Super CFM Air Compressor Idea
Elder User
Joined: Sep 2004
Posts: 941
Likes: 4
Start with the formula
HP = Torque * RPM / 5252
So RPM = 5252 * HP / Torque
The torque required to ovecome ring and bearing friction and spin a V8 engine is around 30 foot pounds. Or so say the engine buildup articles in the Hot Rod magazines. You can measure this on your engine of choice by using a torque wrench. This doesn't include doing anything useful, like compressing air, just to turn it at all.
So our 5HP motor could, in theory, and if the gearing was right, spin a V8 engine against friction only at around 875 RPM. It could not compress ANY air at that speed. You'd have to leave the sparkplugs out to avoid pumping losses or you won't hit that speed. And this number is probably optimistic.
On the other hand, fixnair's number seems excessively pessimistic. Frederic's quote of electric starters being rated at 1.5 HP or so sounds about right to me. And the starter manages to spin the engine at more than 100 RPM, just from my own observations.
But you still ain't gonna get 100 cfm out of this thing...
HP = Torque * RPM / 5252
So RPM = 5252 * HP / Torque
The torque required to ovecome ring and bearing friction and spin a V8 engine is around 30 foot pounds. Or so say the engine buildup articles in the Hot Rod magazines. You can measure this on your engine of choice by using a torque wrench. This doesn't include doing anything useful, like compressing air, just to turn it at all.
So our 5HP motor could, in theory, and if the gearing was right, spin a V8 engine against friction only at around 875 RPM. It could not compress ANY air at that speed. You'd have to leave the sparkplugs out to avoid pumping losses or you won't hit that speed. And this number is probably optimistic.
On the other hand, fixnair's number seems excessively pessimistic. Frederic's quote of electric starters being rated at 1.5 HP or so sounds about right to me. And the starter manages to spin the engine at more than 100 RPM, just from my own observations.
But you still ain't gonna get 100 cfm out of this thing...
Posting Legend
Joined: Sep 2001
Posts: 30,255
Likes: 37
Originally Posted by fefarms
-snip- The torque required to overcome ring and bearing friction and spin a V8 engine is around 30 foot pounds. Or so say the engine buildup articles in the Hot Rod magazines. You can measure this on your engine of choice by using a torque wrench. This doesn't include doing anything useful, like compressing air, just to turn it at all. -snip-
The piston friction will increase with loading also.
Posting Guru
Joined: Sep 2004
Posts: 1,616
Likes: 3
From: Sapulpa OK
My figures may be pessimistic, yes. But I have had experience working on a Schramm air compressor that was a 235 chevy 6 cylinder driven by a 40 HP electric motor at 1100 RPM and pumping 120 PSIG. I am only guessing at the HP required to spin the V8. This is a fun excersize though.
Postmaster
Joined: Jul 2003
Posts: 2,628
Likes: 0
From: Calgary, Canada
What kind of compressor do you have at the moment? Have a look at some of the specs on this page
I think you'd be better served by getting 2 more 40-50 gallon tanks connected together by a large pipe or hose and running a single output through a high pressure regulator to drop the pressure to what your tools need and run 5/8" lines throughout the system after the regulator.
We used to use what we called a 'spindle' which, when turned on, was just like opening up a 5/8" line to the atmosphere. Believe me, there is no substitute for VOLUME at high pressure when you're using a lot of CFMs. We had two of those 7.5HP units and if we used the spindle for any length of time, ithe compressors would both run for about 5 minutes after the spindle was shut off and the roughly 50 CFM that the two compressors put out was just barely enough to keep the spindle running... If someone happened to start sandblasting at the same time the spindle was running, forgetaboutit.
I guess the final answer will depend on how much pressure you and your friends really need at how many constant CFM and for how long. Figure that out and you'll be able to figure out how many tanks you need and how many CFM you need a compressor to deliver.
I think you'd be better served by getting 2 more 40-50 gallon tanks connected together by a large pipe or hose and running a single output through a high pressure regulator to drop the pressure to what your tools need and run 5/8" lines throughout the system after the regulator.
We used to use what we called a 'spindle' which, when turned on, was just like opening up a 5/8" line to the atmosphere. Believe me, there is no substitute for VOLUME at high pressure when you're using a lot of CFMs. We had two of those 7.5HP units and if we used the spindle for any length of time, ithe compressors would both run for about 5 minutes after the spindle was shut off and the roughly 50 CFM that the two compressors put out was just barely enough to keep the spindle running... If someone happened to start sandblasting at the same time the spindle was running, forgetaboutit.
I guess the final answer will depend on how much pressure you and your friends really need at how many constant CFM and for how long. Figure that out and you'll be able to figure out how many tanks you need and how many CFM you need a compressor to deliver.
Last edited by furball69; Aug 25, 2006 at 12:35 PM.
Freshman User
Joined: Feb 2006
Posts: 49
Likes: 0
fefarms, A friend of mine used to have one of the gadgets you mention. You screwed it in place of a sparkplug.
However, it just used the compression pressure to work a diaphram that sucked outside air in and put it out the hose. The air fron the engne never got out of the engine, so it was pumping clean air.
What a "skip" like that would do to a modern engine I hate to think.
Of course, with a new enough one with electronic valves you could turn off the valves and injector for that one and make it work
J
However, it just used the compression pressure to work a diaphram that sucked outside air in and put it out the hose. The air fron the engne never got out of the engine, so it was pumping clean air.
What a "skip" like that would do to a modern engine I hate to think.
Of course, with a new enough one with electronic valves you could turn off the valves and injector for that one and make it work
J
Fleet Owner
Joined: Sep 2005
Posts: 28,609
Likes: 18
From: Lake Tahoe, Nevada
[QUOTE=fefarms
"Invention starts with R&D?"
Sure. But we might as well read some books, and stand on the shoulders of Newcomen and Watt and Newton and Maxwell rather than re-discover what people learned 300 years ago.[/QUOTE]
I've discovered that all my best ideas have been stolen by the ancients!!!
"Invention starts with R&D?"
Sure. But we might as well read some books, and stand on the shoulders of Newcomen and Watt and Newton and Maxwell rather than re-discover what people learned 300 years ago.[/QUOTE]
I've discovered that all my best ideas have been stolen by the ancients!!!
Thread
Thread Starter
Forum
Replies
Last Post
Lee Binder
Aerostar
6
Jun 26, 2020 04:05 PM
mnewbolds
1968-Present E-Series Van/Cutaway/Chassis
9
Mar 12, 2016 10:59 AM
rockittsled
1973 - 1979 F-100 & Larger F-Series Trucks
8
May 11, 2014 10:31 AM
