How about this? Sort of contrary I suppose. I tried vortex generators and they seemed to add some drag. They certainly kept the flow attached to the back window like others have demonstrated. I think they made more lift and thus drag. I decided to try the opposite, force the air to detach. I can't say for sure yet whether this is helping but the glides seem longer. The back window is right at that 30 degree angle where subtle changes can make a difference. This seems to help more at the higher speeds. I know it is opposite to what others find useful.
The 1999 SL was sold and I bought an SC2. Drag rises dramatically with increased speed on the smooth topped coupe. Max mileage on the coupe is around 40-45 mph. The drag increase is much more subtle on the SL with max mileage coming between 55-60 mph. The SL will run up to 85 mph quite easily.
At the higher speeds on the SL I run into a fluke with the Scangauge. At 3000 RPM and a slight deceleration at 16% tps the scanguage will decide it is in idle cutoff and show 999 mpg for 1/4 mile or so. Just a funny anomaly that gets in the way of accurate comparisons.
where is the second half of the post from? the change in optimal speed may have been caused by not having the same engine, trans or other things as well. maybe others would know better, but it seems odd that any car with factory gearing, and hadnt been modified in a way that reduced low end power, would find its better mileage at 55-60 than 40-45
i always thought it was wierd that the sc and sl had the same highway ratings, i would have figured the shape of the rear of the sc would have to be more aero than that of the sl. or maybe its only a half mpg difference or so
i would tend to think that your mod would be a considerable improvement for the sl
It is just my observations. It is all the same post. I just left the picture attachment stuff in the middle when I added the other commets. I thought the SC would be much lower drag than the sedan also but after a few thousand miles I am not so sure. Of course the engine and transmission differences really cloud the comparison.
I plan on adding Somender grooves to the SC2 head this winter. That should help it a bit.
The mileage difference comes from the SC2 using a DOHC engine with a different transmission. More power(about 20%) and it's geared lower for getting all that power up to speed. It's the performance Saturn!
I believe the SC's do have slightly better Cd's (.005 ?) and they're a bit lighter as well which may help FE in an SC or SC1.
What kind of VG's did you have previously. I put mine on to try to get flow reattached to the trunklid. I found the template here to make some. I've seen others which seem to present a lot of frontal are and are quite tall (think airtabs), which on cars seem like overkill.
I put mine on at the same time I installed a full grill block so while i saw a huge increase in coastdown times, I wouldn't point to the VG's as having much of, if any contribution. It does keep the water running straight down the back window though.
It looks like you made your new "kammback?, roof extention?" from coroplast. Is it just taped on or is there more to it?
The VG's were air tabs. I had previously made my own vortex generators for an airplane but thought I would try the Airtabs this time. Maybe I should try the airtabs with the roof extension. Below is where I learned to make them.