Minimum grill opening requirement

[christofoo]

Now I understand the advantage of the ducted, low drag cooling design. Are there any DIY build threads / pages on that approach? I want to think in terms of cost-benefit, it's easier to assess difficulty if it's been done already - bonus points if the benefits are A-B-A tested or CFD'd. This seems like a frontier of ecomodding.

But my calcs may still be useful, as a guideline it probably applies somewhat to both ducted and non-ducted designs. A good ducted design would have the advantage that the Cd is less affected by the opening, so variable blocking would be less of a concern.

[christofoo]

Originally Posted by landsailor

...
Might add humidity level, in-town/stop and go traffic, electric fan vs. full time mechanical fan vs. temp. activated mech. fan
...

Higher humidity increases the specific heat of air which makes it cool more effectively, lessening the required opening (which seems backwards, but that's because humans rely on evaporative cooling, which decreases in effectiveness with increasing humidity). Instead I just used a number for dry air. So you can reduce your grill opening in coastal areas, but only by a percentage.

Stop-and-go traffic is too complicated for me. At low speeds your fan may turn on to compensate for low air flow. Other than that, if you're staying off the brakes and getting good gas mileage, grill opening demand should be no more than a little higher than at cruising.

[metromizer]

My grill block experience with '96 Geo Metro 3cyl 5spd: For what it's worth, I made a roadside, ad hoc grill blocker over a year ago on my '96 Metro. I used cardboard to fashion my behind the grill ducting, made such that the little air that gets through, MUST go threw the tiny radiator. I completely covered the factory openings in the bumper, thick plastic from a 5qt Castrol oil jug, held on with Gorrilla tape. The only air the radiator gets is from the slit that exists between the bumper cover and the lower lip of the hood, about 10" wide x 1-1/2" tall.

I monitor coolant temp and incoming air temp via my scan gauge. I've never had the coolant temp go up, but IAT is slightly higher, maybe 15degF. The only noticeable difference on this vehicle, blocked versus unblocked, is the electric fan comes on more often in summer, at lower speeds, idling, and in stop and go traffic. The fan never triggers to come on while driving over 35mph, and it always keeps up with the additional heat, even with restricted air flow. I did not do back to back testing, but I think the ducting is helping mange what little air does get in.

[TOOSTUBBORN2FAIL]

Originally Posted by aerohead

The mod-data sticky should have Walter Korff's low-drag cooling inlet diagram.You'll want to see it as it is germane to your project.

Just checked this out. This is exactly what I was looking at doing, just didnt realize this was what it was called. I remember seeing something about this in a racing mag a few years back about Fomula One cars using it in the side pods for the radiators.


I'm going to try some ducting experiments this weekend, and post back on here. I'm also going to close off that bottom area where the airdam is supposed to be and see if it gets hot with a duct to the radiator.

[NeilBlanchard]

The one mod I made was to block up the escape vent holes in the chin area, after I had blocked up most of the grill. Because the stock grill opening was way too big, they had to let air escape; but after the grill blocks are in, all the air needs to go through the radiator. So, in my case it is not so much a duct, but rather a plenum.

An exhaust louver in the center of the hood would greatly improved the flow, but that is a lot of work.

[TOOSTUBBORN2FAIL]

I was looking at this, including drawing C in the page that Aerohead mentioned, but after tuft testing the hood, there isnt an area that doesnt show attached flow with the upper grill block in place. So there isnt a way to suck that air on on my car without putting some sort of lip in front the vent, which seems it would be detrimental to overall aero. At this point it seems the rear radiator idea is still the best option for me, depending on this weekends tests.

[gone-ot]

...have you seen Ford's Patent for their "air-deflecting" grill, maybe it can provide some useful info(?): http://www.google.com/patents?id=zyM...ed=0CDQQ6AEwAA

[aerohead]

Originally Posted by Old Tele man

...have you seen Ford's Patent for their "air-deflecting" grill, maybe it can provide some useful info(?): Patent US6527333 - Solid state drag reducing vehicle grille - Google Patents

Is this unlike their Ford of Cologne,'Lamillar' grille of 1978?

[gone-ot]

Aerohead, to be honest, I don't know the answer to your question (FoC'78), only that the current Ford grills, with their multiple, broad, wide, slats are *supposed* to be 'dynamically' aerodynamic with increased speed, ie: air flow 'thru' the grill is reduced as the speed is increased...similar to *how* hydrodynamic water flow becomes 'blocked' through wire-mesh at higher speeds but not at lower speeds.

[aerohead]

Originally Posted by Old Tele man

Aerohead, to be honest, I don't know the answer to your question (FoC'78), only that the current Ford grills, with their multiple, broad, wide, slats are *supposed* to be 'dynamically' aerodynamic with increased speed, ie: air flow 'thru' the grill is reduced as the speed is increased...similar to *how* hydrodynamic water flow becomes 'blocked' through wire-mesh at higher speeds but not at lower speeds.

I'll guess that its a boundary layer effect.The slats are so small,they'll have a low Reynolds number at lower speed and air will have free reign into the opening,then at some higher velocity,it will transition to a turbulent boundary layer,air will stall over the sections because of their relative angle of attack and the turbulence will choke off some of the flow.