How much air (CFM) does our engines move? - Boost Forum

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How much air (CFM) does our engines move?
Thursday, November 11, 2004 8:23 AM
I'm just trying to put some actual numbers into my HowTo page describing why not to buy an electric supercharger and am hoping you guys can help me post up some figures.

You can get bilge pumps made to move over 240 CFM. I suspect that number goes down pretty dramatically when there's resistance to the airflow. I wonder if there's some way to quantify that?

What amount of air does a 2.4L Twin Cam move at which RPM's at full throttle? Where do we get these numbers from?

Is this relevant? 1 cubic foot = 28.32L.

Assuming WOT, on each two rotations of the engine, 2.4L of air is moved through. (not accounting for the fuel so someone chime in if that's significant).

At 3000 rpm then, that's 1500 x 2.4L = 3600L per minute. That's 127 cubic feet.

At 6000 rpm then, nearing redline, that's 254 CFM which is higher than the capacity of the bilge blower to move air under optimal (free flowing) conditions meaning it is a hindrance to airflow.

Is this a proper method of doing these calculations or am I missing some vital parts of the equation?
<br>




Re: How much air (CFM) does our engines move?
Thursday, November 11, 2004 8:42 AM
V = (RPM x CID) / 3456

V = Air flow in CFM @ 100% efficiency, so if you multiply that number by about .8, then you get a nice realistic number.

CID = Cubic INCH displacment, not liter, so for a 2.4, its 146

<br>


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Re: How much air (CFM) does our engines move?
Thursday, November 11, 2004 8:44 AM
Oh, and bilge pumps pump air, they don't compress it, so your engine still won't take in any more air than it can fill. Thats why bilge pumps don't work.

<br>


4cyltuner.com - Information Source For 4 Cylinder Tuners
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Re: How much air (CFM) does our engines move?
Thursday, November 11, 2004 8:52 AM
Your equation gives pretty much exactly the same result as mine did so I'm going to assume mine are correct as well. I'll bear in mind the 80% efficiency number though to make it all more realistic.

Thanks man! More ammo to fight the good fight with...
<br>



Re: How much air (CFM) does our engines move?
Thursday, November 11, 2004 5:48 PM
I have used for my calculations for LD9 engines, an aprox VE=84% with 230CFM max @ 6400rpm.

I hope it help. <br>

___________________________
MAKING MY DREAMS A REALITY
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ELIOT. Now.....boosted.

Re: How much air (CFM) does our engines move?
Thursday, November 11, 2004 11:21 PM
I just had my head ported and polished and flowbenched. Stock my 2.4 head flowed 125 cfm on the exhaust side and about 210 on the intake side. After the port and polish it flowed 295 on the intake and 150 on the exhaust. The exhaust outlet holes are extremely small on the 2.4 head and the machine shop didnt widen them. When I get my turbo manifold I'm giving the head and turbo manifold to them so they can port match it and I will have it flow benched again. I can tell you now that the exhaust ports on the pacesetter header are almost double the size of the ports on the head so I know flow is going to increase on the exhaust side once I get it port matched. <br>

<a href="http://www.carsneffects.com"><img src="http://ourworld.cs.com/cannonfodder%20jbo/cnfxsig16.jpg" border="0"></a>
Re: How much air (CFM) does our engines move?
Friday, November 12, 2004 6:54 AM
just say your running 110% efficiency
<br>


Re: How much air (CFM) does our engines move?
Friday, November 12, 2004 8:25 AM
^ Surprisingly enough, thats not as far fetched as it sounds. Some highly built race engines are known to surpass the 100% efficiency mark...


<br>


4cyltuner.com - Information Source For 4 Cylinder Tuners
Buy stuff from CarCustoms Ebay! Won't be disappointed!

Re: How much air (CFM) does our engines move?
Friday, November 12, 2004 10:42 AM
CNFX>vbz wrote:

Stock my 2.4 head flowed 125 cfm on the exhaust side and about 210 on the intake side. After the port and polish it flowed 295 on the intake and 150 on the exhaust.



wow good stuff.

our intake really @!#$ flows doesnt it, but the exhaust stock is just horendous.

what year head did you have tested? 99+ have .25" wider and .1" taller exhaust ports. <br>

________________________________________________

...bone stock
Re: How much air (CFM) does our engines move?
Friday, November 12, 2004 11:16 AM
Eliot wrote:

I have used for my calculations for LD9 engines, an aprox VE=84% with 230CFM max @ 6400rpm.

I hope it help.


Where'd you get that?

Ray Hall Turbocharging wrote:

Engine VE: Engine Volumetric Efficiency in percent. VE changes with engine RPM, a engine at wide open throttle at 3000rpm could have a VE of 90% and at 6000 rpm 60%. This is a rough guide. At maximum RPM modified engines may have a better VE, e.g.: average overhead valve engines 45% to 75%, overhead cam twin valve 65% to 80%, four valves per cylinder 75% to 90%.


84% N/A would be absolutely impossible with those stock heads. There's built single-valve N/A cars don't put up numbers in the mid 80's. Also, you didn't show your calculations to get that number so apparantly it's an ASSumption.

Wild weasel - you're trying to calculate an engine CFM assuming a 100% V.E. which isn't a very "real world" take to it. First step would be to calculate the VE which in it self is something. I can assure you that it's not going to beat 240cfm though.
Re: How much air (CFM) does our engines move?
Friday, November 12, 2004 12:28 PM
My car/engine is a 1997. <br>

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Re: How much air (CFM) does our engines move?
Friday, November 12, 2004 3:11 PM
Quote:

84% N/A would be absolutely impossible with those stock heads. There's built single-valve N/A cars don't put up numbers in the mid 80's. Also, you didn't show your calculations to get that number so apparantly it's an ASSumption.


Holy $hit man

You have been on this site for a few weeks and apparently your the new "boost forum" moderator. I have no doubt that your a smart guy although you assume (even after I appologized on another thread) that I have an e-degree in engineering and im an idiot.

All this because I diagree with you.

Now your calling other people names just because they may be incorrect but bother to post...

Maybe you havnt learnt this in the 50 or so years youve been on this earth but being arbitraraly rude to people just because you disagree with them is just being an a$$hole.

Youll probably come on here and call me a punk for disagreeing with you yet again, but I can tell you honestly that unless you are the kind of person that just likes comming on here and hearing himself speak, you should probably offer a little common respect to others wether they are right or wrong.

Just my 2 cents, I expect that this will just piss you off and youll post a long rant about how Im wet behind the ears or that I know nothing......so let her fly!

<br>



"Go Before Show Yo."
CARCUSTOMS.NET, THE BEST SERVICE ON THE ORG!!!
Re: How much air (CFM) does our engines move?
Friday, November 12, 2004 3:15 PM
Quote:

Author: Shifted (KickAzz)

Quote:

V = (RPM x CID) / 3456



By the way, Wild Weasel, I would go with this equation but keep in mind that VE falls off as you move away on either side of the rpm where peak torque is maximized.

<br>



"Go Before Show Yo."
CARCUSTOMS.NET, THE BEST SERVICE ON THE ORG!!!
Re: How much air (CFM) does our engines move?
Friday, November 12, 2004 6:08 PM
Doomsday exist many formulas that could be apply to calculate the VE of an engine:
1.- Volumetric Efficiency = Actual CFM * 1728/CID * RPM
2.- Volumetric Efficiency = Actual CFM/Theoretical CFM * 100
3.- VE = (HP * 792001.6) / (AP * CR * CID * RPM) where
HP = Horsepower
CID = cubic inch displacement
RPM = rev./min. at max power
VE = volumetric efficiency
AP = atmospheric pressure in psi
CR = compression ratio
4.- VE=2*(mass flow rate_AIR)/(intake density*displacement volume*engine speed)
5.- VE=1-(exhaust pressure/intake pressure-1)/(ideal gas specific heat ratio*(compression ratio -1))
6.- VE = RealMassFlow / (VolumeCyl * AverageDensityInfrontOfValve)
7.- VE = 9.566 (a constant) x Air flow in Kg/hr x ((273.1 + ambient intake temp-celcius)/(Engine capacity in litres x Engine speed x (Barometric pressure /1000))

But to avoid complicated calculations I used the info/equations/software you mention form the Ray Hall Turbocharger calculations site. In fact is a renamed site with very good info and comments.

Actually you are right when in Ray Hall site mention: Engine VE: Engine Volumetric Efficiency in percent. VE changes with engine RPM, a engine at wide open throttle at 3000rpm could have a VE of 90% and at 6000 rpm 60%. This is a rough guide. At maximum RPM modified engines may have a better VE, e.g.: average overhead valve engines 45% to 75%, overhead cam twin valve 65% to 80%, four valves per cylinder 75% to 90%, so remember that for LD9 engines, as I said in my first post, apply this fact: average overhead valve engines 45% to 75%, overhead cam twin valve 65% to 80%four valves per cylinder 75% to 90%.

So using the Volumetric efficiency (VE) calculator located in this page you easily calc the VE of your engine. So if you use an LD9 engine, 146ci with 150BHp @ 5600rpm (HPmax at XXXrpms when the power curve begins to go down) you get VE=82.43%.... sorry I make an error before......you obtain VE=83.93% (almost 84 @5500rpms.

Also I recomend you using the turbo calc from the same page because is very useful for our boost needs.

Sorry if I make any mistake or do any error...... I am only trying to help as much as I can and share as useful info as I find/have.

I hope this info help.

Regards <br>

___________________________
MAKING MY DREAMS A REALITY
Visit my cardomain site !!!

ELIOT. Now.....boosted.

Re: How much air (CFM) does our engines move?
Friday, November 12, 2004 9:13 PM
First, for an answer to the original post, this page gives reasonable estimates of air needed for a required HP level: http://users.erols.com/srweiss/calchpaf.htm
This should be good enough to show that electric superchargers are about as useful as termites on a wooden ship. And the point about pressure vs flow is extremely accurate, as someone else mentioned. The real goal is to increase air density, not air flow. But that's a discussion for another time.

And this VE argument is a fun one. Here's how I do it.
Quote:

So if you use an LD9 engine, 146ci with 150BHp @ 5600rpm (HPmax at XXXrpms when the power curve begins to go down)


Yep... I'd use a known hp # and known displacement to start with.

Just for starters, plug in GM's published peak hp into the airflow calculator above to get an estimated 146 CFM airflow required to produce 150 hp.

Quote:

Wild weasel - you're trying to calculate an engine CFM assuming a 100% V.E. which isn't a very "real world" take to it.

The original question is about a sanity check, which 100% VE values would have provided. Regardless, you'll always need 100% VE to calculate actual VE. It's actually not difficult.

Calculate 100% VE displacement for any rpm:
engine displacement in ci * (rpm/2) / 1728 ci /cf = cfm

For a 146 ci engine, the following table applies.
RPM	100% VE in CFM
1000 42.24537037<br />2000 84.49074074<br />3000 126.7361111<br />4000 168.9814815<br />4400 185.8796296 (peak torque rpm)<br />5000 211.2268519<br />5600 236.5740741 (peak hp rpm)<br />6000 253.4722222<br />7000 295.7175926<br />8000 337.962963

You can't just use engine displacement for the VE calculation because the engine is spinning multiple times per minute. It displaces 1 engine's worth of air every 2 crankshaft revolutions. At 5000 rpm this happens 2500 times per minute. You have to consider this repetition over time. The CFM numbers above represent the total volume of air that would be displaced if the engine were 100% efficient at the rpm values listed. Now let's calculate actual VE at peak hp rpm.

Looking up 100% VE displacement @ 5600 rpm shows a value of 236.6 CFM. Actual airflow divided by theoretical maximum airflow gives the actual VE, so 146cfm from the java calculator /236cfm = about 62% VE. Is this surprisingly low to some people? We can do slightly better.

Peak efficiency really occurs around peak torque, which occurs at 4400 rpm by GM's published #'s (155 lbs/ft @4400 rpm). Converting torque to hp gives 129.9hp, which requires 126.3 cfm air according to the page above. 100% VE @ 4400 rpm is 185.9 cfm, and 126.3/185.9 = 67.9% VE. Like I said, it's slightly better. FWIW, this type of result agrees with what you'll see in a speed density ecm's VE tables... peak numbers cluster around peak torque.

Hopefully this will be useful to some.

-->Slow

Ford has a great new quality control program. All defective parts are marked with a blue oval.
Re: How much air (CFM) does our engines move?
Saturday, November 13, 2004 12:11 AM
Pimpfire wrote:

Quote:

84% N/A would be absolutely impossible with those stock heads. There's built single-valve N/A cars don't put up numbers in the mid 80's. Also, you didn't show your calculations to get that number so apparantly it's an ASSumption.


Holy $hit man

You have been on this site for a few weeks and apparently your the new "boost forum" moderator. I have no doubt that your a smart guy although you assume (even after I appologized on another thread) that I have an e-degree in engineering and im an idiot.

All this because I diagree with you.

Now your calling other people names just because they may be incorrect but bother to post...

Maybe you havnt learnt this in the 50 or so years youve been on this earth but being arbitraraly rude to people just because you disagree with them is just being an a$$hole.

Youll probably come on here and call me a punk for disagreeing with you yet again, but I can tell you honestly that unless you are the kind of person that just likes comming on here and hearing himself speak, you should probably offer a little common respect to others wether they are right or wrong.

Just my 2 cents, I expect that this will just piss you off and youll post a long rant about how Im wet behind the ears or that I know nothing......so let her fly!


Just for the record - I haven't been on the earth for "50 or so years". Barely half that. I've been building race cars for a damn long time though and covered a shitload of theory and execution in that amount of time and done stuff that Status Quo would have you believe were impossible like 400.3whp and 426ft/lbs with 28lbs/hr injectors on a 4cyl (with the dyno sheet to prove it). Most people would say that you need 62lb/hr injectors or 80lbs/hr injectors at the very least. I can think of dosens of things that go against status quo that I never mention simply because the average person wouldn't believe it nor want to hear it. It's strange the kinds of things you learn doing 36hr tuning and building shifts - but you eventually get tired of trying to force knowledge on people who aren't asking questions for informative purposes - but really jsut to bust balls since they just end up reacting in an ingnorant manor anyway. In any case - I have great respect for the people that don't know something and are actually capable to admit it and ask for elevation. I have a great respect and admiration for the hunger to learn. On the other hand, I have no respect for people who don't know jack @!#$ and act liek they do (insert yourself here), or worse yet - someone who knows half of something and thinks they're engineers (you fit in this catagory too) If you don't liek it - cry about it. What people such as your self do is essentially just bench racing disguised as facts and do more harm than good in the process.


Eliot, you make some good points, but all of them lack one vital ingredient: CFM. Thus far - all your CFM calcs are assumed so all your V.E. calculations are merely guesstimates. If you really wanted to know what your engine is ACTUALLY flowing - "ask the ECU". Ironically - the same source that would tell you the CFM would also tell you your V.E. right down to the thousandths place. It could even tell you the exact number of air molecules, lol. You'd be doing the same job your ECU does: "kPa vs Airtemp = airmass" then it works to generate the desired AFR. Another way to see how much air is in your engine is by simply looking at your AFR (which can be executed using the inverse calculation to the one I just mentioned). It's not as precise since the O2 reading isn't EXACTLY what left the chambers (some particles never make it to the O2) - but it's a hell of a lot more accurate than guestimaging your CFM and working from there. Same thing - you'll need to know your intake temps (something a sensor will be more than happy to tell you) to get it 100% and simply calculate form there. All these formulae and such are great and precise if you have the actual inputs they call for. Without that info though - not very helpful. But...the thought process I've been using for years now goes a little something liek this:

1: What's my AFR?

2: Now..how many cc's (I personally prefer CC's. You can use lbs if you like or liters or even cubic inches) of fuel do my injectors deliver (not to be mistaken for the injectors flow rating!!).

3: Multiply the cc's (if that's what you used) of fuel delivered against the AFR. Congrats - you just got your exact air flow through the engine. Merry Christmas.

I use a derrivitive of this same process to get needed injectors, needed fuel pressure for desired AFR, and damn near everything else I need for a fuel system. FuÁk the RPM, fuÁk the CFM, fuÁk your turbo's efficiency, fuÁk your intercooler, fuÁk your heads and cams and fuÁk your compression along with it. This calculation is absolute. Goodluck finding that in a book though. Now THAT'S the type of functional execution I'm talking about. Tell Status Quo I said it can go fuÁk itself.
Re: How much air (CFM) does our engines move?
Saturday, November 13, 2004 4:30 AM
Again sorry friends for my mistake. I am not an auto expert only trying to share and compare some info. I think that is the main objetive of this forums.

Humans make mistakes so we are starting to know more when we recognize our errors. I have some good points but as Doomsday said, based in some assumptions, because I wasn't know how to get the actual CFM's.

Doomsday and Slow thanks for the correction and great info.

Regards, <br>

___________________________
MAKING MY DREAMS A REALITY
Visit my cardomain site !!!

ELIOT. Now.....boosted.

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