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OBDII app asking for volumetric efficiency and the brake specific fuel consumption

m9199

VibraJeeper
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Joined
Jan 16, 2019
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93
Location
Santa Cruz, CA
I picked up a OBDLink Bluetooth OBDII reader and the app is asking me to put in some info about the engines performance. Right now it's just using the default numbers, but I'd like it to report performance as accurately as possible.

It's asking for the Volumetric Efficiency and the Brake Specific Fuel Consumption.

I was able to find something about VE around here which said it was at least 80%, so that's what I entered into the app. Does anyone know at least a ballpark of what the BSFC is for the 4.0 used in the 05?
 

Southtowns27

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Joined
Mar 31, 2019
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38
Location
Western NY
BSFC = kg/s / W. That's mass of fuel divided by effective power. The problem is that power output (horsepower) is variable since it is derived from torque x RPM / 5252. This results in BSFC actually being a contour map rather than a single line. It doesn't make sense that the program is asking for a single point as BSFC. You'd need to calculate and plot it at many points to even achieve a minimum BSFC curve.
 

JEEPCJTJ

TJ Addict
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Aug 11, 2018
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1,711
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Half way between Pittsburgh and Cleveland
Wow. Someone wasn't smoking pot and drinking beer in college!

It may be possible that something BEYOND that stuff was being partaken by someone at some point. I say this because I have no idea where Volumetric Efficiency and the Brake Specific Fuel Consumption comes from or why the OBD can't tell us what it is. It seems like jumping in a cab to go to the airport and the meth-head driver asks you,"How do I put this thing in gear and which of these pedals do I step on?"
 

Southtowns27

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Mar 31, 2019
Messages
38
Location
Western NY
In simplified terms, VE is the amount of air the engine actually inhales versus the swept volume of the cylinders. In a naturally aspirated engine the actual amount is less than swept volume so the VE is always a number less than 100%. This happens because air is slightly viscous and has inertia.
BSFC is described above. BSFC wouldn't be all that hard to actually figure out. All we'd need is the power/torque curves for the 4.0, then operate it at various speeds at WOT with a flowmeter hooked to the fuel supply.
 

greaseorbounce

New Member
Joined
Oct 10, 2019
Messages
15
Location
Colorado
I'm a month late to this party, but I'm actually quite interested.... Do we think that anyone has performed such a test and has a proper BSFC map? Ideally with the entire family of curves plotted for different RPM? I come from the aircraft world where such BSFC charts are in every owners manual, but I haven't seen one for the 4.0 yet. An easy task for someone with a dyno, hard to believe that chart isn't floating around...