Is too much boost for a given fuel bad?

[8v-of-fury]

The only point I was trying to get across was that boost is directly relative to fuel burnt. You cannot have high boost without additional fueling. It does not work that way. Unless there is more energy going out the tail-pipe to spin the turbo up then there is no extra boost.

70-90psi!? HOLY COW.

I have never really fully grasped the people going to 22+ psi when it is completely counter-intuitive. You are wasting power to compress the air.. it is pointless. When I get the inter cooler setup on the M-TDI it is going to run a cool 15-18psi.

[Thezorn]

This is very true, with my compound setup It pulls hard until about 15 psi and about 2200-2500 rpm, soon after I begin to run out of fuel.
With both wastegates operating at thier lowest boost setting it will still make 22-24psi, but there is clearly no need for that extra 5-10psi.
On the other hand that extra boost does still help keep the EGT's down at higher rpm's..but really serves no other purpose untill it is fed with more fuel..... hopefully soon to come.

[libbydiesel]

The eTDIs with wastegated turbos had the wastegate controlled by computer.  They limited the boost under all conditions in order to accurately match fuel to air to maximize efficiency.  Additional boost for any given fueling always reduces efficiency even if you are within the turbos efficiency range (they are never 100% efficient).  The mechanically controlled engines come close to that with the aneroid functioning properly, but still fall short. 

The ECOdiesel engines were produced to reduce emissions and all the ways they are different from the "true" TD engines hurts engine efficiency. 

[theman53]

8v
Heat spools a turbo, not nessesarily fuel. If you retard the timing and DO NOT change fuel it will reach higher boost, because the later injected fuel isn't burnt completely in the combustion area. It is still burning good in the exhaust port and then spinning the turbo eventhough no more fuel is being injected. So with the timing unchanged if you add more fuel you can add more boost. BUT it is load dependant as well. If you have no load it is harder to make boost. Ex: rev car in nuetral, then rev car in 1st gear, then in 4th gear, the more load the more "potential" for boost.

I had 20+ psi with my k24 because it needed to be cooled. I had less when it wasn't intercooled. For me it was a bunch of trial and error...or mostly error and error and maybe get lucky. I played with that engine constantly to get better results. Right around 22psi intercooled was the best for my EGT situation. More than that it didn't change, less it got worse.

[JerryGTD]

 

[R.O.R-2.0]

and i cant drive my car, so you are going to just have to figure it out..

I have it figured out lol. I have given you nothing but proof and logic to determine what happens with boost relative to fuel.

Until you can get your car operational, I cannot physically show you what I am talking about. I just ask for some qualitative answers to prove what you say is all eh?

ok, there.. some answers that werent from me.. sorry dude, but i knew what i was talking about, just needed a couple others to confirm it.. andrew knew exactly what i was talking about, because i believe he was the first one to ever bring it to my attention..

[8v-of-fury]

Sorry. My points were referring to a properly running car. Retarded timing is not optimal, and was never intended.

Andrew, How do the mechanical engines with the LDA manage to do better than the electronically controlled TDI's?

[libbydiesel]

They don't do better.  As I said, "they fall short".  They come close because with increases of boost the fuel is increased as well, provided the aneroid is tuned properly, but partial load situations still result in less than optimal fuel to air.

[8v-of-fury]

Additional boost for any given fueling always reduces efficiency even if you are within the turbos efficiency range (they are never 100% efficient).  The mechanically controlled engines come close to that with the aneroid functioning properly, but still fall short. 

Oh sorry, I read this wrong. It sounds as though you said the mechanical engines come close to 100%, my bad.

So say you have a manual boost controller in place to make sure your waste gate wont pop open until say 20psi. If you adjust the fuel so that 12-15psi WOT with load is all that is obtained. Then you up the fuel so that now you can produce 18-20psi with WOT on load.

Which situation would you have more power at?

[BillyWillicker]

That would depend upon the turbocharger's flow characteristics as compared to the engine's flow characteristics.

And doing what you wrote in your last post is the part of the process of "tuning" your diesel automobile.  That in a sense is matching the fueling to the airflow of the engine.  <--is what it's all about, and doing it from 500-5500rpm

With any given setup there will be a "magic" boost number that will make the best power, any more or less boost than that number will result in a decrease in power.

Anyways, did you get the TDI working and driving in your car yet?  Did you build your own M-TDI pump and how did it turn out?

[JamesT]

Additional boost for any given fueling always reduces efficiency even if you are within the turbos efficiency range (they are never 100% efficient).  The mechanically controlled engines come close to that with the aneroid functioning properly, but still fall short. 

Oh sorry, I read this wrong. It sounds as though you said the mechanical engines come close to 100%, my bad.

So say you have a manual boost controller in place to make sure your waste gate wont pop open until say 20psi. If you adjust the fuel so that 12-15psi WOT with load is all that is obtained. Then you up the fuel so that now you can produce 18-20psi with WOT on load.

Which situation would you have more power at?

I have played with this and I understand what you're getting at.
Boiled down to the simplest level, you can't have too much mass of air for a given mass of fuel because there wouldn't be enough exhaust gases to spin the compressor to get that mass of air in. If you had a turbo setup that could make high boost with little fuel, it would be inefficient when more fuel is available (except for variable vane turbines, which are designed to function in both situations).
Because of the nature of a diesel engine, fuel doesn't have to be mixed with air in a stoichiometric mixture to get a complete burn of fuel. You can't go rich on the mixture without making smoke, but you can go very lean and still have an efficient engine.
Yes it takes energy to compress a volume of air to a higher ratio, but that energy doesn't just disappear. That larger compressed volume of air is fighting the piston right to top dead centre, then afterwards rebounds like a spring. Whether or not there's fuel injected, that additional volume of air is acting upon the piston during the power stroke.
If "too much" boost for a given volume of fuel is inefficient, why did Volkswagen design an engine to do precisely that, and then throw an "Eco" prefix on it? I think some former gassers need to learn to give up their precious 14.7:1.

[libbydiesel]

James, as I mentioned previously, the ECO diesel was produced solely to reduce emissions and at significant cost to both performance and efficiency.  Additional boost always costs additional back pressure on the exhaust side.  If you are over-fueled, then, depending on the size of the turbine, additional boost will give additional power.  If appropriately fueled, then increasing boost without increasing fuel at the same time will hurt performance.  That effect has nothing to do with gasoline engines. 

[Smokey Eddy]

Jer, its a matter of flow not pressure. Pressure isn't a good thing.
If you flow more oxygen at 1psi than you do at 100psi you will have a better combustion of the fuel.
talking psi all the time is like talking mileage in "tanks of gas"
who cares how much psi there is. If it's not getting into the cylinders with the appropriate amount of fuel you're either fighting the restriction of the turbo + all the turbulance you're going to be creating in the cylinders or you're flooding it with masses of unburnt fuel.

This dude at a DSM shop where i grew up had a talon and a ... rotary supra...
The supra flowed the fuel & air in and the exhaust out better than the talon did but the talon ran over double the "psi" of the supra.
Needless to say, the supra produced over twice the HP as the talon.

[JamesT]

Ok, but how are you magically increasing boost? I turned down my fuel, and as a result I can't produce as much boost. Sure I could make more power for a given mass of air by increasing the fueling, but it doesn't feel like the added boost affects power either way (waste-gate connected or not) for a given volume of fuel. For the test, my setup is an AAZ with a K14 turbo, stock boost pin, stock everything, with a minor adjustment of fueling, and pump timed to .90mm. With the waste-gate connected, it will generate 9psi boost consistently (enough to put the boost pin on the step). Without, it tops out at about 19psi with my current fueling. I'm only using the butt dyno, but it doesn't feel any different, except it's quieter with the waste-gate disconnected. To quell this argument, we need someone to run a few dyno pulls with consistent fueling and variable manifold pressure.

And Eddy, we're only talking in psi because engines are positive displacement pumps. My engine will flow 1.9L of air for every two revolutions at whatever pressure is in the manifold. Volume is constant at a given speed for any manifold pressure. What we should be talking about is mass. m=pV/RT. Volume is a constant, R is a constant, and temperature falls into a fairly consistent range for our purposes (although it would be more consistent if I had an intercooler), so the only real variable is pressure, which is what we're discussing.

[Smokey Eddy]

And Eddy, we're only talking in psi because engines are positive displacement pumps. My engine will flow 1.9L of air for every two revolutions at whatever pressure is in the manifold. Volume is constant at a given speed for any manifold pressure. What we should be talking about is mass. m=pV/RT. Volume is a constant, R is a constant, and temperature falls into a fairly consistent range for our purposes (although it would be more consistent if I had an intercooler), so the only real variable is pressure, which is what we're discussing.

Couldn't agree more. Thanks for that.