I'm not discussing compressor velocity, I'm discussing charge velocity. Are they linearly correlated? I have never considered this.

They shouldn't be, the volume of the cylinder when the intake opens is relatively small, and the charge velocity will be determined by the piston. The speed that the pressure wave travels will be slightly different due to the increased pressure/temperature though. I guess you have a point there.

Although this analogy isn't exact, it is a good way to visualize it:

Think of water pressure.

If you have two water tanks, the same size, on top of a hill.

They both have a 3" hose running down to the bottom of the hill (charge piping).

One hose is restricted with a 1.5" opening at the tank (large turbo), the other is 1.0" (small turbo)

Both of them have the same static pressure at the bottom of the hill (8 psi for example).

If you open the valve at the bottom of the hill for 50 milliseconds (intake valve), even though the pressure is the same, and the 3" hose is the same, the 1.5" opening will be able to push out a bit more water, because it will be able to maintain the dynamic pressure at 8 psi better than the 1" opening.

Poor analogy I know, but this is how I envision it in my head.

At first I thought you meant there were different engines all stock but same displacement but I could have sworn the dark blue was the prince engine from the Mini and Peugeot. I abandoned that idea though because the 250 mark couldn't be any stock 1.6L that I could think of. Then I realized that you meant they were the same engine with different mods. :P

I'm not sure it's fair to compare the first gen mini to the second as the engines are completely different save for the displacement and cylinder numbers. Valvetronic and a turbo sure do make a different curve than a standard cam and a blower huh.

Serial, I think it is a bit of both the smaller turbine choking exhaust, and the turbo blowing out of its efficiency range. Even if efficiency drops a bit, say ~5% the charge will heat up. So the OEMs, for reliability issues, will pull timing and/or reduce boost up top.

Aftermarket tunes will often maintain boost all the way from peak.

The Prince and Tritec engines are indeed quite different. The Prince engine in this plot is from a bone-stock 2007 MINI Cooper S, which is not Valvetronic [that didn't happen on the turbo Prince in the MINI's until MY2011]. It's main advantages over the Tritec are direct injection and Vanos on the intake cam. The comparison here is strictly for entertainment; it demonstrates how different design philosophies and hardware setups can produce significantly different power curves despite both being forced induction and the same displacement. The Prince engine was designed for big area under the curve at lower RPM, a common trend these days with most GDI turbo engines.

You guys are making great comments. Boost is indeed not indicative of power, CFM is what is more correlative to power. The small turbo runs out of flow-rate quickly and then loses efficiency as it slams into its choke zone; the big turbo is bordering on surge until mid-RPM, where it finally comes into its efficiency sweet spot.

If we were to select a turbo halfway between the tiny K03 and the relatively large GT3071R, we'd end up with a power curve averaged approximately between the small and big turbo. We'd have a more well rounded turbo setup, with minimized surge at low RPM and minimized choke at high RPM.


Anyone want to estimate the boost level change between the Red and Dark Blue plots?!

I'll take a stab at it:

Red = roots blower
Indigo = centrifugal blower
Blue = twin turbo
Purple = single big turbo

Any hits?

Yes, you got Red and Purple correct! Add "small" in front of and "scroll" between your words for Light Blue and you got that one too. ;)

The answer is on Post 18, with explainations further down.

Great to see members getting the hang of it. :thumbsup:

Is there a compressor map for the stock turbo? I'm curious about how much the efficiency drops off. In the olden days a highly efficient turbo would have a pretty small 'island' and drop off significantly outside of it.

Since it's OEM, the stock R56 Cooper S compressor map is very tough to get a hold of. Nevertheless, I've attached the chart I have. It's in kg/sec vs. PR. This turbo roughly flows 21.1lbs/min or .16kg/sec

Also, here's the comp map for the GT3071R, for comparison [in Lb/min vs. PR].
http://turbobygarrett.com/turbobygar...2-3&20comp.jpg

As you can [barely] see, the little K03 is done right when the GT3071R is coming into it's own.

^Call me newbs, but I've never could read those graphs. It looks like finger prints to me. Whatta hell am I looking? Help me out there Engine experts

No problem. Your term "finger print" is a great analogy. What you're looking at with the above turbo compresssor maps are basically the aerodynamic finger prints of the compressor, which is the fresh-air side of the turbocharger. There's another aspect of turbocharger finger prints, the turbine side where the exhaust powers the turbocharger, which we've glossed over.

The Compressor maps above are displayed in Mass-Air Flow [X axis / longitudinal] versus Pressure Ratio in the Y axis / vertical. Mass-Air Flow is basically the quantity of air [and thus Oxygen]. Pressure ratio is basically the amount of boost [which is air restriction] after accounting for induction pressure-drop losses.

All the different lines in the Compressor Map show the impeller rotational speed, compression efficiency [how much heat is created], and it's limits of operation [called Surge and Choke lines]

To super-simplify the maps:
*More to the right = more power
*More upward = more boost

I kinda get more to the right = more power & more upward = more boost part...

Sorry, I should of been more detail. Which line should I been looking at? Lines that looks like Finger prints or lines that crossing the finger prints? Or Both???

The concentric lines that look like finger prints are called "efficiency islands". They represent compressor efficiency. The island in the center is the ideal operating zone for the compressor, and every concentric island outward from there is less efficient.

The lines crossing the finger prints are turbo shaft [impeller] speed lines. The further upward, the faster the turbo is spinning. It's mainly for reference. For example, the Garrett GT3071R "big turbo" in this thread can spin at a maximum speed rating of 140,035 RPM. In order to get the turbo to spin that fast, however, you need to be running lots of boost and making lots of power.

I hope that helps,
Ryan