Summary of diesel tuning theory (mechanical injection only)
 

I would like to summarize all I have got to know about diesel performance over the years, mainly from reading over the internet/forum.

As mentionned in the title, I don't intend to explain how to tune a MB, I don't know that yet, I just want to make sure I have got the theory right. Then I will move to specific actions to do on the car...

So, to increase horsepower from a turbodiesel engine (fully mechanical, no electronics for now), we have the following options:

1. Increase max RPM
2. Increase boost pressure, thus requiring fuel delivery adjustment (if boost increases, fuel delivery must go up).
3. Add an intercooler, so to cool down the compressed air prior to its injection into the combustion chamber
4. To further cool air down (I would say for extreme cases only), add a water injection system.
5. Do a mix of all of the above!

6. Reduce restriction in exhaust flow (Thanks to MTUPower)

Am I on the right track?

I am parlicularly interested by the car I owned (the 92) which has the OM602.962

I know it has electronics (the EDS), but there are ways around this as explained by gsxr here:Wastegate Swap Thread

Then, if we really create much more power, we have to consider the handling of that extra power through the transmission and drive shaft. I have the impression I have read many times the differential isn't much of an issue, it could take lots more before requiring any substantial improvement.

Anything that sounds silly in what's above?

Thanks for any comments,

Bye

a c02 cooler on the intercooler would also work.



I hate water/meth injection. with water you get rust, with meth you wash all the oil off the cylinder walls.


the biggest improvement would be weight reduction. 100 Lbs is equal to 10HP or 1/10th in the 1/4 mile.

A diesel usually is on the severe downslope of the torque curve above 3800 rpm. The rather long burn time of the fuel is a detriment. So, attempting to increase rpm in the valiant hope for more horsepower will usually prove fruitless.

On most diesels, additional HP comes from more torque, not more rpm.

Here are the basic workings of a diesel engine: air is put into a cylinder.
The piston comes up and compresses the air.
Near the top of the piston's travel the injector adds fuel to the air.
The air/fuel mixture is compressed (gases are heated when they are compressed, and they are cooled when they are expanded- air is a gas) to the point that the mixture explodes.
This forces the piston back down, creating power.
The amount of fuel, the amount of air, the timing of the injection of fuel, the timing of the air entering the cylinder, the timing of the combusted fuel/air leaving the cylinder, and the temperature of both the fuel and air all effect the power created by that cylinder's power cycle.
The main forms of increasing power in a diesel are to add fuel and air to the power cycle of all cylinders.
By putting a device that compresses the air and forces more of it into the cylinder you can increase the power of the engine.
If you compress the air, you also heat it.
This is called Boyle's law, after the Irishman Robert Boyle.
By cooling the incoming air, you effectively decrease it's volume- than thus are able to add more of it to the cylinders power cycle.
That does not give you more power (actually is does give more power, but in terms of less than one or two percent) so when you add more air the engine also needs more fuel to burn with the air.
All engines are considered forced induction (FI) or naturally aspirated (NA) engines.
There are two forms of FI- superchargers (aka compressors) and turbo chargers.
By adding fuel and air to the power cycle, you add power.
Nearly all diesels increased power over stock levels are concentrated on these two items.
After the power cycle, you need to evacuate the exhaust- and a restriction on the exhaust causes power loss.
This is why larger exhausts are needed with increased power over stock levels.
Factoring in all of these and more is the life long game of tinkering with your diesel to produce the more power.
Water injection both does and does not cool the air, but it does allow you to air more fuel/air at the same temp.
The relationship is not simple.
William

MTUPower,

Thanks for this other very good point.

I'll edit my original post and add your comment in the bullet points.

Bye,

I'm with you. I much more prefer low end torque than high rpm horsepower.

When everything runs slower, it reduces wear and extends life expectancy.

Bye,

I disagree. Look at my dyno chart and you can see that HP is still going up until the point the pump's high idle setting starts to take away fuel. If you were brave enough to take it to 6000rpm I bet you could see a significant increase in horsepower. http://www.peachparts.com/shopforum/diesel-performance-tuning/213471-dyno-results-here.html

I do too. Torque is useful in everyday driving, HP is only good for the drag strip and showing off to your buddies.

Your own chart shows 107 hp @ 3800 rpm..........that's the peak. Going higher results in lower horsepower.........as I attempted to explain above.

Going to 5000 rpm would net you about 80 hp..........even less at 6000 rpm.

With an unmodified pump. My pump has a few gobs of miles on it and I have no doubt the governor is worn and springs weakened.

That is from the fuel curve "programmed" into the injection pump. I'm not sure how to tweak that away in the MW or M pump, but the Finns have done it with the M pump (they regularly go to 6k RPM).

A few more points on top of MTUPower's. A problem with a small turbocharger is high exhaust backpressure. On the OM60x engines that is limited to 30PSI. I think exhaust backpressure affects EGT as well (higher backpressure equals less airflow?). It is commonly believed that the turbos on these cars will handle the extra power from maxing out the injection pump. If you increase to larger plungers/elements you will likely have to increase the size of the turbo, exhaust, intake plumbing, etc to keep EGTs down so you can use all that extra fuel :cool:.

While your pump may suffer from lower delivery at higher rpm's, the fundamental problem with the nature of diesel combustion remains. The engines have difficulty in producing peak torque at engine speeds above 3000 rpm........modified pump or not.

It's very difficult to keep the torque curve flat enough to extend the horspower peak. I sincerely doubt that anyone can get peak hp at 5000 rpm on a 617.

In fact, I think it is possible to get much more horsepower in increasing rpm and fuel delivery. BUT, one problem will occur and it will be incomplete combustion, thus a cloud of black smoke.

So to remain with an acceptable combustion efficiency, running at lower rpm is probably best. What we need to look at is the specific fuel consumption(SFC), lbs of fuel/hp/hour.

I should do the math later on, but I'm quite sure the increased hp obtained from a diesel engine will hardly have the same specific fuel consumption as for the original output (meaning the SFC will be higher)...

to be continued...

Bye,

Not peak HP at those high RPMs, but there is still going to be very usable power up there. If someone saved the dyno of Shadomaker's OM603 with GT37 turbo that was a good example.

Once you're past peak horsepower.........why would you go there?

Yes, if you're racing, there might be some advantages to straddling the horsepower peak upon shifts, but, as a practical matter...........usually going above the HP peak isn't worthwhile.

I'd still like to see if anyone can get the peak anywhere even close to 5000 rpm.
I'm betting a six pack against it.

415hp@5400rpm.

I prefer Coke, not Pepsi. :)