[D335I]

Just curious as to how the stock turbo psi is calculated.

I assume when talking psi on the stock turbos we are talking about a combined total of Psi 8-9psi.

So again I assume this is 4psi per turbo which seems very low and bumping each of these little snails up to 8 psi + should not be a big deal as long as they stay within the efficiency range.

My point and question is are both turbos only pushing 4/5 psi?

Thanks in advance.

[WinoGregorio]

I wish it was that simple. There are a lot of trade offs when designing a turbo system. In theory, one turbo might be able to reach max boost too. Small compressors spin faster and provide max boost earlier but sacrifice volume. A single unit that flows the same volume might be too big to provide enough boost at low RPMs.

[etiliko]

You have to think differently.
The two turbo combined make about 8psi in the pipes when the engine is at WOT. This not means that each turbo is pushing half the boost.
This means that each turbo is making 8psi to fill half the engine

[BreakPoint]

Originally Posted by D335I

Just curious as to how the stock turbo psi is calculated.

I assume when talking psi on the stock turbos we are talking about a combined total of Psi 8-9psi.

So again I assume this is 4psi per turbo which seems very low and bumping each of these little snails up to 8 psi + should not be a big deal as long as they stay within the efficiency range.

My point and question is are both turbos only pushing 4/5 psi?

Thanks in advance.

Its been a few yrs since I've been in the boost game, now I'm back in, let me give it a shot.

Turbos don't push psi..

Psi is a meaurment of how restrictive your engine is.(how much pressure can build up before the intake valves)

Turbos are measured in cfm by looking at the turbo's flow map.

Yes it is true that a turbo does have a psi limit, but that simply means at x psi, the turbo has reached its efficiency.

And you can't bump up the turbos. The only way to increase boost would be to control the wastegates, eaither manually or electronically.

The question I would be most concerned with, is how much hp can these stock internals/block hold?

I don't know the answer to that question (because I'm new to bmws), but if you do, please let me know.

[Clap135]

Originally Posted by etiliko

You have to think differently.
The two turbo combined make about 8psi in the pipes when the engine is at WOT. This not means that each turbo is pushing half the boost.
This means that each turbo is making 8psi to fill half the engine

Being that both turbos are combined into a single pipe prior to intercooler, I would say this is incorrect.

[momstmg78]

+1

[BreakPoint]

Originally Posted by momstmg78

+1

What exactly are you agreeing with? Post count increase?

[momstmg78]

Agree with clap135

[Doug007]

Read this if you really want to know more about the turbo system:
http://www.e90post.com/forums/showthread.php?t=38856

Each turbo produces the same pressure as they are connected to the same outlet pipe. However, each produces about half of the total air flow.

If you want to make 16 psi, each turbo will make 16 psi.

Also psi has nothing to do with how restrictive your engine is. The pressure is built by the compressor filling the intake tract with more and more air. The pressure at the intake manifold will control the mass of air that will enter the engine when the intake valve opens. The wastegate is used to control exhaust flow to the turbine side of the turbo and in reality the turbine speed. The higher the turbo speed the more air it moves and the more pressure can be built in the intake tract.

Now go get a book or start learning about the search button...

[BreakPoint]

Originally Posted by Doug007

Read this if you really want to know more about the turbo system:
http://www.e90post.com/forums/showthread.php?t=38856

Each turbo produces the same pressure as they are connected to the same outlet pipe. However, each produces about half of the total air flow.

If you want to make 16 psi, each turbo will make 16 psi.

Also psi has nothing to do with how restrictive your engine is. The pressure is built by the compressor filling the intake tract with more and more air. The pressure at the intake manifold will control the mass of air that will enter the engine when the intake valve opens. The wastegate is used to control exhaust flow to the turbine side of the turbo and in reality the turbine speed. The higher the turbo speed the more air it moves and the more pressure can be built in the intake tract.


Now go get a book or start learning about the search button...

Good info, with the psi/ restrictive intake mentioned above, I may have been reverting to my blower days. A better flowing intake/head will produce more power but you boost gauge will register slightly lower levels.

[Doug007]

Originally Posted by BreakPoint

Good info, with the psi/ restrictive intake mentioned above, I may have been reverting to my blower days. A better flowing intake/head will produce more power but you boost gauge will register slightly lower levels.

That would be true with a positive displacement supercharger (e.g., roots type) since the speed is fixed by the pulley ratio so the air flow is controlled by engine rpm. If your engine breaths better the SC will not be able to build as much boost in the intake manifold.

Turbos do not have that limitation on speed and will increase in speed as long as enough exhaust energy is available. Turbos will be limited on how much they can flow by the compressor size and ability of the turbine to drive the compressor.

On these cars the stock turbos can produce upwards of 20 psi (at extremely high turbo speeds) but will be inefficient and produce a very hot intake air temperature. At that power level it seems that the stock turbine actually becomes the biggest restriction on air flow, hence the clipped turbines on most of the upgraded turbos available.

Hopefully that clears up some of the confusion that seems to be rampant in this thread! Superchargers, especially positive displacement superchargers are very different animals...

[etiliko]

Originally Posted by Clap135

Being that both turbos are combined into a single pipe prior to intercooler, I would say this is incorrect.

I have idealized the concept to explain that what he thinks is wrong.
The reality is that psi isn't the exact unit to measure the work of the turbo.
Anyhow combined or not doesn't make difference, you can have two separate pipes and two intercooler and is the same thing.

[Ilma]

Here's my 2 cents.....

Both turbos fill all six cylinders with equal boost coming from each turbo.

However each turbo runs off of only three cylinders on the exhaust turbine side, hence the two piece exhaust manifold.

The intake manifold is one piece.

[WinoGregorio]

Originally Posted by Doug007

Also psi has nothing to do with how restrictive your engine is. The pressure is built by the compressor filling the intake tract with more and more air. The pressure at the intake manifold will control the mass of air that will enter the engine when the intake valve opens. The wastegate is used to control exhaust flow to the turbine side of the turbo and in reality the turbine speed. The higher the turbo speed the more air it moves and the more pressure can be built in the intake tract.

You are assuming that the engine's intake and exhaust tract can flow much LESS than the turbo can. Correctly designed, this is the case. In a poorly designed system or quite possibly in the case where one turbo fails, boost pressure at large throttle angles could very well be as little as zero. Remember that pressure is the force exerted on a fixed object. If the intake tract is closed and the turbo is spooling rapidly, static pressure will be quite high. At WOT, the pressure will drop as the air now has an escape. How far depends on how much air the turbo can pump into the intake tract vs. how much the pistons are removing.

[Ilma]

I knew I should have stayed out of this!

[Doug007]

Originally Posted by WinoGregorio

You are assuming that the engine's intake and exhaust tract can flow much LESS than the turbo can. Correctly designed, this is the case. In a poorly designed system or quite possibly in the case where one turbo fails, boost pressure at large throttle angles could very well be as little as zero. Remember that pressure is the force exerted on a fixed object. If the intake tract is closed and the turbo is spooling rapidly, static pressure will be quite high. At WOT, the pressure will drop as the air now has an escape. How far depends on how much air the turbo can pump into the intake tract vs. how much the pistons are removing.

What's your point? Who's talking about pressure with the throttle closed?

It's the mass flow of air to the engine that determines how much power can be made. Mass flow in air is directly proportional to pressure and inversely proportional to temperature. More psi at the same temperature is more mass flow (lb/hr) and more power.

The turbos have to move more air than the engine is taking or they would never be able to pressurize the intake manifold...

Also pressure is force divided by area not necessarily a "fixed object"

[Doug007]

Here you go guys:
http://www.amazon.com/gp/search/ref=...be53dc7227c659

[Veeemdoubleu]

our stock internals are good for 1000whp easy, just do it and push it

[WinoGregorio]

Originally Posted by Doug007

What's your point? Who's talking about pressure with the throttle closed?

It's the mass flow of air to the engine that determines how much power can be made. Mass flow in air is directly proportional to pressure and inversely proportional to temperature. More psi at the same temperature is more mass flow (lb/hr) and more power.

The turbos have to move more air than the engine is taking or they would never be able to pressurize the intake manifold...

Also pressure is force divided by area not necessarily a "fixed object"

yes that is what i'm trying to say but have been drinking too many beers today

[D335I]

Originally Posted by etiliko

You have to think differently.
The two turbo combined make about 8psi in the pipes when the engine is at WOT. This not means that each turbo is pushing half the boost.
This means that each turbo is making 8psi to fill half the engine

Got it, makes sense.

Thanks.

[Shellacked135i]

^ I dont like the way that is worded.

If this vehicle makes 8 PSI.... It means XXX amount of CFM was produced by both turbo's. As someone else mentioned the restriction or back pressure, produced 8 PSI.
It's likely since both turbo's are the same size they will push out relatively the same amount of CFM, to produce XX psi in the engine.

[vasillalov]

Originally Posted by etiliko

You have to think differently.
The two turbo combined make about 8psi in the pipes when the engine is at WOT. This not means that each turbo is pushing half the boost.
This means that each turbo is making 8psi to fill half the engine

Thank you! That's the correct answer. From fluid dynamics (air is a fluid), pressure is not additive, but volume is. This means that each turbo is pushing 8psi, not each 4 psi. You need 2 of them because you need to push enough VOLUME to satisfy the demand of 6 cylinders.