[hotrod]

turbo flow

The turbo flow rates in those charts are generally at the far right side of the compressor map at the stated pressure ratio. In the case of several of the VF tubos as is labeled on the chart they are educated guesses ( ei. estimates) based on observed performance in the real world and basic physical characteristics like the compressor inlet, and turbin outlet sizes which roughly correlate to compressor performance as long as your comparing similar turbos.

If you go to the original thread on Nasioc ( http://forums.nasioc.com/forums/showthread.php?s=&threadid=278517 ) you will find a large section of notes explaining both changes made to the list over time, and the how and why some turbos are ranked as they are. More importantly, I clearly state in that thread that any two turbos that have rated flows that are within 5% - 10% of each other should be considered essentially equal. Don't waste your time splitting hairs here folks, the ranking list is only a first order selection guide so folks can quickly narrow down their search to turbos that are reasonably suited to their needs.

There is a huge range of performance possible with any given turbo depending on how you set up supporting mods and tune, not to mention how you drive and what fuel you choose to use.

Larry

 

[hotrod]

Turbo's

complexx:

Although your question is posed to djres4, I'll take a whack at it.

correct me if I'm wrong, but you can't be at more than one place on those maps at the same time right?

Well the answer to that is sorta yes and no .

Your correct at any given moment you can only be at one point on the map, but at any given boost (pressure ratio) you can be at many different points on the map.

Look at the 13G compressor map for example at the 2.0 pressure ratio line. You see that if you draw a horizontal line across the map at the 2.0 pressure ratio it can flow anywhere from about 100 cfm at the surge line on the far left side to about 360 cfm on the far right side. This is an example of the fact that a turbocharger is a fixed pressure, variable volume compressor.

You use the waste gate system to define a pressure ratio for the turbo to run at but it can flow a wide range of air flows at that pressure ratio.

The obvious question is how do you determine the point on that line that corresponds to the turbo's true point of operation?

That left right postion, is defined by the air flow demand of the engine the turbo is attached to, and the turbos inlet air temperature and pressure (which we will ignore for now).

If you turn a 2.0L engine at 4000 rpm and it has a .85 VE it will try to ingest about 240 CFM or in this example, right about where the right side of the 75% effeciency island intersects the 2.0 PR line.

Push the engine rpm up to 6000 rpm and now the engine wants to flow 360 cfm which is the maximum rated flow of the turbocharger. (at least at reasonable effeciencies).

As you can see at the midrange rpms around 3000 - 4000 rpm the 13G is a highly effecient turbo that will easily support boost pressures over 14 psi. It hits a maximum practical flow of about 300 CFM about 25 psi with acceptable effeciency, when the engine hits about 5000 rpm. ----- Hmmm that sounds a lot like the rpm range the WRX hits maximum torque doesn't it

If you have a boost controller that allows you to map boost pressure to engine rpm, or if you fiddle with a more basic boost controller so it hits peak boost at around the peak torque rpm of 4500 - 5500 the 13G will make you a very happy driver.

I think the thing you need to keep in mind is the turbo is not an independent unit, it is part of a co-dependent system.

You can't define the turbo's performance until you know something about the engine it will be used on and its breathing ability, tune and rpm range.

Larry

 

[hotrod]

abreviations

Sorry --- VE is the usual abreviation for Volumetric Effeciency. That is the percentage of the physical swept volume of the piston that actually gets pulled into the cylinder at a given rpm.

In the above example, a 2.0L engine turning at 4000 rpm actually sweeps out a cylinder volume of 282.4 CFM (Cubic Feet per Minute). But due to mechanical and aerodynamic flow ineffeciencies most common engines seldom can actually move that much air. Most engines run at somewhere between 85 and 95 % VE over most of their rpm ranges.

A small number of ultra high performance engines that have been optimizes for operation at a certain rpm, and actually exceed 100% VE slightly due to ram tuning on the intake and exhaust.

Loss of VE at high rpm is why engines power output eventually drops off at high rpm. The power increase of more power strokes per minute gets overwhelmed by a drop in engine effeciency at high rpm.

Larry

 

[hotrod]

sources

You might want to look over these resources:

http://forums.scoobytech.net/phpBB2/viewtopic.php?t=53

I'd start with the --
http://www.stealth316.com/2-primer.htm and other related links on that web site.

Larry