Any race guys ever run a 3 or 4 inch hose mounted off the front air dam or attached near the outside mirror thru the rear fire wall and directed onto the fan? Does it add any cooling effect? Any pics of setups?

GB

I have... one of my many attempts to cool my engine enough.

I ran 2-3" hoses from my turn signal openings. Each of them went to my fan inlet. It helped, but wasn't enough. I moved to a 6" duct early last year.

It all depends on what you're doing with the car. There's a old thread here somewhere.... let me look for it.


Here it is....
3" Ducts

Some quick calculations:
Fan is rated for 1700cfm if I recall correctly. Maybe you want to shoot for 1/2 of this number as it won't be realistic or necessary to supply the entire volume of air at max fan rating.

So you want to supply ~900cfm. This means that the air would have to travel at over 200mph through a 3" duct to supply this kind of air. Not going to even get remotely close to that.

4" duct would be about 120mph of air. No dice.

But use a 6" duct, and that number drops to about 55mph. Seems fairly realistic. Might get this kind of volume if the car travels at ~80mph (depending on lots of factors).

So you can see that it makes sense that a number of racers use a 6" dia 'sewer pipe' to supply the engine cooling air to the fan. Get too much smaller than that and it won't be real effective.

AJRS once told me that he finally solved heating problems that he had been chasing for years..

when he installed a roughly 6-8inch square duct. His came from a naca duct on the roof and then a clear lexa/plastic square duct through the cockpit and through the lexan rear window.. where it dumped onto a flat central electric style fan.

(Think about the the roof ducting done on the porsche GT1, ralley cars, mcclaren, and other exotics)

he runs all of his hot 4's without the metal front cooling shroud and without the front blower wheel, or front alternator.

His installation of adequate cooling opened up all kinds of HP and longevity options for his -4's

brant

So Demick, for a race car situation, why not just bolt on one of these powerful electric fans and get rid of the mechanical fan altogether?

http://store.summitracing.com/egnsearch.as...k=KeywordSearch

You could, but those axial type fans do not move enough air. Sure, it says 2800cfm or whatever, but that is under no load (free air). They don't move nearly as much when you put resistance in it's way. For airflow against a large resistance, you can't do better than an impeller (which is what the original fan is).

Besides, what is being accomplished with the 'sewer pipe' is getting fresh, cool air to the motor. Volume isn't so much of an issue as getting cooler air. In a stock configuration, the air entering the fan is preheated by 20 to 30 degrees (F) if I recall correctly.

OK.. and the impeller fan probably moves a lot more air depending upon the RPM, right? So it is 1700 cfm at ?RPM, but much more at say 5-6K

As Kevin noted the 3 inch ducts are way too small, with 2 of them only providing 14.13 square inches of cross section area for the air to move down. A SINGLE 6 inch duct provides 28.26 square inches of area so there is way less resistance to the flow into the engine. My racing mentor who used to race 914s back in the early 70's showed me picts of the large single 6 inch duct running right through the firewall into the front of the engine. It was the smooth heating duct type of metal tube. The front mounted fan had only FOUR blades so as long as the car was going fast it was cool. Yellow flag laps were very bad and could actually cook the engine, but then again it only had to last a single race weekend! I think the past post showed the ducts on Frank Beck's car and also the old Wayne Baker #22 IMSA car if I remember right?

From the factory manual: fan delivery volume ~800L/sec @ 4600rpm. This corresponds to about 1700 CFM.

That is probably the peak performance, as I have heard that the fan cavitates at higher RPM's and therefore delivers less air. So a race motor that regularly spins above 5K RPM really wants some fan modifications to make it perform better at those RPM ranges.

Demick

Pull the fan off and mount one of these pointed into the cooling ducts. Good for 800 CFM

http://www.electricsupercharger.com/

The pictures John referrs to at in my Blog.

http://www.914world.com/bbs2/index.php?aut...blogid=230&

Gord, look at my post in the garage forum that shows pics of Kevin Groot's RAT modified cooling fan..

When the fan is spun over 5K RPM constantly it's effectiveness is drastically reduced, no matter how you shove air into it..

Here is a partial view of Frank Beck's setup

Click to view attachment

Here is another solution that John Rogers posted in another thread

Click to view attachment

Simply put, the mechanical fan takes less crank horsepower. If you figure 80% conversion factors, then the alternator & electric fan arrangement is only 64% as effective as a mechanical fan on the end of the crankshaft.

Probably the most efficient method, with all of the %'s aside is to use fans such as in pict #2 above which is the #22 Wayne Baker car and then use an alternator, specially wound, so it will freewheel until over 4K RPM and then put out the 12 volts needed. There is no fan on the engine and the air ducts blow directly on the cylinders and heads. This setup is terrible for auto-x but GREAT for road racing. When Ron Mistak would bring #22 to the stadium in San Diego, his crew would always have a jumper batt on a cart handy since it would nearly always need jump starts.

There is a third fan on the 22 car located to the rear of the motor and dumping air to the two rear cylinders. Mugs914 works on the car and said there is never a heating problem on the track. Car also has a big oil cooler mounted in the location of the fresh air vent opening in front of the windsheild.

Hell of a car. 2.0L with BMW mechanical fuel injection.