Please Explain To Me How This Works
^ that's not the right way to think about it. But even if you do think that way - 22 psi in a "garden hose" UICP form a big turbo is the same as 22 psi from a small turbo. You're not changing hoses here... 22 psi at manifold is just that. No matter which turbo you use to make that.
Temperature does matter though.
Backpressure matters
Speeds of the turbine and compressor matter
Efficiency at certain rpm's and flow (from flow charts) matter
Temperature does matter though.
Backpressure matters
Speeds of the turbine and compressor matter
Efficiency at certain rpm's and flow (from flow charts) matter
Little turbo = little hose.
Big Turbo = big hose.
In the end it's all about volume. At low pressure most turbos will do but if you want to move a large volume of air stuffed into your motor, efficiency does in fact come into play. A bigger turbo (firehose) is a more efficient way to move that volume.
You say that 22psi is 22psi which is true but the reason we use turbos and do head work and mess with cam lift and duration and overlap is ALL about stuffing as much oxygen into the combustion chamber as possible to burn the fuel.
Ummm yeah, actually it is pretty much that way, your just having trouble understanding. Let me make it more simple.
Little turbo = little hose.
Big Turbo = big hose.
In the end it's all about volume. At low pressure most turbos will do but if you want to move a large volume of air stuffed into your motor, efficiency does in fact come into play. A bigger turbo (firehose) is a more efficient way to move that volume.
You say that 22psi is 22psi which is true but the reason we use turbos and do head work and mess with cam lift and duration and overlap is ALL about stuffing as much oxygen into the combustion chamber as possible to burn the fuel.
Little turbo = little hose.
Big Turbo = big hose.
In the end it's all about volume. At low pressure most turbos will do but if you want to move a large volume of air stuffed into your motor, efficiency does in fact come into play. A bigger turbo (firehose) is a more efficient way to move that volume.
You say that 22psi is 22psi which is true but the reason we use turbos and do head work and mess with cam lift and duration and overlap is ALL about stuffing as much oxygen into the combustion chamber as possible to burn the fuel.
The reason a bigger turbo flows more air at the same psi as a smaller turbo is because:
1. lower temperatures (better compressor/turbine efficiencies)
2. Higher VE (lower back pressure)
You have to be looking at the equation for airflow through an engine and apply it to your engine, not just looking at the compressor map solely and seeing what the turbo can do on another engine.
That's it. It's nothing about a bigger turbo flowing more or a bigger 'hose'. As one person stated, it is all about PV=nRT, but the V is our engine volume.
Eric
Here's a decent link http://www.turbobygarrett.com/turbob...o_tech103.html. The graphic is a compressor map of pressure ratio vs. flow, the construct is pretty typical for compressors of any kind - turbo's, jet engines, etc.
Since your assuming both turbo's are boosting the same, the pressure ratio across the compressor is the same. What is different is the volume, hence the ability to have more mass and more mass flow i.e. more air into the engine. Since the compressor discharges into the engine (not into the exhaust like on a jet engine), backpressure does not have a lot to do with the efficiency (pressure ratio or flow) of the turbo, but will IMO have a lot to do with the wind-up speed of the turbo.
Since your assuming both turbo's are boosting the same, the pressure ratio across the compressor is the same. What is different is the volume, hence the ability to have more mass and more mass flow i.e. more air into the engine. Since the compressor discharges into the engine (not into the exhaust like on a jet engine), backpressure does not have a lot to do with the efficiency (pressure ratio or flow) of the turbo, but will IMO have a lot to do with the wind-up speed of the turbo.
- A larger compressor runs more efficiently at high mass air flow rates, which equates to cooler IAT and a denser charge.
- A larger turbine housing equates to lesser backpressure, which improves mass air flow at a given intake manifold pressure, reduces pumping losses, and reduces reversion.
The intake air temp (IAT) and exhaust manifold pressure readings are needed to truly get a clear idea of what is really happening. The boost gauge will show the same 22 psi with the larger turbo, but the IAT will generally be lower, and the exh manifold pressure will be lower. If we check the MAF signal, it will be higher.
Intake manifold pressure doesn't tell much more than that, so don't get too caught up in boost gauge readings.
^ that's not the right way to think about it. But even if you do think that way - 22 psi in a "garden hose" UICP form a big turbo is the same as 22 psi from a small turbo. You're not changing hoses here... 22 psi at manifold is just that. No matter which turbo you use to make that.
Temperature does matter though.
Backpressure matters
Speeds of the turbine and compressor matter
Efficiency at certain rpm's and flow (from flow charts) matter
Temperature does matter though.
Backpressure matters
Speeds of the turbine and compressor matter
Efficiency at certain rpm's and flow (from flow charts) matter
A bigger turbo is more efficient at higher engine rpms (pump curves) because it can move more air at a lower turbo rpms(they can make the same pressure spinning slower). A smaller turbo may become very inefficient at high engine rpms where it will start to just "chop" the air in the housing instead of pumping air (boost taper) and causing more heat.
From my knowledge i think a bigger turbo will make more power if you are running a pressure that a smaller turbo can't do efficiently because according to a pump curve you can get the same amount of head from two different pumps if you spin them at different speeds.
That was all probably confusing but there what i have.
From my knowledge i think a bigger turbo will make more power if you are running a pressure that a smaller turbo can't do efficiently because according to a pump curve you can get the same amount of head from two different pumps if you spin them at different speeds.
That was all probably confusing but there what i have.
Just to clarify, the backpressure I was referring to was for the turbine.
As stated above by others, the compressor backpressure will effect both pressure ratio and mass flow and efficiency and temperature rise.
At a constant corrected speed, compressor backpressure will push the compressor off its line of highest efficiency towards the surge line. Alternatively, very low backpressure will push the compressor to a choked condition.
As stated above by others, the compressor backpressure will effect both pressure ratio and mass flow and efficiency and temperature rise.
At a constant corrected speed, compressor backpressure will push the compressor off its line of highest efficiency towards the surge line. Alternatively, very low backpressure will push the compressor to a choked condition.
works like this:
what has more air in it???
This at 5 psi (meaning 5 lbs of air pressure is distributed among every square inch)
OR
This at 15 psi (meaning 5 lbs of air pressure is distributed among every square inch)
No take both and make them both the same PSI. One still has wayyyy more air in it then the other. Same concept with lets say a stock turbo VS. 35R
-Steve
what has more air in it???
This at 5 psi (meaning 5 lbs of air pressure is distributed among every square inch)
OR
This at 15 psi (meaning 5 lbs of air pressure is distributed among every square inch)
No take both and make them both the same PSI. One still has wayyyy more air in it then the other. Same concept with lets say a stock turbo VS. 35R
-Steve
I've asked this same question here before.
Making power is all abou t helping the engine breath better. When you switch to a bigger turbo, which notmally also means a larger tubular manifold, you are greatly reducing exhaust back pressure. I believe this then allows exhauts gassed to escape the cylinders with greater velocity, which in turn aids the velocity of incoming air because there is overlap of exhaust and intake valve openings.
Net result is less exhaust backpressure = more power. This I believe is 95% of why a bigger turbo will make more power than a smaller one at same boost level.
One other effect I think, is exhaust back pressure also contributes to heat at the exhaust valves, this might effect detonation as well, and so you might be able to run more ignition advance as well I think.
I'm no expert but I think those are the main reasons. The cooler incoming charge, and the garden hose analogy are not so helpful.
Making power is all abou t helping the engine breath better. When you switch to a bigger turbo, which notmally also means a larger tubular manifold, you are greatly reducing exhaust back pressure. I believe this then allows exhauts gassed to escape the cylinders with greater velocity, which in turn aids the velocity of incoming air because there is overlap of exhaust and intake valve openings.
Net result is less exhaust backpressure = more power. This I believe is 95% of why a bigger turbo will make more power than a smaller one at same boost level.
One other effect I think, is exhaust back pressure also contributes to heat at the exhaust valves, this might effect detonation as well, and so you might be able to run more ignition advance as well I think.
I'm no expert but I think those are the main reasons. The cooler incoming charge, and the garden hose analogy are not so helpful.
The amount of air and the inlet temp of that air is the single most critical factor when talking about compressor size because colder charge means much more oxygen molecules that could be used in the combustion process.
If cooler incoming charge doesn't matter, then what does?
