Volumetric Efficiency? How to determine?
Thread Starter
Safety Car
Joined: Jan 2001
Posts: 3,569
Likes: 1
From: Hawaii
Volumetric Efficiency? How to determine?
I was looking at the Holley web site and it had this formula
Cubic Inches * MAX RPM / 3456 * Volumetric Efficiency= CFM Carb size needed
It also said that most engines are in the 80 to 85 percent range, but race engines can get up to 95 or higher.
How does one determine what size you really need?
427 * 6000 / 3456 * 1 = 741 or
427 * 6000 / 3456 *.8 = 593
427 * 4000 / 3456 *.9 = 444
So between 600 on the low end and only 750 on the high? I had a poorly built (by me) Holley 750 and the car ran like junk, I just put on a new (free)570 street avenger and it runs 10x better. For just regular driving, under 4000rpm this should be plenty big eh?
Cubic Inches * MAX RPM / 3456 * Volumetric Efficiency= CFM Carb size needed
It also said that most engines are in the 80 to 85 percent range, but race engines can get up to 95 or higher.
How does one determine what size you really need?
427 * 6000 / 3456 * 1 = 741 or
427 * 6000 / 3456 *.8 = 593
427 * 4000 / 3456 *.9 = 444
So between 600 on the low end and only 750 on the high? I had a poorly built (by me) Holley 750 and the car ran like junk, I just put on a new (free)570 street avenger and it runs 10x better. For just regular driving, under 4000rpm this should be plenty big eh?
Melting Slicks
Joined: Dec 2001
Posts: 2,321
Likes: 0
From: Reno NV
St. Jude Donor '08
Re: Volumetric Efficiency? How to determine? (Maurice)
This explains it really well....im gonna check out the engine analyzer thing on the page right now.
http://www.auto-ware.com/combust_bytes/eng_sci.htm
http://www.auto-ware.com/combust_bytes/eng_sci.htm
Drifting
Joined: Oct 2000
Posts: 1,825
Likes: 56
From: Shawano WI
Re: Volumetric Efficiency? How to determine? (Maurice)
dd2003 will show you volumetric efficency but it is a bit optimistic. Nothing short of running a motor on a dyno with an air sensor will give you an exact number. My dyno experience show that 80 to 85% on a street drivable motor would be about right.
