levnubhin

iTrader: (30)

Can someone help me understand this please. Id like to know what the max psi my trubo is efficient for.

http://www.turbobygarrett.com/turbob...R_471171_3.htm

Thanks
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patsmx5

iTrader: (16)

Haha, that's not a very good question. They are more than a function of PSI alone. I'm no turbo expert though. But in short IF that was the proper size turbo, then it's efficient from 8-14 pounds ish. But I dunno, IMO that's a small turbo.

ZX-Tex

iTrader: (15)

Read through the turbo tech information located at the link you posted. It tells you step-by-step how to calculate turbo sizing factors.

Thucydides

What size motor?

Braineack

iTrader: (62)

27 lb/min = roughly 245BHP

Savington

iTrader: (31)

Pressure ratio is (atmosphere + boost)/atmosphere. lb/min is airflow. You want to stay as close to the center of that map as possible (ideally), but that usually ends up providing worse spool and lower power potentials than moving towards the upper right-hand corner.

Basically, I have a GT2554R at 14psi on **** gas and I'm probably seeing 230whp. With a great tune and water injection, mabye 250whp. Tops.

JasonC SBB

People's experiences show the GT2554 is good for 220-240 whp. Upper end for 99+ motors, lower end for stock 1.6's.

On a '99 it'll do 10 psi at 2800 rpm.

levnubhin

iTrader: (30)

1.6 motor
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Mach929

iTrader: (3)

wow i can't believe nobody said "SEARCH", seriously this gets discussed all the time

oilstain

Seriously, it really doesn't. Since the thread I started a few months ago, I haven't recalled any decent discussions of mapping, and the nuances of reading said maps. Now, I may have missed one or two, but examples of things that get discussed here would be stupid cl ads, stupid threads at m.net, cats, and Hustler.

Now, "SEARCH" would have probably been provided, had he asked, 'how much hp can the GT2554 make?' But he actually asked how much air his "trubo" could move efficiently, which makes for interesting conversation.

Feel free to look up my old post, as it was interesting. But looking back, I feel that I was going at the issue in an odd way.

This pretty much sums up compressor maps, by Brain:
"calculations to determine the amount of boost you need is almost silly. I can make 200rwhp at 12psi or 240rwhp at 12psi. all dependant on the size of my exhaust.

the best thing that you can determine is if the compressor is large enough for your goals. And if so, will you be in the most efficient part of the turbo at that power level."

Thucydides

Then, assuming a 1.6 liter motor, A/F=12, BSFC=0.55 lbs/hp*hr, IM temp 130 F, VE = 95%, redline at 6750 rpms, and various reasonable pressure losses before the compressor and between the compressor and intake valve:

at 200 rwhp you need a pressure ratio of 2.2 and and a flow rate of 22 lbs/min;

at 225 rwhp you need a PR of 2.45 and and a flow rate of 24.8 lbs/min;

at 250 rwhp you need a PR of 2.7 and and a flow rate of 27.5 lbs/min;

so at 200 hp your efficiency is just over 70%;

at 225 hp E~68%

at 250 hp you're below 60%

I've put together an Excel spreadsheet that does the grunt work for you, and you're welcome to it, but there's no substitute for reading the procedures on Garrett's website, Corky's book, and Mark Warner's book. Otherwise you're taking my word, and spreadsheet, for fact, and quite frankly my brain isn't as sharp as it used to be.

An interesting sideline is that according to Garrett's charts the 2554 will put out a bit more pressure than the 2560, and so the bigger turbo, though it generates more flow volume, doesn't necessarily get you the greater efficiency or power in the smaller 1.6 liter motor that you might expect.

Thucydides

And therein lies the difference between theory and practice.

Though theory is cheap, and therefore a great place to begin any evaluation of a system, there are critical parameters (like exhaust flow) which aren't taken into account in our crude calculations and so theory and practice are often at odds.

That doesn't mean that the theory is bad, or that there aren't folks with much more sophisticated analytical models which are really quite accurate; it's just that we don't necessarily have easy access to those models and so comparison of results is usually more valuable and meaningful.

Braineack

iTrader: (62)

Determining the level of boost needed, on paper, is nearly impossible and never correct. Case in point above.


fwiw, 2.45PR = 21.3psi



The main thing to think about is that 27 lb/min equals roughly 245BHP. But you gotta think, when you get to that point, you're running out of heat efficiency, as most flow maps only plot to 60%, where the turbo has diminishing returns.

If your goal is say 200 rwhp, you'll wanna see where that lands on the heat efficiency island. 200rwhp = roughly 22 lb/min. [ 200 * 12:1 AFR * .00916 (.55 BSFC/60) ] This lands you in the most efficient zone for that turbo. The more boost and power you make, the further less efficient the turbo is until it simple starts dumping out heat.

Like I said, determining how much boost you need is a hard task to plot out on paper, with multiple formulas to try to do so. I just like to draw a vertical like from your power goal and see how it looks on the map. If it falls outside of the island, then you know it's not the right size turbo for you. You want something that put it's in the 3/4 to middle of the island for the most amount of efficiency.

A map with a tall narrow shape like the 2554 means it can work at high boost, yet not a lot of airflow. As opposed to something like the 2871 which covers a wide airflow range.

Thucydides

That would be a shitload of pressure, but my calc's show actual "boost" is closer to 15.1 psi.

Ummmm, not really. If you take the time to do a careful and thoughtful analysis, the task is actually very straight forward and the results can be surprisingly accurate.

Using the methods presented in Garrett's website "Turbo tech 103" the pressure ratio is defined as the ratio between the compressor inlet and compressor discharge pressures. Inlet pressures are a bit less than atmospheric because of the airfilter, hoses, bends, etc. So for the 2.45 PR example, and the assumptions I've mentioned before, inlet pressure is 13.2 psi and outlet discharge pressure is 32.3 psi for a difference of 19.1 psi. That's to get you a manifold pressure with losses through the intercooler of 29.8 psi absolute pressure. Subtract manifold absolute pressure from atmospheric pressure to determine the boost that is measured at the manifold, and actually doing the work, and you get 15.1 psi. All of the sudden it makes sense and the calculations are in reasonably good agreement with what folks are seeing in their own cars. 15 psi, more or less, in a 1.6 liter motor, is good for about 225 hp.

When you look to see where that vertical line falls at your power goal, do you consider that the only time your car reaches the power goal is at or near redline, and to get there the pressure/delivery points on the efficiency curve travel from left to right towards that island? It's only a partially rhetorical question because I know you do, but folks just beginning to look at efficiency maps might not see the importance just yet.

And the importance is that, for say a daily driver, you might pick a turbo where the vertical line for your power goal is just to the right of the island, knowing that as you row through the gears, and for the widest range of power your motor develops, you're never far from the most efficient turbo range. In other words you might be interested to know what the turbo efficiency is at 3k, 4k, 5k and 6k rpms as well as at redline.

For a motor that sees more consistent and higher average rpms - a track car for example - you might want to plant your vertical line very near the center of the island and what happens to the left of that line be damned.

Toddcod

iTrader: (8)

True. But with a 2554 on a DD car, You are ripping boost like a monkey on crack. From red light to redlight you might rip up a 2860 car. Mid range is more than people give credit for on a DD.
Tracks are another story.
But on a street car. Alot of low end will rip high hp cars. You just never have enough room to open up the top end hp cars between red lights.

For instance the fox body 5.0's only came with 225hp and 300lbs/tq. They were tearing up everything when they came out. Top end wasn't all that compared to some other cars out there. Sure they would get high speed to 140-150mph. But say 93 z28's where way faster on top end acceleration. But the 5.0 would get win red light to redlight. But if you punched it from 50mph, the z28 would walk the mustang.

So it all goes back to "numbers are not everything" and build the car for the purpose.