Volumetric efficiency of the turbo'd 4g63

[Van]

I'm wondering if anybody has a formula, for figuring out the volumetric efficiency of our dsm's...NOT taking into account intake and exhaust restrictions.
Roughly, a basic v8 is say, around 85% N/A. And a decent 4-valve per cylinder overhead cam engine can be at 100% N/A.
When we add boost this increases VE, but to what extent?

Boost psi is a measurement of restriction to air flow. But we all know you need more fuel for the air mass difference between 11psi and 16psi of boost, even at the same rpm point.

You can do all of the volumetric flow calculations based on the 122ci for different rpm points and find out basic cu/ft min of air moved; then correct for absolute temp and absolute pressure, figure out different boost pressures and figure out lbs of air moved... But what VE you use can change this number quite abit.

There has got to be a reasonable formula to figure this out for each rpm point at different pressure ratios. Anybody know it or maybe have a decent theory about how to figure it out?

[Edited by Van on 06-08-2001 at 02:29 AM]

[Rdy2race]

Very good Q but no answer form me but a bit of info..

it's 121CDI not 122 =-)

I have never head of any NA motor being over 85% VE

this is a good one I will be hunting for some site on this =-)

BM-

[verserv]

go to this website they have a claculator for it.
http://www.turbofast.com.au/javacalc.html
i downloaded one called Turbo Fast "EngineVE"

[dsm4eva]

From my Engine Dynamics Book:

Engine output is based on how much air and fuel it can burn. It's proficiency at burning the air/fuel mixture is defined as it's Volumetric Efficiency. If you know the amount of air your engine can move at a specific rpm you can use this calculation to estimate volumetric efficiency.


Volumetric Efficiency = (Actual CFM * 1728)/(CID * RPM)

or

Volumetric Efficiency = (Actual CFM / Theoretical CFM) * 100


Or, if you know your horsepower at a given rpm (peak HP is what you want to use here) you can approximate your Volumetric Efficiency at sea level by using a variation of the previous Horsepower calculation:


VE = (HP * 792001.6) / (AP * CR * CID * RPM)

AP = atmospheric pressure in psi
CR = compression ratio
VE = volumetric efficiency
CID = cubic inch displacement
RPM = revolutions per minute



Have fun, oh and its 121.25 CID. :)

[Edited by dsm4eva on 06-08-2001 at 01:48 PM]

[Van]

Originally posted by dsm4eva
Or, if you know your horsepower at a given rpm (peak HP is what you want to use here) you can approximate your Volumetric Efficiency at sea level by using a variation of the previous Horsepower calculation:
VE = (HP * 792001.6) / (AP * CR * CID * RPM)

AP = atmospheric pressure in psi
CR = compression ratio
VE = volumetric efficiency
CID = cubic inch displacement
RPM = revolutions per minute



I too have a couple of those books lying around. :D Thanks for the replies.

In all of the "calculators," they ASK for the VE, instead of giving it or figuring it out. In the above formula, what if you didn't know HP? e.g. no dyno runs. And I know we could get a rough HP from weight and e.t.

I'm very familiar as to what VE is defined as, but a turbo increases an engine's VE. Although, I do understand the HP formula...

Let's generalize this some... Say we can move 30 lbs/min at a given rpm, now up the boost and we can move 40 lbs/min at that same rpm...10 more lbs/min moved than the original 30lbs/min. I know we are now talking mass instead of volume but, couldn't we say that we just increased VE by about 33%?



[Edited by Van on 06-09-2001 at 03:25 AM]

[dsm4eva]

Sorry bro, its been almost 5 years since I took this class, but what I can say is it isn't that simplistic. It wouldn't be a 33% increase, since it is based on volume not on mass, but you are on the right track. I ran through that equation using my estimated HP based on my quarter MPH, I came up with a VE of 2!?!

[danl]

Originally posted by Rdy2race
Very good Q but no answer form me but a bit of info..

it's 121CDI not 122 =-)

I have never head of any NA motor being over 85% VE

this is a good one I will be hunting for some site on this =-)

BM-

THeir are a few production engines on the market that are over 100% VE while NA. It has to do with tuning the intake to "ram" air into the engine. Theoretically at a resonant rpm, the engine will make max torque, and possibly break the 100% VE barrier because of the way the tuned intake uses the inertia of the incoming air to shove the cylinders full of AF mixture. Some stock honda engins do this, and many racing engines do (formula one :))

[fatass92]

Unfortunatly the resonant effect is only happens over a very narrow RPM range. If you look on the ENDYN site you will see that they used to use transducers on the manifolds to make the resonant effect work over a wider rpm range.

-JOHN

[danl]

Yeah, its way more complicated that what i had room to write in, but n/a can go substantionaly more than 100% VE.

[galantvr41062]

1997cc is 121.864416957ci to be exact,
I said I had 270hp atr 16psi, compression of 7.8 and rpm at 6,000rpm. VE=2.3434 so like %234 not bad. I used my TI-86 calculator to figure it out it has conversions for the cc into ci.

~John

[danl]

After reading Maxium Boost (didn't get the whole way through it) the author gives a formula where VE in n/a form is used. You then use the pressure ratio to calculate airflow in CFM's. I know, its not lbs/min and its not taking into account compressor efficency, and thus density changes (amoung other things) but its a start?

[BlueShadow]

Originally posted by Rdy2race
Very good Q but no answer form me but a bit of info..

it's 121CDI not 122 =-)

I have never head of any NA motor being over 85% VE

this is a good one I will be hunting for some site on this =-)

BM-

Hey everybody!

I'm new to this site, but I have been visiting this site getting some good info on Mitsu turbos. (I plan on getting a Greddy Kit for my Lude)

Anyways for Rdy2race,

Here is a link to Honda-Tech.com it's about the VE% of the Prelude and the S2000. The max VE of a "Lude" is 102% @ 7000, and the max VE% of the S2K is 112% @ 8000 RPM.

click this link and read the last reply, and also click the link to autospeed.com

http://www.honda-tech.com/zerothread?id=124704

[BlueShadow]

Originally posted by Van

There has got to be a reasonable formula to figure this out for each rpm point at different pressure ratios. Anybody know it or maybe have a decent theory about how to figure it out?


I don't know if the same theory would apply to factory turbo cars but her it goes.

Just like everyone else has been doing I use the formula:

(CID * RPM * VE * 0.5) / 1728 = CFM
CFM * PR = CFM with boost

the first calculation takes the Naturally Aspirated CFM which you multiply by the PR right? The only numbers that should change with the first calculation is the RPM, and the VE at that RPM right?

so after you get the different CFM's at different RPM points, you just multiply it by the different PR's at those RPM points?


So for a Turbo'ed Eclipse I guess you would have to figure out what the VE is at different RPM points with NO BOOST first. Than later you multiply the CFM by The CFM...

EDIT: That's what I had to do when I needed to find out the CFM of a 3G RX7 without boost. The people at RX7club.com said that the FD has a 70% VE @ 6500 RPM

so the calculation for a rotary was:

(79.3 * 6500 * 0.70) / 1728 = 208 CFM (FD's CFM NO BOOST)

**the 0.5 is left out intentionally cause it's a rotary.

[mike156]

If you are calculating VE on a FI engine then you have to figure the theoretical 100% VE under the same amount of boost as actual CFM...say at 14.7 PSI of boost (or 29.4 PSI absolute pressure) our ~122 CI motor would be (at 100% VE) the same as a 244CI N/A motor (at 100% VE and forgetting compressor efficiency and all the other effects that factor into actual airflow)...VE is a function of % of cylinder fill and not so much airflow (although they are both directly related). This is difficult to explain because so many factors are involved.
I will through up some numbers to show what I am trying to say, but that is all they are.
Our motor at 6000 RPM will ingest ~210 CFM (122/2 [only two cylinders ingest air per revolution]*6000 RPM/12^3 [converting CI to CFM])
That said, theoretically at 100% VE, our motors would ingest 420 CFM at 14.7 PSI of boost at 6000 rpms.
Now lets say we measure an actual airflow of 380 CFM at 6000 RPMs, we have a VE of 90.5% (380/420). Therefore, we are filling 90.5% of the cylinder to 14.7 PSI...or the actual cylinder pressure is 13.3 PSI (before any dynamic compression takes place)...however, dynamically this does not work this way but it gives you the correct idea. A real formula would be something along these lines (actual CFM at "x" boost pressure/theoretical CFM at "x" boost pressure, both values corrected for barometric pressure and temperature)
Almost all turbo motors are not above 100% VE (although it is possible, turbo F1 comes to mind) because the turbocharger creates a considerable restriction in exhaust flow.

[Crackerman]

as a general rule..most n/a engines are about 85% VE for newer variable valve engines their VE can sometimes exceed 110% it is still entirely possible for an older v-8make well over 95%. pro stock cars are running somewhere near 130% VE. as a general rule turbocharged engines run somwhere between 110% and 150% depending on compressor efficiency and other small variables, where as i have seen many old v-8's also in the 60% range too so a completely stock 4g63t might be pushing 110-120% or vry close, although it is VERy hard to figure it all the time because nothing is really ever constant with a turbo( compressor speed and whatnot)