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Turbo Compressor Mapping and Volumetric Efficiency
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Author:  Solerpower [ Wed Nov 25, 2015 12:10 am ]
Post subject:  Turbo Compressor Mapping and Volumetric Efficiency

I had already posted this on GeoMetroForum but figured it probably would be put to better use here. I know there is some of this information here, but not in combination with volumetric efficiency. It will take me a couple days to post the compressor maps, and when I get a chance I will even run data points colorized to indicate the different engines.

There are a few easy to use calculators out there that calculate the information for matching engine air flow with turbo compressor map. However, I wanted to create one that housed the specific information for the g10 and g13B engines. I also want to post up the various different compressor maps for quick reference. I will edit as I go.

Airflow rate = cid(cubic inch displacement) x rpm x 0.5(four stroke cycle engine fill its cylinders only on one-half the revolutions) x Ev(volumetric efficiency) divided by 1728 (12x12x12x12, converts cubic inches to cubic feet).

Then multiple this by your pressure ratio. You can adjust these numbers using the above formula for your desired pressure ratio.

For turbo compressor match up you want to look through the entire rpm range to see where the efficiency lies at your desired pressure ratio. You don't need more than five data points to get a reasonable approximation where your compressor lies.

Volumetric Efficiency Note
The volumetric efficiency is only a guess, it could be as low as 0.65 or even as high as 0.95. It is difficult to calculate volumetric effieciency of a car without the right equipment, but from what I have read the literature suggest that you take a modern production car's volumetric effieciency somewhere between 75% and 85%. 95% would be excellent. Although in some applications 100% can be exceeded; turbo charging and other ways including designs on naturally aspirated engines. The literature out there also suggest that the DOHC engines have a higher volumetric efficiency than SOHC. This means that the G13B could be considerably higher in VE; as high as 110% to start with. Reading on down below you will see that I have charted decent numbers for volumetric efficiency. For the first two compressor mappings I ran with three possible VEs, and the third being the best statistical estimate.

Estimated Volumetric Efficiencies
Below is the G10, G13B, and the G13bb output in cfm. I also used comparisons between the G10, G13B, and G13BB with known horsepower at a given rpm, with the use of a horsepower to cfm calculator to get a much better estimate of the volumetric efficiency for all three engines. I estimated that the G10 has a volumetric efficiency of 82.5% and the G13B has a volumetric efficiency of 100.05%, and the G13BB has a volumetric efficiency of 86%.

For the G10 .993 liter compressor mapping
993 cc to cid = 60.6 cubic inches
airflow rate= (cid x rpm x 0.5 x VE)/1728
1728 converts cbic inches to cubic feet

1. First example taking an educated guess for VE:(60.6 x 5700 rpm x 0.5 x .80 VE)/1728 = 79.96 cfm. (most of us don't rev a g10 above 5000).
2. Another example where I was comparing the G10 and G13B with known HP for VE: (60.6 x 5700 rpm x 0.5 x .75 VE)/1728 = 74.96 cfm.
3. Another example where I compared the G10 and G13B with known HP at given rpm and using cfm calculator for given HP: (60.6 x 5700 rpm x 0.5 x .825 VE) / 1728 =82.5 cfm


For G13B DOHC 1.3 liter Compressor mapping
1.3 liters = 1298 cc = 79.21 cid

1. First example taking an educated guess for VE :(79.21 x 6500rpm x 0.5 x 0.90 VE)/ 1728 =134.08 cfm
2. Another example where I was comparing the G10 and G13B known HP for VE: (79.21 x 6500 rpm x 0.5 x 0.91 VE)/ 1728 = 135.57 cfm
3. Another example where I was comparing the G10 and G13B known HP, and rpm, and using cfm calculator for given HP: (79.21 x 6500 rpm x 0.5 x 1.005 VE)/ 1728 = 149.72 cfm
(6500 is close enough to redline, and is where HP is maxed out stock)

If you compare the known horsepower output of a 1 liter Geo Metro 55 Horsepower @5700 rpm to the 1.3 DOHC Suzuki swift GT(i) 100 Horsepower @6500 rpm you see that these numbers are reasonable. Horsepower and airflow calculator will put cfm at 150 to get 100 horsepower, and 82.5 cfm to get 55 horsepower. The VE numbers that I came up with using the equation that included HP, and CFM at a given rpm are the best numbers that I can use for the compressor mapping. They have the most statistical input; they can certainly be off, but they are good numbers. I am actually blown away with where they are at.

For Compressor Mapping for G13BB
As far as I can read up on the G13BB has the same displacement as the G13B at 1298 cc or 79.21 cubic inches of displacement. The compressor mapping will be relatively the same except for volumetric efficiency due to sohc and compression ratio. I will see if I can get a good number on the VE and run a single example here. I'll Run the numbers of 79 horsepower at 6000 rpm.

(79.2 x 6000 x 0.5 x (X))/1728 = 118.5 cfm
237600(x)/1728 = 118.5 cfm
237600(x) = 204768
(x) = .86



Pressure ratio = 14.7 + boost/14.7

5psi = 1.34
6psi= 1.41
7psi = 1.48
8psi = 1.54
9psi = 1.61
10psi = 1.68
11psi = 1.75
12psi = 1.82
13psi = 1.88
14psi = 1.95
14.7psi = 2

Examples:
G13B: 149.72 x 1.68 = 251.53 cfm at 6500 rpm at 10 psi
G13BB: 118.5 cfm x 1.68 = 199 cfm at 6000 rpm at 10 psi
G10: 82.5 x 1.68 = 138.6 cfm at 5700 rpm at 10 psi.

Examples at equal rpm for all three: (Note that VE will most likely change at different rpm, below VE is kept constant. When plotting you would keep it the same)
G13B: 140.50 x 1.68 = 236.04 cfm at 6100 rpm at 10 psi
G13BB: 120.22 x 1.68 = 201.97 cfm at 6100 rpm at 10 psi
G10: 88.24 x 1.68 = 148.24 cfm at 6100 rpm at 10 psi


Side note on turbo cold side pipe size selection:
For turbo pipe sizing you want to take our highest rpm or highest number of cfm's than use a turbulence formula based on pressure resistance inside a tube. I have calculated cfm's up to 400 and never saw a reason to go above 2" piping unless you can't find a way to put the pipping in without using a lot of 90 degree bends. The larger pipping will reduce the pressure resistance across these bends. Anything using smaller than a 2" piping the turbo lag created by the additional volume of piping is something less than 1/10 of a second. I would recommend 2" to make pipe purchasing with fitting and bypass or blow off valves a lot easier.

Remember these are approximations that are used to match up a turbo to your engine's cfm. Your final cfm output is ultimately also determined by a lot of other variables not to say the least the turbocharger you select and the air cooling system you have or don't have.



I am going to add the information about aftermarket cams and volumetric efficiency right here so it is one place.

Aftermarket cam vs. Volumetric Efficiency

Although I have not had the need to buy or use a cam different from stock, changing the duration and lift can have rewarding changes to the efficiency or performance of an engine. There are a lot other things I would add or change to a car first before I considered cam changes for both efficiency and performance or even potentially both. I am no expert on the effects of duration and lift changes, but breaking it down to its root changes you are adjusting volumetric efficiency and you are doing this at different rpm bands. It is difficult to calculate volumetric effieciency of a car without the right equipment, but from what I have read the literature suggest that you take a modern production car's volumetric effieciency somewhere between 75% and 85%. 95% would be excellent. Although in some applications 100% can be exceeded (namely the G13B) lets take a reasonable figure of a 10% jump in volumetric effieciency.

Lets make that imaginary jump from 82.5% to 92.5% than apply it to the cfms of air flow of the 3 cylinder Metro.

993 cc to cid = 60.6 cubic inches
airflow rate= (cid x rpm x 0.5 x EV)/1728
1728 converts cubic inches to cubic feet

Before
(60.6 cid x 5700 rpm x 0.5 x .825 VE)/1728 = 82.46 cfm (most of us don't rev a g10 above 5000)
After
(60.6 cid x 5700 rpm x 0.5 x .925 VE)/1728 = 92.45 cfm

I don't know what the rpm band jumps are for the different cam configuration, but there is several good threads on this.

10 cfm difference according to online calculator is 6.7 horsepower. Now that 10 cfm can even additionally be less depending on other factors (SOHC vs. DOHC, head porting, compression ratio, intake and exhaust systems).

Now take those same numbers and add boost.
Before
82.46 cfm x 2 pressure ratio (14.7 psi) =164.92 cfm
After
92.45 cfm x 2 pressure ration = 184.90 cfm

Difference: 184.90-164.92 = 19.98 cfm. Better but still not great (about 13 horsepower).

G13B VE jump from 1.01 to 1.11

Before
(79.21 x 6500 rpm x 0.5 x 1.01)/1728 = 150.47 cfm
After
(79.21 x 6500 rpm x 0.5 x 1.11)/1728 = 165.36 cfm
Difference = 14.89 cfm

Boosted
Before
150.47 x 2 = 300.94 cfm (2 pressure ratio, boosted)
After
165.36 x 2 = 330.72 cfm (2 pressure ratio, boosted)
difference = 29.78 cfm, good, but not as impressive as is you can get with a higher revving engine.

G13BB .86 to .96 VE
Before
(79.2 cid x 6000 rpm x 0.5 x .86 VE)/ 1728 = 118.25 cfm

After
(79.2 cid x 6000 rpm x 0.5 x .96 VE) 1728 = 132.00 cfm
Difference = 132.00 - 118.25 = 13.75 cfm

I hope this sheds some light on the effects of changing a cam(s) . You need to consider what rpm band you signed on for with the duration and lift changes, but at the lower rpm bands the cfm difference will be even less. For those of you who got one for efficiency there are several articles out there as early as 1922 that talk about not needing or the benefit of not having the highest volumetric efficiency.
Now take into consideration that a dohc can become an even higher revving engine.
Again these numbers are imaginary until tested, but within reason.

Lets run the numbers with the potentially higher rpm on the G13B

Before
(79.3 x 8000 x 0.5 x 1.01)/1728 =185.4 cfm x2 pressure ratio = 370.8 cfm
After
(79.3 x 8000 x 0.5 x. 1.11 % / 1728 =203.8 cfm x 2 pressure ratio = 407.6 cfm (this would be crazy fun in a GT)
difference = 407.6 -370.8 =36.8 cfm; Not bad at all.

What also might not be clear here is that in the above comparisons the rpm band itself is staying the same. By changing the cam(s) you can open up those upper rpms. It's not a apple to apple, but apple to oranges.

G13B Comparison with both Increased RPM and VE

Before
(79.3 x 6500 x 0.5 x 1.01)/ 1728 = 150 cfm x 2 pressure ratio = 300 cfm.
After
(79.3 x 8000 x 0.5 x 1.11)/ 1728 = 203.8 cfm x 2 pressure ratio = 407.6 cfm
Difference: 203.8 - 150= 53.8, and 407.6 - 300 = 107.6 (now you see why someone would want these, 71.73 horsepower; this same comparison can be made on a G10 and G13BB also)

Longevity
Anytime you change something where you are adding or removing materials you have the potential to lose longevity of a part. Running an engine consistently above 5000 rpm especially in that 8000 rpm band will definitely have consequences for longevity. The trade off is you now have a little pocket rocket monster that will be simply amazing while it lasts.

Author:  Solerpower [ Fri Nov 27, 2015 2:18 pm ]
Post subject:  Re: Turbo Compressor Mapping and Volumetric Efficiency

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Author:  Solerpower [ Sat Apr 30, 2016 8:50 am ]
Post subject:  Re: Turbo Compressor Mapping and Volumetric Efficiency

More compressor maps:

GT15

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