How much airflow to radiator?

[jaybee]

Does anyone know how much grill area is really required to cool a car?

[enjenjo]

Ideally, you should have as many square inches of grille opening as you do radiator area. This should also be in a high pressure area. That is why most modern cars are bottom breathers, the radiator air is picked up under the bumper as that is a high pressure area.

[BFS57]

Hello;
Just got my new issue of Rod and Custom Magazine which covers cooling problems (page 36 thru 41). One thing I found interesting was the information that heat from the engine can rise (it always does) and flow foreword over the top of the radiator and be brought through the cooling surface of that radiator making the engine heat up at slow speed and at idle in traffic. The cure was a pair of "blanking" plates made to block that flow over the core support which forces cold air through the radiator rather than over, at speed.
Learn something every day!

Bruce

[UGLY OLDS]

If you look under the hood of an original 40's or early '50's car you will see those "blank off panels" built into the car as OE .. On GM cars they are usually found in the hood above the radiator .. Ford did the same thing by filling the area around the hood latch at the top of the grille .....
This forces two things ..
A..ALL the air that goes into the grille goes through the radiator at speed ..
( Not "over or around" it )  
B.. No "engine compartment hot air pullover" at slow / idle speeds ....

 It's amazing how well an early car will cool when all the original panels are in place ....My "Ugly Olds" even has rubber strips about 1" wide to seal the inner grille panel edges to the underside of the fenders .....Works like a champ...  


Bob.....

[jaybee]

All good stuff, and it all shows there's more than one way to keep your cool.

Regarding keeping that air from recirculating that's one of the things that looks like it shoul
d be a problem with a tilt front. The radiator has to just sit there with room around it for the doghouse to tilt. Turning it into a bottom breather with proper ducting might be the solution.

As for that high pressure area, I read a pretty detailed description of how someone reduced the tendency of his 80s Grand Prix to lift at high speed (track days) by blocking off the grill, putting a flexible air dam under the radiator, pulling cooling air from that high pressure area, and putting vents roughly over the front of the cylinder heads to exhaust the underhood pressure. He had photographs at 150mph that looked pretty convincing.

Block off panels...the OEMs obviously put a lot of thought into these things even in the way back...pretty smart guys and it's always worth a thought before we just throw away their work and start over. Air coming forward under the radiator to be sucked back through can be a factor as well. I wonder if that's part of the reason some 50s-60s cars had gravel pans between the radiator and grill.

[idrivejunk]

To further support the bottom-feeding and baffles and block off panels theories, look at just about any Grand Prix. My '69 has a small beak of a grille, completely sealed over the core support. Not many holes in the core support and a flimsy but critical (at highway speeds) air deflector underneath. Even my '99 GTP has a tiny pair of grilles and a giant opening over the splitter under the front bumper. Plus a big ol air dam back under the core support. So I concur- all the air ought to be channeled through the core. But as far as a formula that defines how much airflow is enough I can only say hmmm. I would have to say that the only definite indication of too much engine compartment airflow would be, as previously mentioned, front end lift. Don't want to blow a hood off! Nor lighten steering traction at speed. Grand Prixs did tend to have roomy engine bays, funny how GPs made mention twice now.

[wayne petty]

i can verify the air dam under the core support will assist in cooling as my sisters 85 T/A bottom breather would over heat at any speed above 57.. even with the most powerful fan motors i could find.. i ran across a magnehelic gauge which is a vacuum gauge with hoses on both sides.. sort of a tug of war.. i positioned one tube behind the core and the other in front of it..  at 53. the pressure started switching.. it was becoming higher behind the radiator.. at 57.. it was much higher..  so the air pressure build up at the cross member was pushing it forward.. when i cut off the stock short air dam.. and used the rigid 87 up air dam.. the pressure in front of the radiator always stayed higher and the cooling problems vanished..

i cobble on some cars. i have used the black corrogated floor runner to replace the fiber rubber surrounds in front of the radiator support that limit the ram air from escaping..  its not OE.. but it worked .. smooth sheets are also available.


the answer to the original question needs more info.. how many BTU's does your engine create thru the cooling system that you have to dissipate into the air stream.. and at what ambient temps..

[1800guy]

I went through this with a friends vintage race car (old Volvo).  The previous owner/builder had made "lightening holes" in all the shrouding above and beside the radiator.  Even with a new oversize aluminum radiator it still over-heated.  I never could convince him to restore the shrouding and our relationship ended on a sour note.  After all, I was just an amateur and the car had been built by a professional.

[jaybee]

Wayne, really interesting information about the T/A. More air was getting under the car than could get back out. It probably could have used fender vents like the previous generation T/A had. The Grand Prix I referred to above took those same vents and put them in the hood.

1800, I guess the moral of your story is that some things just shouldn't be lightened!