improving a softtop convertible

[serialk11r]

Originally Posted by kach22i

Will you be taking the 2-inches out of the middle to retain the end arc?

One inch off either end. The distance between my taillights is around 38 inches or something, and the S2000 spoilers are 40 inches wide apparently. I think it's better this way because the spoiler ends up higher and that's kind of what this car needs, though it's fractions of an inch either way. The more important reason is because it's easier to make :P

Another idea is to raise the spoiler half an inch with some mini supports and then cut off only 0.5 inches from each end as it'll clear the taillights, but I think that might look odd.

[aerohead]

Originally Posted by serialk11r

Okay, I put tufts on it today, attempted to videotape but I couldn't figure out how to hold the camera still for my life (besides it's not safe to be staring at my phone while driving) so I will enlist some help tomorrow if it's not raining.

The placement of the tufts was done in a manner that would allow me to see the ones on the side through the side mirror and the ones on the rear bumper through the rear window (but not the rearview mirror). I know there is a giant bubble of separated air on the back so there's no point in putting tufts there.

I did go for a little drive and noticed a handful of things.
First of all, I placed one yarn tuft near the top of the side scoop, and it seemed to be flapping in the wind, so perhaps the intake isn't super aerodynamically clean. Oh well, nothing I can do about that.

Second was that the tufts along the side of the car at the end were all wrapping towards the center of the car, and the tufts on the softtop were wrapping steeply upward along the surface of the top. I'm guessing there is a big vortex that's doing that.

The air blowing the tufts is seeking a lower pressure in an attempt to achieve equilibrium,or actually caught inside some circulation (vorticity) induced by separation.

[serialk11r]

Originally Posted by aerohead

The air blowing the tufts is seeking a lower pressure in an attempt to achieve equilibrium,or actually caught inside some circulation (vorticity) induced by separation.

The tufts were at an almost right angle to the axis of the car, which makes me believe it's coming from vorticity. If the air were seeking a lower pressure region, it would not be able to have so much velocity in that direction at equilibrium. Looking at the paint, the typical "swirl" scratch marks don't exist in that area; the scratches are all at a 70-80 degree angle going inwards towards the engine compartment.

[aerohead]

Originally Posted by serialk11r

The tufts were at an almost right angle to the axis of the car, which makes me believe it's coming from vorticity. If the air were seeking a lower pressure region, it would not be able to have so much velocity in that direction at equilibrium. Looking at the paint, the typical "swirl" scratch marks don't exist in that area; the scratches are all at a 70-80 degree angle going inwards towards the engine compartment.

It makes perfect sense.
There are some photos of the Kamm/K-Fachsenfeld FKFS wind tunnel models which had square body edges down the length of the body.
In the photos you can see the tufts all sticking up into the air,held by the attached longitudinal vortices circulating at these edges.
Their measurements showed that rounding off the intersection cut drag a little over 16%.About Cd 0.174 vs 0.21.
Charles Lindbergh's Spirit of St.Louis suffered from this vorticity.
Ditto for the 1944 WACO CG-4A assault glider.

[serialk11r]

Okay thread revive! I've finally decided I'm switching my FR-S for an MR2 Spyder. I don't use the FR-S much, and so it's sitting there depreciating to the tune of 2k a year without being much fun to drive, so I figured I might as well have a more fun toy that's also cheaper. For less than half the price, an MR-S with 2ZZ would be faster, far more exciting, and much cheaper to own.

Since the FR-S has incredibly low drag and a much newer engine, I'm probably going to see a decrease in highway mpg, while the 500 pound weight reduction will get me some more city mpg. There's a 2ZZ car I'm going to look at but if it doesn't work out I'll get a higher mileage 1ZZ car and swap the engine.

I've talked to the Thai guy who makes the Lambo lookalike kits and he can do the hardtop (advertised at $1833, not bad), but communication is slow and I'm ironing out details but I think it'll work out. Profile is similar to the stock top, but I was surprised by how much I like the looks of an OEM top with a smaller rear window.

The downside of that top is that I may need to cut my own rear window into the back, and I have to pull the front fenders to bolt it on (it wraps over the windshield frame).

So to start I'll be getting that and a spoiler from the same place, hopefully bringing the Cd down from I'm guessing 0.34 ish (a lowered car) to maybe like 0.31 (if it actually knocks 10% of the drag off, that would be amazing), while decreasing lift.

The next aero things that I think would be reasonably easy and cheap to do would be:
-Radiator intake (large sheet of rubber curled up to shrink the duct opening?)
-Rear diffuser (bolt an aluminum sheet on...should be easy enough?)

Things I am not so sure about:
-Radiator exhaust (not confident I can shape it correctly to get any gains)
-Passenger side intake block (the curved shape is probably hard to make...)
-Racing mirrors (the base that bolts onto the door may be hard to fabricate...how hard is it to learn 3d printing software?)

I probably need to buy some stuff to make getting under the car easier, there are a few places where a coroplast sheet would probably do a lot of good.

[kach22i]

Originally Posted by serialk11r

I've talked to the Thai guy who makes the Lambo lookalike kits and he can do the hardtop (advertised at $1833, not bad), but communication is slow and I'm ironing out details but I think it'll work out. Profile is similar to the stock top.............

Pictures?

[serialk11r]

But without the silly fake scoop.

[serialk11r]

So turns out that Thai hardtop doesn't have seals...because it goes OVER the stock soft top. The stock soft top frame is quite heavy and would be something I'd rather get rid of, so back to the drawing board.

Have a car lined up, still waiting on confirmation from seller. I am considering leaving the soft top alone for a while since a hard top is such a large expense, probably a good idea to focus on first getting the underbody and rear spoiler done.

While I was not really a fan of the warm air intake mod, I realized that on this car all I have to do is tape off the driver's side intake and the engine intake will start sucking hot air from the engine bay due to the intake's placement. Easy gain for a longer journey on the freeway.

[kach22i]

Originally Posted by serialk11r

So turns out that Thai hardtop doesn't have seals...because it goes OVER the stock soft top. The stock soft top frame is quite heavy and would be something I'd rather get rid of, so back to the drawing board.

I wonder if you could take off the convertible frame/seals and just use some standard automotive seals from your local NAPA store as the interface between the hard shell top and windscreen frame/body/side glass.

Weather proof 3M double stick tape perhaps could be used.

I mention NAPA because our local store seems to carry the stuff (basic stuff) other stores do not. I'm sure if you need some exotic profile you could find something on-line or special order it.

[serialk11r]

Originally Posted by kach22i

I wonder if you could take off the convertible frame/seals and just use some standard automotive seals from your local NAPA store as the interface between the hard shell top and windscreen frame/body/side glass.

Weather proof 3M double stick tape perhaps could be used.

I mention NAPA because our local store seems to carry the stuff (basic stuff) other stores do not. I'm sure if you need some exotic profile you could find something on-line or special order it.

Hmmm...that's a good suggestion, although it makes me kind of nervous. I think people have DIYed weatherstripping like that on this car before for other hardtops that didn't come with it.

The car I was looking at has a nice new soft top which I feel bad about throwing away, if I get that one I might just ditch the hardtop plan. The Honda "baby NSX"/"export S660" rumors came back again, so maybe I'll be switching to that car afterall...