|
|
|
|
| Author |
|
|
Registered
Join Date: Nov 1999
Location: Montreal, Canada
Posts: 728
|
Volumetric Efficiency of a 3.2?
Does anyone know the volumetric efficiency of a stock 3.2 Carrera? How is this calculated?
Thanks Mike 86 Carrera t |
||
02-05-2002, 05:49 AM
|
|
|
Registered
Join Date: Mar 2001
Location: swamps of Jersey
Posts: 201
|
If I remember correctly, volumetric efficiency is the cylinders ability to completely fill itself with air on the downward (intake) stoke.
I supppose to measure this you would need to find out the volume of air that has entered the cylinder....or If you capture the amount of air that is pumped out of the cylinder on the exhasut stoke you could compare this to the theoretical "filled" volume @ atmospheric pressure. Or somethn' like that..... |
||
|
02-05-2002, 06:46 AM
|
|
|
Registered
Join Date: Nov 1999
Location: Montreal, Canada
Posts: 728
|
Thanks John, I know what it means but I want to know HOW to measure this.
Thanks Mike 86 Carrera t |
||
|
02-05-2002, 04:12 PM
|
|
|
Registered
Join Date: May 2000
Location: Los Alamos, NM, USA
Posts: 6,044
|
I believe it has to be measured in a dynamic test as it varies with speed; I vaguely recall backing this efficiency out of the data from a engine dyno run in an engineering lab. I'll have to dig out my notes but here's the textbook blub on IC engine volumetric efficiency: Volumetric efficiency is the ratio of the volume of air (for a liquid-fuel engine) and charge (for a gas engine) actually admitted, measured at atmospheric pressure and temperature, to the displacement volume. High manifold and cylinder temperatures and resistance to flow reduce volumetric efficiency. High-output aircraft engines have maximum volumetric efficiencies of 85 to 90 percent at rated speeds. Supercharged (this includes turbocharging) engines may have volumetric efficiencies above 100 percent or may be designed to maintain high volmetric efficiencies with an increase in speed. Volumetric efficiencies of automobile engines diminish appreciably as piston speeds exceed 1,200 to 1,600 fpm (feet per minute), decreasing to about 60 percent at top piston speeds of 2,500 to 3,200 fpm. These vary appreciably with valve timing.
 Jim
|
||
|
02-05-2002, 04:33 PM
|
|
|
Information Junky
Join Date: Mar 2001
Location: an island, upper left coast, USA
Posts: 73,167
|
Quote:
You can go more basic and use a Pitot tube, but that gives a more pin-point flow measurement. Of couse any of the FI systems of the past 25 years are already sensing the flow, and outputing a useable signal. . .but what are you needing it for? |
||
|
02-05-2002, 06:42 PM
|
|
|
Registered
Join Date: Nov 1999
Location: Montreal, Canada
Posts: 728
|
I figured there would be an easy way to calculate the VE of an engine with a simple formula using inputs such as displacement, bore stroke, rpm, cam timing, hp curves, etc. I want to know the 3.2 VE because I want to calculate the airflow rate of my engine to size my turbo's compressor with a more efficient than I am currently using. I don't want to rely on my turbo supplier's recommendation anymore.
Thanks! Mike 86 Carrera t |
||
|
02-05-2002, 09:38 PM
|
|
|
|
Information Junky
Join Date: Mar 2001
Location: an island, upper left coast, USA
Posts: 73,167
|
No doubt Porsche has these numbers for mapping chips, among other reasons. Getting these curves/ data would be a good way to go. Where to get them, I don't know. . . .but Roland likely does.
|
||
|
02-05-2002, 09:48 PM
|
|
|
Registered
Join Date: May 2000
Location: Los Alamos, NM, USA
Posts: 6,044
|
Mike, I believe if you have hp vs. rpm curves (along with the air temperature, atmospheric pressure and humidity during the tests) for your engine configuration (camshaft, intake, exhaust, etc.), along with "actual" displacement, compression ratio, and some idea of the "non-pumping" mechanical and aerodynamic losses (bearing friction, valve train losses, crank windage, etc.) you can calculate volumetric efficiency. It been a long time since I ran one of these tests but I believe one can obtain all of this information from a proper dynometer run. The engine has to be up to temperature and there's a procedure to sort out and determine the various losses by motoring the engine with the dynometer and disabling cylinders one at a time, etc. If you can obtain the hp vs. rpm curves you could make assumptions for some of these other variables with the mechanical and aerodynamic losses being the most uncertain as these will vary significanrtly and in a non-linear fashion with engine speed. If you do a web search I believe the formulae to calculate volumetric efficiency may be found. I don't have them handy as my son has made off with my IC engine text. Jim
|
||
|
02-06-2002, 07:21 AM
|
|
|
Registered
Join Date: Oct 2001
Location: Redondo Beach, CA, USA
Posts: 78
|
Volumetric Eff.
The fromula you are looking for is
VE = Volume of charge taken in the cylinder / Volume of the cylinder This is per cylinder. The only way to have a volume metric efficiency higher than 100% is by boosted |
||
|
02-06-2002, 07:32 AM
|
|
