Hello, I am trying to find my volumetric efficiency (VE), I know the formula but I need to know my CFM. But to find the CFM, I need to find the VE. Here's the formulas if it would help..

VE = (CFM X 3456) / (CID X RPM)
CFM = CID X RPM X VE / 3456

By the way our CID is 121 in^2 .
CID = Number of cylinders X 0.7854 X bore X bore X stroke
CID = 4 X 0.7854 X 3.44 in X 3.44 in X 3.27 in = 121.5669514752

I don't have my book with me that has that information because i'm at work now, but i believe this site has some info that you will find useful...

http://www.ondoperformance.com/tech.html

Enjoy Dude:thumbsup

No expert ( far from it) but using your formula
VE = 252 x 3456 / 121 x 7200(max rpm)
or VE = 870912/871200 which is .9996694

>No expert ( far from it) but using your formula
>VE = 252 x 3456 / 121 x 7200(max rpm)
>or VE = 870912/871200 which is .9996694

Sorry I forgot the brackets..

VE = (CFM X 3456) / (CID X RPM)

Thanks

~Tacoman

you can't just look a forumal and find the VE.. so to try and do them is pointless.
but I've been told that in a DOHC 16-valve engine the VE ranges between 87%-95% depending on RPM.. the percentage getting lower as the RPM's go up of course.

If i remember my literature correctly, .85 is a nice, concervative number to base any paper-and-pencil calculations on when it comes to these cars. The thing to remember, the math you are doing isn't designed to e 100% accurate, only marginally close. Racecars aren't built by math, but by "fell" - the math only goes so far.

>Racecars aren't built by math, but by "fell" - the math only goes so far.

I'm not trying to question you, cuz I know you're hella lot smarter than me :-) ..

But, racing is mostly math. Like, there is a difference between 5 and 15 psi ( X < Y ). With math, you could easily do everything and find out what you need and what results you would get.

Is there any scientific way to find out volumetric efficiency? Like hooking up sometime of gadget or gizmo or guage or whatever?

Thanks

~Tacoman

Not as far as i know. In general, VE is an educated guess.

if you had a machine that measured air flow.. you could hook it up to the intake, run the motor at a certain RPM and measure the amount of flow the motor is pulling in, and then compare it to the amount of flow it should be if VE = 100%, that'll give you what your motor's VE is at a certain RPM.

Do you know whats the name of the machine that finds out the CFM in the intake?
Thanks

I think all you need is a Mass Airflow Sensor.


95 Eclipse RS : 5 speed
Gude cams : test pipe : AFX UDP : ram air : Thrush glasspack : Dual air horns : Kenwood KDC 5000 : AutoCommand remote start
incomming - lower strut bars

It can't give me a digital readout can it?
Is there something I can hook up to the ECU, that tells me what CFM I get?
Would a data logger tell me?
Thanks

that might work tacoman.. but I thought eclipse's didn't have MAF's (mass air flow) sensors.

The factory turbo models do. They read in karman vortex. If you can figure out how to use that to help find VE, then be my guest.

Why do you need to know what the VE is?

>Why do you need to know what the VE is?

Cuz I do ;-) ..

Really, I am trying to find out how much CFM comes in and out of my motor at certain RPM's for a setup I was thinking about..

The setup is secret for now. ;-)

>>Why do you need to know what the VE is?
>
>Cuz I do ;-) ..
>
>Really, I am trying to find out how much CFM comes in and
>out of my motor at certain RPM's for a setup I was thinking
>about..
>
>The setup is secret for now. ;-)

He's planning a twin turbo setup... or at least asking questions about it.....

If you goal is to get the best low end boost reponse as well as a high top end boost and cfm... then theres easier ways of doin it with one turbo than with two..... cheaper and not as complex also.....

Brezio's right - our cars don't have one. You'de have to buy one and install it.

Why don't you just use 85% and move on. We may be more efficient at certain RPM's but it's a good baseline.


95 Eclipse RS : 5 speed
Gude cams : test pipe : AFX UDP : ram air : Thrush glasspack : Dual air horns : Kenwood KDC 5000 : AutoCommand remote start
incomming - lower strut bars

>>>Why do you need to know what the VE is?
>>
>>Cuz I do ;-) ..
>>
>>Really, I am trying to find out how much CFM comes in and
>>out of my motor at certain RPM's for a setup I was thinking
>>about..
>>
>>The setup is secret for now. ;-)
>
>He's planning a twin turbo setup... or at least asking
>questions about it.....
>
>If you goal is to get the best low end boost reponse as well
>as a high top end boost and cfm... then theres easier ways
>of doin it with one turbo than with two..... cheaper and not
>as complex also.....


I'm sorry, but you are wrong. That twin turbo setup idea was in the past, after Murix and some of the explained ( :-) ). But, I am thinking of something else.