There's got to be a number on that somewhere. I know that there are a few different fans but what I was thinking about is how many CFM do they move. I was just thinking about the air flow out of the back of a car. If the air exiting from the engine is so high that I can't remove it from the car that I will need to move it out through some sort of diffuser. I would like to have no air build up under the rear of the car. Speaking of exhaust I have no idea what I'm going to do for it. And all of this still will need a diffuser. The fans in the oil cooler move 3200 CFM, I am just hoping that that would be enough.

IIRC, the early ones do 1500 liters/sec (not min). That's near redline though.

Thanks Mark, now I have to do some math.

According to google 1500 liters per second is
3178.32 cubic feet per minute

Nice as I mentioned earlier I have 3200 CFM of fans taking air out of the engine bay. That balanced nicely.

Those oil cooler fans are not moving 3200cfm when mounted on a cooler. Most aftermarket fans flow fans in open air, put a restriction on them and flow will plummet.

The problem with the 911 fan is airflow to the areas that need it. There has been plenty of information about putting that fan on a T4 and the issues associated with it. Also look on the Shoptalk Forum.

https://www.spalautomotive.it/axial-fans

The 1500 l/sec matches what I've read.

Are you looking to evacuate the spent cooling air from the engine area? Usually the air just needs a place to go - it doesn't necessarily need help getting out, unless you've closed off the underside of the engine bay or something.

Thanks Bert. Hey Scott, I'm just looking to evacuate the engine air. I just ordered enough aluminum to flat bottom the car back to the engine bay. I don't know where I'm going after that. But that is just like everything else in the car. I have no idea what I'm doing. I'm just winging it. But that should get me to the diffuser. The only thing I can be certain of is I will have to do something with the exhaust. Right now I am working on the exhaust fan housing. Scribing it to the trunk.

Click to view attachment

Cool. Putting a diffuser on a 914 is some WORK. But I enjoyed it. First I had to make a custom exhaust (regular 914 headers are right where you want to put a diffuser), and I had to make a custom shift rod to get it out of the way too. Making the diffuser was a bit of an exercise.

Speaking about evacuating the spent engine cooling air ... a diffuser / flat bottom does block the spent cooling air existing the bottom of the engine. I saw oil temps go up 20 degrees after I put on the diffuser (which included a flat bottom that extended under the engine bay). And the engine bay was getting hot as hell. I wound up making some engine tin to direct the air out the sides and put louvers in the side of the rear fenders. Made things better.

I don't know the fan rpm, but I do know the 914 had rubber body flappers on the bottom of the body before the engine compartment so that the engine air had a flow path that wasn't competing with the under car air.

I think they were added in 73', my 74 has them but my 72' does not.

Thanks guys, at this time I have only ordered enough material to take the flat bottom to the front of the engine bay because I don't have any idea of what to do from there back. I think I have the engine air handled.
Well I've got too many things going on right now and I can just let all of these thoughts meld. Like the jack points are going away. What is there that I don't want to cover. I like the noise level of the stock pipe but it's in the way big time.
I ordered some more stuff for the oil cooler today so that should be happening in a day or two.
On a side note, I am really enjoying the new welder.

Joe,

I think they have updated the photo gallery at Patrick motorsports...

this is Jim's old race car
I believe the old photo's had a full belly pan

but some of these pictures now show open also

still some of the photo's show the belly pan... (maybe this was the older set up and they revised it?)

PMS

Gosh Brant, I got a smile from ear to ear and I only cruised thru the pictures. Now I have to go back and read the hole article. Now I have a good idea about separating the engine air from the air flow under the car.

That car and set up would not have (or not for long) used a full diffuser under the engine. The two aluminum diffusers PMS built create a low pressure zone directly under the engine allowing the air to tumble down and behind the car.

This set-up is interesting but i do not see functional value of enclosing the lower trunk area - they created a hot-spot that wouldn't fully expel the heat. Those large aluminum units obviously replace the rubber diffusers that Porsche later added.

It is always impressive to see PMS workmanship - even if it always doesn't make complete sense.

PS: I thought this discussion was about the engine fan...?

Cracker

Thanks Tony, it is about the fan and I learned that it flows about 3200 FPM which is about what my fans put out. I'm thinking that the car will be run for 1 minute and sit for twenty so the oil will never get hot and the rake in the car should provide a low pressure area under the back of the car which is what I was looking for.
Really just giving me something to do. Much better than staring at the tube.

It would be interesting to see how the rear section of that PMS pan mates to the underside of the engine. guiding the air flow away from the bottom of the cylinders and preventing the airflow from being trapped in the rear section of the under pan would be essential in making this whole package work effectively.

It is sometimes overlooked that cooling airflow that flows through the car creates as much drag as the air that flows around the car ( of course relative to the volume of the flow). That is why so much engineering is put into the design of cooling air exits in race planes and high end race cars like F1. Guiding that cooling air out and returning it smoothly to the surrounding airflow can produce significant reductions in drag and improvements in cooling

Here's one of the "flat bottom" PMS cars from 20 years ago. Unfortunately I don't think I shot the engine compartment at all.