Go Back   The Ford Barn > General Discussion > Model A (1928-31)

Sponsored Links (Register now to hide all advertisements)

Reply
 
Thread Tools Display Modes
Old 04-14-2021, 08:29 AM   #1
Bob Bidonde
Senior Member
 
Bob Bidonde's Avatar
 
Join Date: May 2010
Location: Long Island, NY
Posts: 3,429
Default Volumetric Efficiency

Up to now, I have been using a 50% Volumetric Efficiency in my calculations for the Models "A" & "B" engines. I suspect it is actually lower. For those who are wondering what volumetric efficiency is, a 100% would mean that each cylinder would intake 50 cubic inches of fuel (fuel intake = 100% of displacement).

What volumetric efficiency do you engineering & inventive types use? I am guessing I should use 40%????
__________________
Bob Bidonde
Bob Bidonde is offline   Reply With Quote
Old 04-14-2021, 09:59 AM   #2
Oldgearz
Senior Member
 
Join Date: Aug 2020
Location: Sagle, Idaho
Posts: 359
Default Re: Volumetric Efficiency

I just add gas and drive.
Oldgearz is offline   Reply With Quote
Sponsored Links (Register now to hide all advertisements)
Old 04-14-2021, 11:44 AM   #3
Jim Brierley
Senior Member
 
Join Date: Jun 2010
Location: Temecula, CA
Posts: 4,066
Default Re: Volumetric Efficiency

Most of us aren't that technical!
Jim Brierley is offline   Reply With Quote
Old 04-14-2021, 01:55 PM   #4
alexiskai
Senior Member
 
alexiskai's Avatar
 
Join Date: Apr 2018
Location: Mebane NC
Posts: 2,329
Default Re: Volumetric Efficiency

Bob, in 2018 you used 50% to calculate a max CFM of 100. BZR's flow tests a year later clocked an A block with a Weber carb at 84.9 CFM @ 2500 rpm, which would give VE of roughly 55. So possibly your original estimate was good?
alexiskai is offline   Reply With Quote
Old 04-14-2021, 01:58 PM   #5
McMimmcs
Senior Member
 
McMimmcs's Avatar
 
Join Date: Sep 2019
Location: Fort Gratiot, Michigan
Posts: 2,296
Default Re: Volumetric Efficiency

Quote:
Originally Posted by Jim Brierley View Post
Most of us aren't that technical!
very, very true Jim. Most of us just want to enjoy our Model A.
McMimmcs is offline   Reply With Quote
Old 04-15-2021, 01:19 PM   #6
johnneilson
Senior Member
 
Join Date: Jun 2010
Location: 34.22 N 118.36 W
Posts: 1,043
Default Re: Volumetric Efficiency

Sponsored Links (Register now to hide all advertisements)
Bob,

I am not sure that the terms "volumetric efficiency" and Model "A" should be used in the same paragraph, let alone the same sentence.

As I am sure, there are many critical factors in the design of an engine, CR alone does not make an efficient engine.

In my opinion, the basic intake port arrangement and crank layout makes it less efficient. And this is just one small aspect.

The stk "A" is rated at ~40HP, or .20 HP per Cu Inch displacement.
With some massaging, it can easily be raised to .50 HP/CID.

Most changes made have a point of diminishing returns, after CR, intake and Cam.

Enjoy and experiment, that is almost as much fun as driving them, John
__________________
As Carroll Smith wrote; All Failures are Human in Origin.
johnneilson is offline   Reply With Quote
Old 04-15-2021, 04:53 PM   #7
BRENT in 10-uh-C
Senior Member
 
BRENT in 10-uh-C's Avatar
 
Join Date: May 2010
Location: Eastern Tennessee
Posts: 11,484
Default Re: Volumetric Efficiency

Bob, ...yes some of us do care about VE, and we strive to increase the efficiency. Much akin that like some folks have studied Ohms laws and learned how electricity works and how to make it more efficient. Others just flip a switch and expect it to work without feeling the need to understand it. That is OK to be either way.

Just remember that your comment about 50 cubic foot at 50% VE gets skewed when fuel is added and elevation is factored in. The air pressure is about 14.76 at sea level, however the amount of air to fuel mixture affects things too. Optimum fuel mixture for economy will be around 15.5 parts of air to 1 part of fuel however to make the most power at sea-level, you need to be around 12½ to 1 ratio. Part of the other issue is the shrouded valves and small bowl sizes at come with 1.500" intake valve. These are all great restrictors which cuts VE. With higher compression heads, the roof of the chamber is often lowered which shrouds the path of the flow and generally hinders the cylinder being filled efficiently. That is why too much compression (-typically above 10:1 CR) does not make as much power as say 8:1 CR in an L-head engine.

Bill Stipe and I have discussed this at length before, and I feel pretty comfortable with free flowing port work, and a good chamber roof design, you should see in the 65%-70% VE range. Bill would be a good one to discuss this with further.
__________________
.

BRENT in 10-uh-C
.
www.model-a-ford.com
...(...Finally Updated!! )

.
BRENT in 10-uh-C is offline   Reply With Quote
Old 04-17-2021, 09:04 AM   #8
Bob Bidonde
Senior Member
 
Bob Bidonde's Avatar
 
Join Date: May 2010
Location: Long Island, NY
Posts: 3,429
Default Re: Volumetric Efficiency

Why is it that there are always nay-Sayers who dislike a post and they just have to voice their negative opinions????? This is America. If you do not like the topic of my post, don't open it.
Being an engineer, my love of the Model "A" is in its engineering as well as its other aspects. If you don't like its engineering aspects, do not bother to open my posts.
Thank you to those who stayed on topic.
__________________
Bob Bidonde
Bob Bidonde is offline   Reply With Quote
Old 04-17-2021, 09:22 AM   #9
Woodys29
Member
 
Join Date: Dec 2017
Posts: 33
Default Re: Volumetric Efficiency

Bob and Brent I enjoy both of your posts and understand what you are talking about. I am a lifelong model A lover (65 years) so keep up the good work.
Woodys29 is offline   Reply With Quote
Old 04-18-2021, 09:15 AM   #10
nkaminar
Senior Member
 
nkaminar's Avatar
 
Join Date: Jan 2012
Location: Western North Carolina
Posts: 3,812
Default Re: Volumetric Efficiency

The volumetric efficiency has to vary by rpm. At low rpm the air/fuel has a longer time to enter the cylinders. At higher rpm the valve configuration will limit how much air/fuel gets in, assuming a larger carburetor and intake manifold than stock. The overhead conversions are meant to fix this.

As an old automotive engineer, this stuff is interesting to me. I have learned that not all persons think the same way I do. I am married to one. She has no idea what a piston is and doen't care.
__________________
A is for apple, green as the sky.
Step on the gas, for tomorrow I die.
Forget the brakes, they really don't work.
The clutch always sticks, and starts with a jerk.
My car grows red hair, and flies through the air.
Driving's a blast, a blast from the past.
nkaminar is offline   Reply With Quote
Old 04-18-2021, 09:42 AM   #11
Jack Shaft
BANNED
 
Join Date: Dec 2019
Posts: 1,196
Default Re: Volumetric Efficiency

Quote:
Originally Posted by Jim Brierley View Post
Most of us aren't that technical!
The 'seat of the pants' dyno/volumetric efficiency calculator works for me..it uses asphalt and has painted stripes on it.
Jack Shaft is offline   Reply With Quote
Old 04-21-2021, 09:01 AM   #12
KGBnut
Senior Member
 
KGBnut's Avatar
 
Join Date: Jul 2011
Location: Southwestern Connecticut
Posts: 931
Default Re: Volumetric Efficiency

Also, not an engineer...but curious.

Does a VE below 100% suggest that something in the intake is constricting airflow? Does that mean that when the intake valve closes when the piston is at the bottom, that the air pressure in the cylinder is lower than the current barometric pressure outside?

Ken
__________________
Style beats speed any day, and with a lot fewer tickets.
KGBnut is offline   Reply With Quote
Old 04-21-2021, 09:28 AM   #13
MikeK
Senior Member
 
MikeK's Avatar
 
Join Date: May 2010
Location: Windy City
Posts: 2,919
Default Re: Volumetric Efficiency

Excellent question and of course the one-star bandit tagged it immediately for it's validity.

The VE becomes a valid quantitative data tool if you are working with a properly calibrated flow bench or possibly with some over-the-top dynamic flow modeling software. Sans that, if you are looking backwards to calc it from existing dyno data it becomes clouded with outside indeterminate variables.

I'll add nothing further. Nothing says progress like watching a forum dumb down with bad post ratings and off topic replies...
MikeK is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Sponsored Links (Register now to hide all advertisements)


All times are GMT -5. The time now is 03:45 AM.