Best approach for aero improvement on sedan roof?

[19bonestock88]

I've been reading into tuning as well, and I do plan on doing it, but first I want to maximize results with the stock tune... There is a guy that I've been following on the Malibu forums who is using HPT to tune his 09 3.6 LTZ... So far, he has gained 2mpg and is running low 14s in the 1/4mi...

[freebeard]

...but first I want to maximize results with the stock tune...

While I agree that a full Kamm-back is the ideal solution, I don't currently have the material to build one, while I have enough scraps lying around to build a VG array...

One of these is not like the other.

[19bonestock88]

I see what you're getting at... I did plan on eventually doing a full Kamm-back to maximize aero benefit, but I need 6' wide sheets of material (not even sure what I want to use)to work with, and I can't even find it without ordering a bundle... I however, do have the stuff to try the VG array for now once I get some tuft testing in and determine proper placement...

My above thought was that the HPT software/hardware runs $500+, so that would be a pretty low ROI...

[Xist]

It just does not seem like aerodynamics can be improved with vortex generators without a wind tunnel and an engineer, but the VGs are the market would fall into two categories:

1. Designed by engineers with access to a wind tunnel.
2. Designed by advertising to separate customers from their money.

Not only are you planning on skipping #1, but I cannot imagine how small bits of coroplast will make anything more aerodynamic.

I see you have already started making proven modifications that are popular around here. Thinking out of the box is great. We need innovation. You really want to do this, so go ahead, but please tuft test and A-B-A test fuel economy.

[freebeard]

Once moving beyond scraps you might have laying around is on the table and you are looking at new material, I suggest considering PolyMetal or equivalent.



Here is some of the experimentation I did with scraps. It consists of a 3-6mm thermoplastic core with aluminum skin on at least one side (usually both) of .007 or .014" thickness. About the same as an aluminum can, with enamel finish in various colors; available in 4x8, 4x10, 4x12 and 5x10ft sheets. It's used for commercial signage and the big wings on dirt track race cars.

The stiffness of 5/8" plywood at 1/10th the weight. It's more expensive, but the gains in not needing finish work are immense. Rolling and shearing (by hand) worked great but braking failed and dimpling would require a hydraulic press with a bigger throat than what I have.

It falls between hand-formed and planished aluminum and coroplast, in cost and effort.

[19bonestock88]

Where can I get that? Looks nearly ideal for this kind of thing...

[freebeard]

Signage shops, possibly. The vendor local to me is Multicraft Plastics. They have three pricing levels, approach them business-to-business instead of as an individual.

PolyMetal

Grimco have MAX-metal and AlumaCorr, an aluminum skinned coroplast.

[19bonestock88]

Man, there are just not many sign shops here in WV to even just buy coroplast from, let alone some AlumaCorr... I might have to stick to eBay or the like and only buy what I absolutely need...

[19bonestock88]

Okay, so I've made the vortex generator array for my roof, but haven't tested it due to lack of additional people to take photos of tufts and/or run stopwatches(coast down testing)...

So, I basically paraphrased the details from the Mitsubishi Lancer EVO: 8 fins(plus one in the center that was the antenna on the EVO), 5mm thick(the coro I used was 4mm), 30x60mm(I used 1"x2" because I was using a measuring tape), 100mm apart(I used 4"), at a 15* angle relative to airflow(I didn't have a protractor handy, so used 1/4"width for 1" length and it looked close), and 100mm from the point of separation... I could have tested that but instead assumed it to be the top of the back glass and went 4" forward from that... I can't tell any FE gain, but I did this at basically the same time as finishing my wheel skirts, so I might need to remove it and actually do some ABA testing, and/or tuft testing...

What I found was, that before, when the back glass was wet, the middle 50-60% would take forever to clear, without running the defroster... After installing the vortex generator array, the top half of the middle 50-60% clears much faster, but the bottom half still takes a while...

Yeah, I know, I still need to tuft test to show any attached flow on the glass, but it seems promising... However, I'm also aware that in ideal conditions, with probably millions in R&D budget, the above mentioned Mistubishi engineers only got a .006 Cd reduction, which basically amounts to nearly no fuel savings for the effort...

[19bonestock88]

I think that even if I only gain 0.5% in fuel mileage due to drag reduction, the ROI will be nearly instant; I spent nothing on this at all, not even the tape to hold it to my roof was purchased...

However, I might end up building a Kamm-back extending to the end of the trunk lid if I can get some materials...

I found a shop that can sell me sheets of coroplast for $25 each, and they can order AlumaCorr for $120 a sheet(too rich for my blood)... Once I decide on whether the VGA is actually working or not, I'll see about designing a Kamm-back that hinges with the trunk(but doesn't come off in wind)... However, that'll be after the belly pan is finished, and other, simpler gains are pursued...