Turbo sizing, deeper discussion

So we all have our favorite turbo's that are ranging from stock to box stock to lightly modded to very custom. I however want to know WHY these sizes happen. I have been reading extensively over the last week trying to understand.

Like how everyone wants a big inducer for the potential airflow but how would a bigger exducer help in regards to surging. From what I read, bigger exducer's help reach high PR's. Does this help make the turbo more efficient at higher PR's?

Now there's the turbine side which I find next to nothing on. How does a turbine help capture and use the exhaust? How does the inducer and exducer of that help?

Instead of taking a box stock and modify with a T3 housing, what if you can build a turbo that works efficiently at a certain horsepowers.

Like for a fuel only Cummins, 500-600hp. Would it be better to use a 63/99 or a 63/84? Since the Cummins are more restricted in the head, would a higher PR help? Making the 63/99 more desirable?

Now why would a 71mm drive a turbo harder than a 68? I am guessing it captures more exhaust but would it improve response?

I am hoping I can be able to get what I want, the first time. I also want it efficient. I just want to know WHY it works vs this is what WOULD work. Make sense?

Its more than just PRs. If you've had very many of the custom stuff in your hands to look at it. Its hard to explain. Usually the larger exducer compressor wheels will have the MWE groove opened up to help push the surge line up in the map. Otherwise the PRs would be sky high, and that is one reason most custom chargers run a billet wheel. They handle higher PRs alot better than the cast wheels.

Turbine wheels. Its all about "leverage" is usually how I explain it. You obviously can't run an 80mm compressor with a 83/74 turbine and expect that small turbine wheel to keep control of the compressor wheel and keep it out of the surge line. I have a flow sheet of the Borg Turbine housings, let me see if I can find it. Just wish it had MAP for the turbine wheels, thatd be nice.

I've been wondering some of the same things actually, I hope this turns into a good discussion. Something I've been looking at is the compressor inducer vs exducer size. Say two wheels with the same exducer size but different inducer. Would the larger inducer move more total air than the smaller one, but at the same pressure since the exducer is the same? I'm sure it's more involved, I'm trying to learn the basics though.

It's shaft hp in from the turbine, generating shaft hp out to the compressor....man. Look up fan laws, for one.

Speaking in generalities - It takes a specific amount of horsepower to drive the compressor. You are faced with moving a certain mass of air at given operating points of the engine based on the exhaust energy available to the turbine. So how you capture that air to drive the turbine is critical, and also evident in how an improperly sized A/R ratio or turbine.

Sub'd.

Comparing compressor/turbine wheels based on size alone is very short sighted, blade design plays a crucial role in how the turbocharger will react, and where it will make power. This is not exactly a topic that can be simplified or compressed into a short version, most manufacturers utilize different ideas/principles when testing or manufacturing these components.

Subscribed, these conversations are fascinating.

Just a fact here that you may not have thought of yet: for two identical turbos except different exducer size on the compressor wheels, running the same shaft speed, the larger exducer has higher blade end speed.

How exactly that effects peformance, I'm not sure, but I would guess it has some effects on air velocity, PR performance efficiency, "spool up" characteristics, etc.

I'm am trying to see what the wheel sizing means.

Like a GT4294 vs a S471. Both have a 1mm difference inducer but have a 7mm difference in exducer. Then the turbines have the same spread.

Obviously Smokem has a key point here, but let's say blade shape and count remain unchanged. If a compressor's inducer or exducer is machined to a smaller size could some assumptions be made about the resultant performance?

Given the same blade design, a larger exducer will often create more pressure and suffer a small loss in overall flow. It is common to see large exducer compressor wheels with fixed engine speeds such as stationary power units, however this is not typical in automotive applications that see constant changes in engine speed.

The following is a comparison of a Garrett GT42 compressor wheel on left, and an S400 compressor wheel on right, as you can see they are quite different in design.

Thank you for the reply Smokem. It's interesting you say that a larger exducer would reduce flow. Speaking just in very loose generalities, would any of the following be wrong?

Inducer: huge influence on flow capability.

Exducer: ultimately limits shaft rpm.

Ratio of inducer to exducer (aka trim) correlated with pressure ratio capability.

More blades raise pressure ratio, whereas fewer blades allow for more flow. Staggered hub designs (6 + 6, 7 + 7, etc.) effectively get the best of both worlds (flow and pressure).

oldestof11, if I could make a recommendation:

[ame="http://www.amazon.com/Turbocharging-Performance-Handbook-Motorbooks-Workshop/dp/0760328056"]Turbocharging Performance Handbook (Motorbooks Workshop): Jeff Hartman: 9780760328057: Amazon.com: Books@@AMEPARAM@@http://ecx.images-amazon.com/images/I/51hI7shOzXL.@@AMEPARAM@@51hI7shOzXL[/ame]

I read it a few years back and I remember it going into detail about blade design, size, number, etc...as well as housings and intercooling, etc etc etc. Highly recommend and would probably have some answers for you.
I wonder if I still have it somewhere...I should read it again.

Watching to learn.

CTD2500 said:

oldestof11, if I could make a recommendation:

Turbocharging Performance Handbook (Motorbooks Workshop): Jeff Hartman: 9780760328057: Amazon.com: Books

I read it a few years back and I remember it going into detail about blade design, size, number, etc...as well as housings and intercooling, etc etc etc. Highly recommend and would probably have some answers for you.
I wonder if I still have it somewhere...I should read it again.

Click to expand...

Thanks!

And Weston, thanks. Now how does a turbine wheel determine available shaft HP to drive the compressor? You have often said that turbine sizing has been left behind in the diesel world of sizing.

I also understand that ball bearing can help by reducing drag thus freeing up shaft power and decreasing spool time. Does blade design and sizing have a great affect when it comes to 2 closely sized units?

RyanMayo said:

More blades raise pressure ratio, whereas fewer blades allow for more flow. Staggered hub designs (6 + 6, 7 + 7, etc.) effectively get the best of both worlds (flow and pressure).

Click to expand...

I am not willing to say there is a set answer to this, you need to understand areas of compression in the wheel profile between a full blade design and splitter blade design along with the blade inlet and exit angles. But again generally speaking less blades will tend to flow more with a narrower power band, and more blades will tend to flow less with a wider power band.

oldestof11 said:

Does blade design and sizing have a great affect when it comes to 2 closely sized units?

Click to expand...

Yes, in most cases more so than the compressor wheel.

http://competitiondiesel.com/forums/showpost.php?p=2341300&postcount=9

Interesting. That reminds me, my S2E turbine wheel was spec'd 74x65mm with 11 blades which was seemingly identical to the typical S200/S300 turbine wheel. But when I actually got the turbo in the mail, I found the wheel looks like this:



It has machine marks on the tips and everyone said it was clipped, but the wheel looked new to me (very possibly Chinese) and in person when you see it I don't think it's possible to cut that curve without it being cast that way.
Measuring confirmed that it was in fact 74x65mm.



I had the local turbo builder look at it, he thought maybe it was a higher flow version of the 65mm wheel. Weston, your last post of the S400 wheels kind of confirms that theory.

That is a machine clipped wheel, I have never had my hands on an S2E so I cannot say if they come this way or if it were done after the fact.

I'd like to have a look at another S2E myself just to see.

I forgot I had this photo comparing it to the typical Super B on the left, I should have posted it earlier.

The 73/80mm S300 turbine wheel on left is machine clipped from the manufacturer, it is clearly a different blade profile than the 68/76mm S300 turbine wheel on right.