blocked grill, better mpg?

[ackattacker]

BTW, doing some reading on this subject I found some interesting info. The P-51 mustang had a belly mounted radiator but the design was such that it had zero cooling drag. The heated air exiting the radiator exit expanded enough to add a little "jet engine" type thrust, enough to offset the drag of the radiator itself...

[freezin4]

^ That's an interesting design.

Also it just occured to me that the OP was asking about "grille block" and some of the info may have been confused with "radiator block".

Grille block covers or blocks frontal area body opening with a shaped foam or fiberglass "plugging" the opening in front of the radiator and rad block is just a piece of flat obstruction directly in front of radiator. The two theories are:

- Grille block helps with reducing aerodynamic resistance. (Smoothing out the front.)

- Rad block is supposed to help by helping to warm up engine faster. The idea is to block the air from flowing through the engine compartment.

[ackattacker]

A radiator block (cardboard in front of the radiator) should reduce drag similar to blocking the actual grill. It's not intuitive but...

Imagine if you will the scenario where you block the radiator entirely. No air can flow into the grill opening since there's nowhere for it to go. Instead you will just build up a slight high pressure in the grill opening. The airflow will encounter this high pressure and be diverted around, similar to if there was a physical obstruction there.

Another example: Imagine the aerodynamics of a solid cylinder. Now imagine the aerodynamics of a bucket with the opening facing into the wind. Which one has more drag? The answer is they are almost the same.

Yet another example, imagine a hollow point bullet vs. a traditional round-nose round. Which one has better ballistics? Believe it or not the hollow point is actually slightly *better*. It's true. Match shooters use hollow points as target rounds. (The reason it's slightly better is because the center of mass is further aft)

Anyway the point is that when you reduce the airflow through the engine compartment you reduce drag, whether you block the air in the entrance, the exit, or anywhere in between.

[ghammerly]

Originally Posted by ackattacker

Another example: Imagine the aerodynamics of a solid cylinder. Now imagine the aerodynamics of a bucket with the opening facing into the wind. Which one has more drag? The answer is they are almost the same.
Anyway the point is that when you reduce the airflow through the engine compartment you reduce drag, whether you block the air in the entrance, the exit, or anywhere in between.

I agree with ackattacker and seen it in person on wind tunnel models. (40% and 50% scale race and production cars)
The only detail is that the air-box in front of the radiator has to be sealed for this to be 100% true. Blocking at the radiator will increase the air-box pressure and a good part of that air will end up slipping through open gaps, but yes the increased air-box pressure will force more air to divert around the car reducing drag.
I worked as a Model Maker for five years.

[Cobb]

Been there, done that, got written up by my home owners association. Also it had no effect that I can measure on fuel economy. It just reduced warm up time by a few minutes.

Originally Posted by livfreely

If you get the engine block heater would it solve this problem? Just plug it in over the night. And then you could also say you have a plug in hybrid.

Ive found that blocking the opening on the front of the vehicle does more for faster warm ups, noticable mpg savings as well as better acceleration at or above highway speeds. I tried the radiator block, but it actually hurt mpg. On the other hand I found my addition of foam inserts between the condensor and radiator that would require air to pass through both to actually help mpg.

For a car that holds less than a gallon of antifreeze we got one large radiator.

[firsthonda]

I have a question. If grill blocking does what some folks claim it does, then why didn't the engineers at Honda incorporate a grill block(partial or otherwise) into the design of their vehicles?

[ackattacker]

Originally Posted by firsthonda

I have a question. If grill blocking does what some folks claim it does, then why didn't the engineers at Honda incorporate a grill block(partial or otherwise) into the design of their vehicles?

They design the vehicle to operate at the extremes of climate (hot day, climbing a mountain, full load) without overheating and without requiring mechanical intervention by grandma Jones driving over hill and dale to see her grandkids.

They could have incorporated a variable opening controlled by computer and servos, but that's complex and expensive, and it's one more thing to break. Expense vs. reward wasn't there.

[Willie Williford]

Check out the 2012 Focus if you are intereted in a very good variable grill block.

Willie
FYI.......A lot of Semi's have basically the same system.

[Cobb]

FYI, this shouldnt be attempted unless you have a way to monitor the vehicle temperature by the odb2 port and you should make it easily reversable incase the temp gets warmer faster than you expect. This car seems to like 177-181. Any more hurts your fuel economy.