Best approach for aero improvement on sedan roof?

[19bonestock88]

So, I wonder how much benefit of the Kamm I could gain if I terminated it about halfway down the back glass? That way, it wouldn't interfere with trunk operation...

I might still experiment with a VG array, since I don't have enough material for the kamm, but have the stuff for the VG array... I did buy some coroplast, but not a wide enough piece to do the roof(still need to find sheets at least 6' wide)

[kach22i]

Double Post

[kach22i]

Or this?

http://ecomodder.com/forum/showthrea...1-a-19525.html


I assume this can be done in a transparent material.

Arerohead has posted data/diagrams on truncated Kamm's before, check out his forum gallery.

[aerohead]

Slats and slots are for 2D-flow wings at very large angles of attack,to prevent stall during short field takeoff or landings.
A fastback car is more a half-body with 3D-flow.Since the belly of the car is flat,there is no camber,no angle of attack,and no lift.If the roofline is proper there won't be any separation,and separation-induced lift.
Spirit of EcoModder is more like the half-body with it's mods and is a zero-lift vehicle.

[aerohead]

Originally Posted by 19bonestock88

So, I wonder how much benefit of the Kamm I could gain if I terminated it about halfway down the back glass? That way, it wouldn't interfere with trunk operation...

I might still experiment with a VG array, since I don't have enough material for the kamm, but have the stuff for the VG array... I did buy some coroplast, but not a wide enough piece to do the roof(still need to find sheets at least 6' wide)

Unless you extend the Kamm addition to the rear of the car,it will have little effect.
You might even end up with higher drag.

[19bonestock88]

That's what I was fearing; part of the reason I considered a vortex generator array was that it(on the evo) produced a smaller wake, which can't hurt FE

[aerohead]

Originally Posted by 19bonestock88

That's what I was fearing; part of the reason I considered a vortex generator array was that it(on the evo) produced a smaller wake, which can't hurt FE

Here's an early investigation for VGs on a notchback by Gary Wheeler.



Ideally,you'd have a wind tunnel at your disposal and a lot of time and money.
*there are VGs like these.
*there's also a 'wishbone' variety as well.
*the kind Subaru used on the Lancer EVO
*co-rotating VGs
*counter-rotating VGs
*angled grooves
*trip-wires
*and sub-boundary-layer-thickness 'nub' VGs
Theoretically,one would have to investigate them all,and test for quantity,and placement.The best application might include a variety of different VGs used together.

[freebeard]

I'm not sure about that detour through leading edge slats.

To me it's 'how much pain are you willing to suffer to achieve your goals?' and I doubt vortex generators will get you there. The Blackfly Metro pictured in Permalink #23 is a good start on implementing Dr. Alberto Morelli's Fluid Tail Technique (FTT); it just needs lots of work below the beltline. See the PDF at https://www.google.com/url?sa=t&rct=...9cFbTNPI2EPR0A

You mention trunk access. The best solution I've seen was done by christofoo on his notchback.



The Kammback is raised by the act of opening the trunk and acts as a shade/raincover while it's open. All conforming to Morelli of course.

[19bonestock88]

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 like the one used on the Evo... It just consisted of 30x60mm triangles(about the thickness of coroplast) fixed four inches apart, and four inches from (ahead of) the flow separation, and at a 15* angle compared to the airflow, eight in total(plus the antenna)...

[Koots]

Originally Posted by 19bonestock88

Well, my car has the 4T45E transaxle(still despise it's being an automatic but no manual was offered on this car) with the 3.63 final drive ratio, and I turn around 2600 at an indicated 80mph... Other final drives were offered (the 4T45 behind the 3.5V6 was 3.08, and the Malibu Maxx had like a 3.23 ratio to compensate for weight), but I don't know how well my L61 (2.2 L4)PCM would play with a taller transmission... Not that it has power to turn taller gears anyway... The main issues with getting great highway mpg is the interstate on which I do much of my highway driving(most of it is two lane at 55-60mph), it has lots of 5 and 6% grades, on which the engine struggles, and the trans kicks down, and then I'm turning 4000+RPM getting an instant reading of about 12... Figuring out how to get the trans to stay in OD and still maintain speed is just a matter of reducing resistances(drag, rolling resistance, weight), but I'm just getting started...

With HPTuners you can command the transmission to shift faster (for less time spent shifting, spinning and creating friction) and cater your shift points to how you want. You can have the transmission shift at certain TPS%, load, speed and pressures. You can fine tune the TCC lockup points to command to stay on for longer or early, so you can stay in OD longer. It's not something anyone can do and it's something I've rarely messed with, but it can be done by a skilled tuner. I'm just a novice tuner at best.

Depending on ECU, you might have access to it's lean burn modes, deceleration fuel cut off points, you can command when the drive by wire throttle hits PE mode (power enrichment, which adds extra fuel to prevent lean conditions on sudden acceleration), some older models can have the O2 sensor trigger/switch points adjusted to keep the engine running leaner for better economy (doesn't seem to work with my 09 Sierra, but it did with my 02 Silverado, for example).

Even a proper adjustment to the VE and MAF tables to follow the true curve of the airflow coming into the engine can improve power delivery and efficiency, when you're commanding the perfect AFR for your driving conditions. Monitoring AFR with a wideband is definitely needed to start running lean like that, but it's all possible with a tune. You're not going to magically get 3-4MPG, but I can see a bunch of these changes squeezing 1-2MPG out of most engines, especially GM's. They are generally tuned very conservatively to make sure they can run on the worst kinds of fuels in all weather conditions in various states of disrepair. This means they run kind of rich by default, it's safer for everyone, but is not ideal for performance and economy.