Turbo Charger Upgrade for Older Kubota

SkyPup · Oct 6, 2005

( ( Diesel and gasoline engines both lose the same % of power as altitude increases. )

Why? Let's go through the physics of it, so somebody can show me where the error in my thinking is.

Diesels, on the other hand, do not rely on a flame front to keep combustion going ...
Where am I going wrong here? )

Major 100% WRONG -> Diesels are extremely sensitive to the ignition flame front as it expands throughout the combustion chamber, this is why their combustion chambers are so specially designed. The Ricardo "COMET" diesel combustion chamber was utilized for decades specifically due to its extremely well placed flame front.

RobJ · Oct 6, 2005

Where are you going wrong? I think your reading this from a book and not really understanding what you are reading (in a nice way).

To keep the a/f mixture in the combustible range, fuel must be reduced in proportion to the loss of oxygen, or eventually the fire goes out when it gets too rich.

Why would this not happen in a diesel? At sea level a diesel piston goes down and sucks in all the air it can. The air is heavy, dense. At 10,000 feet the diesel piston goes down and sucks in all the air it can...both by volume. But the air is thinner and has less O2. Can't burn as much. The diesel is getting no outside help to replace the loss of O2 at 10,000. That is where a turbo comes in. It compresses more air into the cylinder, we call it boost. More air more power. Fuel pumps are set for this. If you're just putting around at 10,000 feet you may not notice any real loss, but the greater the load the more the loss of power. At 500 rpm's the turbo really isn't putting out any boost, under a no load (high idle) the turbo isn't really putting out any boost, but as the load increases so does the heat and the turbo starts to really kick in.

You may be hung up on this ratio thing, sure at idle there is more air in the chamber than is needed to bun all the fuel, wasted air. But as the load and rpm increase they become more balanced, and eventually the load is greater than the power produced and the tractor will stall. There is always only so much in there, by going higher there is less to start with. I really can't see where you are missing it.

But to say a diesel will perform the same at 10,000 as it will at sea level means you are really missing it.

Sorry, not trying to attack you, JMHO.

cp1969 · Oct 6, 2005

Why the diesel is not subject to the mixture requirements or flame front is because the air in the cylinder is hot enough to start the combustion process regardless of where the fuel molecule happens to be. Combustion has to have fuel, oxygen, and a heat source to initiate the reaction. In a gas engine, the spark plug is what gets it going, and the flame front is what keeps it going. In a gas engine, each fuel/air reaction is dependent upon receiving enough heat from somewhere to get it started. In a diesel, the air itself is hot enough that no further heat source is required for oxidation to commence. If a fuel molecule finds an oxygen in a diesel, it's game over--combustion occurs as the initiation heat is already in the oxygen molecule. In a gas engine, each fuel/oxygen match-up has to be near enough to one that is already burning to receive the heat required to start the reaction. Hence, the upper limit of ~18 to 20:1 because that's about as far apart as these molecules can be and still light one another. Diesels, even at full throttle, are in the 35:1 range which is far beyond the range at which gas engines can run. Hence, the surplus of air.

Fuel makes power, not air. If enough air is present to combine with all the fuel molecules, anything more than that is wasted. It isn't until the point that fuel is going out the exhaust because it couldn't find an oxygen to combine with that any power loss should be noticed.

Skypup, I suspected that you of all people might be able to delve a little deeper in the physics of power production that just attribute a loss of power to decreased manifold pressure. I've outlined my reasons why it seems to me that, to some degree at least, a diesel should not react quite the same as a gas engine. Maybe you could shed some light? It would seem to me that this power loss might be more attributable to inefficient injection than lack of oxygen.

RobJ · Oct 7, 2005

OK I give up, gonna let someone else take over. The others and have a consenus and I agree with it. Not sure why your asking SkyPup, he's already stated what I've been trying to explain but you're caught up in this ratio thing.

I suggest a field trip.

Oh and you can't keep pouring fuel into the cylinder to make up for the loss, you'll raise exhaust temps and burn up the engine. I replaced a V12 in a 500 ton moble crane once. The engine and pump were set for to run in the hills of Europe, intermitting load. They shipped the crane to the US and were running it on the gulf coast. toasted the motor after an hour running flat out (about 50 mph). I replaced the engine and had the pump recalibreated for near sea level and a continuous duty load. In that case the fuel/air ratio was a bit high don't you think?

Good Luck.

cp1969 · Oct 7, 2005

Why am I asking Skypup? Because, if I'm not mistaken, he is astute in the field of chemistry and that's what kind of question this is. Another reason is that I have read enough of his posts to conclude that he is someone who can point out the error in another's thinking without resorting to insult. That's something I respect in a forum member.

rocketman128 · Oct 8, 2005

WOW... I never thought I would get so much banter on one of my first post...very cool. I think if you add up most of the points in this thread, you get the point, and the basic concepts.

Now if I could just find a turbo that is small enough for my engine, I should be in business.

I found a realy cool website that lets you down load a suite of software that calculates all the size requirements based on your engine specs. But when you go to look up the recommended size turbo, they don't have one that small.

Here is my current thinking on the original question:

- If I can find a small enough turbo, plumbing it in should not be that hard or expensive.
- If I boast to back around sea level, ie. 6-8 psi, the current mech injection system won't know the difference
- I can use the oil pressure sensor to feed bearings, return line to new fitting tapped into the valve cover

KennyV · Oct 8, 2005

That should work but you may have to restrict the oil flow so you don’t loose all your oil pressure. You might also consider an oil cooler… your oil will be hauling a lot of heat away from the turbo…
You might look into a belt drive (some lost power)… a small super charger is also fun to work with. KennyV.

CTyler · Oct 9, 2005

I'n not sure how to calculate the size of the turbo you need to get you to a sea level equivilant at x feet. However if the smallest turbo is still a little big then can't you use an adjustable waste gate to max out at 6-8psi?

This would be a question for the turbo experts.

On the other hand a small blower is very easy since it has a linear boost rate vs the expotenial curve of a turbo. To change the max boost you just change the pully size. Its' a lot easier to plumb in as well.

ZackaryMac · Oct 10, 2005

If I could add two comments here....80's Ford turbo diesel Ranger had a small turbo (I have seen one) that could be something to look for if used is what you seek, though finding one may be a bit tricky.
Also, I read once where turbo oil draining was very important, ie not going uphill, as this oil will be VERY hot, and the last thing you want is to boil or cook this oil in the turbo, as is a common problem with turbo's that aren't allowed a cool-down period after a hard work-out. Turbo's typically spin in the 100,000 rpm range and need adequate lube, hence the smooth flow of cool lubricating oil.

rocketman128 · Oct 12, 2005

All,

Yep, I am starting to think a oil cooler on the return side of the turbo might not be a bad idea, and they are cheap.

Found the turbo I think I am going to use, RHF3:

http://www.ihi-turbo.com/turbo_RHE-RHF.htm

Bob