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Old 06-10-2022, 11:21 AM   #1 (permalink)
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Hi pressure in front of truck at cruising speed

I am looking to find out if anyone has info on if the high pressure zone a tthe front of a truck has an impact on mpg's... meaning (forget engine cooling for this discussion), if its 100% blocked off, most of the airflow goes over and under the truck.

Is there any value in letting that high pressure bleed off into the engine compartment? ...effectively reducing some of the high pressure areas at the front grill...


The reason I ask is I had previously installed a grill insert that was behind the grill at the top, blocking the top half of the grill. What I immediately noticed on the freeway was improved front end stability. To me that equaled more downforce on the front of the truck. I have to assume that comes at a mpg cost. I left it there for 2+ years and removed it last summer when doing an aero before & after test (before had all aero in place, after removed it all). And... no ABA test, did not have the bandwidth to get that done. What ended up happening, and the details are fuzzy but its all documented on Cumminsforum.com... is mpg's took a good jump w/o some of those mods in place. I ultimately reinstalled 2 mods, the 2nd lower air dam and the bed seals between the cab & the bed. With how I left it (and other things going on with the truck last summer) I ended up getting ~12-15 tanks of 23.0 mpg or better. That was a shocker to me as the only other time I'd done anything over 23 was during the year of a bet with a co-worker back in 2018... had 5 tanks over 23 that year... ugh, I think I squirreled with my thoughts... sorry.




One of the things I'd considered trying to do was the front air curtains for the front wheels, taping into some of the high pressure off the front and use it to come out the sides.



could also use that front airflow bled into the engine compartment in other ways below the truck, the goal being to control it and not let it flow as it wants to into the engine compartment.

Anyways, thoughts?

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Old 06-10-2022, 12:19 PM   #2 (permalink)
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[QUOTE]Is there any value in letting that high pressure bleed off into the engine compartment? ...effectively reducing some of the high pressure areas at the front grill...[/QUOTE

Ultimately, the high pressure at the stagnation point is matched by a low pressure area at the rear. How one gets from the one to the other determines the drag. IOW the high pressure is a feature not a benefit.

All air into the engine compartment should go though the radiator. Outflow can be between the frame rails or through the inner wheel well.

Air curtains can be beneficial, but the 2022 Dodge seems to have none so you'd be on you own. I think Ford has a horizontal slot feeding a vertical one.
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Old 06-10-2022, 12:32 PM   #3 (permalink)
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[QUOTE=freebeard;669401]
Quote:
Is there any value in letting that high pressure bleed off into the engine compartment? ...effectively reducing some of the high pressure areas at the front grill...[/QUOTE

Ultimately, the high pressure at the stagnation point is matched by a low pressure area at the rear. How one gets from the one to the other determines the drag. IOW the high pressure is a feature not a benefit.

All air into the engine compartment should go though the radiator. Outflow can be between the frame rails or through the inner wheel well.

Air curtains can be beneficial, but the 2022 Dodge seems to have none so you'd be on you own. I think Ford has a horizontal slot feeding a vertical one.
Thanks... one of the thoughts was to push the air out the back in a controlled direction... but thats at the other end of the truck. The 2005 I have, it has a piece on the fender that is intended to be a wheel liner retention of some sort, the thinking was to slot that and feed air into it to create that air curtain as much as possible. I realize there is a lot of work to get that one pulled off and the benefit is an unknown.
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Old 06-10-2022, 02:04 PM   #4 (permalink)
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Oops, too late to edit in the missing right bracket.

An invisible OEM style air curtain might be a lot of work, do you care about that?

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Old 06-10-2022, 02:46 PM   #5 (permalink)
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yeah it would be, mostly controlling the air flow to the exit by the wheel. Externally I would not go that route, truck needs to look stock for personal preference.

Another thought I had a few years back was to create a vacuum source from under the car and add a connection to the wheel liner to draw air out of there via a vent (currently have vents that go into the engine compartment, to relieve pressure in that area). A possible solution might be to leverage that high pressure area and create flow along the frame with the vent connection off the wheel liner. That way the faster the truck is running, the greater the pull out of the wheel well area. I would dump that flow out the back of the truck into the vacuum bubble... would be a lot of work to get that done.

edit: And oh yeah, I have one of Edgars books... interesting stuff!

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