[DeTomaso] Stock fan output vs. Flex-a-lite

[zumzum at cox.net]

I have been watching your mails about fans and felt that I can help. Regarding the statement from some SEMA salesperson about whether a fan is pushing cool air or it sucking hot air is just pure hot air.  And when a car runs hot at high speeds the fan IS NOT the cause.  Water flow, exhaust pressure or stagnant fin outflow will be the cause.The purpose of the fan is to move air from the fins. A puller fan is more efficient for these reasons: a puller fan lowers the air pressure within the fins which allows air to move easier, a puller fan does not impede air flow into fins in other words a pusher fan offers radiator fin area blockage to air flow which disturbs air from going through the fins on a laminar flow level,  a pusher fan raises the air pressure within the fin cavity which causes stagnant air which is low % and last a pusher fan will blow air in a swirl pattern which then must be realigned to go through the fins whereas a puller fan pulls air through the fins then that air is a wasted swirl into the engine bay area.  With high speeds the fan plays a very small roll in keeping the temps low, if any. As you know a fan may blow air at 30+- mph so at 125+ the electric fan is Nothing but an air blockage device. Moving air in and out of the fins is the issue. What the trap doors do is to remove this static air and resume proper flow.  Good idea. Now on air flow, aircraft designers many years ago found out that the best cooling for an engine was to have the air intake area to be 1/4 the area of the fin area. What this does is to slow down the air so it will spend more time removing hot fin temp on a laminar level instead of creating boundary and laminar flow separation which then would just coat the fins with non moving static air. If one of my mechanics were to put on a pusher fan I would have him change it instantly and then explain so he would learn. My wife's car which she uses daily in her sales job from industry site to site is a 98 E430 and we live in Louisiana which is hot. Three years ago I did major conversions on the condenser set up. The OEM condenser was 24" H x30"W, which I change to 8" H x24" W.  This allowed me to remove the 2 Benz aux fans which would straighten the air flow to the radiator. I then placed two 12x12" condensers in the leading edge of fender wells behind the frontal valence panels and attached two 12" electric fans wired to the OEM a/ac temp pressure switch. Now these condensers blow hot air into the low pressure fender area and which at high speeds is sucked out by the venturi effect of high air speed flowing over the fender leading lip. Then I removed the original mechanical 19"  fan and placed in a 16" electric puller fan in front of the water pump pulley. This is a 4300 pound car with 8 nitrous injectors, 4 solenoids, the a/ac compressor is always on when engine runs, 25 pound nitrous task, lowered 43mm, euro ECU, 33 gallon fuel tank with Boeing foam, 300 pounds of sound deadening sponge rubber neoprene and heat insulating extruded silica 1" mats, ceramic coated exhaust manifolds and header pipes. So what I am trying to point out is here is a heavy and fast car in a hot state having only one fan on the radiator and two fans on 2 of the 3 condensers. My result was a car that; runs much cooler at all speeds even up to 163 in 4rth gear of the 5 speeds without nitrous, will spin its right rear tire when shifting into 4rth at 108mph in the automatic mod, a/ac is NEVER off which gives great dehumidification, engine runs much cooler, never overheats even when she got caught for 9 hours in the Katrina traffic, is quiet due to putting fans in fenders and last the car is more stable at very high speeds due to less air flow pressure zone mess at grill intake. Air can now flow through the grill, do its job and get out. And the a/ac is ice cold! Moral of this story is to use only puller fans and  have your air flow move in and out. If the rest of your machine is up to spec then you will have no overheat problems. Now there are unusual cases where Water Wetter, duct sealing, additional exit air vent holes, ceramic coatings, air dams and or splitters will help. But this thread was about fans. Hope I helped, Jeff Cobb, 67+69 Ghiblis, 69 Bordinat Mangusta, 71 Espada, 73 Bora and others