Grill Block Revision - Work in Progress Photos
 

Here's what it started as, when I first decided to do a grill block:
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I was still having overheating issues with the huge hole I ended up cutting, plus I read some more on here and determined it's a bad idea to push air under the car rather than over and around it, so I revamped things. Here's the new version:
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I still have to work on the belly pan today, and figure out how to get air to go through my radiator. My air intake started out as a small hole, about 1/2 the area of the license plate, and grew as I was driving home from my in-laws saturday night and the car 's temp gauge wouldn't stay in the normal range. Even with this monster hole, the car wouldn't have made it home unless I turned on the heater. Something's gotta be better once I make some ductwork forcing air through the original grill. Here's the underside.
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And here's what you see if you look slightly downward through my intake hole now..
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If anyone's got ideas or suggestions on helping with cooling airflow or if the hole is big enough, I'm open to whatever you have!
Thanks for reading,
Matt

I'm curious to know myself.
I have the same car as AndrewJ , but my car is an automatic. Even with a much larger hole than he has open on his car, I seem to get overheating.
My guage never moves at all, but my coolant drains from the top of the cap.
I don't trust the factory guage at all.

So your radiator is directly behind the opening ?

No, there's a big space there - almost 20 cm - then the condenser for the a/c, then the radiator. My space is 47 square inches, and my car is similar to yours - 88 horsepower (I think that's at the wheels, so it's probably like 100-110 hp)
I made my opening much bigger than AndrewJ's because I have to have a/c for when other people are in the car.
As you may be able to see in my pictures at my blog (I'll post smaller ones here), I worked today to make a duct to force air back through my old bumper, delivering it about 5cm shy of the condenser so it can spread out. The total area of my grill now is basically the same as the original one was, so I hope this works nearly as well!
I think part of the problem is eddy currents caused by the air dam, but with my new belly pan, that should be mostly solved. I have to appear as a state's witness in court for another county on Thursday, so I'll have a nice long drive to test this out. If I have to drive with the heater on to avoid destroying my car, I'm going to be pissed!!!!
Here's today's progress.
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I've found that it's hard to figure out the right size of the hole, but I usually err on the side of too big. If possible, I would try to get a temp gauge so you could see what the engine's running at, rather than relying on the gauge.

Looking good, :thumbup:

Yeah, I should - I was planning on putting one in my mustang this summer - I already have the gauge pod for it, but money is tight at the moment.
The factory gauge is pretty sensitive, although it doesn't tell you the right thing, on all of my Ford cars. The needle oscillates around "O" in "normal" when the engine is at 195-210F. If it gets to the "AL" region, it's boiling or around 235F, and beyond the "L", you need a new cylinder head. :(
Matt

I second getting a new guage. I plan to do so myself, since I don't even have numbers on my guage.

Is that coroplast under the engine ??

I made my 'pan out a couple of old aluminum signs.
I'd hate for you to start a fire !

The coroplast covers the gap from the new air dam back to the radiator, plus a little space past it. On the engine side, the coroplast almost reaches the "under oil pan" zone. On the transmission side, there's lots of space between the transmission and the coroplast. In the center, where the exhaust manifold and catalytic converter are, the coroplast doesn't get within 6" of being below where the exhaust components come down vertically from the manifold. It's kind of hard to see in the photo, but you can tell the center part is way shorter than the rest. I'm hoping to use window screen to eventually finish the rest.
Matt

Sweet... I drove the car to my wife's OB visit today (expecting our first any day now!!) and was pleased with the grill block's performance.
1st - most importantly, the car didn't overheat on the highway. I was so overjoyed that I decided to try the a/c and see if it was safe too. It was hot and steamy outside, so this was a good test. Temp gauge read approximately 10F higher than normal, but stayed where I'm not worried.
2nd - (this isn't an official test, btw), I EOC'd from 65 mph in a 60 zone before a long downhill + offramp on the way home. Normally when I did this, I slowed slightly going down the hill, and by the time I hit the turn in the offramp, I was moving ~35 mph (30 mph turn, so I usually didn't have to hit the brakes), plus I typically have 2-3 cars behind me who catch up on the slowdown.
Tonight, the car accelerated to ~73 mph and I was doing about 50 and had to hit the brakes when I entered the turn! Either there was a hell of a tail wind (could have been some, since it was storming), or the grill block works!!! Official data to come later.

I think your original problem was the new deep air dam so far in front of your actual radiator. This caused there to be too low of an air pressure in front of your radiator (not enough pressure change across the core to aid flow) that even with air dam openings the air flow bled down under the car rather than through the core.

Adding the pan between the air dam and the core support is what likely saved you. I would have suggested doing a dual-stage dam; one straight down from the core support and another one from the leading edge of the bumper straight down to the height of the top of the core support dam, with a horizontal plane in between (nose pan?). This should keep the pressure drop under the car around the back side of the radiator and let the duct opening pressurize air in front of the radiator to assist cooling flow. The dual-stage air dams should let air pressure build up under the nose pan, while the opening builds pressure above it, keeping it from getting ripped off.

From your first pics of your new dam I would have suggested taking the ends further all the way to the wheel well and maybe flaring the edges to push air away from the front edge of the tire (actually bend the coroplast just past 90 degrees and screw it into the inside lip of the front of the wheel well). This will also cause a vortex to draw air out from the engine compartment through the wheel wells and aid cooling flow.