Is too much boost for a given fuel bad?

[8v-of-fury]

it goes now pretty good, after ~17psi I don't feel much change in power.  i notice that the EGT drops when the boost hits which is nice.

thats because your turbo is pushing more air than needed.. if you have marginal fueling, and lots of boost, it will make less power that way, rather than having decent fueling, and marginal fueling..

if you havent cranked up your fuel screw, then i would back the boost down to about 12-13 psi.. there is absolutely no reason to run that much boost to an engine with stock fueling..

Is boost not directly affected by how much fuel you are giving? Stock fueling is only good for x amount of boost. Why limit it? If stock fueling wants to make 15psi whats wrong with that?

[R.O.R-2.0]

it goes now pretty good, after ~17psi I don't feel much change in power.  i notice that the EGT drops when the boost hits which is nice.

thats because your turbo is pushing more air than needed.. if you have marginal fueling, and lots of boost, it will make less power that way, rather than having decent fueling, and marginal fueling..

if you havent cranked up your fuel screw, then i would back the boost down to about 12-13 psi.. there is absolutely no reason to run that much boost to an engine with stock fueling..

Is boost not directly affected by how much fuel you are giving? Stock fueling is only good for x amount of boost. Why limit it? If stock fueling wants to make 15psi whats wrong with that?

stock fueling will let the turbo explode with boost.. like literally grenade..

there is no reason to be running more boost than you have fuel for.. you are actually going backwards if you have 10psi worth of fuel to burn, and you are burning it with 20psi.. the piston has to fight the boost before TDC.. so you are actually LOSING power by running MORE boost than it takes to make the car run efficiently..

TOO MUCH BOOST for a given amount of fuel is bad..

do you think you would get more power from a small fuel charge and 10psi, or a small fuel charge, and 20psi?

well, of course with marginal fueling, you want marginal boost..

you WILL make less power with TOO MUCH boost..

this topic has been gone over many times before..

[8v-of-fury]

stock fueling will let the turbo explode with boost.. like literally grenade..

Stock fuel levels can produce enough boost to grenade a turbo.. Ok, but at what RPM? Gotta be something above what our diesels spin. I have driven a bone stock TD (with stock fueling) and the waste gate does not bleed boost off. So this tells me stock fueling cannot even produce the 12-13psi needed to open the stock waste gate.

there is no reason to be running more boost than you have fuel for.. you are actually going backwards if you have 10psi worth of fuel to burn, and you are burning it with 20psi.. the piston has to fight the boost before TDC.. so you are actually LOSING power by running MORE boost than it takes to make the car run efficiently..

If you have enough fuel to produce 10 psi of boost (because the boost in said engines is directly related to fuel injected, ie. energy to spin the turbine) how are you making 20psi of boost? You have got some things jumbled up with how you are understanding this. Yes too much boost is bad, but not while your still in the efficiency range of the turbo. If you have the fuel set so you can produce 25-27psi out of a T3 and you make X amount of power, you can make X amount of power with less fuel and have boost somewhere in the turbos efficiency range. But this only applies when you have exceeded the turbos range of efficiency.

TOO MUCH BOOST for a given amount of fuel is bad..

Well no not really, because you cant have boost without fuel. So therefore, really.. Too much fuel for a given amount of air is bad..  That is why the OP said from 18 psi up to 22psi he did not feel anymore power. Too much fuel, not enough air.

do you think you would get more power from a small fuel charge and 10psi, or a small fuel charge, and 20psi?

If the fueling remained exactly the same? and did not change one bit? You would have WAY more power with X amount of fuel and 20psi then you would have with X amount of fuel and 10psi. Because if you had enough fuel to support 20psi.. then you have too much fuel for 10psi.

well, of course with marginal fueling, you want marginal boost..

What is marginal? For power you want as much boost and fueling as your entire setup can handle. Efficiently. If your turbo can efficiently produce 18psi, and you can provide enough fuel to do so without raising EGT's too much then you have found your systems maximum power for smallest amount of fuel given. Add an inter cooler, drop the EGT's, cool the charge air. You can now effectively run MORE fuel while maintaining the same boost level, Within the turbo's efficiency range.

you WILL make less power with TOO MUCH boost..

Too much only meaning outside of the turbo's efficiency. What happens when you have a big turbo that can support big boost? is it gonna make less power too?

Yes it has been gone over before, yet you still don't quite grasp how it works.. Interesting.

[R.O.R-2.0]

my VNT would make 30+ psi on stock fueling from a n/a pump.. it was SLOW!

i made WAY more power with lots of fuel and 15psi than i did with no fuel and 30 psi..

grasp it or not, it actually works that way..

think of boost as variable compression.. if you have TOO MUCH compression for a given application, it will HINDER performance..

[8v-of-fury]

I don't know if we can quantify the data obtained from your VNT setup. It is known fact you never had the vanes hooked up or working properly. SO yeah vanes closed, i feel a small VNT, with its vanes closed, could reach those boost pressures with very little fueling. If it were properly working? I doubt it.

think of boost as variable compression.. if you have TOO MUCH compression for a given application, it will HINDER performance..

They are in direct relation though man. Now that you have a waste-gated turbo go turn your fuel way down and get back to us. I want you to see if you can still hit the same boost numbers.. but here lies the challenge, with the same amount of power as well.

I'm not hating on you man, I do this to everyone spouting incorrect information. Interwebz or real life.

[R.O.R-2.0]

I don't know if we can quantify the data obtained from your VNT setup. It is known fact you never had the vanes hooked up or working properly. SO yeah vanes closed, i feel a small VNT, with its vanes closed, could reach those boost pressures with very little fueling. If it were properly working? I doubt it.

think of boost as variable compression.. if you have TOO MUCH compression for a given application, it will HINDER performance..

They are in direct relation though man. Now that you have a waste-gated turbo go turn your fuel way down and get back to us. I want you to see if you can still hit the same boost numbers.. but here lies the challenge, with the same amount of power as well.

I'm not hating on you man, I do this to everyone spouting incorrect information. Interwebz or real life.

one thing tho man, i never changed my vane position ever, as long as i had my VNT..

retarded timing and marginal fuel would make LOADS of boost..

[R.O.R-2.0]

its not a secret.. too much boost for a given fuel quantity is a bad thing..

[8v-of-fury]

one thing tho man, i never changed my vane position ever, as long as i had my VNT..

retarded timing and marginal fuel would make ASS LOADS of boost..

Then they must have been closed. I have read on here that people with open vanes not being able to build any boost at all.

its not a secret.. too much boost for a given fuel quantity is a bad thing..

No it is not a secret, but you are using this information in the wrong context. Fuel and boost being relative to one another, you can only have as much boost as you have relative fuel. Meaning so long as you are in the turbo's efficiency range there is no too much boost for a given fuel. If you only have enough fuel for 10 psi, you only have enough fuel for 10psi. You cant magically make the turbo produce 10 extra psi of boost with no additional fueling. Now if you have the fueling turned up so you can hit 20psi, and you turn the waste gate down to open at 10psi you do not have too much fuel for a given boost pressure because the waste gate bleeds off and the injection pump stops fueling for boost.

Please, prove everything I have said wrong. Go outside, turn your fuel down, and try and hit the same power and boost numbers. It is all I ask, and if you are right, it is a very simple simple way to shut me up .

[8v-of-fury]

i made WAY more power with lots of fuel and 15psi than i did with no fuel and 30 psi..

I cannot fathom how this works. More fuel less boost, less fuel more boost.

[R.O.R-2.0]

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

[8v-of-fury]

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?

[libbydiesel]

Excessive boost reduces engine efficiency by causing excessive back pressure on the exhaust side and will hurt power.  The compression of the added air is not the issue.  Compression of air is an effective spring and the energy of compression is recovered when the piston goes back down on the power stroke.  15psi with appropriate fueling will result in more power than 20 psi with the same fuel.

[rallydiesel]

Most of the time, more boost at the same fueling is due to too much heat. I understand what you are saying, Jeremy. Most of the time you want to maximize boost but once you are outside of the turbo's efficiency, you are just making hot air. For the vnt-15, it's efficiency drops drastically over 18 psi.

[8v-of-fury]

Excessive boost reduces engine efficiency by causing excessive back pressure on the exhaust side and will hurt power.  The compression of the added air is not the issue.  Compression of air is an effective spring and the energy of compression is recovered when the piston goes back down on the power stroke.  15psi with appropriate fueling will result in more power than 20 psi with the same fuel.

What about if you are using a turbo that can support 20+ efficiently?

Most of the time, more boost at the same fueling is due to too much heat. I understand what you are saying, Jeremy. Most of the time you want to maximize boost but once you are outside of the turbo's efficiency, you are just making hot air. For the vnt-15, it's efficiency drops drastically over 18 psi.

Right, as long as you are in the turbo's efficiency, maximum fuel is what brings maximum power.

[belchfire]

What about the ECO engine? My regular TD has the aneroid enrichment but the ECO doesn't. In theory, the ECO has an excess of fuel and the turbo matches it creating a neutral fuel/ air mix. I don't know what the ECO's boost limit is. My blow off ran at 12 psi until I blocked it off and the waste gate cracks @ 15. If mine is set properly then the ECO should have a lot less boost or there is indeed an excess of air. I can't imagine that there's a lot of valve overlap but the fact that EGT's go down when you hit the boost indicates that air is getting by the exh valve and diluting the exh gasses. The spring argument makes sense. I found a chart somewhere and our 23:1 engines @10 psi = 38:1 effective  compression. It takes a lot of energy to do that and I can see a drop in power possible without the additional fuel to go bang. I've heard of some Cummings running 70-90 lbs boost with compound turbos but they must have fire hoses for fuel lines.