Aerodynamic Suburban or GM SUV (92-99)

[aardvarcus]

All,

I am starting this thread to discuss the aerodynamics and potential improvements for a 90's model Chevy or GMC Suburban or other SUV. The models I am discussing are the 1992 through 1999 and carryover 2000 body style also known as eight generation, gmt400, or OBS. The same years of Blazer, Tahoe, Yukon, Denali, and Escalade are also very similar and open for discussion.

There are a lot of reasons why someone would or would not choose this particular generation or type of vehicle, so let's basis our assumptions for the discussion that someone has already determined this type and generation of vehicle meets their needs the best, and is looking for ways to best improve it aerodynamically.

Several users on here have these generation vehicles, and I am in the planning stages of a fairly thorough project based on this platform. The idea for this thread is to post ideas, parts, solutions, etcetera and have a healthy discussion of the aerodynamic benefits and practicality of the proposed modifications. I will kick it off with some of my ideas I have come up with, but everyone jump in.

For starters, this generation has some aerodynamics built in from the factory. Most of the leading edges are reasonably rounded off and several of the body details appear quite optimized such as the flush door handles. Other noteworthy factory aerodynamic items include a factory air dam, optional fairly smooth hubcaps or wheel covers, and the 1999-2000 Denali models have completely redone front ends that look similar to the newer models but yet built on the old platform.

[aardvarcus]

One of the most major aerodynamic needs of the Suburban is more rear taper. A boat tail could be added to the rear of the vehicle, however the Suburban is already fairly long with significant rear overhang so that may not be the best solution. The shorter Blazer/Tahoe/Yukon/Denali could probably better adapt to this type of solution.

The more extreme solution to rear taper on the Suburban would be to boat tail the rear cargo area of the Suburban. This obviously would be a major undertaking and could potentially disrupt the utility of the vehicle.

Some have done what is known as Avalanche conversions, which is to basically turn the suburban into a crew cab truck by chopping the roof off the cargo area and grafting in pickup truck body panels and parts. It would not be unreasonable to think that for a similar level of work you could create a hatchback Suburban, which would basically be an Avalanche conversion with a sloping bed cover. This would seem to be a better option with a rear tailgate.

Alternatively the rear of the vehicle could be tapered by changing the rear roof pitch over the cargo area, but not removing or hinging the roof. This would decrease the size of the opening in the back of the vehicle, and would seem to be a better option to resize and keep the rear barn doors.

[aerohead]

Here is a boat tail tested for a GM SUV.It was good for a 26% drag reduction (about 13% mpg).Kinda long.

You wouldn't necessarily want the length around town,but for open road cruising,any length would be welcome.
I looked at a JEEP Wrangler Rubicon the other day.It has a very stout bumper-mounted,swing-away spare-tire mount which would be ideal for a swing-away boat tail.
A tail could be fabricated and mounted to the JEEP-like mount,which would allow access to the regular rear doors.

[gafhj]

Originally Posted by aerohead

Here is a boat tail tested for a GM SUV.It was good for a 26% drag reduction (about 13% mpg).Kinda long.

Can you clarify, 26% reduction was for such simplified body?
Less than I'd expect.

[ChopStix]

@aardvarcus, Your project has basically the same aero problems as my van. One of which is that the doors round in on the bottoms which exposes the tires to straight line air. I'm working on a spat design to direct the air outward around the tires to see what that gets me.

As for a nose spoiler, my vans bumper cover is almost straight in line with the cross member. So there's no need for an additional chin spoiler. But maybe a nose pan would help a little bit over none at all.

I have skipped on the grill block idea as others have made posts about the GM HEI's overheating from not enough air flow. I don't want to be broken down for a fried distributor module.

Beyond that, I gained 1mpg from removing the roof rack, and 2mpg from changing wheels/tires. My stock aluminum wheels with winter tires are 10lbs heavier each, over a set of steel rally wheels with LRR tires and moon hub caps.

I'm presently working on installing an electric fan, and reduction pulleys to see what that gets me. I expect another 3mpg from these. Plus I need to clean out my van as its got a bunch of junk in it right now.... The mods are easier than cleaning it out!

[freebeard]

The GTI w12-650 retains the gross outline of the standard rear body but tucks in a wing good for 200mph and a bubbletop coupe body for wake reduction. No added length.



The Citroen Tubik may only have flow-through ventilation, but with appropriate inlets on the top and in the rear quarter windows could be topologically equivalent to the GTI top.

Somewhere in between? Open up the back and graft a hatchback body extension in place?

Edit: I almost forgot:

[aardvarcus]

Aerohead,

I am also surprised there wasn’t more gain for the length; I would wager a guess that maybe the other drag components (like non-faired tires) took over? It also looks rather aggressive in the back and the edges look rather sharp.

I had thought about a folding boat tail mounted to the rear doors, but even with a folding version I would end up somewhat length limited for practicality reasons. I am imagining something like the drawing of the lower jeep, except that the sides and top would fold in. But if I could get the drag reduction I wanted without touching the existing bodywork that would be great. I could even camouflage the folded in boat tail and make it look like an exploration style rear ladder/tire carrier add on.

[aardvarcus]

Chopstix,

Yeah, the Suburban also needs some tire spats. I am thinking of a conveyor belt design that has been discussed on here a few times, that way it can stand up to road/offroad abuse. I want to figure out a way to fit the OEM semi-smooth hubcaps to stock 8 lug alloys so save some weight over stock 8 lug steels.

I understand about overheating GMs because of air flow, I had a 1991 k2500… one engine and multiple transmission repairs later I figure out the AC condenser is clogged up and won’t let air through the radiator. (FYI go check and/or gently clean your condenser and radiator.)

If you are looking to DIY a electric fan conversion, search on here for the one I did on my Tacoma. It wasn’t cheap, but it is reliable. Also look at ducting the air into the radiator so it can’t just flow around. I did a partial grill block on a car I used to have, but also ducted the remaining opening direct to the radiator and my temperatures decreased, mainly because the massive airflow from the huge grill opening was going around the radiator not through.

[aardvarcus]

Freebeard,

Wow. Just wow. I wonder if it is possible to build something like that and have it work appropriately without a wind tunnel? It almost reminds me of very wide NACA inlets. You have gotten the hampsters in my head spinning their wheels for all they are worth.

As you suggested, replace the back window with a curved in version and add an inlet in the roof. I wonder would this idea work with a boat tail? Such as boat tail the back with a folding tail normally as discussed above, and have the air inlet feed the wake from inside the boat tail once folded out? Throw a finned aluminum rear-heatsink style radiator into the mix for good measure (existing rear heater lines)…

[freebeard]

I'll defer to aerohead on the details, but you might start with tuft testing. If the air is rising along the sides, it's moving faster over the top, so then doing just the windows might be enough.

Here's an example (lower left) of using hot air in a Coanda nozzle. VWs produced about 1500cfm of cooling air. I'm not sure a heater core would affect the amount of air that would be moving through the [sub]system.



Can you see some resemblance to the Tubik?