Zeek's Turbo Map Primer

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Ezekial
Quote:
T2 = 535 (24.7 ÷ 14.7)0.283 = 620 °R

Taken from the Turbo section ...

I'd like to know how it came to = 620

My calculator doesnt seem to think that ...
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Chas

Ok try my figures:

1. T1 = Ambient temperature
2. Airflow = (litres x rpm) /120
3. Volumetric Efficiency (VE) ~ 0.85
4. Adjusted volume = l/s x VE
5. Pressure ratio (PR)= (compressor guage pressure kPa + atmos) /atmos = (compressor gauge pressure kPa + 101.325)/ 101.325)
6. Temp rise ideal gas T2 = T1 x PR^0.283 (note T is absolute °k = celcius + 273°)
7. Adjusted T2 for adiabatic efficiency T3 = (T2 -T1/ between 0.6 and 0.75) +T1
8. Density Ratio DR = T1/T3 x PR
9. Compressor size Inlet l/s = adjusted volume x DR

Then convert back 1 l/s = 2.12 cfm
1 cfm x 0.075 = lbs/min (note this is @ 50% RH and 24°C, some sources quote 0.069)

i.e 1l/s = 2.12 x 0.075 = 0.159lbs/min
l/s x 0.0011655 = kg/sec (@ 50% and 25°C specific volume of air is 0.858m^3/kg)

based on 14.7 stoichiometric ratio and fuel being 34.656 Mj/litre, with a specific weight of between 0.71 and 0.79, @ 0.72 and engine efficiency of 30%, = 69mg/kW (0.0958cc) fuel and 0.868 l/s/kw air.

Note: when reading compressor maps with cfm along the x axis, manufacturers tend to rate nominal at 2PR (pressure ratio =2) on the y axis. The cfm is the intake volume i.e. at atmospheric pressure.
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Ezekial

So from the original post ...

Except using CB70 running 20psi

Aiflow = 132.4 CFM
Using 85% VE
Airflow = 112.5 CFM

Pressure Ratio = 2.36:1

Temperature Rise = 147 degrees F
70% Ambient Efficiency
Temperature Rise = 210 degrees F

Density Ratio = 1.70

Inlet Air Flow = 191.25 CFM
or 13.2 lbs / min

So how do you use that to find a suitable turbocharger?

chas

You find a map that suits @ 70%

eg http://www.turbofast.com.au/FlowTS.html
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Ezekial

OK so for example ...

Pressure Ratio = 2.36 (y axis)
Air Flow = 13.2 lbs/min (x axis)

That gives the blue dot ...

Is it meant to fall on the 70% circle?

What are the lines that run the other way ... red arrow?

Also ... this is just for selecting compressor isnt it ... how do you figure out which exhaust housing?

chas

Red arrow is the impellor (wheel) speed contours in RPM.

Try to keep the selection in the right hand efficiency contour terrains.

The area outside the right hand efficiency curve is the choke area where the impellor spins super fast for no gain. This occurs when you stuff a big impellor into a small housing.

Max flow is where the max rpm line meets the least efficiency curve.

Hang on a minute !

Actually Zeek why don't you read up on compressor maps, AR, diffuser area, inducer, exducer, volute, turbine etc and post for the FAQ?

Ezekial
Quote:
The area outside the right hand efficiency curve is the choke area where the impellor spins super fast for no gain
As in to the right of the circle/curves?

Quote:
This occurs when you stuff a big impellor into a small housing.
Or when you run HUGE BOOST through a tiny turbo?

Quote:
Try to keep the selection in the right hand efficiency terrains

Quote:
Max flow is where the max rpm line meets the least efficiency curve
So can you put a dot where that is? On that diagram?

Quote:
Actually Zeek why don't you read up on compressor maps, AR, diffuser area, inducer, exducer, volute, turbine etc and post for the FAQ?
Coz i'd probably get it wrong

chas

Ezekial wrote:
Quote:
The area outside the right hand efficiency curve is the choke area where the impellor spins super fast for no gain
As in to the right of the circle/curves?

Draw a vertical line from the intercept of the 154,200 rpm line and the 65% and everything to the right is choke area

Quote:
Quote:
This occurs when you stuff a big impellor into a small housing.
Or when you run HUGE BOOST through a tiny turbo?

Quote:
Quote:
Try to keep the selection in the right hand efficiency terrains

Where you have the blue dot is to the left of the centre (lefthand). If you stay on the righthand the turbo will spool up quicker and will be physically smaller. The closer to the surge line you go the more unstable and oversized it becomes

This because you are trying to pump more air than the motor can handle and air reversion occurs.

Quote:
Quote:
Max flow is where the max rpm line meets the least efficiency curve
So can you put a dot where that is? On that diagram?

I don't know how to answer simpler. Where the furthest right point on the least efficiency curve intersects the max compressor wheel rpm = the max flow

Quote:
Quote:
Actually Zeek why don't you read up on compressor maps, AR, diffuser area, inducer, exducer, volute, turbine etc and post for the FAQ?
Coz i'd probably get it wrong

You should plot multiple performance lines (luglines) for different rpm (say 2k, 3k, 4k, 5k, 6k, 7k) with two boost pressures per rpm band. This will give you some positive gradient lines. If each of these lines falls between the surge line and the choke area, with the desired boost/rpm sitting in the 70% terrain (righthand) you have found your selection.

Now get cracking make post for the FAQ.

Ezekial

Quote:
Draw a vertical line from the intercept of the 154,200 rpm line and the 65% and everything to the right is choke area
Red Line Correct?

Quote:
I don't know how to answer simpler. Where the furthest right point on the least efficiency curve intersects the max compressor wheel rpm = the max flow
Least efficiency curve = 65% correct? Max Compressor wheel rpm ... how do ya know that? Do you mean 154200? In which case you're saying max flow is on the choke line

Quote:
You should plot multiple performance lines for different rpm (say 2k, 3k, 4k, 5k, 6k, 7k) with two boost pressures per rpm band. This will give you some positive gradient lines. If each of these lines falls between the surge line and the choke area, with the desired boost/rpm sitting in the 70% terrain (righthand) you have found your selection.
So by that ... do you mean in the initial calculation of CFM, you use different RPM's instead of redline 7500rpm?

chas

Ezekial wrote:

Also ... this is just for selecting compressor isnt it ... how do you figure out which exhaust housing?

Same procedure really except instead of pressure ratio you have Expansion Ratio (ER)

Ideally the exhaust manifold pressure should be less than charge pressure so reversion doesn't occur. Use exhaust manifold pressure equal or less than boost and calculate the expansion ratio:-

ER = (Exhaust Manuifold Pressure + atmos)/ (dump pipe pressure + atmos). You can see how a low pressure exhaust influences the ratio. Allow about 1 to 2 psig for dump pipe pressure)

Do the corrected flow based on temp like you did for the the compressor. Remember the corrected flow will be less than the initial calculated flow (lbs/min)

On your compressor calcs dont forget to factor in the intercooler and air filter in you compressor calcs: PR = (Boost + Intercooler PD + Atmos)/ (Atmos- Filter PD) :- allow about 0.1 psig for filter and about 2 psig for intercooler. The filter is insignificant, but the I/C has an effect
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chas

Your post before my last = answers are all yes
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Ezekial

Very Interesting ...

What boost pressure would you use for 2000, 3000 rpm etc ...

Wouldn't make must boost at those RPM's ...

Or just use say base 15psi and 20psi for each 2k,3k,4k,5k,6k,7k ...

You already know all this ... why you want me to post in the FAQ?
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chas

Ezekial wrote:
You already know all this ... why you want me to post in the FAQ?

Its not something I do every day, although I do pump selections fairly often. Theres more to the selections and I think you can put a better spin on it, with input from the other members.
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chas

OK Zeek, Glen has split this out of the FAQ so it has more exposure and more room for chatter, without clogging the FAQ.
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Ezekial

Ezekial wrote:
What boost pressure would you use for 2000, 3000 rpm etc ...

Wouldn't make must boost at those RPM's ...

Or just use say base 15psi and 20psi for each 2k,3k,4k,5k,6k,7k ...

chas

Its up to you really. But if you plot a low pressure and a high pressure , you will get two co-ordinates that you can scribe a line through. The line will contain all the PR/CFM combinations for that RPM, so all you have to do is pick a PR or CFM to read the other value, via the intercept.

You might find for instance that the boost is in an undesirable choke or surge area at a certain pressure/rpm and take steps to avoid it.

Try to keep your A/Rs around the 0. 50 mark

Brado with his mechanical expertise and Tedium with his mixed flow prowess should be able to contribute in this thread.

tedium

chas wrote:
Tedium with his mixed flow prowess

Tedium only has axial flow prowess (and reasonable competence in general fluid dynamics theory).

Tedium has little practical experience with radial or mixed flow turbomachines.

Tedium is reading and learning.

*zoink!*

tim
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Ezekial

Quote:
PR = (Boost + Intercooler PD + Atmos)/ (Atmos- Filter PD)
Shouldnt it be ...

PR = (Boost - Intercooler PD + Atmos)/ (Atmos- Filter PD)
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chas

No. You are sizing the compressor to supply enough boost to overcome serial restrictions, so it can deliver the required boost at the throttle body
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Ezekial

Ahh yep. Got it

Ezekial

Turbo Compressor Flow Calculations

This might help ...

Excel File Here
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chas

Did you do that? Well done. Too bad its not in metric
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Ezekial

Yeah I did that ...

I can do a metric one but all the flow maps seem to be in Imperial anyway

Now I just have to find some flow maps for smaller turbo's

Anyone know where to find any?
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grog

try the websites for the turbo manufacturers..

Back to top


chas

Howse this thread going Zeek? You don't seem to have massaged and added to it much since your last post. Chop chop get it to a publishable article for inclusion in the FAQ

Ezekial

Have a look at this ...

Tell me what I have to change in the Turbine Selection ...

Turbo Flow Calculations

Excel File Here


chas

Ezekial wrote:

Have a look at this ...

Tell me what I have to change in the Turbine Selection ...

Turbo Flow Calculations

You mean I have to use imperial! Damnit anyone else out there into faranheit and lbs who can plug the figures and verify? Bill ?
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chas

Zeek you haven't done much on this thread for a while.

By now you should now about trim, wheel (turbine and impellor) diameter, exducer, inducer, hybrid, clipping, etc.

How about it partner? There's newbies out there that need your wisdom.



chas

Zeek does this help you any?

RHB5 (vf10) Specs:
Air Flow Rate: 23 - 180 l/s // 49.4 - 381.4ft3/min
Max Pressure Ratio: 2.8
Maximum Speed: 180 x10^3 rpm
Max Allowable Gas Temp: 950°C // 1742°F
Diesel Engine Application: 54-154Ps
Gasoline Engine Application: 73-208Ps
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Turbo_G200

Ezekial wrote:

Yeah I did that ...

I can do a metric one but all the flow maps seem to be in Imperial anyway

Now I just have to find some flow maps for smaller turbo's

Anyone know where to find any?

The GT12-17 series has some data sheets on the egarrett site, i have often wondered if they would be any good as a replacement for my ageing turbo. good size come on some 1.3L and stuff. and some bigget bikes have them. ball berring too would go very good i think
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chas

Turbo_G200 wrote:
Ezekial wrote:
Yeah I did that ...

I can do a metric one but all the flow maps seem to be in Imperial anyway

Now I just have to find some flow maps for smaller turbo's

Anyone know where to find any?

The GT12-17 series has some data sheets on the egarrett site, i have often wondered if they would be any good as a replacement for my ageing turbo. good size come on some 1.3L and stuff. and some bigget bikes have them. ball berring too would go very good i think

I posted a pic of my GT17 already in this thread: http://forums.eis.net.au/viewtopic.php?t=5831
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Trim and A/R

Compressor Side

Trim is the % ratio of the impellor inducer area over the exducer area of the wheel (small wheel diam^2 divided by larger diam^2). The higher the trim the greater the air flow.

A/R is the ratio of the diffuser (eg snout,tongue or throat) area (sq.inches) of the volute (spiral/snail housing) and the radius (inches) from the centre of the turbine spindle to the centre of the volute where the diffuser area is being taken. The A/R is constant at any point of measurement chosen. Metric equivalent is P and is A/R multiplied by 25.4.
Compressor range of discharge pressure is affected by A/R while Trim will affect the actual operating range of compression/flow within the A/R constraints. Compressor A/R has minimal affect, but large A/R are used to optimise low boost applications and vice versa.

Turbine Side

Trim is the % ratio of the turbine exducer (minor) area over the inducer (major) area of the wheel (small wheel diam^2 divided by larger diam^2). The higher the trim the greater the exhaust gas flow.

A/R is the ratio of the infuser (eg snout, tongue or throat) area (sq. inches) of the volute (spiral/snail housing) and the radius (inches) from the centre of the turbine spindle to the centre of the volute where the infuser area is being taken. The A/R is constant at any point of measurement chosen. Metric equivalent is P and is A/R multiplied by 25.4.
Turbine range of inlet pressure is affected by A/R while Trim will affect the actual operating range of turbine pressure within the A/R constraints. The smaller the R the faster the shaft speed but lesser rotating torque. A/R is a significant affect on flow capacity of the turbine. A large A/R lowers gas velocity, delays boost, lowers backpressure and aids high end rpm power and vice versa.

Be careful that A/R values are compared within the same family of turbine housings. A very large exhaust housing can have the same A/R value as a small hosuing.

When upsizing the flow rate will increase proportionally with increase in A/R (within the same turbine group). The actual formula is Q= A*V/R where V in this case is a constant tangential velocity so Q = A/R, therefore (A1/R1)/(A2/R2) =Q1/Q2

A/R =Area divided by distance from centreline of volute to centre of spindle.

A small A/R indicates small interior volume and vice versa. A small A/R will spool early, but air volume will tail off at higher revs.

Trim = (D1/D2)² (can also expressed as percentage i.e multiply by 100)

A trim of 0.5 will give 11% more volume than a trim of 0.45

What happens when you mess with trim? Well say you decided to increase a compressor's inducer (D1) and exducer (D2) and maintain the same trim value, then you are going to place more work on the turbine, but obviously it will have a higher flow capability, albeit much later in the engine revs where the increased flow through the turbine provides enough torque to spool into the req'd revs. If you increase trim by keeping the exducer the same, but increase the inducer diameter (D1) you'll get the same lag as the previous condition, but you will also move everything towards the surge region as the engine finds it hard to injest the extra air. Conversley if you reduce the trim by reducing the inducer, there will be less work for the turbine and the pressures will become more peaky, come on earlier and favour the choke region. Let's say you increased the exducer, but kept the inducer the same size, then the trim value will drop, the tip speed is going to be faster, so the pressure will build faster and higher for the same flow rate.

Just remember though, it's not much good going out to buy a bigger wheel and finding that the inducer won't fit into the infuser. In fact chances are, if you want to retain the compressor housing you will have to maintain the inducer diameter (D1) and worse still the exducer is actually rebated into the diffuser with buggerall opportunity to increase it's diameter. So check before you buy, because nine times out of ten you will be up for a new larger A/R housing.

Rough Guide For A/R Selection

Note if the compressor wheel is oversized it will be more inefficient at a given flow/pressure, so expect higher discharge temps.

Rule of Thumb: compressor trim is 85% squared of the turbine trim i.e. 0.85 x0.85 x turbine trim. This allows for pumping losses and sufficient torque to rotate the compressorat nominal engine speeds. If the compressor wheel trim is increased then obviously the engine revs must inrease to pump more exhaust and thus get the turbine up to speed, with the increased load of the bigger compressor impellor.

Clipping

Clipping the fins of the exducer oulet side of the turbine at a slight angle, reduces restriction to gas flow. The cut angle is somewhere around 7° to 10°. Clipping increases high end power at the expense of low end torque and increased lag. Not recommended unless you really know what you are doing

Hi Flowing

Loose term that has come to mean putting a bigger compressor wheel and housing on, while retaining the turbine side.