Quick question

[freebeard]

Think about a partial belly pan. If you don't do something about the air exiting the plenum of the engine compartment, is will just speed up the air passing through the remaining opening.

[carolina guy]

Originally Posted by freebeard

Think about a partial belly pan. If you don't do something about the air exiting the plenum of the engine compartment, is will just speed up the air passing through the remaining opening.

So...essentially "sucking" more air through the remaining opening in the grille? Hmm...hadn't thought about that. Might be easier to just close the remaining grille opening and do more of a air dam then the belly pan. That's a lot of real estate underneath with the suspension to work around.

But, it also highlights the next experiment that I will try using the baseline (w/o grille block) and get the mechanical air swatter removed and see what difference that makes. My guess is that it will be a bigger improvement on FE given the large amount of air it is always moving...two drives up the driveway clears most of the leaves!

[aerohead]

The only way to really know the impact of the mod is to do back-to-back runs with a fully warmed up vehicle on exactly the same route,with and without the mod,in rapid succession on the same day.
Otherwise,there's just too many variables which can impact your mpg.
It's why these things are developed only in a wind tunnel,where everything can be accounted for and measured to high precision.

[carolina guy]

I know...ABABA type testing. I am using about a years worth of SG driving on the exact route daily with appx the exact same driving and within 1mpg consistent results.

I did remove the mechanical fan this weekend and will do a couple days driving to test the results and get a new baseline. I will be installing an e-fan shortly (have all the parts) and then will retest with a more complete grille block that can be removed for some proper testing.

Already with the fan removed, the engine does rev more easily/quickly. I suspect that the fan clutch was bad.

[Zach]

In order to do the ABABA testing do you need something like a scan gauge? Would doing an entire tank of gas for each be good enough? I don't have any means to track MPG without dividing my miles driven by # of gallons filled at the pump.

[aerohead]

Originally Posted by Zach

In order to do the ABABA testing do you need something like a scan gauge? Would doing an entire tank of gas for each be good enough? I don't have any means to track MPG without dividing my miles driven by # of gallons filled at the pump.

*Speaking in loose terms,a complete grille block might net a 12% drag reduction.
*A partial grille-block would only address the entry of the cooling system.
*6% of the drag, downstream of the radiator would not be addressed.
*You might be looking at a 3% drag reduction.
*If so, you could only be looking at a 1-1/2 % mpg improvement.
*It would be virtually impossible to detect this unless you had a fully-instrumented and documented test session on a closed course, back-to-back, within minutes of the original run.
*Some investigators at the Motor Industry Research Association wind tunnel in England claimed that in any given year, that they might see 7-days when weather conditions would be stable enough to do accurate outdoor testing.
*In the U.S.A., crosswind is considered the norm in all driving.(JPL,Pasadena,Calif.)

[freebeard]

IOW, nothing worth doing is easy.

[Gasoline Fumes]

But is there a need to test a grill block? Do they ever not work?

[freebeard]

Variables include the vehicle, the driving style, the road and the weather. So, maybe.

[aerohead]

Originally Posted by Gasoline Fumes

But is there a need to test a grill block? Do they ever not work?

It might have been a 1987 SAE Paper by FIAT in which some mods lowered under body drag,while increasing upper body drag,for a net-zero gain.
Every vehicle would have to be addressed on a case specific basis.
Since all modern cars are grille-blocked from the factory,additional blocking may experience severely diminished gains.Hucho calls it 'saturation.'