Your thoughts please

Evening all.
I have the chance of a 4.0 petrol Range Rover on a P reg. Body and interior are immaculate for year. It has good long mot and about 7 months tax. Asking price is £1795.

Would welcome advice.

Forgot to mention it is an auto

Thanks in advance

Not cheap or expensive. If everything works then great buy it. I'd look for a 4.6 instead, same mpg and noticeably more grunt. However if it's a good car - it'll fill your desire for a wallet emptying weekend hobby.

StuckAgainSteve said:

Not cheap or expensive. If everything works then great buy it. I'd look for a 4.6 instead, same mpg and noticeably more grunt. However if it's a good car - it'll fill your desire for a wallet emptying weekend hobby.

Click to expand...

How?
It's essentially the same engine isn't it but with a bigger bore?

TCubed said:

How?
It's essentially the same engine isn't it but with a bigger stroke?

Click to expand...

***

A larger stroke means more torque.

marccleave said:

***

A larger stroke means more torque.

Click to expand...

Ah thanks, but more power must come with more fuel if there wasn't a major fuelling redesign.... It's like the chipped diesel allegedly improving performance and economy theories

TCubed said:

Ah thanks, but more power must come with more fuel if there wasn't a major fuelling redesign.... It's like the chipped diesel allegedly improving performance and economy theories

Click to expand...

Petrol. Longer stroke = more cylinder capacity = more air = more fuel = less MPG. Simples. Chipped Diesel. More torque + more BHP = more fuel = less MPG. Simples.

wammers said:

Petrol. Longer stroke = more cylinder capacity = more air = more fuel = less MPG. Simples. Chipped Diesel. More torque + more BHP = more fuel = less MPG. Simples.

Click to expand...

It's not that simples. Weaker engine = more right foot = more fuel used for the same amount of go. I have driven loads of petrol p38s the 4.0 litre is no better on fuel in the real world. I suspect the 4.6 can be driven on lighter throttle openings short-shifting on the wave of extra grunt hence the similar fuel economy when driving to keep up with the traffic flow. It was the same deal with my two xj8s 3.2 vs 4.0 both averaged 30 mpg with mainly motorway driving, around town the 3.2 was very slightly better.

StuckAgainSteve said:

It's not that simples. Weaker engine = more right foot = more fuel used for the same amount of go. I have driven loads of petrol p38s the 4.0 litre is no better on fuel in the real world. I suspect the 4.6 can be driven on lighter throttle openings short-shifting on the wave of extra grunt hence the similar fuel economy when driving to keep up with the traffic flow. It was the same deal with my two xj8s 3.2 vs 4.0 both averaged 30 mpg with mainly motorway driving, around town the 3.2 was very slightly better.

Click to expand...

Even the 1.6 Escort was more economical in real life than the 1.1 as it didn't have to be thrashed to within an inch of it's life.

Datatek said:

Even the 1.6 Escort was more economical in real life than the 1.1 as it didn't have to be thrashed to within an inch of it's life.

Click to expand...

Definitely true (demonstrated in Top Gear 13x03) but the 4.0 is pretty quick (based on my experiences with the 3.9), so how fast are people trying to move to necessitate having to thrash it??

The 4.6 presumably is better though as it was slightly re-thought for the P38 rather than just the 3.9 renamed? Or am I wrong there?










(still should get the 2.5D... )

TCubed said:

Definitely true (demonstrated in Top Gear 13x03) but the 4.0 is pretty quick (based on my experiences with the 3.9), so how fast are people trying to move to necessitate having to thrash it??

The 4.6 presumably is better though as it was slightly re-thought for the P38 rather than just the 3.9 renamed? Or am I wrong there?










(still should get the 2.5D... )

Click to expand...

3.9 and 4.0 are same engine 4.6 is same engine but stroked to give 75 cc more capacity per cylinder. A chipped diesel is as quick as the 4.0 litre or not very far behind it.

TCubed said:

Definitely true (demonstrated in Top Gear 13x03) but the 4.0 is pretty quick (based on my experiences with the 3.9), so how fast are people trying to move to necessitate having to thrash it??

The 4.6 presumably is better though as it was slightly re-thought for the P38 rather than just the 3.9 renamed? Or am I wrong there?

(still should get the 2.5D... )

Click to expand...

The p38 4.0 litre and classic 3.9 are named differently to mark them apart but share the same bore and stroke.

My old classic 3.9 drank fuel for fun, despite being lighter and smaller capacity, I never managed much more than 15mpg - and that was a dealer serviced two year old car. On a gentle cruise I can get 22+ mpg (brim to brim figures) with my 15 year old past-its-best 4.6 Thor.

The Prius vs M(5?) piece on Top Gear you mentioned explains my point exactly, they drove a Prius fairly hard round the track for an hour (the repeated heavy braking would have been great for recovering energy) shadowing it with a 500bhp V8 Msomething BMW. The BMW achieved far better fuel economy because it was achieving the same acceleration on a whisker of throttle.

StuckAgainSteve said:

It's not that simples. Weaker engine = more right foot = more fuel used for the same amount of go. I have driven loads of petrol p38s the 4.0 litre is no better on fuel in the real world. I suspect the 4.6 can be driven on lighter throttle openings short-shifting on the wave of extra grunt hence the similar fuel economy when driving to keep up with the traffic flow. It was the same deal with my two xj8s 3.2 vs 4.0 both averaged 30 mpg with mainly motorway driving, around town the 3.2 was very slightly better.

Click to expand...

I am afraid it is that simple, larger cylinder, more air, needs more fuel.

wammers said:

I am afraid it is that simple, larger cylinder, more air, needs more fuel.

Click to expand...

I know you are an intelligent man but you really do have a blind spot sometimes. Given identical amounts of throttle - yes the larger engine will use more fuel, but the larger engine may give the REQUIRED amount of acceleration on a smaller throttle opening and then use less fuel. For argument's sake, if a driver's driving style demands 0.3g of acceleration, the 4.0 may require 25% throttle and 3,000 rpm before shifts to do it - the following 4.6 will achieve the same acceleration with 18% throttle shifting up at 2,000 rpm using less fuel in the process. Explain how the Top Gear 500bhp V8 BMW used much less fuel than the the 1.5 Prius it was following? This extreme example explains the point I'm making.

StuckAgainSteve said:

I know you are an intelligent man but you really do have a blind spot sometimes. Given identical amounts of throttle - yes the larger engine will use more fuel, but the larger engine may give the REQUIRED amount of acceleration on a smaller throttle opening and then use less fuel. For argument's sake, if a driver's driving style demands 0.3g of acceleration, the 4.0 may require 25% throttle and 3,000 rpm before shifts to do it - the following 4.6 will achieve the same acceleration with 18% throttle shifting up at 2,000 rpm using less fuel in the process. Explain how the Top Gear 500bhp V8 BMW used much less fuel than the the 1.5 Prius it was following? This extreme example explains the point I'm making.

Click to expand...

You're thinking of Top Gear 11x01 (yes I'm a nerd ) with that example.. but it's a better one! (I was referencing the test where they compare the Skoda Roomster, Toyota iQ and Alfa Mito, and Clarkson notes how you have to "mash your foot down just to do 20mph, you're better off with the bigger engine")

The M3 uses less fuel in that because the engine is more efficient at that power usage, whereas the prius was being driven flat out so would be beyond its efficient fuelling range. I don't think that equate to the 4.0 vs 4.6 though because they're the same basic engine (there is NO similarity between an M3 V8 and prius.. thing ).

More importantly though the message from that test was "it isn't what you drive that matters it's how you drive it", so the best thing to do is get a 2.5D AND drive it economically, and then it's the best

It's the same reason that mopeds aren't amazingly efficient; they weigh about 1/10 of a car, so given the linear relationship between force and acceleration they should use 1/10 of the fuel... but they still only manage ~75mpg because they're constantly being revved to very high levels beyond the efficient range.

I'd say that the 4.0 vs 4.6 is equivalent to 2 outboards engine, both the same, but with one on 80% throttle and the other on 100% - the 2nd must use more fuel. Whereas the earlier example with Prius and M3 would be like a 30hp outboard on 100% throttle vs a 60hp outboard (or more like a 250hp outboard to keep the comparison equivalent ) on 30% throttle - in the most efficient part of the fuelling.

TCubed said:

It's the same reason that mopeds aren't amazingly efficient; they weigh about 1/10 of a car, so given the linear relationship between force and acceleration they should use 1/10 of the fuel... but they still only manage ~75mpg because they're constantly being revved to very high levels beyond the efficient range.

I'd say that the 4.0 vs 4.6 is equivalent to 2 outboards engine, both the same, but with one on 80% throttle and the other on 100% - the 2nd must use more fuel. Whereas the earlier example with Prius and M3 would be like a 30hp outboard on 100% throttle vs a 60hp outboard (or more like a 250hp outboard to keep the comparison equivalent ) on 30% throttle - in the most efficient part of the fuelling.

Click to expand...

With an engine that uses as much fuel as the Rover V8 in the first place you'd only need a small change in efficiency to see quite a difference at the pumps. The 4.0 and 4.6 have different bore to stroke ratios, therefore the crank angle at which point maximum combustion pressure is attained will be different. The valve and port sizes are identical - the larger capacity will therefore increase inlet charge speeds at lower rpm increasing cylinder charging efficiency. So at trundling around revs you may find a 4.6 is operating at 29% thermal efficiency and the 4.0 only at 25% - that difference alone could make the larger capacity engine more fuel efficient in the real world - as I said it's not as simple as more capacity = more fuel. Some engine configurations will be much more tolerant of lean mixtures before NOx goes through the roof - so the fuel map the 4.6 could be lean where it needs to be rich with the 4.0 - which again may coincide with the revs the engine spends most of its life - there are so many parameters I couldn't even begin to explain them here! With modern fuel injection systems the fuelling is mapped to be as weak as you can get away with at various points in the rev/load combinations without upsetting emissions or the cats. It's not a matter of chucking the right amount of fuel in to maintain the stoichiometric ratio across the board. These parameters will be markedly different from a 4.0 to a 4.6. I have up-most respect for Wammers - but in this case he is simply wrong.

To be fair, the official figures do actual indicate a slight improvement on the 4.6. I'm still bemused though as this doesn't seem to work given the engineering but there we go

This is a question that's puzzled me for years; I used to wonder how supercars had such poor economy even when seemingly using the same amount of energy as an efficient car to move around!

TCubed said:

To be fair, the official figures do actual indicate a slight improvement on the 4.6. I'm still bemused though as this doesn't seem to work given the engineering but there we go

This is a question that's puzzled me for years; I used to wonder how supercars had such poor economy even when seemingly using the same amount of energy as an efficient car to move around!

Click to expand...

The official figures are on a rolling road - the computer model just says open the throttle to x,y,z until cruising speed is met - in this gear (if manual) as I said much earlier on - in the real world you might require less throttle on the 4.6 to achieve acceptable acceleration - on the rolling road test a fixed 20% throttle test on both cars will probably see the 4.6 use more fuel - but it'd be accelerating much harder. This is not applicable to real world driving.

I mentioned the original Jag AJV8 on purpose - it was designed from the outset to be a square (bore and stroke) 4 litre engine so the crank throw angle against PMAX and other parameters are optimised for that configuration - the 3.2 made similar power per litre but used nearly as much as much fuel - despite being nearly a quarter smaller as the engine was "over-valved" at 3.2 litres killing low-down torque and efficiency at low revs but breathed very freely at the top end. The 3.2 would have required to share the 4.0's bore to stroke ratio and correspondingly smaller valves to have a hope of being as fuel efficient at the smaller capacity - but car manufacturers don't want to make two optimised sets of everything - so one of the capacities will be less than optimum in terms of crank angle against PMAX, airflow at low revs and therefore thermal efficiency.

Traditional supercar engines are tuned to make top-end power, masses of valve overlap and hot cam timing destroying inlet charge momentum at low (normal road) revs, this will cause inlet charge to stall and inlet and exhaust gases to mix (poor cylinder evacuation) - the burn efficiency will be terrible wasting fuel - when you rev it hard, the timing overlap will create lots of power and burn even more fuel!

Its a RV8 they all drink like a depressed irishman !!

StuckAgainSteve said:

I know you are an intelligent man but you really do have a blind spot sometimes. Given identical amounts of throttle - yes the larger engine will use more fuel, but the larger engine may give the REQUIRED amount of acceleration on a smaller throttle opening and then use less fuel. For argument's sake, if a driver's driving style demands 0.3g of acceleration, the 4.0 may require 25% throttle and 3,000 rpm before shifts to do it - the following 4.6 will achieve the same acceleration with 18% throttle shifting up at 2,000 rpm using less fuel in the process. Explain how the Top Gear 500bhp V8 BMW used much less fuel than the the 1.5 Prius it was following? This extreme example explains the point I'm making.

Click to expand...

I am not talking large and small engines running at different RPMs for the same power output, with different gear ratios, different cars with different aerodynamics and body weights, of course there is a difference. I was talking a 4.0 litre Land rover V8 as opposed to a 4.6 litre Land rover V8. Same car, same weight, same frontal airflow resistance, same gear ratios. At any given RPM the 4.6 will use more fuel than the 4.0 litre. That is where the simples comes in. Land rover seem to agree with me, as the mileage figures for the 4.6 are marginally worse than those claimed for the 4.0 litre engine under all conditions. So your argument is out of the window i am afraid.