Turbocharger Air Flow
Turbo Mini Forums

I've often wondered why some turbocharger maps hit a flow limit on the choke line on the right hand edge.

Take the GT2056 for instance. It can't get past 30 lb/min whatever the speed and pressure ratio.

My theory is that it is being "choked" of air at the inlet.

So I've gone through the Garrett catalogue picking turbos that have this well defined choke line. Then I have plotted the results:



You can see what looks like a nice trend which would confirm that inlet air velocity is the determinate factor in maximum air flow.

Edited by Paul S on 24th Oct, 2010.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

And the point of this thread ???

If someone claims a power output for a turbo, you can make a quick check based on the compressor inducer diameter.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

go on then whats the theoretical max for the gt17 and gt20? :)

edit, forgive my laziness i have just realised i can work it out from your graph

Edited by Brett on 25th Oct, 2010.

Yes i moved to the darkside

Instagram @jdm_brett

Good stuff Paul. Do those with the choke line have a certain wheel inducer vs wheel diameter ratio? - i.e. any wheel of a certain inducer/ diameter ratio is guaranteed to have this issue?

I think that they all do, it's just that Garrett do not plot the whole map for most turbos.

I've used these turbos in the analysis:

GT2056
GT2252
GT2259
GT2554
GT2859
GT2860
GT2871
GT2871
GT2876
GT3582
GT3776
GT4088

There is no particular pattern. Trims range from 48 to 62.

The other thing to bear in mind is that once at the choke line the turbo is in trouble with very low efficiency. Best work to a maximum air flow of around 90% of that given by the formula on the graph.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Not the gt3076 or the 71?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Just looking through some flow charts I can across this and then noticed you didn't filter into your results.
Surely this is another good choice for us?
Thought I'd leave it to you experts as I'm still trying to understand these compressor maps.
http://www.turbobygarrett.com/turbobygarre...4R_471171_9.htm

http://photobucket.com/quintonrose

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

there is ony 0.8 mm turb diam difference from these two, don't think it will be any noticable , especially that the disco potatoes have a 10% more efficient turbine.
The only back side of this turbo is that it have a 0.64A/R exhaust and so doesn't spool the compressor at full boost before 4500/5000 rpm c/r depending, but thennnnnPsshhiiiiiiiiiiiiiiiiiiiiiiiiiiiii

Don't guess, do the calcs on the turbine map:

http://www.turbominis.co.uk/forums/index.p...tid=182558&fr=0

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I do like calcs,
still my prefered way to find is also thru try and test, you'll sometimes end with surprising results
though I'm interested to know how you calculated that it would take longer to spool..
a bit like un grand plat de rien comme le brouillard.
which when applied come with:
une assiette vide cachée dans la brume:
you can guess that the dish is containing food as this is his purpose, but then as it can't be seen, being in the fog, you cannot know that it is empty....
think it doesn't mean anything when a bit translated, anyway that's yours know

Schrödinger's cat...

calculer deux fois, une fois la construction

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Damn you Kropotkin.