engine air consumption (CFM's)

does anybody know how many CFM's of air that our 4.0's use at idle? ar redline? 2k? 3k? 4k?
cuz ive got an idea for the electric fan forced induction..... the cheap ass ones on ebay say they boost power with 150 CFM's.... but after feeling the ammount of air comming through the exhause at idle i thought it was like 80CFM.. but i dont know at 3k i definately think the electric inducation would only be a blockage in the intake... basically i want to know the CFM's cuz i can get an electric fan that'l push 260 CFM.... so ya. . . ne1?

since the 4.0 pushes (in a static world) 2 liters per revolution
add 50% for thermal expansion etc.
3 liters equals about .1 cubic foot
that being said
2000 rpm ~ 200 cfm
3000 rpm ~ 300 cfm
and so on

Yeah, but boost is every bit as much a function of pressure as it is of volume, and you won't find a ducted electric fan that will give you enough pressure while using power efficiently - which is why superchargers are belt-driven, and turbochargers are exhaust-driven. The amount of power that would be needed is more than practical. Also, "squirrel cage" fans can cause a restriction in the airstream when they are not running, while "roots" blowers can "windmill" while idling, and the restriction from that is negligible.

If you are serious about supercharging, you are better off using a real supercharger. A turbo is also an option, but not my favourite.

Got any other ideas you want to play with?

5-90

well im not looking for any major boost in power.... but ya any little bit would be nice ..... this is the fan im thinking about putting in
http://www.frozencpu.com/cgi-bin/frozencpu/fan-88.html

comments? suggestions?

Don't bother. You won't get anything useful out of that.

You might want to look up Dino "Dr. Dyno" Savva's homepage (the link is all around here) and see a batch of his homebrew mods - you can pick up some power with a little work. Most mods do not require major invasion of the engine, and there are some parts swaps that can do well for you. Also, the Adjustable MAP sensor sounds useful - tuning the air-fuel ratio a little finer is usually a good thing anyhow.

The problem with most fans is there is nothing to maintain the pressure you might get - if you look at the design of a real supercharger - especially a roots blower - you will note that it is not so much a fan as an air pump, and it forces air forward by not allowing a return path. Most fans you will see (even the squirrel cage versions) will allow backflow, so you won't maintain the needed pressure gradient you need for forced induction.

So, you should focus on making what you have more efficient. Dino has found useful ways to do just that for low bucks.

5-90

Those who are considering installing an electric "supercharger" or "turbocharger" should read this article:

http://www.autospeed.com/cms/A_0237/article.html?popularArticle

Those devices are nothing more than a huge waste of money.

aha.... i c so ya even if i get it on there there wont be any boost. . . kool thats off of my mod list then. . . save myself $30...

thanks

witt said:

does anybody know how many CFM's of air that our 4.0's use at idle? ar redline? 2k? 3k? 4k?
cuz ive got an idea for the electric fan forced induction..... the cheap ass ones on ebay say they boost power with 150 CFM's.... but after feeling the ammount of air comming through the exhause at idle i thought it was like 80CFM.. but i dont know at 3k i definately think the electric inducation would only be a blockage in the intake... basically i want to know the CFM's cuz i can get an electric fan that'l push 260 CFM.... so ya. . . ne1?

Click to expand...

The CFM is found with an equation:

CFM = CID x RPM x VE ÷ 3456

Typical VE factors are in the low 0.8 range for an aspirated 4.0L.

The 4.0L is 242 CID. This results in 182 CFM with a 0.82 VE at 4000 RPM.

Work the equation for various RPM's and you can get an answer.

The goal of any supercharger is to increase the VE (better than 1.0 if possible). This requires something that can pressurize the intake enough to overcome all friction losses (5-7 psi). Uncompressed airflow is easy, but when you try to channel air through something like an engine it takes considerable pressure to overcome the restrictions.

Considering that a typical DWDI blower (squirrel cage fan) only develops 4 inches of water gage pressure, and it takes 28" WG to equal one psi, you find the electric blower undergunned by a factor of at least 35 (140"WG required for 5 psi).

I do understand a company has built an electrically driven roots blower, good for 5-7 psi for ~15 seconds, before discharging a bank of industrial batteries, but I doubt it's what you found on e-bay (and I have yet to read how they match the fuel with the increased airflow).

Did this help you learn anything?

Ed A. Stevens said:

Did this help you learn anything?

Click to expand...

I've certainly learned a few things over the years but one thing always sticks in the mind. Anyone can post bullshit on the Internet; it's making it sound believable that separates the winners from the losers.

Excellent explaination Ed. As far as using a "squirrel cage" blower for a supercharger....P.T. Barnum's rules come into play... A. " Give Em what they want".... B. "There is a sucker born every minute"....

Some good info (and some soap-opera BS) on the gizmo Ed refers to here:

http://www.pirate4x4.com/forum/showthread.php?s=&threadid=211952

Additional fuel is added by a supplimental injector.

I don't think this device is worthwhile for the 'typical' Jeeper, but that's JMHO.

I know that the bilge pump fan set-ups on e-bay are BS, but what about this one?

http://www.electricsupercharger.com

Its listed as 750 cfm at 1 psi drawing ~50 amps. Looks like it could actually work. Has any one ever seen/used/heard about them? Dr Dyno what do you think?

I'm not impressed with it. An extra 750cfm of airflow will only add about 5hp so I'd rather spend my $300 elsewhere. You'd probably get the same result from adding a homebrew intake.