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# 80+ PSI boost, single stage, how ?

## 80+ PSI boost, single stage, how ?

(OP)
Hello,

I seen many engines with single turbos with around 60 to 80 pounds of boost ( 4 or 5 bar) they did so in f1 in the 80's

How is it possible with a single turbo ? Its way off the compressor map !

https://youtu.be/_yeJB2-mELM

### RE: 80+ PSI boost, single stage, how ?

Hi Ebuet,

I don't think that a 5:1 pressure ratio is all that difficult. The centrifugal compressor impeller tip speed should still be around 600 meters/second, which is very do-able with forged titanium wheels.

While this doesn't directly address the OP, I think the real question is not how but why. Compressor designers (turbochargers, aircraft engines, industrial compressors, etc.) have long ago determined that supersonic inlet relative mach numbers result in losses that can be avoided with subsonic inlet relative mach numbers. Two stages of compression can readily achieve 9:1 pressure ratio without the inlet relative mach numbers going transonic.

The above assumes sea level ambient temperatures. The Euler work equation yields the energy transfer (temperature rise) as a function of wheel tip speed, But the pressure ratio is a function of delta T upon T. Lower the inlet temperature of the air and the pressure ratio will go up when the rotational speed and tip speed are held constant. I have done it with high altitude turbocharger application in both the altitude test chamber and actual flight vehicles.

http://www.personal.psu.edu/faculty/c/x/cxc11/pape...

https://www.sciencedirect.com/topics/engineering/m...

### RE: 80+ PSI boost, single stage, how ?

6.5:1 pressure ratio

If I'm not mistaken, 6:1 with a single stage centrifugal impeller was already achieved in aviation in the early 60s. I believe it was a helicopter powerplant.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

### RE: 80+ PSI boost, single stage, how ?

It is certainly easier in larger sizes where the required tip speed can be achieved at lower shaft speed.

je suis charlie

### RE: 80+ PSI boost, single stage, how ?

[quote gruntguru]It is certainly easier in larger sizes where the required tip speed can be achieved at lower shaft speed/quote]
I'm not following that logic. Perhaps you could elaborate.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

### RE: 80+ PSI boost, single stage, how ?

The logic is lower shaft speed and lower centrifugal stress at the tip - should be easier to manage? Not to mention the increasing blade clearance concern with smaller turbos.

Just shooting from the hip here - from the tone of your question, I sense you are poised to enlighten us?

je suis charlie

### RE: 80+ PSI boost, single stage, how ?

Pressure ratio is a function of tip speed. The centrifugal stress at the tip should be the same whether the compressor is large or small.

### RE: 80+ PSI boost, single stage, how ?

In fact, all the physics of a centrifugal compressor scale quite nicely. The one bugaboo, when scaling down, as gruntguru identified, is it is hard to keep the relative tip to wall clearance, as the shaft motion and manufacturing capability drive to a higher relative clearance. There may be a cost element embedded in these factors as well.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

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