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Old 07-09-2010, 09:53 AM   #1
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Max turbo output: psi vs. flow potential

I need some turbo theory clarification, because I've apparently missed something.
First, the max flow potential of a turbo is defined by the cross-section at the compressor inlet. Yes/no?
Looking at a compressor map, this max flow is the "choke line" on the right side, sweeping upward.

In comparing my dyno chart to the compressor map it appears the max HP is seen when the max turbo flow is met.
HP will drastically drop after this flow is met, as does torque.
It also appears the max torque is met within the map's "island" and will gradually drop off outside that island.
(If you see this like I do, your turbo is either too small or best-case this happens right at redline)

These things being noted, I've read where people get more HP from the same turbo by increasing the psi, even though the turbo's flow potential was already met at a lower psi.
My question is: doesn't this seem to violate the first rule that the max flow potential is defined by the compressor inlet?
So if a compressor wheel is rated to flow 400CFM, how does someone get 450CFM worth of power out of it? Internet BS? (I'm serious)
Aside from that, if the max flow is met at a lower psi, then increasing the psi would only result in the max flow being met at a lower RPM and dropping off sooner, correct?


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Old 07-09-2010, 10:48 AM   #2
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Flow charts and compressor maps are great and they tell the TURBOS ability what it doesnt tell you is the pipings , down pipe , TB , intake , turbo manifold , heads ability to work with the turbos info

Idealy you want to hit your boost target at a reasonable rpm then hold the HP line (load on the datalog )flat till redline this is hard to do because there are sacrifices that have to be made , spool time vs strong top end is one of them

I know that doesnt answer your direct question but your question is some what hard to answer looking at the complete picture

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Old 07-09-2010, 11:33 AM   #3
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Right Tom, those other variables come together for the real-world output result, which we can see on a dyno.
Then we can plot that on a compressor map to get the "actual" potential of the turbo.
That's where I am now.

I started with a 350CFM (max) IHI RHB52 turbo, which saw it's max flow at just 5,300 RPM.
Recently I sent the turbo off to upgrade the compressor wheel to a TD0H 16T wheel, which flows 440 CFM.
The turbine side has not been opened up yet.

With that upgrade and a better tune it gained 5mph in the 1/4, and moved the max flow to appx 6,000 RPM.
There is still room though as it's clear I didn't get all of that 440CFM. More like 390-400CFM.
I'll definitely open up that turbine outlet some to help out, but until then I had ideas floating around.

One idea was to increase the boost a bit. (already at 10psi)
Well if it already sees max flow then there's no point right?
That would really just move my powerband down, which I don't want to do.

This thought took me back to some reading where I came across a Volvo owner making a supposed 282whp with that 16T, whereas average numbers were 240whp, which is what 440CFM should result to.
So this is why I actually posted. How can one get that much more power from a turbo supposedly restricted to 240whp?
I'm not wanting to, I just want some clarification.
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Old 07-09-2010, 12:04 PM   #4
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Yes you can add more boost and if you get more HP then the turbo still had some left to offer , to a point at some point adding past the efficiency of the turbo you just start pumping super hot air and little power

If you add more boost and dont make more power then turbo is through

A quick look at your dyno and I can tell you by how the TQ and HP falls off how your turbo is doing

I would up the boost

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Old 07-09-2010, 05:23 PM   #5
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Yeah, I would say most turbos are not out of breath at 10psi, even taking into account the airflow. You may be confusing max efficiency with absolute maximum power output of a turbo. The turbo I have is quite efficient at 15 - 20psi. Many people push past this, though. You can run this turbo at 30psi if you want. You will be waaaay off the compressor map for efficiency, but the power will still go up a little bit. Like Tom said, the air will be getting damn hot, but there would still be something left.

I would try bumping up to 12, maybe even 15psi with your turbo. Your torque will go up quite a bit, if not your hp.
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Old 07-09-2010, 07:50 PM   #6
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Take my car for example....

My turbo (GT28Rs) is supposed to be a 350whp max turbo with the "sweet spot" being around 28psi.

In reality I make over 365whp (havent dynoed since I reworked the tune) at 19psi...... Hmmm more power than the turbo is rated at a lower psi.
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Old 07-09-2010, 09:06 PM   #7
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OK so this is actually answering my question even though not directly, so a big thanks for the feedback.
bmylez, I'm not confusing the two.
I'm dealing with a much smaller turbo than most people on here run, so it might not sound like I maxed out the thing at 10psi but I honestly did.
See dyno around 5,300 RPM.
This was 204whp, or appx 235bhp which is exactly what a 350CFM turbo should produce.
What happens after that 350CFM is reached is really my question...
What occurs, or "can" occur after that choke line is reached, even at a higher PSI?
I'll also attach the map. My PR is about 1.9 at my altitude.
So you can see a higher PR, going by the map, shouldn't net anymore HP.





Here is the compressor map for the new compressor wheel (16T):
Appx .233 = 440CFM, or the "max flow" that people quote.
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Old 07-10-2010, 09:35 AM   #8
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Your turbo is to small and I can tell that by just looking at the dyno

You turbo can make the boost but cannot maintain enough flow to hold it , I wish people didnt worry so much about quick spooling and work more to maintaining the flow needed to hold the TQ and HP longer , both can be had but like I have allways said its a combination

Tom
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Old 07-10-2010, 09:47 AM   #9
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Quote:
Originally Posted by 1turbofocus View Post
Your turbo is to small and I can tell that by just looking at the dyno

You turbo can make the boost but cannot maintain enough flow to hold it , I wish people didnt worry so much about quick spooling and work more to maintaining the flow needed to hold the TQ and HP longer , both can be had but like I have allways said its a combination

Tom
Yeah in hindsight I wouldn't have chosen this particular turbo.
However the 16T upgrade to it has already made a big difference.
At this point I'm just trying to make the best out of what I have.
I do think this turbo will take the stock bottom end to its limits after I open the turbine side.
So if I go to the effort of building the bottom end I'll also switch turbos.
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Old 07-10-2010, 10:53 AM   #10
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you & me both brother...lol i bought that tiny tincy wincy itcsy bitsy little bitty small ass turbo also....way back b4 i new better......soon as this season is over i'm going bigger!!
not that i'm not having fun, cause i am..! just want better flow, stronger top end. with a little later spool like 3200-3500 rpm..lol
aiming for 230whp now then 325whp later down the road! so prob. a comp. turbo
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