed in a Diesel.

Also, where will you be using it? There's a growing anti-Diesel movement and I suspect that in the next couple of decades Diesel-engined vehicles will be banned or seriously-restricted from use in many cities/suburban areas - which is likely to see the resale value of Diesel vehicles fall faster than petrol.

A nicely set-up 2.5 petrol engine [highest compression-ratio you can achieve, Weber progressive carb, head-work, tubular exhaust-manifold and free-flow silencer] would be my preference. You should be able to get at least 120BHP and it'd be nicely quiet and free-revving.

[smallfry]

The ONLY reason to use the 2.5 diesel would be fuel "economy". In every other respect the petrol wins hands down.

If you wanted a diesel, a 200 Tdi is much more driveable and more economical.

[jordan_meakin]

Current climate for diesels (although misguided) suggests petrol is a better option.  They're lovely engines.  I'm a big fan of a decent diesel engine but the driving experience of a petrol is vastly more comfortable.

[Gazzar]

I have to agree, I'm fitting a 2.5 petrol with an ACR head to the lightweight, with RRC diffs (truetrac LSDs).

I'm nearly 90% convinced that I'll be using mega squirt as the fuel and spark solution.

I think it's a good compromise between period, cleanliness and usability.

[Chicken Drumstick]

As others have said, what is your intended use? The diesel makes a claimed 67hp iirc, vs 72hp for a 2.25 petrol. A 2.5 petrol makes more than either.

The diesel will be better on fuel, but tbh probably not massively so and it will be a lot more noisy and unrefined. But in some ways one running well should need very little fiddling with to keep it sweet. A carb petrol might need a bit more TLC a bit more often. Ultimately the performance of either is not all that great though.

A 200Tdi is almost as easy to fit as a 2.5 diesel, the Tdi will actually be even less refined, but it will make a lot more power, be better on fuel and unlike the n/a diesel, will offer the big fat low/mid range torque. The 2.5 na diesel is not a torque monster by any stretch of the imagination.

 

If you are considering other engine, then the Rover T-Series 2.0 DOHC as fitted to the Discovery MPi model looks an interesting swap. More power than a Tdi, less weight and more torque at 1500rpm than a 2.25 petrol makes at PEAK.

 

Rover V8's are also a nice engine to consider too.

[Ex Member]

41 minutes ago, Chicken Drumstick said:

The diesel will be better on fuel, but tbh probably not massively....

Umm.  No.  The petrol uses twice as much fuel.

Stock, they are almost identical in power at the engine speeds people actually drive at.  The petrol has more power above 3500 rpm, but nobody drives there.  Driven both extensively.  Done side by side fuel consumption comparisons.

[monkie]

In my opinion mpg is heavily dependant upon driving style, if you are used to a petrol version then switch to the diesel equivalent but drive it hard then I would say that is not a fair comparison.

[deep]

I have owned 110 Land Rover hard tops with both engines.  I agree that the petrol is much nicer in many respects but the one I own now is diesel.  That is largely because the fuel economy is considerably better (25-30 m.p.g. diesel versus 16-19 m.p.g. in the petrol over the same range of conditions - probably an even bigger difference if you are off-road a lot) but also because I love the farm tractor idle-all-day feel of the diesel.

I've put a lot of sound-proofing in my diesel but it's still as louder as my petrol was.  The same sound-proofing with a petrol would make for something approaching luxury!  The petrol is far less demanding on batteries/starter motors.  I've had two Land Rover diesels and everything has to be right to start them reliably on a cold morning, sigh.

Performance on road isn't radically different but, looking back, I used to drive the petrol a little faster than the diesel (60 m.p.h. versus 55 m.p.h.).  Both will cruise faster faster than that but those are the comfort zones I have found.  Off road, the petrol has it all over the diesel.  While the ordinary 2.5 diesel produces more torque below 1,400 r.p.m. than all other (proper) Land Rover diesels, you can drop the revs to a few hundred in the petrol and it won't stall.  The petrol is also stronger at the other end of the rev range.  That flexibility makes a far bigger difference off-road than the charts can tell you.  Essentially, you end up driving the diesel one gear lower, which loses impetus.  However, the diesel has far better engine braking.  By the way, I find the 200 T.D.i. worse than either in some off-road situations as it has a smaller comfortable rev range, which is not what you will often read here! 

Maintenance isn't bad for either.  Both need clean fuel filters (that Weber carb has tiny idle jets).  In my cars, neither use(d) significant oil but I feel more inclined to do early oil changes in the diesel (just 'cos it goes black so much quicker).  The petrol does have an ignition system to keep an eye on.  It's not hard though.  The diesel injection system is quite reliable but is a giant pain when you need to do something with it.

At the end of the day, both suited me very well indeed and I love(d) driving them but sheer economics mean I wouldn't be able to use a petrol as much, if I had one.  In fact, I sold my nicely tweaked Stage One (3.9V8, RR transfer gears, Disco seats) to buy my 2.5 diesel 110 and couldn't be happier with that decision.

[Gazzar]

I wonder how many people decide the engine based on economy, but seldom do more than 2k miles a year? I went TDI on the 109, but that was when I used it as a break down tow horse. Today, I'd go petrol, as I'm not doing near as many miles.

 

Horses for courses, less than 5k per annum? Petrol

 

[Ex Member]

Well, I don't know what purpose you guys get a Land Rover for...but remote travel is really the only point, IMO.  Driving around on roads is the last thing I would use one for.  Having the highest range possible is very important.  I can do 700 miles in my 90 and 1100 miles in the 110.  Off road the fuel consumption on the petrols gets even worse.  The diesels don't change nearly as much.

[monkie]

I'll be honest, I have no real need for my 110. I could easily get away with having a transit van or even just hiring one every now and then. My 110 leaks, it is smokey, unefficient, slow, noisey, cold, damp, uncomfortable, not cheap to run - but I love owning such an iconic vehicle.

[Chicken Drumstick]

On 11/23/2018 at 5:32 PM, Red90 said:

Umm.  No.  The petrol uses twice as much fuel.

Stock, they are almost identical in power at the engine speeds people actually drive at.  The petrol has more power above 3500 rpm, but nobody drives there.  Driven both extensively.  Done side by side fuel consumption comparisons.

I doubt the diesel will be double the mpg. The petrol will happily do 14-18mpg and over 20 on a gentle cruise (imperial). There is no way a 2.5 NaD will be 36-40mpg. Probably more like 10-20% better than the petrol at best.

[Chicken Drumstick]

On 11/23/2018 at 8:31 PM, Red90 said:

Well, I don't know what purpose you guys get a Land Rover for...but remote travel is really the only point, IMO.  Driving around on roads is the last thing I would use one for.  Having the highest range possible is very important.  I can do 700 miles in my 90 and 1100 miles in the 110.  Off road the fuel consumption on the petrols gets even worse.  The diesels don't change nearly as much.

Not really an issue in the UK, nowhere is really all that remote, apart from a few places in Scotland. You must also be running auxiliary fuel tanks for that kind of range.

[Ex Member]

2 hours ago, Chicken Drumstick said:

I doubt the diesel will be double the mpg. The petrol will happily do 14-18mpg and over 20 on a gentle cruise (imperial). There is no way a 2.5 NaD will be 36-40mpg. Probably more like 10-20% better than the petrol at best.

14-18 * 2 = 28 to 36.....

Driven both extensively with many side by side comparisons with trucks driving together and filling up together.  You will average 14 mpg with the petrol and 28 with the diesel.

[Ex Member]

2 hours ago, Chicken Drumstick said:

Not really an issue in the UK, nowhere is really all that remote, apart from a few places in Scotland. You must also be running auxiliary fuel tanks for that kind of range.

Hopefully people leave the little island once in a while and see the world.

[monkie]

2 hours ago, Red90 said:

14-18 * 2 = 28 to 36.....

Driven both extensively with many side by side comparisons with trucks driving together and filling up together.  You will average 14 mpg with the petrol and 28 with the diesel.

That sounds like Tdi mpg - were those figures achieved in a 2.5NA? I get about 18-22 mpg in my 19J since I rebuilt it.

[deep]

42 minutes ago, monkie said:

That sounds like Tdi mpg - were those figures achieved in a 2.5NA? I get about 18-22 mpg in my 19J since I rebuilt it.

You'd better fix your 19J then!  Seriously, that sounds pretty bad.

[Ex Member]

Yes.  You can do a little better with the TDI if you can convince yourself to drive as slow.  This is highway mileage at 100 km/h.  With the TDI, you get into the 30s at that speed.  The only way to get down to 22 mpg would be a complete tank off road.

Edited November 26, 2018 by Red90

[FridgeFreezer]

3 hours ago, Red90 said:

You will average 14 mpg with the petrol and 28 with the diesel.

Wow, that's low for the petrol - you'd get better MPG from a V8 and be arriving earlier too I had to drive the 127 at 90mph to get it down to 14mpg!

The 4-pot petrols do have some upsides when nicely set up - they run like sewing machines, they're robust, and give a very original look & feel with no mods to the vehicle to make them fit, and although the BHP figures are low they have decent grunt and flexibility and are low-stressed.

The 4-pot diesels are equally robust and useful but could never be described as running like a sewing machine - perhaps some sort of industrial rock-crusher...

With the value of older LR's going up these days I would be doing whatever keeps the vehicle "most original" - so if the V5 says it was a 4-pot petrol that's what I'd stick with, unless you want more performance in which case you may as well go TDi for MPG or V8 for power.

[Gazzar]

My 2286 petrol was virtually silent at tick over.

Not so much at full throttle.

The TDI isn't.

[monkie]

1 hour ago, deep said:

You'd better fix your 19J then!  Seriously, that sounds pretty bad.

Nope it's in fine fettle. It's just not on particularly long journies and it's often weighed down with carrying stuff in a 110. I'm probably not that gentle with it either. I can do better if its driven gently with nothing in the back. I think driving style is the biggest factor with mpg.

[Gazzar]

That and tyres.

Thin, skinny, high pressure tyres are best for economy.

Super swampers running at 15psi, not so much.