New lower air dam for 2017 Chevy Full size van

[EcoVan]

Been looking for an air dam that would work for the van since we bought it. Finally noticed the air dam on the 2015- 2019 Suburban. Picked one up and just installed it. Turned out pretty nice. Its about 3 inch too wide for the van bumper, but the ends can be easily and neatly be pulled in. If you want something about an inch higher the Yukon air dam my work for you. Looking for better mileage and safer highway driving. Now that the air dam is in place, I can start closing up the extraneous air leaks in the front end so only air will go through the radiator and intercooler. Then a front belly pan to help smooth the air flow under the engine.
Ahhh, Got the picture to work. The new dam reaches about 3 inches lower than the stock. I've been able to 33MPg @ A STEADY 68mph (trans just barely in 8 th gear) previously.... I wonder how much this may help.

[aerohead]

It's not a straightforward call.
1) Some researchers have reported 'optimums' for a given 'lowering' of an airdam.
2) Beyond a certain 'depth', drag increases again ( Brett Herndon ( Bondo ) experienced this on his 2012 F-150 ) ( A Master's Thesis from a Naval Officer reported ditto ).
3) At some 'extreme' depth ( appropriate only on a race course ) drag falls to a 'minimum'.
4) There is a risk that General Motors already optimized the OEM airdam, both in CFD and in their wind tunnel.

[EcoVan]

I basically was trying to get the dam to shield all the low hanging components and the tires, but no lower. The center is still about 1 1/2 inch above the lowest components and with a belly pan I suspect this should work out well. This body had a small 3 foot wide 2 inch or so deep air dam just below the radiator mounted on the bumper and then in 2016 or so, went to a full air dam that dropped lower in front of the tires ( per 1960's Fiat design). The chassis also changed around 2003 with the same body.
I've seen some of those same research results... too low is not good, until it is dragging on the ground like a race car. Also, I suspect attaching the belly pan directly to the bottom of the air dam makes a lot of difference. The low pressure zone drag right behind the air dam will be eliminated or at least moved rearward where air exiting the engine compartment will be sucked into the low pressure zone at the back of the front belly pan. My 93 escort with an extended air dam saw little improvement in mileage. However, when the front belly pan was attached and pretty well sealed to the bottom of the air dam, my fuel mileage skyrocketed from 33 MPG highway to near 50MPG. I don't expect that big of percentage gain in this case because that apparent drag reduction on my escort allowed the 1.9 SEFI engine to go into lean burn on the highway. I don't know how diesels respond to reduction in drag, but I expect some improvement since drafting a semi does provide a 10 to 15% boost in fuel mileage. I don't drive the vehicle much ( it a business work van) but I'll need to take it out to check out how it does.

[aerohead]

1) Is there any difference between the van and Suburban as far as engine bay air extracting through the front wheel-wells or not ?
2) And could the transmission cooler be affected by a change to the airdam?
3) And does transmission cooling rely to any degree at all on airflow physically sweeping through the transmission tunnel, and directly across the aluminum case as you drive?
4) You may have a full-synthetic lubrication package already, which can handle pretty extreme temperatures, but you'd want to know.

[freebeard]

[citation needed] but maybe aerohead can provide a reference.

There existed a post on Ecomodder that asserted that a bellypan with a chamfered step up from the suspension's level to the bumper level was tested as superior to an air dam.

No vena contracta?

[Vman455]

Originally Posted by EcoVan

I basically was trying to get the dam to shield all the low hanging components and the tires, but no lower.

This is a "rule of thumb" that appears to have sprung up ex nihilo here, since it has no basis in any literature that I've seen (and I've read a lot of references).

The good news is, you can easily test to see if an air dam is reducing drag, and what height might be optimum.

[aerohead]

All my pea-brain can connect to is, Tesla's front underbody design.
The forward-most belly section curves gently down from the nose to a lower elevation where the belly pan levels off.
Ahead of the hour-glass, wheel-flop, openings, the plastic 'pan' section has angled aircraft carrier jet 'blast-fence-like ' extensions, like Goro Tamai's 'taco fairings' from MIT, which presumably kick the flow downwards, across the open span, reattaching downstream of the Beechcraft Bonanza-esque front wheel trailing edge half-ducts, which blend into the outer extremities of the center belly pan section, perhaps handling the Tesla's radiator and AC condenser flow, dumping through slots into opposite front wheelhouses, ahead of the front tires.
Peter Rawlinson, now of Lucid may have had a hand in the design.
It's quite exquisite, very 'intentional' in its execution. A worthy benchmark.

[freebeard]

That sounds about right.

A step and a concave curve should be pretty equivalent.

[aerohead]

Originally Posted by Vman455

This is a "rule of thumb" that appears to have sprung up ex nihilo here, since it has no basis in any literature that I've seen (and I've read a lot of references).

The good news is, you can easily test to see if an air dam is reducing drag, and what height might be optimum.

There's been a bit published about airdams since 1960, when Chevrolet Division of General Motors introduced it to the motoring public.

[EcoVan]

Originally Posted by aerohead

1) Is there any difference between the van and Suburban as far as engine bay air extracting through the front wheel-wells or not ?
2) And could the transmission cooler be affected by a change to the airdam?
3) And does transmission cooling rely to any degree at all on airflow physically sweeping through the transmission tunnel, and directly across the aluminum case as you drive?
4) You may have a full-synthetic lubrication package already, which can handle pretty extreme temperatures, but you'd want to know.

Both vehicles have nearly identical front overhangs with the much of the engine and the whole transmission well behind the wheel wells. The installed height of the air dam on the van is about the same as the Suburban/Tahoe ( about 9 inches above the pavement in the middle and 7 1/2 at the sides). They are both mounted at the front most point of the vehicle ( the bottom of the bumper). All radiator/ intercooler cooling air is coming from above the bumper on both vehicles, not like most cars that pull air from under the bumper. The Suburban has wheel well liners, while the van wheel wells are open at the front. I plan on closing these too when installing the belly pan and may run the liner down lower below the belly pan to deflect air away from the tires. However, I am concerned about brake cooling. However, I just checked the brakes and after 80,000 miles of mostly city driving, the pads aren't even half worn yet. The brakes are plenty big, the vehicle is rated at a GCWR of about 14,000 lbs.
I probably have significant room to play with in cooling....I am running a 180 HP 2.8l Diesel instead of a 400HP 6.0L Gas v-8. Currently, cooling is so plentiful that the vehicle won't even warm up often times in the winter. Fortunately the cargo area interior is insulated so it requires very little heating (and little cooling in the summer) to be comfortable.

I have noticed that the radiator has baffles nearly all the way around to direct air from the grill into the radiator instead of it just blowing everywhere. However, I did notice that there is a significant opening at the bottom baffle behind the air dam location. I wonder if this is a relief opening when traveling at highway speeds to reduce the airflow through the radiator. I suspect a bigger air dam would create a stronger pressure bubble at the front of the vehicle, but the backside of the bigger air dam would create stronger vacuum at this relief opening.

A front belly pan should do a much better job than just the open underside at directing air flow across the engine and transmission. You'll no longer have the vacuum right behind the air dam pulling cooling air down below the vehicle. The high velocity air at the rear edge of the pan should create a strong vacuum to pull air through the engine bay.

I wonder if creating a "blast fence" here would do any good when the underside of a van is a giant open cavity with the walls on both sides. I've also wondered about extending these "rocker panels" down to reduce air coming in from the sides per Semi trailer design.

The air dam is similiar in design to most newer SUVS's. It tapers down and back at first and then becomes at right angles to the ground. It appears most newer suv's are trying to divert the air around the jagged mechanicals with a back tapered air dam and directing the air smoothly under the vehicle.

This sounds alot like what Freebeard said

Time to head to find some full size SUV front wheel well liners and to pick up some ABS sheet. But a few other vehicle repairs first.