Turbo effeciency tech question.

[yo2001]

I've been thinking. (O, nooo ) I was looking about a compressor effeciency map and came up with a question. You know the map looks like weather map with most effecient range in the center. I know you can create more heat when your cfm/psi is right of the center or top of the center of the map. But how about on the left side of the center? The effeciency is lower but is the heat also greater then? If heat isn't higher, then why is it less effiecient? not enough CFM? I'm hurting for an answer.

[SleeperZ]

The amount of heat you need to dissipate to get the temperature down is going to be proportional to flow (or mass). So you can afford to run in a less efficient part of the map, as this should not be taxing to you intercooler. Depending on how you intend to run your engine, on setup would place your maximum power in the most efficient range (for drag racing). Or if you want best streetability, you might consider putting the efficiency in the middle of your flow range...your intercooler should be able to handle running out of the efficiency once in a while on a WOT excursion.

[240Z Turbo]

To answer this question, ask yourself what does the x-axis on the compressor efficiency map represent? What is it based on? The y-axis is the pressure ratio ((desired boost-14.7psi)/14.7psi). The x-axis is flow...but flow of what?

[yo2001]

air!?

 

so if you don't have enough air, the compressor is less effiecient right ? not because there are too much heat.

[zolorin]

actually the x-axis of the compressor map is the normalized air that includes accounts for the temperature increase and density of the air. So this is a "true" amount of air in. Since the compressed air gets hot it reduces the effect of the compression. IE PR=2 does not mean that you have twice as much air it is only about 1.9 times as much air (the rest of the PR is accounted for the heat). That is why you want a more efficient TC (to reduce charge temperature out of TC). Then you use IC to cool it down and thus you condense the air into more denser form (so you can shove more air in but at the cost of the PR).

[yo2001]

Well this is why I was wandering.

 

 

I think this is little conservative. With 85% VE all the way.

3500, 4000, 5000, 6000rpm are the points.

 

Just looks like the turbo is too big. But my HP # doesn't seem to be too low.

[zolorin]

That turbo can take you to PR of 2.8 (26 lbs of boost) unless you what that kind of boost don't take it. It is not as efficient as you want it to be. Take the TO4E - 50 trim you will be in the 78% range for the upper end and have enough more room to raise the boost. This is my choise (at least on paper, still in progress)

[zolorin]

Oh yea, the turbo lag on the 60-1 would be a killer then say T3-60 because. Here is how I choose, I keep the RPMs constant and see how much boost I can raise without surging the compressor, that should give you the theoretical turbo lag (at what RPMS you will have boost)

[yo2001]

Actually it really doesn't surge much. (inless it's below 2k rpm) Or may be I just don't think it's surging. On a dyno after fully heat soaked, it was hitting full boost at 3500rpm. On the street about 3200rpm or so I think. (I can't keep up) The car dynoed 253RWHP and 275ft/lb at 3500rpm at 12psi.

 

Doesn't the effeciency chage when you have a different turbine housing and a wheel on? I mean the compressor can turn much faster at lower exhaust cfm right?

 

It really can't beat To4E wheels, there are just more effiecient. Unless 60-1 is in T04E housing.

 

I was thinking about 50 trim T04E before I got this 60-1

 

O, I'm about 500ft above sea level. (I got me a GPS)

[zolorin]

Hmm, trick question. From my understanding of Turbodynamics (Turbines, I was working with them for the last 3 years and only now I begin to understand the process, just a tiny bit ). But here it is:

 

Say we have a trully adiabatic (perfect) compressor. So all of the work inputted into this compressor will go into compressing and not into heat and say to compress it it will take dH of energy (Joules / ( sec * kg ) ) -- how many Watts does it take to comress a kilo of air.

 

Now say we have a real compressor with efficiency of 75% (hey you know these). So this dH of energy (enthalpy) is going to be higher, but how much higher is given by this formula:

 

dH (real) == dH(adiabat) / GC_efficiency

 

So 75% efficient compressor will use 33% more energy.

 

Now for the turbine wheel, it needs to supply the energy required for the compressor so for the ideal compressor and ideal turbine is

 

dH (compressor) = dH (turbine)

 

for non ideal turbine (here is the efficiency goes in place again)

 

dH (real turbine) = dH (ideal turbine) / PT_efficiency

and

dH (ideal turbine) = dH (compreesor needed) = dH(adiabat) / GC_efficiency

 

dH (real turbine) = dH (adiabat compressor) / (eff PT * eff GC)

So PT are about 70% efficient and lets do this math together

 

So to compress to a specific PR which ideally would require you N watts of energy would require you 1.91N in real life. So the overall efficiency of the turbocharger is only 52.5%. So 40% of wasted heat goes to additionally heat your charge and 60% is wasted down the tail pipe.

But this improved the efficiency of the engine by using the wasted heat that would end up in the tail pipe anyway

 

Say our Car is 35% efficient (overstatement) and 65% is wasted, then with turbo we recovered half of that waste and brough the car to being whopping 69% efficient.

 

Back to the housing question. It can provided a better spool up time / performace if the clearance between the housing and the blades is decreased. Possibly done on the newer models to improve efficinecy. But if two housings with sufficient airflow and similar blade clearance, they should produce equal chacactersitcs.

[yo2001]

Great info. I would have to read it over couple more times to really understand it.

 

I was also thinking about this too. My 60-1 is in a Hi-Flo .60A/R T04B housing and I do believe the 60-1 in the compressor map are actually bigger .70 A/R. If that makes different. It just seem that the 60-1 and 62-1 maps are just too good to be true considering how much it can flow. (if they are to be in .60A/R housing) I mean pumping out 900+ cfm out of .60a/r with 2 inch outlet is just untrue.

 

Thanks for the info.

[Guest bastaad525]

quick question, kinda off topic... at what boost level is the stock T3 at it's peak efficiency? Assuming it's not intercooled, and if it IS intercooled, does that number change at all?

[zolorin]

Intercooling does not change the efficiency of the compressor

T3 will give you max 74% efficiency at the range of PR = 1.3 to 2.3 with Mass flow of 10 to 17 lbs/min (45 trim)

The intercooler will cool the charge that is all (PR of 2 raises a temp quite a bit from 70F to 140-160F (may be more))

[Guest bastaad525]

okay now in english j/k okay so what boost level is that in psi (for the 74% efficiency)??

[zolorin]

4.5 to 19 psi at 74% but assuming that you get that mass flow. If you don't your efficiency will suffer

[Guest bastaad525]

T3 is still 74% efficient at 19psi???? okay I see the catch there though "IF you get that mass flow" again... an idea that's outside of my small area of knowledge... so in real world terms, with all known factors considered (pretty much bone stock L28ET and stock T3) what boost level does the T3 stop being efficient or start to fall off in efficiency?

[zolorin]

Here what you are looking for

http://www.turbofast.com.au/turbomap.html

This will give you points in the compressor map

With T3-45trim

you can have 15lbs of boost at 2000RPM (VE=80 and Comp 70)

The low range for the optimum boost 2500 rpm at 8lbs

The upper range is 19lbs at 3300 rpm, so you see if you rev too high you will go out of the range of the compressor

at 4500 and 19lbs you are at 70% efficiency and at 6000rpms and 19lbs you will overspeed the shaft, you can't maintain that PR at that mass flow

 

Now if you go T3-50trim (press next map)

you can be at 75% at 4500 rpm and 19 lbs of boost and your upper range can maintain 6000 rpm at high 60% efficiency

 

now if you take T3-60trim (next map)

you will see that 15# at 2000 rpm is not attainable : surge line

you can only get 12# at 2000 rpm, but the benefit is that you have max efficiency of 74% at 6000rpm with 20# of boost

 

Now if you add an intercooler everything will shift to the right (more flow) because with intercooling you can increase the density (decrease the volume) of the air and thus pack more into the engine so your mass flow is increased

 

Now have fun with the program