The Mitsubishi 4D and 4G type engine has been around for quite a while, and so are the Ford DI engines. Both engines have been around since 80s but there are a number of differrences.
Specificaiton Comparison:
4D56 Ford DI
Displacement: 2477cc 2496cc
Bore x Stroke 91.1 x 95.0mm 93.67 x 90.54mm
Compression: 21:1 19(18.3):1
Injection: Pintle Indirect Multi port direct
Opening press: 147 - 168 Bar 241 - 275 Bar
Pre-heat: 1 Glow Plug/cyl N/A (available as optional feature for cold climate region)
No of Valves: 8 8
Port Orientation: Turn Flow Cross Flow
Cam shaft: OHC OHV
Cyl Block Iron Iron
Cyl Head Alu Iron
Other: Balancer Shafts N/A
So, what is the difference?
These are both diesel engines of 2.5L capacity 8 valve with somewhat similar power output with various turbo and engine management systemsalthought there are some differences in injection method and device and intake/exhaust port orientation etc.
The real difference is somewhat invisible to unsuspecting eyes.
The key difference is that this model of Ford engine was an engine purposely designed to do heavy hauling all day long whereas the 4D56 is an engine derived from 4G54 Galant engine primarily designed for smootheness and relatively speaking... for a refinement.
However no matter how smooth, durable and reliable the old OHC Galant engine was, it still was a petrol engine. Therefore it would never be sbujected to pressure spikes and high compression of a diesel engine so for being a diesel engine there was something lacking in terms of durability.
At any rate I would imagine a lot of people who drove a number of 4 cylinder large dispalcement diesel would notice how smoothly it feels in a 4x4 with mitsubishi diesel. However when you get into a Ford Transit pre-CDI engines, it it loud, harsh, also vibrates a lot in comparison.
The smooth power dilivery was infact thanks to the balancer shafts synchronized to cancel the 2nd order vibraiton so it is not like they did something really special just a couple of unbalanced shafts rotating at high speed to fight back the vibration of large reciprocating pistons...As a commercial engine, it would add to a bit of complication due to additional belt required to drive those shafts, complex lubrication requirments does not help matters either...
There was one occasion which I have come across of a guy who owned a Pajero with 4D56 he kept up to date with the cam belt change but did not bother with the balancer belt replacement...One day, the balancer shaft belt snapped and got tangled into cam belt...You can imagine the rest, the bent valves and broken rockers...1 valve actually poking through the cam cover...
A quotation from a Mitsubishi dealer for a belt replacement job is €850 including labour...Can you blame him??
So in a quick summary in my opinion, 4D56 engines are primarily designed to be used in a passenger vehicles for comfort and refinement at a cost of added complexity instead, the Ford DI engines are designed to perform reliably in harsh conditions over extended time with minimal maintenence at the expense of refinement and comfort...
OHC vs OHV
Now onto the other point that really stands out...OHV vs OHC
Of all things why is it OHV??? In fact I know some people laugh at it for being so outdated, inefficient and just plain so un-cool...
But wait a minute...? What the hell is wrong is OHV??? Only difference is to lave a rod to push the valve rocker or to have a rocker pushed directly by a cam shaft...
The inertia of rod going up and down will only become a problem if the engine starts revving fast...Makes no difference what so ever at the nomal operating conditions of diesel engines which is between 1000 to 3000 rpm.
In fact still a lot of high performance V8 engines do use push rod configuraiton for 1 distict advantage.
It is simplicity...there are no bearing mounts to upset the thermal distribution, no cam shaft that you'd have to worry about distortion, no strange loading that would change stress characteristics...It is just like a lid of a pressure chamber...Means it can be made very very strong of course at a fraction of the cost associated with developing a fancy multi valve variable timing engines of equivalent performance. Also, lack of cam shaft in the cylinder head structure means the head can be made significantly smaller therefore lighter. Makes it easier to fit it into a tight spece of a sports car chassis. Take a Rover V8 engine for an example the original standard version only produced about 190hp...but it would not be to difficult to make it produce 300hp... Yet lighter than ford pinto engine...
Indirect Injection vs Direct Injection?
Actually, the direct injection technology maybe the oldest and most original way to inject fuel into the combustion chamber of a diesel engine...The indirect injeciton was developed later to make the combustion characteristics gentler than a simple direct injection. Back in early days the diesel engines are so rough, noisy and smokey no one bothered using it so eventually auto manufacturers must have opted for indirect injection for smoothness at a small expense of efficiency and performance.
In the last 8 years or so, thanks to the advancement in precision machining and better understanding of metallurgy and semiconductor technoloogy, they can mass produce fuel pumps that can generate pressure as much as 2000 Bar and inject fuel in multiple stages with amazing accuracy so the indirect injections have been phased out gradually and now there are not many of them left.
However, the DI engine used for this conversion project has none of the fancy stuff I have mentioned above...It is simple, rough and ready single stage injection with bosch rotary pump...
It was designed in the 80s and 90s at the height of Indirect injection boom, why did Ford opt for a direct injection instead of the smoother running indirect injects...?
Again, it goes back to durability...Having a swirl chamber in a cylinder head creates a hot spot, also complicated geometry upsets thermo dynamics a lot. Somehow the heat form a little chamber about the size of a pingpong ball must be conducted to the engine exterior via coolant. As a result, precious heat generated by the fuel gets dumped the moment it enters the chamber ending up with a weak engine no matter what.
Mercedes seemingly did something clever on that matter with indirect injection although I am not sure how it works but on the OM605, 606 have cups over the swirl chamber port basically covering the port and the cups have number of smaller ports placed radially on its cylindrical face just like a bigger version of injector tip of a direct injection nozles...Maybe it restructs the air flow into the swirl chamber during compression stage keeping the chamber cooler or somehting while improving flame propagation in the combustion chamber...The result is surprisingly high revving (5400rpm) high power engine even without turbo... (110hp is not much these days but 35 hp more than Ford DI of same displacement...Mitsubishi can only produce roaring 65hp without turbo)
But what about direct injection...? Actually there is no swirl chamber inside cylinder head. Instead, there is a dip in each piston but having a bit of dip in pistons would hardly cause any complication as cylindrical shape of piston its self expand evenly. So the cylinder head design is simple and durable in comparison. By sacrificing the refinement, engine can be designed much stronger structuraly than other indirect injection equivalents from other manufacturers of the era.
Iron head vs Alloy Head
Another seemingly outdated tecknology...But, it is for a reason...
How many cases of head gaskets blowing or head cracking on Transit DI engines??? It is quite rare. Whereas, you get a lot of complaint about 4D56 head causing a lot of problems...
Here is the reason. The 4D56 engines have alloy head and the cylinder block is cast iron. When you heat them together obviously the aluminum alloy conducts heat bettter also having lower specific heat capacily it heats up quicker than cast iron means there is some sliding action somewhere on the contact face between the cylinder block and the head...
Another expected problem is that the swirl chamber heats up locally first causing localised expansion...also contributing to increased internal stress withing the head material.
If the head is manufactured in a ideal situation probably should be able to withstand the displacement but since we live in imperfect world, there is hardly a perfect process. What most commonly happens is that you get a bit of impurity in the cast, small pockets and weldlines...
In a harsh environment, a few micron void is enough to act as fracture initiation point...As a result, you can get a cracked head from the weakest point of the head...
What about cooling?
Aluminum alloy would conduct heat much more readily than cast iron therefore can be less prone to overheating.........is it though? Aluminum alloy maybe 3 times as good a thermal conductor but it only has 1/2 the strength of cast iron with about 1/3 of the weight. At the end you will need double the amount of material to make it as strong so the total benefot would be 1/3 in terms of weight saving and cooling efficiency. However there is a catch to it in that Aluminum alloy expands 2 times as much as iron with given temperatture increase making it half as tolerant to heat than iron...
At the end...only benefit there is the weight saving of 1/3 which is about what 6 to 8kg? Does that sound about right? There is much more significant weight variation with empty fuel tnak vs full one...
Cross Flow vs Turn Flow
Cross flow is a type of cylinder head with Intake port enters the chamber form one side of the ehgine and Exhaust port exits form the other side of the engine and the Turn flow is an engine with a port configuration which intake port and exhaust ports are on the same side of the engine.
There used to be many models of engines with Turn flow heads as it creates more aggressive turbilence in the combustion chamber at lower rev range (1500 to 3000 rpm) which suits normal family cars and diesel engines as that would be the speed range the engine was most likely to be used at. This effect is important typically for petrol engines when fuel meets with air, for efficient combustion the fuel should be mixed uniformly in the chamber and also when the fuel ignites turbulence aids propagation of flame so that most of fuel is combusted before the exhaust valve opens.
However the down side of the turn flow is that at higher rev range (over 3500rpm) there is so much of turbulence in the chamber it will no longer benefit the combustion as it gets excessive the gas mixture would not ignite properly in the end a lot of unburned fuel will get dumped through the exhaust.
For diesel engines it would mean that we get a lot of black smoke from the exhaust.
Whereas a cross flow engine in general more tolerant to higher engine speed as fuel air mixture follows more or less a straight path. A down side of it is that at low engine speed the gas flow would not generate much turbulence therefore it is less efficient at lower engine speed. However there are ways to get around it using differnt chamber shapes, port design and optimized valve sizing.
Therefore, what it means is that the with cross flow port configuration, the engine can be designed to have useful torque range over wider speed range than the turn flow port configuration.
Availability
Another advantage of Ford DI engines are that there are rakes of them...for fraction of the price you pay for a Mitsubishi Diesel...
An average Mitsubishi 4D56 straight out of low mileage vehicle sold as long engine (full engine without injector, injection pump, turbo, alternator, etc) is about €700 to €1000. A rebuilt unit sold as long engine would be over €1500 ex shipping and tax.
However, the ford DI engines you can buy one with transmission and all other ancillaries attached for less than €500 (ex shipping)...and abundant in supply thanks to its rot prone body wrork...
Another Cool Fact
Another real cool thing about the Ford DI engine is that it can start without use of Glow plugs!!!! I love it !!!
Conclusion
All aspects considered, the Ford DI engines, as noisy and unrefined they are not so bad at all. It is a purpose designed work horse which will keep on running no matter what. Sapre parts are so cheap which is about 1/2 of what you would pay for Mitsubishi parts...
It is designed to to wha it does best...