contactpatch

(a little O.T., but)
I'm looking at some app info from Garrett, and one of the
graphs is, corrected turbine flow Vs. Pressure ratio.
Turbine flow (lbm/min) is the Y axis.
I'm confused about the units of the X axis.
its 'Pressure Ratio (T/s) P1T/P2S' .
There doesn't seem to be enough info, considering that
engine demand can vary.
Perhaps the X axis is turbine pressure, divided
by compressor pressure, perhaps not.
Somebody, please clue me in.
All comments welcome.
contactpatch

FireBird88

Pressure Ratio:
(14.7+ Boost)/14.7

ex.
15psi
(14.7+15 )/14.7 = 2.021

How to read a turbo map

thats what got me started.

the bottom of the map it the flow in lbs/hr

to convert lbs/hr to cfm * 14.472

ex.
30lbs/hr = 434.16CFM

83 Crossfire TA

iTrader: (2)

Just to better explain this, it’s the ratio of your boost pressure divided by atmospheric pressure in PSIA (Pounds Per Square Inch Absolute). Atmospheric pressure is 1.47psia.

Close I guess. CFM is a volume flow measurement, and Lb/Hr is a mass flow measurement. You can’t actually convert directly between the two without knowing the density of the air that you’re flowing (or pressure, temp… so you can calculate it). Using a conversion like that is fine if you’re talking about inlet air flow, which stays in a relatively small range of temp/pressure, but could cause all sorts of problems if you start treating that estimated conversion as fact under all conditions.

contactpatch

'88 and '83, thanks for reponding to my post.
I didn't make my first post clear enough, I'm asking
about turbine characteristics.
.....
After some looking, I came across this chart.
http://www.turbomustangs.com/turbote...rinciple_g.jpg
......
The X axis is only turbine.
.....
Unfortunately, now, in the application I am thinking about,
I'm kinda worried about not having enough flow to get the
turbo spinning. Oh Well.
...
contactpatch

83 Crossfire TA

iTrader: (2)

I’m sorry, I was just adding to what FireBird88, not really replying to what you were asking.

If I (and for that matter anyone with any certainty) knew the answer to your question I would have answered it when I first saw it rather then replied to the response later on. The problem is that turbine maps are all fine and nice, but you could typically change the energy content of the exhaust 20% easily by just changing surface finishes, plumbing or adding some minor coatings, so all the turbine maps in the world will not tell you how a specific turbine will work with a specific engine. Forget the fact that we don’t even have a clue what the application that you’re discussing is like.

If you specified what you were trying to do, on which engine with which turbo, then someone that has some experience with this could probably give you a reasonable guess at what will happen, but it isn’t like they can plug some numbers in and give you a point on that graph (at least not without first building the engine package, fully instrumenting it and then measuring what it was doing).

contactpatch

The app is planned to be a sbc383, that breathes good.
Goal is 15 psi boost, over a wide rpm range, up to 6000rpm.
By calculation, that implies a max airflow of 80 lbm/min.
Would prefer (one turbo) from Garrett or other big name,
that supports their turbos with rebuild kits, but multiple
junkyard turbos are a possibility.
A low CR can be arranged. Pump gas.
Water injection, if needed and useful, is OK.
...
I need to see the numbers, myself. I just can't take the
word of a salesman, or somebody who only has
narrow experience. There are companies in the blower
business, selling to the general public, that do not publish blower maps.


You would think that in the internet age, hotrodders would refuse
to be kept in the dark. Mushrooms, Arise, demand info about
the products you buy.
It would be neat if could decide for myself, what would be the optimum configuration, then I could look for the closest
turbo offered for sale.
Happy Boosting

83 Crossfire TA

iTrader: (2)

Yea, but the fact is that there aren’t any hard and fast numbers WRT to turbine sizing. You could get some rough idea about the total possible airflow for a turbine by the exducer diameter, and how that crossection is used from the A/R (or just area in some cases like holset and mitsu), but past that you have to rely on someone’s educated guess or try it and change it and try it again.

You’re saying that you’re comfortable with the compressor side stuff… well what compressors do you like for the application? Go from there.

contactpatch

>that there aren’t any hard and fast numbers WRT to turbine sizing.<
???
Please elaborate.
Perhaps related to exhaust gas temperature variations,
or whatever.