ok guys, I just finally finished doing some math to properly match a compressor to my 2200 OHV. So I figure I'll let some of the other 2200 guys in on my calculations and my source for all the math involved in my calculations.

The calculations also let you do corrected air flow, so you have the same conditions that the turbo was tested in.

In order for this to work you need the displacement on the engine, the volumetric efficiency, and assumed intake temperature

For my calculations, I have the 2200 engine, I'm assuming 85% volumetric efficiency (most DOHC can assume 90, and my intake temp will be 85*F. This is the ambient temp when the turbos are tested, and is a good average to work with.

My plans for the engine is to run up to 10psi on stock internals, then to up it to 15psi when I install some forged rods and pistons down the road. I figured I'd like to buy one turbo, and not out grow it.

So I needed to select a turbo that would be happy feeding my engine at 10psi, and at 15psi.

I bought a manifold for the T3 series turbos, and they come in a variety of trims ranging from 40 to 60 to the vastly popular "super 60", which made selecting one kind of harrowing... so I figured I'd do some serious math homework in selecting the best one suited for my plans.

...so I did initial calculations for 10psi of boost starting from 1500rpm all the way up to and beyond the rev limiter to 6000rpm.. kind of stupid, which is why I limited my numbers from 3000 and up here. The following are my calculations... using these numbers, you can plot points on a compressor map of your choice to see what kind of a match you make. I only did 10psi and 15psi tho.

Boost: 10psi
My pressure ratio would be 1.78
and my CFM (corrected mass flow rate) for each RPM is as follows


RPM (CMF) lbs/min

3000 14.67
3500 17.11
4000 19.56
4500 22.00
5000 24.45
5500 26.90
6000 29.35

these are the numbers you need in order to plot points on a compressor map. I tried a few different maps in order to see which one would fit my needs the best, and the T3 "Super 60" was the best for not only 10psi, but also 15psi. Here's my numbers for 15psi:

Boost: 15psi
My pressure ratio would be 2.12
and my CFM (corrected mass flow rate) for each RPM is as follows


RPM (CMF) lbs/min

3000 17.66
3500 20.60
4000 23.54
4500 26.48
5000 29.42
5500 32.36
6000 35.32

so using these numbers I plotted the following points:


the horizontal lines are my pressure ratio, and the Xs are 3500rpm, 4500rpm, and 5500rpm... the lines are labeled 10psi and 15psi.

As you can see, this compressor will be happy boosting my engine at 10psi, as well as 15psi. 10psi stays inside the optimum efficiency region a bit longer, but 15psi runs throught it pretty good too. Looks like a match made in heaven

if anyone wants me to write out the 4 steps used to get these numbers, just post here and I'll write it up...

Any input on these numbers? let me know what you guys think...

I have roughly the same setup as you have prior to mod's. I would like to inquire not only the numbers but how hard it would be to duplicate your feat. I would like to add 50-80 hp. I don't care about cost but would like to make the transition as safe as possible to my car.

First off I cannot take credit for this being my own words, this is merely paraphrased from the June 2003 issue of Sport Compact Car...

not that hard at all... here's the steps I followed...

I'll give examples after the formulas for a 2200 running 10psi of boost...

Compressor map matching

STEP 1

-Pick proposed boost level
-pressure drop assume 1.5psi
-atmospheric pressure (14.7psi)

with these numbers, you can calculate absolute pressure out of the compressor (Pco)

Pco = Boost + atmospheric pressure + Intercooler pressure drop

so for me....
Pco = 10psi + 14.7psi + 1.5psi
Pco = 26.2psi

Now you can find your pressure ratio (Pr)

Pr = Pco / Atmospheric pressure

for me again...
Pr = 26.2psi / 14.7psi
Pr = 1.78

now we have our pressure ratio, the horizontal line on the compressor map.

This is the first half of our calculations. The easy part is over. The next three steps are more difficult, but slightly more important.

STEP 2

Next, we want to calculate the approximate density of the air after the intercooler. This is called Di.

To do this we first have to guess what the post- intercooler temp might be. 130*F is a good starting point, and its normally what we see on turbo charged cars with a fairly good intercooler.

Di = (Boost pressure + Atmospheric pressure) / R x 12 x (460 + post intercooler temp)
Di = (Boost pressure + Atmospheric pressure) / R x 12 x (460 + 130)

In this case, R = 53.3. This is a constant, and happens to be the same R from the ideal gas law, PV = nRT

The number 12 is there to preserve the inch units in the equation.

460 is to convert degrees F to degrees Rankin (absolute temp)

so...

Di = (10psi + 14.7psi) / (53.3 x 12 x 590)
Di = 24.7psi / 377364
Di = 0.0000654

STEP 3
Now that we have the density of the air after the intercooler, we can use it to determine the mass flow rate (Mf) of the engine at the RPM we want to match.

Volumetric efficiency is different per engine, but DOHC can assume 90%, and for my pushrod I assumed 85%

to figure displacement from cubic centimeters to cubic inches, multiply cc by 16.387.

2200 / 16.387 = 134.252

Now that we have this, use the following formula over and over to plot in different engine RPMs and generate a useful picture of the turbo's performance.

Mf = (Di x Displacement in cubic in. x RPM) / (2 x Volumetric Efficiency)

for this step, I assumed 85% volumetric efficiency for my pushrod engine.
Mf = (0.0000654 x 134 x 2000rpm) / (2 x 0.85)
Mf = 0.0000654 x 134 x 2000rpm) / 1.7

Pick a useful power range, and go at 1000rpm intervals, plugging in the RPM values and solving for Mf. I went from 3000rpm up to 6000rpm just to make sure I have all the bases covered, although the OHV can't go much past 5500rpm.

Fill in a table with the RPM on the left and the Mf across the top.

RPM Mf
3000 15.46
3500 18.04
4000 20.62
4500 23.19
5000 25.77
5500 28.35
6000 30.93


We're not quite done yet, but almost there...

STEP 4

Compressor maps use corrected airflow. "corrected" means its adjusted to the test conditions used to make the compressor map.

85*F or 545*Rankin is the standard temp Garrett uses in its compressor maps. Assume ambient temp is the same to make the math easier.

Garret uses 13.95psi as compressor inlet pressure considering press. drop across an air filter.




Simplified...


now take your values for Mf and use the above formula for the corrected values


RPM CMf
3000 14.67
3500 17.11
4000 19.56
4500 22.00
5000 24.45
5500 26.90
6000 29.35

now we have everything we need!

Theres a few websites online that have compressor maps available for download. Performance Turbos was where I got my T3 maps.

Now we take our Pr and plot a horizontal line across the graph, this is where our intersects will be. Remember our Pr = 1.78

Next, take RPM points of importance (I chose 3500, 4500, and 5500) and plot them on the line above the CMf values across the bottom of the graph. This will give you your intersect points, and this is where the turbo will be operating on your engine, granted you calculations are correct.

Sport Compact Car, June 2003 wrote:
The compressor map is a graph of the compressor's efficiency plotted against boost (expressed as pressure ratio on the Y-axis) and the mass airflow (expressed as pounds of air per minute on the X-axis). The compressor map is two-dimensional and reads like a topographical map, but with the islands representing compressor efficiency rather than altitude.

The dashed line to the left is the surge line. Compressor surge is when air pressure after the compressor is higher than the compressor can generate. This causes the airflow in the compressor wheel to back up and stall. This, in turn, causes the pressure to drop, allowing the flow to resume until pressure builds up and it stalls again. In severe surge, this can become a violent oscillation that destroys the thrust bearing of the turbo and can even cause mechanical failure of the wheel. Any compressor match should avoid crossing over the surge line.

Have fun guys... break out a calculator, and use a PENCIL... not a pen