Calculating Volumetric Efficiency with a dyno graph
06-22-2005, 05:02 PM
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Calculating Volumetric Efficiency with a dyno graph
Does anyone know how to do this? I am learning alot of engine theory and calculations and alot of them use VE of course so i am trying to figure out how i can get a rough estimate of mine...since i do have a dyno graph and ive heard of people doing this. i do know the formula for VE but how do you find actual CFM lol.
06-22-2005, 05:09 PM
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Re: Calculating Volumetric Efficiency with a dyno graph (dornon13)
CFM = (cid x rpm x .5 x VE%) / 1728
cid is cubic inches displacement to convert liters to cid multiply it by 61
rpm is self explanatory
0.5 is a given and so is 1728
VE% for your average VTEC motor is between 102-112%, and it typically occurs at the same RPM as your highest HP. A H22A has a VE% of 102% at 7000 RPM's, and an F20C hs a VE% of 112% at whatever RPM they have their peak HP. VTEC and other variable cam/timing motors are the exception to the rule that VE% happens at peak torque RPM. For VTEC peak VE% is, as mentioned earlier, at the same RPM as peak horsepower. I can show you a very credible article that states this. The article got that quote from an SAE paper tat was published by a group of Honda engineers.
EDIT: here is the link I was talking about. I found it a long time ago when I was searching for the VE% of my H22A4.
http://www.autospeed.com/A_1127/page1.html
cid is cubic inches displacement to convert liters to cid multiply it by 61
rpm is self explanatory
0.5 is a given and so is 1728
VE% for your average VTEC motor is between 102-112%, and it typically occurs at the same RPM as your highest HP. A H22A has a VE% of 102% at 7000 RPM's, and an F20C hs a VE% of 112% at whatever RPM they have their peak HP. VTEC and other variable cam/timing motors are the exception to the rule that VE% happens at peak torque RPM. For VTEC peak VE% is, as mentioned earlier, at the same RPM as peak horsepower. I can show you a very credible article that states this. The article got that quote from an SAE paper tat was published by a group of Honda engineers.
EDIT: here is the link I was talking about. I found it a long time ago when I was searching for the VE% of my H22A4.
http://www.autospeed.com/A_1127/page1.html
06-22-2005, 05:13 PM
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Re: Calculating Volumetric Efficiency with a dyno graph (BlueShadow)
that is the formula for theoretical CFM i am trying to find the actual CFM, im sure you know VE is a ratio of the two.
What is the article you are refering to? i am pretty sure ive read from AutoSpeed?
What is the article you are refering to? i am pretty sure ive read from AutoSpeed?
06-22-2005, 05:21 PM
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Re: Calculating Volumetric Efficiency with a dyno graph (dornon13)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by dornon13 »</TD></TR><TR><TD CLASS="quote">that is the formula for theoretical CFM i am trying to find the actual CFM, im sure you know VE is a ratio of the two.
What is the article you are refering to? i am pretty sure ive read from AutoSpeed?</TD></TR></TABLE>
The article was from autospeed http://www.autospeed.com/A_1127/page1.html
If you are trying to figure out the actual CFM of a motor, then IMO the best way to do that is not with formulas but by setting up some air meters in your system. However if you are trying to figure out actual CFM based on formulas and equations then you're gonna have to factor in a lot of other variables. Air temp, altitude restrictions in the intake/charge piping, those sorts of things.
What is the article you are refering to? i am pretty sure ive read from AutoSpeed?</TD></TR></TABLE>
The article was from autospeed http://www.autospeed.com/A_1127/page1.html
If you are trying to figure out the actual CFM of a motor, then IMO the best way to do that is not with formulas but by setting up some air meters in your system. However if you are trying to figure out actual CFM based on formulas and equations then you're gonna have to factor in a lot of other variables. Air temp, altitude restrictions in the intake/charge piping, those sorts of things.
06-22-2005, 05:27 PM
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Re: Calculating Volumetric Efficiency with a dyno graph (BlueShadow)
not really looking to do with formulas because of exactly what you are saying but i have heard of people figuring out the VE with a dyno graph ive even found some with links to places that do it for you but the links have all come up dead...
06-22-2005, 05:30 PM
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Re: Calculating Volumetric Efficiency with a dyno graph (dornon13)
Yah those numbers from autospeed are probably from a stock Lude and S2K. You average car off of the street is obviously going to have slightly different VE%. And if you do a lot of head and internal work then it is going to be way different then the autospeed numbers. The extent of my research on finding VE and CFM was limited to just that formula above. Once I found the autospeed site Istopped looking for VE numbers too. I figure that if an H22 and a S2K is 102% and 112% then the other VTEC motors are somewhere between the two.
06-22-2005, 06:29 PM
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Re: Calculating Volumetric Efficiency with a dyno graph (BlueShadow)
well the thing is im not really interested in just knowing what x engine's VE is i am interested in how it works and how you can figure it out for any motor
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06-23-2005, 04:44 PM
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Re: Calculating Volumetric Efficiency with a dyno graph (dornon13)
Max VE happens at peak torque. I don't think you can really calculate VE from a dyno graph. You can use a dyno graph to find your BSFC though.
You can use the pulse width or duty cycle of your injectors to calculate VE.
I don’t have the conversion numbers or the exact weight of air handy, but it should look something like this:
Injector duty cycle x injector size (in lbs/min.) x the number of injectors you have x the specific gravity of your fuel = the weight of the fuel your engine consumes at that given rpm.
Take that and multiply it by your AFR = weight of air consumed at that RPM
Now find out how many CFM your engine would consume at 100% VE at that same rpm.
Multiply the CFM by the weight of air per cubic foot..... compare the 2.
You can use the pulse width or duty cycle of your injectors to calculate VE.
I don’t have the conversion numbers or the exact weight of air handy, but it should look something like this:
Injector duty cycle x injector size (in lbs/min.) x the number of injectors you have x the specific gravity of your fuel = the weight of the fuel your engine consumes at that given rpm.
Take that and multiply it by your AFR = weight of air consumed at that RPM
Now find out how many CFM your engine would consume at 100% VE at that same rpm.
Multiply the CFM by the weight of air per cubic foot..... compare the 2.
06-23-2005, 05:00 PM
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Re: Calculating Volumetric Efficiency with a dyno graph (TrueNorthStar)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TrueNorthStar »</TD></TR><TR><TD CLASS="quote">Max VE happens at peak torque. I don't think you can really calculate VE from a dyno graph. You can use a dyno graph to find your BSFC though.</TD></TR></TABLE>
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Sonny »</TD></TR><TR><TD CLASS="quote">It is highest at peak torque. You can scale it based on that.</TD></TR></TABLE>
According to several personal sites I found on the web and one even one reliable one, VTEC motors have max VE occuring at peak horsepower RPM. They all say that most motors do have max VE occuring at peak torque. But VTEC motors, and probably other variable valve technology engines, have max VE occuring at peak horsepower. Below is a a small tidbit from autospeed.com. The "paper" they are referring to is a study conducted by a group of Honda co. engineers which was written on the S2000 and published by the SAE.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Autospeed.com »</TD></TR><TR><TD CLASS="quote">To their credit, Honda R&D Co Ltd permitted their engineers to write an engineering paper about the S2000's F20C four-cylinder, one published by the Society of Automotive Engineers. (For US$10 you can download the 2000-01-0670 paper from the http://www.sae.org site.) Unfortunately the SAE guards their copyright so closely that I cannot write an article based on the paper for AutoSpeed (well I could, but I wouldn't be able to use any of the diagrams) so this brief coverage will have to suffice.
*snip*
Intriguingly, the paper also shows a graph of the full-throttle volumetric efficiency at all rpm from idle to about 8700 rpm. The line peaks at a staggering 112 per cent at just over 8000 rpm. For comparison, the engineers also show the VE of the H22A 2.2-litre Prelude engine (still brilliant with 149kW at 7000 rpm) - <u>has a peak VE of 'only' 102 percent, again achieved at peak power. So much for the traditional engine view that maximum volumetric efficiency occurs at peak torque!</u></TD></TR></TABLE>
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Sonny »</TD></TR><TR><TD CLASS="quote">It is highest at peak torque. You can scale it based on that.</TD></TR></TABLE>
According to several personal sites I found on the web and one even one reliable one, VTEC motors have max VE occuring at peak horsepower RPM. They all say that most motors do have max VE occuring at peak torque. But VTEC motors, and probably other variable valve technology engines, have max VE occuring at peak horsepower. Below is a a small tidbit from autospeed.com. The "paper" they are referring to is a study conducted by a group of Honda co. engineers which was written on the S2000 and published by the SAE.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Autospeed.com »</TD></TR><TR><TD CLASS="quote">To their credit, Honda R&D Co Ltd permitted their engineers to write an engineering paper about the S2000's F20C four-cylinder, one published by the Society of Automotive Engineers. (For US$10 you can download the 2000-01-0670 paper from the http://www.sae.org site.) Unfortunately the SAE guards their copyright so closely that I cannot write an article based on the paper for AutoSpeed (well I could, but I wouldn't be able to use any of the diagrams) so this brief coverage will have to suffice.
*snip*
Intriguingly, the paper also shows a graph of the full-throttle volumetric efficiency at all rpm from idle to about 8700 rpm. The line peaks at a staggering 112 per cent at just over 8000 rpm. For comparison, the engineers also show the VE of the H22A 2.2-litre Prelude engine (still brilliant with 149kW at 7000 rpm) - <u>has a peak VE of 'only' 102 percent, again achieved at peak power. So much for the traditional engine view that maximum volumetric efficiency occurs at peak torque!</u></TD></TR></TABLE>
07-22-2005, 04:10 AM
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Re: Calculating Volumetric Efficiency with a dyno graph (BlueShadow)
Okay, I am no where close to being in your league, but I have been looking at compressor maps to find the right turbo for my car and have been using the standard eq for finding cfm's. I am worried here as I have been using 85% for Ev, because I have been reading Corky Bell's "Maximum Boost" (I know the book is old, but it is more on my level, the nub level that is). Is this incorrect? I am running a b18c1. Is there a place where I can find or calculate more correct Ev?? Thank you. I'm sorry, I don't mean to take over your thread. I definately hope that the Ev of my engine is higher than 85% though. 
I know this thread is old, but I am curious about this.
I know this thread is old, but I am curious about this.
07-22-2005, 06:17 AM
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Re: Calculating Volumetric Efficiency with a dyno graph (dornon13)
Wow, that's nice to know. That will take me further away from that dreaded surge line. Are you taking classes on this stuff or reading a particular book to get this info. Cause I would like to learn more about it. Thanks.
07-22-2005, 06:29 AM
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Re: Calculating Volumetric Efficiency with a dyno graph (KeyserSoze)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by KeyserSoze »</TD></TR><TR><TD CLASS="quote"> or reading a particular book to get this info. Cause I would like to learn more about it.</TD></TR></TABLE>
Check the autospeed link a few posts up, that's where I found the VE. It doesn't specifically say what it is for a B18C, it just tells us what it is for a H22 and F20C. So your B16's, B18C's would fall somewhere between the H22 and F20C.
Check the autospeed link a few posts up, that's where I found the VE. It doesn't specifically say what it is for a B18C, it just tells us what it is for a H22 and F20C. So your B16's, B18C's would fall somewhere between the H22 and F20C.
07-22-2005, 06:31 AM
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Re: Calculating Volumetric Efficiency with a dyno graph (BlueShadow)
Cool thanks alot. This .85 Ev has been really messin me up with findin a turbo for my car. Now I should be nowhere near the surge points I was looking at before.
07-22-2005, 06:41 AM
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Re: Calculating Volumetric Efficiency with a dyno graph (KeyserSoze)
You can use 105% for redline, and gradually decrease the VE% as you lower the RPM's. Technically you'll have peak VE at peak HP RPM which isn't gonna be at redline. But to make it easy just use 105% for redline, and maybe 80% for VTEC x-over RPM.
07-23-2005, 05:22 AM
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Re: Calculating Volumetric Efficiency with a dyno graph (KeyserSoze)
Maybe you guys can be generous enough to help me out with something.....
I have been looking at compressor maps to find a suitible turbo for my car. The guys from performance techniques in San Bernardino CA suggested a garrett t4 s-3 trim turbo (well they say that the turbo they would give me actually has a little bit smaller turbine wheel, but the comp map for the s-3 trim would be very close, just with the surge line moved over a little bit to the left of the map). I have a gsr with .020" over pistons which gives me a cid of 111.03 in^3. I will was thinking of boosting ~15psi.
Comp map can be found here: http://64.225.76.178/catalog/compmaps/fig6.html
Stock flow (using Ev = 105) = 17.73 lb/min
Flow @ 15pis = 35.81 lb/min
PR = 2.02
Corky Bell's book says to calculate max flow (using Ev = 85%) and plot vs. PR, then find 50% of max flow and plot that vs. PR, and finally plot 20% max flow vs. PR = 1.
So by him my numbers would be.
Flow stock = 15.07 lb/min
flow @ 15 pis = 30.44 lb/min vs. PR = 2.02
.5 * max flow = 15.22 lb/min vs. PR = 2.02
20% max flow = 6.08 lb/min vs. PR = 1
Which concerns me as being close to the surge line of the comp map
Then I tried Ev = 105% at max rpm and Ev = 80% at 5500 rpm both at PR = 2.02 on the advice of Blueshadow, but was confused about what to use for the third point on the graph. I would appreciate any suggestions of how I should better approach this.
BTW : Performance Techniques is a very large distributor of turbos on the west coast. If you type in turbonetics.com you will be directed to their site. The guy there said that "You will not surge this compressor with your 1.8L engine." I hope he is right about this.
Modified by KeyserSoze at 6:39 AM 7/23/2005
I have been looking at compressor maps to find a suitible turbo for my car. The guys from performance techniques in San Bernardino CA suggested a garrett t4 s-3 trim turbo (well they say that the turbo they would give me actually has a little bit smaller turbine wheel, but the comp map for the s-3 trim would be very close, just with the surge line moved over a little bit to the left of the map). I have a gsr with .020" over pistons which gives me a cid of 111.03 in^3. I will was thinking of boosting ~15psi.
Comp map can be found here: http://64.225.76.178/catalog/compmaps/fig6.html
Stock flow (using Ev = 105) = 17.73 lb/min
Flow @ 15pis = 35.81 lb/min
PR = 2.02
Corky Bell's book says to calculate max flow (using Ev = 85%) and plot vs. PR, then find 50% of max flow and plot that vs. PR, and finally plot 20% max flow vs. PR = 1.
So by him my numbers would be.
Flow stock = 15.07 lb/min
flow @ 15 pis = 30.44 lb/min vs. PR = 2.02
.5 * max flow = 15.22 lb/min vs. PR = 2.02
20% max flow = 6.08 lb/min vs. PR = 1
Which concerns me as being close to the surge line of the comp map
Then I tried Ev = 105% at max rpm and Ev = 80% at 5500 rpm both at PR = 2.02 on the advice of Blueshadow, but was confused about what to use for the third point on the graph. I would appreciate any suggestions of how I should better approach this.
BTW : Performance Techniques is a very large distributor of turbos on the west coast. If you type in turbonetics.com you will be directed to their site. The guy there said that "You will not surge this compressor with your 1.8L engine." I hope he is right about this.
Modified by KeyserSoze at 6:39 AM 7/23/2005
07-23-2005, 05:50 AM
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Re: Calculating Volumetric Efficiency with a dyno graph (KeyserSoze)
Someone else with more experience can step in and correct me if im wrong but that turbo doesnt seem like a good choice for you. At 15psi and ful rpm by my calculations you would be substantially out of its efficiency...
07-23-2005, 07:49 AM
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Re: Calculating Volumetric Efficiency with a dyno graph (KeyserSoze)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by KeyserSoze »</TD></TR><TR><TD CLASS="quote">Sounds like a plan. Thanks a lot, much appreciated.</TD></TR></TABLE>
Wow, why did that post again?? Strange. Ok, what I am really looking for is a a very streetable low to mid 300whp engine. I don't really know what psi I will run for that, but I figured since I just got my block rebuilt ~15psi seemed appropriate, perhaps 12psi will get me what I want. Correct me if I'm wrong (please). Here's my setup:
Head:
gsr
light pnp
crower valvetrain
itr cams
Block:
line honed
fully balanced
stock sleeves
9:1 comp
JE pistons (.020" over)
JE rings
eagle h-beam rods
race bearings
Misc:
Walbro 255lph fuel pump
fpr
str fuel rail
dsm 450cc injectors
NGK iridium plugs
Deltagate wastegate
Greddy bov
Aem ems
Aem 3.5 bar map sensor
Victor X IM
3" dp and exhaust
Exedy Stg I clutch
Oil cooler kit
NIB ES bushing set
NIB Brembo blanks and Ultimate pads
NIB driver and passenger axels
This is all going in a 95 civic ex coupe
Pretty much a whole damn new car........
Modified by KeyserSoze at 6:12 PM 7/23/2005
Modified by KeyserSoze at 9:01 PM 7/23/2005
Modified by KeyserSoze at 9:03 PM 7/23/2005
Wow, why did that post again?? Strange. Ok, what I am really looking for is a a very streetable low to mid 300whp engine. I don't really know what psi I will run for that, but I figured since I just got my block rebuilt ~15psi seemed appropriate, perhaps 12psi will get me what I want. Correct me if I'm wrong (please). Here's my setup:
Head:
gsr
light pnp
crower valvetrain
itr cams
Block:
line honed
fully balanced
stock sleeves
9:1 comp
JE pistons (.020" over)
JE rings
eagle h-beam rods
race bearings
Misc:
Walbro 255lph fuel pump
fpr
str fuel rail
dsm 450cc injectors
NGK iridium plugs
Deltagate wastegate
Greddy bov
Aem ems
Aem 3.5 bar map sensor
Victor X IM
3" dp and exhaust
Exedy Stg I clutch
Oil cooler kit
NIB ES bushing set
NIB Brembo blanks and Ultimate pads
NIB driver and passenger axels
This is all going in a 95 civic ex coupe
Pretty much a whole damn new car........
Modified by KeyserSoze at 6:12 PM 7/23/2005
Modified by KeyserSoze at 9:01 PM 7/23/2005
Modified by KeyserSoze at 9:03 PM 7/23/2005
07-23-2005, 09:41 AM
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Re: Calculating Volumetric Efficiency with a dyno graph (KeyserSoze)
go for 400 no sense in wasting the money spent on that motor..imo you can do that pretty reliably...
I would look into the Garrett GT series Turbos...they say once you go ball bearing you will never go back...maybe a gt30r?
I would look into the Garrett GT series Turbos...they say once you go ball bearing you will never go back...maybe a gt30r?
07-23-2005, 09:45 AM
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Re: Calculating Volumetric Efficiency with a dyno graph (dornon13)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by dornon13 »</TD></TR><TR><TD CLASS="quote">go for 400 no sense in wasting the money spent on that motor..imo you can do that pretty reliably...
I would look into the Garrett GT series Turbos...they say once you go ball bearing you will never go back...maybe a gt30r? </TD></TR></TABLE>
Well with DSM 450's he cant get much more then 280-300 HP
KeyserSoze,
You might be giving the whole compressor sizing a little to much thought. You setup is pretty common so you can just tell us how much power you're looking for and whether you also want good low end response and we can recommend a turbo for you.
I would look into the Garrett GT series Turbos...they say once you go ball bearing you will never go back...maybe a gt30r? </TD></TR></TABLE>
Well with DSM 450's he cant get much more then 280-300 HP
KeyserSoze,
You might be giving the whole compressor sizing a little to much thought. You setup is pretty common so you can just tell us how much power you're looking for and whether you also want good low end response and we can recommend a turbo for you.