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Old 10-14-2011, 12:48 PM   #1 (permalink)
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I was going through my Ultragauge and found the Volumetric Efficiency gauge. I did some research and for most cars the average 80-100%. In my car, going a constant speed it stays at 75%, so only 3/4 of the total space of the cylinder is being utilized, which seems lousy. The closer the percentage is to 100 the more power the engine produces, but would that mean more FE?
If so what are some ways to increase VE? Like would a better air filter help?

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Old 10-14-2011, 02:24 PM   #2 (permalink)
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Regearing or going to a taller tire would boost VE at a lower RPM.
End result, better fuel milage.
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Old 10-14-2011, 05:22 PM   #3 (permalink)
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Open the throttle all the way; that will help VE.

Pressurize the intake. A supercharger or a turbocharger are very good at this.

Note that with any of those you will be making more power, so you'll wind up accelerating. For going a constant speed, your VE is going to be lower.

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Old 10-14-2011, 06:10 PM   #4 (permalink)
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Only time my VE shows that high at steady speed is on cruise going uphill.

But, at idle it shows 49 so not much difference.

The higher the VE the better your motor is at making power, but unless tuned for 1-2K rpm's at 100% VE, the higher number will equate to less MPG.
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Old 10-15-2011, 12:19 AM   #5 (permalink)
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can not Measure VE

note on the graph , at high flow calculated and actual air flow are very close , differences measured on the grid on the right , but at low flow , calculated and actual are much farther apart - differences can be huge , depending on the system -
you can measure change in efficiency by measuring calculated load at WOT under consistent condition s , a higher value of calculated load at WOT means you have improved your systems ability to flow

the system above is in very poor condition as on that system , calculated load should peak close to 150% at WOT as it is a turbocharged AWM engine
during this test , fuel trim should be within +/- 5% from zero , the system above is in heavy add indicating an under reporting MAF sensor OR restricted fuel to or through the injectors
, on a normally aspirated engine calculated load or engine load of 100% is the goal but real world values will be closer to 90%

an NA engine with an under reporting MAF sensor , fuel trim is adding over 15% mac engine load is 80% , defective new MAF sensor

an increase in calculated load is always an improvement in flow IF and only IF test conditions are IDENTICAL.
if you wish to test your system
use calculated load or engine load at WOT ,
never use Absolute load , it will always be 100%

you can not measure VE accurately at any throttle position besides WOT so
i would focus on something else

when doing these "tests" , use a copilot to monitor scan data - so you remain alive to post your "test" results
using VE graphed at WOT with good and a bad MAF sensor , same car , same test conditions

Last edited by mwebb; 10-15-2011 at 12:31 AM.. Reason: proof read
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Old 10-15-2011, 08:18 AM   #6 (permalink)
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In an old article by a gent who was rebuilding a dyno at the University of Maryland, he found that using a mid 80s GM 2.5 4 cylinder, when you increased the load from 20 to 50 HP the fuel consumption only increased by 50% while the power generated increased by 150%.

That's the "majic of high VE", an operational tactic that uses as close to possible to a 0 manifold vacuum or 100% MAP as possible under all of the vehicle operatinal parameters, without enrichment.

In order to do this you must incorporate some form of energy storage to separate engine load from vehicle speed, but this is where you incur losses that in most systems eliminate the advantage of an all or noting max VE tactic.

This is the reason I advocate hydraulics for storage and application. Since max VE can more than double the power per BTU in energy conversion, and hydraulic systems are at close to 80% right now, and have been for a decades, the development of new designs that increase that efficiency beyond 80% would have a dramatic effect in overall mileage from just a few percentage points in increase.

Pulse and glide maximises VE by employing an all or nothing engine operation. The real secret in the future will be to do exactly the same thing, WITHOUT A CHANGE IN VEHICLE SPEED. This requires storage and application of energy in an environment of constantly changing storage pressures with infinitly variable ratio machines. Accumulators can reach 99% efficiency and pumps are close to that as long as you keep their RPM below 1000 (wheel speed works great).

It's getting very close to reality.

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Old 10-15-2011, 11:16 AM   #7 (permalink)
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i don't know the conversion efficiency of an internal combustion engine to electricity and batteries, but this is the whole idea behind series hibrid systems. The engine is run constantly at peak effeciency, and it charges a battery. The vehicle is ultimately powered by electric motors.

Trains are series hybrids, and I often wonder if it's a good system for tractor-trailer big rigs.
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Old 10-15-2011, 07:02 PM   #8 (permalink)
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...a series of automotive EQUATIONS worth studying:

T = 5252*HP/RPM

HP' = T*RPM/5252

HP" = (AP*CR*VE*CID*RPM)/(5252*150.8)

HP = (T*RPM/5252) = (AP*CR*VE*CID*RPM)/(5252*150.8)

VE = (T*150.8)/(AP*CR*CID)


T = torque, lb·ft
HP = horsepower
RPM = engine speed
AP = air pressure, psi (~14.7 psi)
CR = compression ratio
CID = engine cubic-inch-displacement
VE = engine volumetric efficiency, %

...use the HP@RPM and T@RPM values for your engine and backsolve for its' VE at those two operating points (remember it's not a constant, but varies with engine load and rpm).
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Last edited by Old Tele man; 10-15-2011 at 07:15 PM..
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Old 10-15-2011, 08:52 PM   #9 (permalink)
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bottom line
Calculated load is directly related to fuel consumption
monitor calculated load and reduce your calculated load at a consistent vehicle speed and you reduce
fuel consumption

you can reduce calculated load by improving the efficiency of the ability of the engine to pump air - but most people have no way to do much that could have any effect at all on VE on a modern day fuel injected engine -

the engine has already been engineered and produced and installed in your car

you can also reduce calculated load by reducing aerodynamic drag and by reducing rolling resistance

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