Thread: Which engine to use?

Originally Posted by Series3 GT

Well I can certainly agree with using 2.25 because mine just keeps on going and seems to have the down low torque you expect from a diesel. They are really simple to work on and parts are fairly easy to find and pretty cheap.

The 2.25 (petrol and diesel) is, as far as I can think, the only engine ever designed from scratch specifically for a utility four wheel drive. So it is hardly surprising that it is good at it!

John

Originally Posted by JDNSW

The 2.25 (petrol and diesel) is, as far as I can think, the only engine ever designed from scratch specifically for a utility four wheel drive. So it is hardly surprising that it is good at it!

John

This is true most engines in 4WD utes are originated in other vehicles and are kind of adapted to suit.

Originally Posted by Series3 GT

This is true most engines in 4WD utes are originated in other vehicles and are kind of adapted to suit.

Not just most - can you think of a single engine other than this that was so designed? Certainly not any of the other engines ever fitted to Landrovers. Probably partly because Rover is the only company that has ever had utility four wheel drives as their major product line. And in recent years, emissions and fuel consumption rules have meant that new engines cost so much to develop that this can only be done if they can be fitted to a wide range of vehicles, and utility four wheel drives are not and never have been an enormous market, except when the US was gearing up for WW2.

John

Why, out of interest, is it important that an engine was designed for a 4WD? The LR2.25L is an almost square engine that is massively over engineered because one block casting catered for both petrol and diesel. It didn't need to be a long stroke, because the RAC horsepower tax system had ended, and there were no space restraints or vehicle design requirement to give advantages to being over or under square. OHV was fairly standard at the time, and I can't think of anything else that marks this engine out as 4WD specific. It is long lasting, abuse and poor fuel tolerant because it runs a low compression ratio and is largely over-engineered. But none of that makes it special, or better suited to a 4WD than anything else. Cam timing and profile can be changed to suit whatever requirements exist, as can carb choice etc. Whilst it is true that it WAS designed for use in a 4WD, it seems to be a fairly run-of-the-mill engine for it's time, and appears much less specific in its design (and less advanced) than something like the Coventry Climax FW.

But I've only just started playing with these vehicles, and I'm genuinely interested in learning more...!

Originally Posted by Warb

Why, out of interest, is it important that an engine was designed for a 4WD? The LR2.25L is an almost square engine that is massively over engineered because one block casting catered for both petrol and diesel. It didn't need to be a long stroke, because the RAC horsepower tax system had ended, and there were no space restraints or vehicle design requirement to give advantages to being over or under square. OHV was fairly standard at the time, and I can't think of anything else that marks this engine out as 4WD specific. It is long lasting, abuse and poor fuel tolerant because it runs a low compression ratio and is largely over-engineered. But none of that makes it special, or better suited to a 4WD than anything else. Cam timing and profile can be changed to suit whatever requirements exist, as can carb choice etc. Whilst it is true that it WAS designed for use in a 4WD, it seems to be a fairly run-of-the-mill engine for it's time, and appears much less specific in its design (and less advanced) than something like the Coventry Climax FW.

But I've only just started playing with these vehicles, and I'm genuinely interested in learning more...!

Well the longer stroke of the engine means you get more torque. More torque is better for a utility of any sort. The over engineering is to make sure it can stand up to punishment and it's simple to work on and doesn't reguire much attention which is better for a 4WD. It was also designed for that vehicle so it should be (and is) perfect for the job. It just does everything it was intended to. I was recently considering the engine swap idea and going for a holden engine but they were designed for a on-road vehicle. I know that it's tempting to go for the bigger engine but you really don't need it. The 2.25 will go all day and not miss a beat, they don't have much power but they have a fair amount of torque which is better for pulling heavy loads. Another way to look at it is would you fit this engine to a standard road car I think the answer would be NO.

Originally Posted by Warb

Why, out of interest, is it important that an engine was designed for a 4WD? The LR2.25L is an almost square engine that is massively over engineered because one block casting catered for both petrol and diesel. It didn't need to be a long stroke, because the RAC horsepower tax system had ended, and there were no space restraints or vehicle design requirement to give advantages to being over or under square. OHV was fairly standard at the time, and I can't think of anything else that marks this engine out as 4WD specific. It is long lasting, abuse and poor fuel tolerant because it runs a low compression ratio and is largely over-engineered. But none of that makes it special, or better suited to a 4WD than anything else. Cam timing and profile can be changed to suit whatever requirements exist, as can carb choice etc. Whilst it is true that it WAS designed for use in a 4WD, it seems to be a fairly run-of-the-mill engine for it's time, and appears much less specific in its design (and less advanced) than something like the Coventry Climax FW.

But I've only just started playing with these vehicles, and I'm genuinely interested in learning more...!

A couple of points that are unusual for the time - roller cam followers (camshaft does not wear, even if oil changes are neglected), high camshaft and very short pushrods, together with the bronze camfollower bodies ensured that there is no change in valve clearance with temperature - means you can have easy maintenance and a very quiet engine without hydraulic tappets (which need clean oil), overengineering in general. While it could be said that this is simply because it uses a shared design with the diesel, both engines were designed at the same time, and it should be pointed out that the original diesel did not share the block with the petrol engine - it was wet sleeve.

While most engines as you say were overhead valve at this time (I think the Yanks were still selling cars with side valve engines in the mid fifties when these engines were designed!), Rover had not built a side valve engine since the early twenties, and all their engines since WW2 had been overhead inlet/side exhaust with hemispherical combustion chambers. They did not follow this layout with this engine, probably because of maintenance concerns with those engines - exhaust valve clearances are hard to adjust and tend to be neglected, resulting in burnt valves. (The next new, and last from scratch before the Td5) Rover engine, in the Rover 2000, was twin OHC).

John

Originally Posted by Series3 GT

Another way to look at it is would you fit this engine to a standard road car I think the answer would be NO.

Absolutely right there.

Mind you, I wouldn't have fitted it to anything and I also don't think that there is anything special about them apart from them being over engineered - like most in that time.

I also don't think that because it was only fitted to 4WD's makes it 4WD specific (like the TD5) in any way. There are a lot of motors out there that have dynographs with power and torque curves that never go below that of the Rover motors and will last just as long. I think what makes the motor 4WD friendly is its ability to work on all of the awesome angles that they seem to get themselves (with some assistance) into.

Longer stroke doesn't mean more torque. It means more crankshaft stress, so long stroke engines are normally tuned to produce torque at low rpms because high rpms+long stroke increases the stress even further. It also means small valves must be used, because the bore isn't wide enough for larger ones, so again the volumetric efficiency suffers and long stroke engines are more suited to low rpm tuning - so torque not power, but less of both! Long stroke engines are normally tuned to produce torque at low rpms rather than power at high rpms because they are generally less suited to high rpm use. But a short stroke of the same capacity will produce as much torque, if it's tuned to do so. Normally however shorter stroked engines are not tuned for low rpm, because why would we limit their high rpm potential? So it's not that long stroke engines inherently produce more torque, it's just that they don't rev!

Long stroke engines were popular in the past largely because of the RAC horsepower taxation system used in the UK. That system ceased in the 1950's (late 40's?), so long stroke engines also declined in popularity. That's why the 2.25L ISN'T a long stroke engine, its more or less square.

As for fitting it to a road car, Rover used it for 3 years in the P4 80. The trouble is that it is heavy, because of it's petrol/diesel nature, so power to weight ratio is poor compared to a lighter "petrol only" design. This makes it ideal from a manufacturing viewpoint, less tooling etc., but doesn't make it a "better" engine for the vehicle, especially a road car.

The rugged nature of the Land Rover allowed the manufacturers to cut costs by sharing the block with the diesel, because the extra weight didn't matter given the nature of the vehicle. But again, that doesn't mean its a better engine for the vehicle, just a better engine for the company!! The nature of the vehicle allowed the designer to make a cost saving compromise on the engine without too much downside to the driver.