Rad. fans and air flow

Dean Lampe · 02-19-08, 10:29 PM

On a GT 40 the air needs to flow through the radiator and out, up over the windshield. My question is about the fans. Do they block a lot of air? This air flow creates some down force on the car and I would like to keep this area clear but I might need the fans at low speed around town. Should I make the whole fan assembly a quick disconnect or am I over thinking it?
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Sorry Chuck for using your picture!

Jac Mac · 02-19-08, 11:19 PM

Quote:

Originally Posted by Dlampe

On a GT 40 the air needs to flow through the radiator and out, up over the windshield. My question is about the fans. Do they block a lot of air? This air flow creates some down force on the car and I would like to keep this area clear but I might need the fans at low speed around town. Should I make the whole fan assembly a quick disconnect or am I over thinking it?
Attachment 27458

Sorry Chuck for using your picture!

I would say your thinking too hard Deane, spend some time blocking off those exits into the wheel arch if you have not done so already and/or seal the radiator core size to the nostril. Then do something about preventing air from getting under the car.

Russ Noble · 02-19-08, 11:19 PM

The answer to ALL your questions is........ YES.

Big-Foot · 02-19-08, 11:21 PM

You know what Dean - I bet with a Chin Spoiler you'd put enough air through that grill opening that you'd not need the fans except for idling around the paddock..
I'd check with Ross and some of the others that race and see what the consensus is..

Phil · 02-19-08, 11:32 PM

Dean
My experience is very similar to what Jac Mac said, and I might add that a general rule of thumb is to have twice as much area behind the radiator than in front. Most production cars don't use the fans above 40 or 45 mph as the fan will actually impede the airflow above those speeds. Make sure you have sufficient pressure in the front, and a good exit for the air at the rear and you should have no problem providing that the radiator has the capacity to cool your motor.
Cheers
Phil

Howard Jones · 02-19-08, 11:34 PM

Dean, I don't believe that you can run this car without fans on the street or for that matter at speeds less than 40MPH unless it is really cold outside. One of the tricks is to "bank" cooled water when you can. What I mean is when you anticipate a need for cooling such as a traffic light ahead you can switch on the fans and begin the cooling before you come to a stop. The worse thing you can do is sit there and get hot and then put on the fans. No fans, no cool water.

On the track, waiting on the grid with the engine at idle will heat up the coolant and when you need the extra cooling it will have been used up on the pit lane. Especially when the car has been really run hard and everything is good and hot after a session. On a hot day it will take a good hour to really cool things down in the pits. If you go back out with water/oil temps all the way up and sit in the pit lane for ten Min's waiting to go out without fans I think things won't work out very well. Maybe on a 50F day you can get away with it but forget it when it's 90F. Fans are your friends.

As far as performance goes. I don't believe that you can really get much down-force on the front without keeping the air out from underneath the car. I've tried just about everything that can be done on TOP of the car to gain down-force but unless you use a real wing on the rear, keep the air out from under the sills along the side and a splitter on the front as part as a big ugly air dam then these cars are not going to produce down-force. In fact it would be quite an achievement to reduce lift to zero. The main thing when on the track is to keep the front ride height about a inch lower than the rear and as low as it will go in the front without screwing up the front geometry.

The good news is at most tracks top speeds will be under 160MPH and then for only for a few seconds. My car feels pretty good and stable approaching these speeds so I have been concentrating on mechanical grip more than aero. Besides I love the look of these cars too much to change mine much beyond what was done to them in their day.

So put in the fans and you won't be sorry. There is nothing worse that a overheating problem in an otherwise nice hotrod to ruin your day.

Dean Lampe · 02-20-08, 09:36 PM

It looks like I will be installing the fans! I think you are right about air movement under the car. I have been thinking a lot about that too. I have a little over 2 months to get it all done.

Ross Nicol · 02-20-08, 10:03 PM

Yes I wouldn't run without fans but then again I'm the guy that buggered his motor by not having enough oil in it. I have a single nostril and i modified it to gather all the air from the rear of the radiator.A lot of nostrils I've seen stop half way up and therefore only vent air from the top part of the radiator.I've had the fans come on during a race but only when I had engine problems, so plenty of cooling air comes through the radiator on my car at speed.

Ross

Howard Jones · 02-21-08, 01:23 AM

I should add that I think I have gained some aero by trying to seal the front of the car to the point that all the air that goes into the front of the car goes through the radiator.

Unless you intend to run a brake air scoops and their rotor vents and intakes then close off all the holes in the nose that don't intake air that flows through the radiator. Also as it has been said above seal the outlet side of the radiator opening area so that all the exhaust air goes out the top of the nostril(s) and over the top of the car. In this regard I think that the single nostril type would be better if the exhaust hole extends all the way to the floor of the area behind the radiator.

The last thing would be to seal the bottom of the car completely including the engine room and under the engine. I think the duckbill at the rear will be more effective if the airflow under the car is not disturbed by the turbulence created by the air flowing up into the engine room from below and then out the back. It should be better if airflow at the rear was only coming from the bottom and then straight up and back and from the top straight back across the duckbill. This may effect heating (neg) more that it is worth but it is an area to be investigated.

That's about it, unless you want to build a MK4.