Turbo Charger Upgrade for Older Kubota

SkyPup · Oct 3, 2005

Diesel and gasoline engines loose the same % of power at altitude in direct relation to the loss of atomspheric pressure.

cp1969 · Oct 3, 2005

Why would that be? The power is in the fuel, not the air. If the diesel runs 35:1 at max power at sea level and 25:1 at altitude, where does the power loss come from? Gas engines lose power because they have to reduce the amount of fuel in proportion to the loss of air to maintain an a/f ratio of ~14:1. The amount of fuel injected by a diesel is unchanged and even at 25:1 that is more than enough air.

rocketman128 · Oct 3, 2005

This one, I think I might be able to shed a little light.

The idea is to get the right number of air (oxygen) molecules and fuel (diesel) molecules together under pressure for complete and efficient burning. Most modern cars & diesels have an electronics package that measure air pressure, and O2 in exhaust, air flow, etc.. to adjust the mixure to get as close as possible to the ideal mix.

Old tractors with mech injectors are designed for sea level operation. At altitude I will not be getting as many O2 molecules as I would at sea level, hence, I will be wasting fuel that does not burn. All things being equal, I should lean out the mixture for optimal combustion. I don't think there is an adjustment for this on these old guys.

So, this brings be back to the Turbo question. At sea level we are under 14.7 psi (average), and at 10,000 feet the pressure is about 9.5 psi. Delta of about 5.2 psi. If I could get a turbo in this range, would round up to say 8 psi at max, I think this little guy would run like a champ.

After a little more research, the primary variables for pick the right size unit is the volume of exhaust curve, volume of intake air curve (both from idle to rated RPM), and the desired boast presure.

Sorry for the rant.

Bob

ZackaryMac · Oct 3, 2005

( Never heard that a diesel runs with a surplus of air??? Diesels must have more air because it's used to ignite the fuel. (

What he is referring to is gas engines use a choke plate (throttle plate) to limit the airflow into the engine, where a diesel has no throttle plate, therefore no air restriction entering the head. Gas engines must have a steady 14.7:1 air/fuel ratio (by weight) for efficient running, but a diesel controls it's combustion by fuel alone, since the air runs wide open all the time. A gas engine has to do this by restricting the air entering the engine, as it cannot give just a little fuel for 100% air, otherwise it would lean out so much it would quit. So, a little air, a little fuel. Lots of air, much more fuel (as you all know if you drive with a lead foot /forums/images/graemlins/tongue.gif)

Diesels always have an abundance of air for the fuel to be burnt. When it doesn't, it smokes black.

A turbo will help both a gas and a diesel. Diesels react better to a turbo, typically. However, a turbo increases heat and pressure quite a bit, so the engine has to be able to handle it without burning up.

Ok, I'll stop now.

SkyPup · Oct 4, 2005

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

rocketman128 · Oct 4, 2005

I think Zak & I both have it about half right.

If you control the rpm/power by how much fuel you add at max power you can't suck enough air in to max out the combustion. Hence the turbo.

RobJ · Oct 5, 2005

(Diesels always have an abundance of air for the fuel to be burnt. When it doesn't, it smokes black. )

I think your confusing "volume" of air with the "content" that's actually in the air...IE oxygen(O2). As someone mentioned before it's the O2 in the air that burns. Cooler air has more, hotter air has less. Higher altitude air has less. A tubo's compressor wheel compresses more air into the cylinder, thus more O2 molecule.

A gas engine regulates it's speed with the amount of air coming in, a diesel with the amount of fuel. But as with both, you can have to much fuel for the availabl O2 to burn.

cp1969 · Oct 5, 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.

The gas engine is limited in the air/fuel ratio that it is able to combust, from about 10:1 to 18:1. Outside of that range, the a/f mixture simply won't burn because it depends on a flame front to propagate combustion within the cylinder once the spark plug fires. With an increase in altitude, pressure (and available oxygen) decreases. 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.

Diesels, on the other hand, do not rely on a flame front to keep combustion going and can run virtually any f/a mixture you can feed it. One need only go to a tractor pull to see examples of diesels running f/a ratios of about 5:1--the cloud of smoke coming out of one resembles a tornado. A typical diesel runs at about a f/a ratio of 35:1 at full throttle--there is PLENTY of extra air to support combustion of more fuel, which leads me to the corrolary that air intake can be reduced considerably, by gaining altitude, without a loss of power, unlike the gasoline engine.

Where am I going wrong here?

KennyV · Oct 6, 2005

Hello Charles…
Assuming a 30 cubic inch cylinder at sea level, it will hold more air than that same cylinder at 10k foot, unless you pressurize it.
Tractor pull diesels run lots of boost pressure and some amazing injector pumps. I think those tractors could pull very large mowers /forums/images/graemlins/grin.gif… KennyV.

SkyPup · Oct 6, 2005

The physics is very simple, the barometic air pressure is decreased equally for all internal combustions engines at a particular altitude no matter what kind of fuel they are using or what method of fueling they use or what kind of combustion chamber they employ.