Fixing my Poor Cd, 97 Civic .36
 

Well i've been unhappy with my cars performance and a few weeks ago I did a 90% grill block (cardboard and duct tape covering the whole bumper radiator inlet. There's 2 small holes above the bumper that i left open. I also put on a WAI on my car. Completely sucking intake charge from behing the exhaust manifold via aluminum dryer ducting. I swore I gained 5-8mpg.

So today I did some tests. I went to my mile long stretch and reset my mpguino at the start of the A-b and the B-A runs. My cruise control isn't accurate for this (long story), so I get the car up to 40mph and hold my foot as best i can at 40mph, I did 3 runs each way with and without the grill block.

A-B tests with bumper radiator inlet block off.
83.1, 84.4, 83.11 ave = 83.53mpg

B-A tests with bumper radiator inlet block off.
76.09, 75.5, 75.8 ave = 75.79mpg


A-B tests NO radiator blockoff.
77.4, 79.5, 76.8 ave = 77.9mpg

B-A tests NO radiator blockoff.
70.4, 69.8, 69.8 ave = 70.0mpg

Well I didn't do ABA testing where I would have put the radiator block back on, but I'm pretty convinced by the results. With A-B route I saw a 7.2% gain with the block and with B-A tests there was a 8.2% gain.

I really wish I had a wind tunnel with a dyno to test this more easily :) I'm curious how this would effect the MPG at 65mph, and at 25mph. My tests were just at 40mph because that's the easiest road that's mostly flat near where I live.

By the way, I have zero bellypan under the engine bay. I was wondering how not having a belly pan was going to effect the results, but WOW, 7-8% increase.

FINAL NOTE: DON'T PUT DUCT TAPE ON YOUR PAINT IF YOU DON'T MIND IT COMING OFF. I lost some paint when i took it off. I'm going to now try making a styrofoam grill insert with perhaps a piece of cloroplast connected to it to cover the grill area.

cool info.
thank you very much for sharing.

No problem. Of course every car is different, but i'm wondering if I saw large gains because my car has an already relatively poor Cd compared to insight, prius, crx, civic VX? Or since most cars have as large of a grill as mine does, would every car see this type of gain?

The results you got are typical for a car and shows why grill blocks are so effective. The cooling system airflow on most cars is poorly designed, featuring an oversized, fixed size radiator opening with the various emblems and other visual doodads plastered on the grill, followed by the fan blades and the non-aerodynamic bulk of the fan motor creating a turbulent airflow into the radiator (this flow should be as laminar as possible). Then once the hot air exits the radiator, it has to negotiate its way through a cluttered engine compartment and out of the bottom of the engine bay creating lots of turbulent air under the car in the process.

The following link is about designing aircraft radiators, shows how it should be done. But it would take a bit of work to retrofit this into the average car using a pop-up cooling fan that would be retracted out of the airflow when not in use. When you compare the aircraft version to what you find when you look in the engine bay of the typical automobile, the lack of engineering finesse found in the car is staggering.

Contrails ! Radiator aerodynamics

Thanks basjoos. I'll have to read up on that link you sent. For now I have to design a new radiator block that isn't effected by rain as my duct tape setup. If I decide to keep this car for a while, I'm going to just fiberglass the whole bumper radiator inlet smooth. I havn't experienced super hot summer days yet, so maybe I should hold off on the permanent setup until after that.

I've seen on turbo cars like the eclipse/laser/talon Dsms that their side mount intercooler is set up in front of the right front tire.

Would this location be better for cars, as the radiator could be smaller, ducting to and from the radiator would be easier to impliment, and it would also free up some engine bay space?

thanks basjoos - some great thought provoking discussions.

I'm still processing and thinking about it all.

That is a better location than the usual OEM location. You'd probably want to use twin radiators, one in the space ahead of each front wheel well. The layout would be; adjustable inlet door, retractable (when not in use) cooling fan, radiator, and then exhaust it into the front wheel wells. With smooth duct work all of the way following the principles laid out in that Contrails article.

The best location aerodynamically would be at the rear of the car using NACA ducts on the sides or top of the car as radiator inlets feeding into single or twin radiators, followed by a retractable (when not in use) cooling fan, adjustable radiator doors, and exhausting into the space behind the car. This could be built into a boattail.

Once upon a time I talked at length to the chief mechanic of a Le Mans winning team for Porsches. They used radiators on the front corners. The theory is there is a high pressure area in the front of the air dam, and a low pressure on the side of the air dam in front of the front tire - basically the air going around the corner is accelerating and has good velocity, creating a low pressure area to suck the air out of the radiator. Further, this is "free" and produces almost no additional drag on the car.

Energy, or "Horsepower" is work done over a period of time. It seems to me air going THROUGH the front grill is horsepower. The more air we slow down, push through the grill, then accelerate back up to speed at the back of the car, the more horsepower we are using.

Therefore, the less air which goes through the grill, the less energy lost.

which is maybe obvious to the rest of you, but it takes a bit for me to get my head wrapped around it.