Engine Volumetric Efficiency

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MerkXRTurbo
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Engine Volumetric Efficiency

Post by MerkXRTurbo »

Anybody know what it is for the 2.3T? I would think that it would be lower than a standard 2 valve per cylinder engine due to the poor flow charasteristics of our stock engines.
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Post by John Brennan »

Maybe when not under boost, but I'll bet it goes up quite a bit then. Wonder how you average it out?
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Post by svo855 »

VE is the same under boost as it is with out boost. There is really no need to know VE. Just tune the thing on a dyno and what ever power number you get is just what you get.
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Post by mk96 »

the ve is increased when boosting...it will go over 100%
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Post by M E R K U R »

uhh what is ve?
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Post by M E R K U R »

oh crap i see now lol!!!
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Post by John Brennan »

mk96 wrote:the ve is increased when boosting...it will go over 100%
Of course it will. That's the whole point of forced induction.
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Post by svo855 »

John Brennan wrote:
mk96 wrote:the ve is increased when boosting...it will go over 100%
Of course it will. That's the whole point of forced induction.
I doesn't work that way. Forced induction will not change VE. The volume of air is the EXACT same with or without boost; the only thing that changes is the mass of that volume of air.
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Post by rat_n_a_cage »

svo855 wrote: I doesn't work that way. Forced induction will not change VE. The volume of air is the EXACT same with or without boost; the only thing that changes is the mass of that volume of air.
um, yes it does. It's been a while since I looked at this in depth, but as I understand it, if you fill a 2.3L engine with 2.3L of air "at standard pressure and temperature" that is 100%. If you cram more than 2.3L of STP air in it, that's >100%. What is left to do is correct the air charge (since it is heated) to STP which will tell you how many L of STP air you crammed into the cylinders. So yes, the actual volume of air remains the same, but the fact that it is above standard pressure makes it a greater volume with respect to standard values.

This is why intercooling is so good. On a good day, you can be sending a volume of air at 15psi (or more) that if you cool it to room temp, you can greatly exceed 100% VE.

The key is correcting it to Reference temperature and pressure (standard temp and press) which I believe is about 14.7 psi and 0 deg C. Ironically, there are slightly different standards depending on the issuing agency. THE STP is 14.7psi, 0 deg C, 0% moisture content. Standard room temp is 25 deg C and 14.7 psi, for aviation it's 15 deg C.
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Post by flylear45 »

Volumetric efficiency (VE) is used to describe the amount of fuel/air in the cylinder in relation to regular atmospheric air. If the cylinder is filled with fuel/air at atmospheric pressure, then the engine is said to have 100% volumetric efficiency. On the other hand, super chargers increase the pressure entering the cylinder, giving the engine a volumetric efficiency greater than 100%. However, if the cylinder is pulling in a vacuum, then the engine has less than 100% volumetric efficiency. Normally aspirated engines typically run anywhere between 80% and 100% VE.
A sample from an article on VE. Note the line stating regular atmospheric air. That is why by definition supercharged engines have VE's over 100%. (We have turbosuperchargers):wink:

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Post by rat_n_a_cage »

Furthermore:

Assume standard temp and press = 0 deg C at 14.7 psi (273.15 K and 1 atm...you have to use Kelvin by the way):

NA Case 1: P=1, T=273.15K, V=2300
Boosted Case 2: p=2 (15psi of boost), T=(273.15+75 after intercooling)=348.15 K, V=2300

Using the general form PV/T, divide case 2 by case 1 and you get 157% VE.

y'all nerds feel free to correct any boo-boo's I may have made, but the general principle applies. 8)
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Post by wilky »

Whoa - the good old Ideal Gas Law. PV=nRT but you still can't push a rope!

Great info there - thanks.

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Post by Cozz »

Stock 2.3 VE= about .75-.80 without boost.
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Post by rat_n_a_cage »

wilky wrote:Just what did you do on that sub anyway rat-n-a-cage??
I was a reactor operator (nuclear propulsion plant). If I'm an expert at anything, it's boiling water! :lol:
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Post by John Brennan »

THANK you...! 8)

I knew some of you wiz kids would step up and define in exact terms what I understand but lack the precision to express.
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