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Discrepancy in Volumetric Efficiency Calculator. #4452305
07/07/17 12:44 PM
07/07/17 12:44 PM
Joined: May 2005
Posts: 2,201
Toronto, Canada
George7941 Offline OP
George7941  Offline OP
Joined: May 2005
Posts: 2,201
Toronto, Canada
https://www.otctools.com/ve

With my truck on the highway at WOT, 2033 rpm, 68F IAT, MAF is reporting 66.1 g/s. Doing the calculations - swept volume of 4.3l every two revs gives 72.85 l/s, air at 68F weighing 1.204 g/l yields air flow of 87.7 g/s. 66.1 is 75.4% of 87.7, yet the OTC VE Calculator yields 65%.

What am I missing?


2006 GMC Sierra 4.3l, NV3500,G80 , Mobil 1 5W30, Dexcool.
1987 BMW R80 - sold
2015 Honda CBR300R

Staying out of the right lane a lot.
Re: Discrepancy in Volumetric Efficiency Calculator. [Re: George7941] #4452333
07/07/17 01:09 PM
07/07/17 01:09 PM
Joined: Aug 2003
Posts: 12,896
NE,Ohio
Rand Offline
Rand  Offline
Joined: Aug 2003
Posts: 12,896
NE,Ohio
pumping losses? not like you get 4.3L of air in there perfectly?


2019 Jeep Cherokee Trailhawk 2.0T
Re: Discrepancy in Volumetric Efficiency Calculator. [Re: George7941] #4452367
07/07/17 01:51 PM
07/07/17 01:51 PM
Joined: Jul 2010
Posts: 18,669
PNW
ZeeOSix Offline
ZeeOSix  Offline
Joined: Jul 2010
Posts: 18,669
PNW
How do you know how accurate the on-board air temp and MAF are?

Also, is the engine's displace actually 4.3L ... most manufacturers round up when designating an engine displacement label, so the actual engine displacement might be a bit less than 4.3L.

Re: Discrepancy in Volumetric Efficiency Calculator. [Re: George7941] #4452394
07/07/17 02:37 PM
07/07/17 02:37 PM
Joined: Oct 2014
Posts: 11,839
Idaho
CT8 Offline
CT8  Offline
Joined: Oct 2014
Posts: 11,839
Idaho
Nothing is exactly as how it seems to be. Engines efficiency varies at different RPMs do to the intake, Exhaust and everything in between. Some where in the engines operating range should be a "sweet spot" that will give the best numbers.Though not 100% unless the engine is supercharged then maybe not.


2015 Ford F150 2.7
2018 Ford F350 6.2
Re: Discrepancy in Volumetric Efficiency Calculator. [Re: George7941] #4452412
07/07/17 02:56 PM
07/07/17 02:56 PM
Joined: Jul 2011
Posts: 1,224
Houston, TX
Coprolite Offline
Coprolite  Offline
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Posts: 1,224
Houston, TX
The 4.3L Vortec LU3 has a displacement of 4.30019 L from my calculations.

Re: Discrepancy in Volumetric Efficiency Calculator. [Re: George7941] #4452795
07/07/17 09:17 PM
07/07/17 09:17 PM
Joined: May 2005
Posts: 2,201
Toronto, Canada
George7941 Offline OP
George7941  Offline OP
Joined: May 2005
Posts: 2,201
Toronto, Canada
Every one of the replies skirted my question.
1) The actual displacement really does not matter, whether it is 4.25l or 4.34l. 4.3 is the figure used in my calculations and in the OTC app, so it is the exact same figure in both.
2)Pumping losses would explain why the efficiency is less than 100%, but that was not my question. All I am doing is questioning the discrepancy between my figures and the app's. Ditto "sweet spot", "supercharging" etc.
3) The air temp and Maf are the values reported by a scantool, but, again, all immaterial to my question.

WHY IS THERE A DISCREPANCY BETWEEN MY FIGURES AND THE OTC APP?


2006 GMC Sierra 4.3l, NV3500,G80 , Mobil 1 5W30, Dexcool.
1987 BMW R80 - sold
2015 Honda CBR300R

Staying out of the right lane a lot.
Re: Discrepancy in Volumetric Efficiency Calculator. [Re: George7941] #4454374
07/09/17 03:23 PM
07/09/17 03:23 PM
Joined: Jul 2010
Posts: 18,669
PNW
ZeeOSix Offline
ZeeOSix  Offline
Joined: Jul 2010
Posts: 18,669
PNW
Originally Posted By: George7941
Every one of the replies skirted my question.
1) The actual displacement really does not matter, whether it is 4.25l or 4.34l. 4.3 is the figure used in my calculations and in the OTC app, so it is the exact same figure in both.
2)Pumping losses would explain why the efficiency is less than 100%, but that was not my question. All I am doing is questioning the discrepancy between my figures and the app's. Ditto "sweet spot", "supercharging" etc.
3) The air temp and Maf are the values reported by a scantool, but, again, all immaterial to my question.

WHY IS THERE A DISCREPANCY BETWEEN MY FIGURES AND THE OTC APP?


Hard to say how they are calculating VE in their on-line calculator. The VE is simply the ratio of how much air the engine actually takes in vs. how much it could 100% ideally take in based on displacement. Pumping losses and intake/exhaust restriction are what makes VE less than 100% and should already be taken into account when using intake mass flow (g/s) and intake air temp vs. what the 100% ideal intake based on displacement could be.

Seems it should match your numbers better as it should be a pretty simple calculation as you've shown. Maybe they have an error in their calculation model, or their are accounting for something not obvious.

You should email them and show them the issue to see if they look into it and respond why the discrepancy.
Email: [email protected]

Re: Discrepancy in Volumetric Efficiency Calculator. [Re: George7941] #4454579
07/09/17 06:57 PM
07/09/17 06:57 PM
Joined: Jul 2010
Posts: 18,669
PNW
ZeeOSix Offline
ZeeOSix  Offline
Joined: Jul 2010
Posts: 18,669
PNW
Originally Posted By: George7941
https://www.otctools.com/ve

With my truck on the highway at WOT, 2033 rpm, 68F IAT, MAF is reporting 66.1 g/s. Doing the calculations - swept volume of 4.3l every two revs gives 72.85 l/s, air at 68F weighing 1.204 g/l yields air flow of 87.7 g/s. 66.1 is 75.4% of 87.7, yet the OTC VE Calculator yields 65%.

What am I missing?


The VE is defined with air at "standard temperature and pressure" ATM conditions. At IUPAC standard temperature and pressure (0 C and 100 kPa), dry air has a density of 1.2754 kg/m3 (same as 1.2754 g/l).
https://www.google.com/#q=air+density+at+standard+temperature+and+pressure

As a check of their calculator, use the standard 1.2754 g/l at 32F to get 72.85 l/s times 1.2754 = 92.9 g/s if the engine was 100% VE, and when using those numbers in their calculator it shows 98% (close). So the standard temp, and also probably standard press, have a factor in their calculator. 100 kPa = 14.5 PSI which is slightly less than 14.7 PSI.



Re: Discrepancy in Volumetric Efficiency Calculator. [Re: George7941] #4454729
07/09/17 09:43 PM
07/09/17 09:43 PM
Joined: Jun 2003
Posts: 5,920
Illinois
SHOZ Offline
SHOZ  Offline
Joined: Jun 2003
Posts: 5,920
Illinois
What does the absolute load value say? It's based on VE and the MAP/MAF. Does it seem low (<80% at peak torque)?


2008 Hyundai Accent 1.6L 5 sp manual hatchback
2010 Hyundai Genesis Coupe Track 2L Turbo 6sp manual
Re: Discrepancy in Volumetric Efficiency Calculator. [Re: George7941] #4454795
07/09/17 10:55 PM
07/09/17 10:55 PM
Joined: Jul 2010
Posts: 18,669
PNW
ZeeOSix Offline
ZeeOSix  Offline
Joined: Jul 2010
Posts: 18,669
PNW
Looks like the OTC Tools calculator is using 0 deg C (32 deg F) and 1 ATM air density for their "standard" air temp/press, which would be a density of 1.2922 g/l (94.14 g/s at 2033 RPM). That gives a VE of 100% if the 4.3L engine was ingesting air at the "standard" 0 deg C and 1 ATM to it's full displacement.





Re: Discrepancy in Volumetric Efficiency Calculator. [Re: SHOZ] #4455696
07/10/17 08:55 PM
07/10/17 08:55 PM
Joined: May 2005
Posts: 2,201
Toronto, Canada
George7941 Offline OP
George7941  Offline OP
Joined: May 2005
Posts: 2,201
Toronto, Canada
Originally Posted By: SHOZ
What does the absolute load value say? It's based on VE and the MAP/MAF. Does it seem low (<80% at peak torque)?


Not sure. The Actron 3130 scanner I was using only gave calculated load and gave it as 95.6%. My Tech2 has a engine load pid but I do not know if it is the absolute load.


2006 GMC Sierra 4.3l, NV3500,G80 , Mobil 1 5W30, Dexcool.
1987 BMW R80 - sold
2015 Honda CBR300R

Staying out of the right lane a lot.
Re: Discrepancy in Volumetric Efficiency Calculator. [Re: ZeeOSix] #4455706
07/10/17 09:05 PM
07/10/17 09:05 PM
Joined: May 2005
Posts: 2,201
Toronto, Canada
George7941 Offline OP
George7941  Offline OP
Joined: May 2005
Posts: 2,201
Toronto, Canada
Thanks, ZeeOSix for your explanation. So the OTC calculator gives the right result when IAT is 32F, but the results seem to be off when the temp is not 32F.


2006 GMC Sierra 4.3l, NV3500,G80 , Mobil 1 5W30, Dexcool.
1987 BMW R80 - sold
2015 Honda CBR300R

Staying out of the right lane a lot.
Re: Discrepancy in Volumetric Efficiency Calculator. [Re: George7941] #4455798
07/10/17 11:16 PM
07/10/17 11:16 PM
Joined: Jul 2010
Posts: 18,669
PNW
ZeeOSix Offline
ZeeOSix  Offline
Joined: Jul 2010
Posts: 18,669
PNW
Originally Posted By: George7941
Thanks, ZeeOSix for your explanation. So the OTC calculator gives the right result when IAT is 32F, but the results seem to be off when the temp is not 32F.


My example with 32 deg F shows that their calculator is using a standard baseline of 32F and 1 ATM at 101.325 kPa (14.7 PSI) to define the "standard air conditions" for measuring VE. So their calculator is correct, and if the air temp and pressure isn't at the standard conditions then a NA engine will never hit 100% VE. In other words, the ATM conditions have an effect on the VE.

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