MSP volumetric efficiency

TurfBurn · May 27, 2005

Protege2ner said:
If im not mistaken the 14.7 is a ratio as in 14.7:1. It is the stoiciometric air/ fuel ratio ("read" perfect mix). Atmosperic pressures are usually alot higher unless expressed in BAR

You are getting confused because 14.7psi atmospheric which = 1 bar, or 1 atm or 101 Pa is roughly the same number as the AFR ratio of 14.7:1 that is stoichometric. But it is not a ratio in pressure terms... 14.7 is the the absolute PSI pressure of atmospheric... if you run 14.7 psi of boost you are running 1 bar or 1 atm of boost, but you have a pressure ratio of 2.0 because you have (14.7+14.7)/2 And that Pressure Ratio (PR) is what you need in combo with engine air consumption (cfm or lb/min or m^3/min or kg/min) to read a compressor map.

Chojin · May 27, 2005

O.K. -

For the sake of comparison:

Here is the same Mitsubishi TD05-16G (Large) Compressor Map posted by TurfBurn with the airflow requirements for an FS motor operating to 7000 rpm using an 80 % VE, shown at various Pressure Ratios:

I added the PR of 2.4 (17.88 psi) on this map. It does go past the surge line at 3000 rpm, but you never reach 17.88 psi at that low of an rpm.

I've also added the PR of 2.4 to the Disco Potato map.

Enjoy.

-Shawn

TurfBurn · May 27, 2005

The disco.. so it is closer in the thread

TurfBurn · May 27, 2005

Amazing how comparable those turbos are as far as capability... granted the Disco has the 5-6% efficiency peak working for it.

peepsalot · May 27, 2005

TurfBurn said:
You are getting confused because 14.7psi atmospheric which = 1 bar, or 1 atm or 101 Pa is roughly the same number as the AFR ratio of 14.7:1 that is stoichometric. But it is not a ratio in pressure terms... 14.7 is the the absolute PSI pressure of atmospheric... if you run 14.7 psi of boost you are running 1 bar or 1 atm of boost, but you have a pressure ratio of 2.0 because you have (14.7+14.7)/2 And that Pressure Ratio (PR) is what you need in combo with engine air consumption (cfm or lb/min or m^3/min or kg/min) to read a compressor map.

Just to confuse things more, 1 bar is not the same as 1 atm.

http://www.google.com/search?hl=en&lr=&rls=GGLG%2CGGLG%3A2005-19%2CGGLG%3Aen&q=1atm+in+psi
http://www.google.com/search?hl=en&lr=&rls=GGLG%2CGGLG%3A2005-19%2CGGLG%3Aen&q=1bar+in+psi

TurfBurn · May 27, 2005

Yeah.. I knew that... but no point in freaking people out over the decimals: 14.7 psi = 1 atm = 1.014 bar = 101.4 kPa

twilightprotege · May 28, 2005

the dyno2003 results are engine power, but the results arent the same at the moment. i think the program assumes a good tune. i certainly done have that. but hopefully when i do have a good tune i'll have what it says i should get - 206hp at 7000rpm

TurfBurn · May 31, 2005

here is a great calculator for you guys to fit your turbos and match up the VE's and everything else AND see a projected horsepower from that setup!

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

Spooled · May 31, 2005

TurfBurn said:
here is a great calculator for you guys to fit your turbos and match up the VE's and everything else AND see a projected horsepower from that setup!

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

That's pretty cool, but I've always liked this one:

http://not2fast.wryday.com/turbo/glossary/turbo_calc.shtml

Spooled · May 31, 2005

The really weird thing is that when I put in my "guess-timates" for my almost-stock MSP, I get about what most people dyno at with my setup, but if I change the 9.5:1 AFR to 11.5:1 (thinking that leaning it out would raise the HP number), it actually lowered the power output. Something is really odd.

TurfBurn · May 31, 2005

yeah it doesn't do AFR right.. because the richer you make it the more it puts out... its' kidna funny... peak output is at 12.5 AFR... so going richer should hurt you...

most of those things really underestimate power for some reason... but they do give you a good conservative ballpark to figure with.

Spooled · May 31, 2005

TurfBurn said:
yeah it doesn't do AFR right.. because the richer you make it the more it puts out... its' kidna funny... peak output is at 12.5 AFR... so going richer should hurt you...

most of those things really underestimate power for some reason... but they do give you a good conservative ballpark to figure with.

Yeah, I'd like to see something like that made specifically for the FS-DE. It would be interesting to have a calculator that could estimate power from certain combos of mods. I'm sure that you could ballpark some figures just knowing that, for example, a K&N filter increases intake flow by roughly 2% over the entire powerband (factual number, obviously). By figuring out which mods alter which primary aspects of the engine, you could almost draw a simulated dyno graph. Of course, this would take a LOT of variables, but it could almost be a learning tool to give people a basic idea of how certain mods will change the powerband.

Spooled · May 31, 2005

It would be ideal to have the calculator be setup for SAE factor of 1.0 so that people don't get confused by humidity, ambient pressure, ambient temp, etc.

JDM Sam · Jun 1, 2005

Cam specs courtesy of Edwin TheMAN. </END plug shameless>

Kooldino · Sep 29, 2005

Where are you guys getting the numbers for the X-axis on the chart (the CFM numbers @ given rpms)

TurfBurn · Sep 30, 2005

You can yield CFM based on the assumed displacement... assuming 100% volumetric efficiency your CFM is roughly speaking displacement * rpm. Since it takes 2 revolutions for all 4 cylinders to pull in and we have a 1991cc motor (.07031 cubic feet) we draw that total volume in per 2 revolutions... so at 3000 rpm's at 100% VE you would require 105.46 cubic feet of air per minute... that is assuming atmospheric pressure as well.... if you assume post turbo the CFM is still correct...

Otherwise... given a particular fuel ratio and a known injector open time and flow etc you can try to back out the actual cfm occuring in the motor based on the chemical reaction... take that and compare it against the assumed actual values from the calculation above and then you get what your VE is.

That help?

Spooled · Sep 30, 2005

I like that second method. It's probably more accurate for the real world since it's telling you exactly how much of that air and fuel that it's really using. Thanks for the info, Turf.

TurfBurn · Sep 30, 2005

Spooled said:
I like that second method. It's probably more accurate for the real world since it's telling you exactly how much of that air and fuel that it's really using. Thanks for the info, Turf.

But it's REALLY hard to be accurate with.. you need to know exactly the average CC delivery per second that your injectors do at the given fuel pressure... then at that given moment and pressure you need to know your AFR... then from there you really need to know your exact AFR's throughout the rpm band combined with your injector times and fuel pressure... you can "estimate" the rest of the VE's based off of the power output, but that doesn't account properly for output changes due to timing and AFR variation...

The simplest way to do it with that above method is to have your injectors mapped out.. then run them at a static fuel pressure relative to the manifold pressure (if you hold the fuel pressure truly static, then as boost rises the pressure differential at the injector tip changes and that alters the output of the injector) and you need to hit an exact AFR through all rpm's at full throttle with no boost... so in theory 0 vaccum/boost manifold pressure... do that across the full rpm band at 14.7 AFR exactly and then you can back out your VE's correctly...

So the best we can do for now is try to find a way to figure out the peak efficiency of the motor which will occur at the single highest fuel consumption peak (around 4.5K on our motors from my fuel maps) and then figure out how much fuel drops off as rpm's increase and use that percentage assuming you are keeping AFR relatively constant...

Later!

Steve

Kooldino · Sep 30, 2005

That works.
Now since we know that our VE is around 80%, can I multiply the final nuber by .8?

Based on what you wrote, I'm looking at:

(.07031 cubic feet x RPM) / 2

If your VE is .8, would it be:

.8 ((.07031 cubic feet x RPM) / 2)

?

TurfBurn · Sep 30, 2005

Kooldino said:
That works.
Now since we know that our VE is around 80%, can I multiply the final nuber by .8?

Based on what you wrote, I'm looking at:

(.07031 cubic feet x RPM) / 2

If your VE is .8, would it be:

.8 ((.07031 cubic feet x RPM) / 2)

?

Is our peak VE really that bad??? Ick... but yes your calculations are correct... in theory the .8 changes with the rpm's... so you'd need to replace it per the correct value at each rpm point that you calculate..

Based on my dyno... the torque held from 4.25K to 5K and then fell off linearly to about 6.25 k.. I lost 8% torque through that range... my AFR's were pretty stable... so in theory there is roughly an 8% drop in VE from 4.25K to 6.25K and then it droped another 10% from 6.25 to 6.75K but that could have possibly been compensated for by timing too.. timing curve affects all this.. so again it's a really hard calculation to do at all accurately.

MSP volumetric efficiency

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