improving a softtop convertible

[serialk11r]

Hi guys, been a rather non-active member around here for a bit. Today I just agreed to purchase what will be my first car, a 2000 MR2 Spyder!

The fuel economy is already really good, should be a piece of cake to get 35-40mpg, but of course the nerd in me wants to improve stuff. When test driving, the 5th gear was definitely too short, but I looked into a 5th gear swap and it sounds too hard, especially if I want to avoid spending 230 dollars on an OEM gearset:/ Call me a wimp. Since the car is already at 138k miles I figure I might as well just wait for something in the driveline to die and then do something about it. I am considering a Miller cycle 1NZ setup for when it dies, but that's just a fantasy currently. A 6 speed gearbox would be really nice, but they cost too much. Here's to hoping Toyota brings a new 1.5L ish engine with 6 speed gearbox standard to the US someday.

Of course, the next thing to look at is aero. The aero on this car is a complete mess just quickly eyeballing below the car and at the softtop. So of course, as a good nerd should, I am planning out aeromods to do in the future when I have some time. Part of the reason for doing this is also to reduce the noise.

I am requiring myself to make any mods aesthetically pleasing, as the car is such a beauty. Aside from the obvious grill block and belly pan (will require exhaust modification as there is a massive heat shield sticking out under the bumper :\), a few ideas I've thought up of are:
1. Spoiler mounted to softtop window. I think the top storage area has a little bit of excess space to accomodate this, but not sure. Will draw and upload a photo of what I am thinking sometime. As far as construction goes, I am thinking a thin acrylic sheet bent at the appropriate places, aluminum brackets, and held together with silicone glue (clear, durable, easy to apply, not brittle, reasonably high tensile strength) held to both the vinyl bonded to the glass as well as the glass itself, to reduce stress on the glass to vinyl bonding.
2. Trunk (engine cover) mounted "vanes" to reduce trailing vorticies. No idea how to optimize shape, and no idea how to fabricate, but maybe some experimentation will help. Comes much later down the road obviously.
3. Reworked exhaust and side intake ducting. The side ducts could potentially pipe a lot of air straight into the wake, which is great for drag. This is 75% of the reason I was so excited about mid engine. Fake bumper grills will need some material cut away, exhaust outlet can hopefully be moved upwards to the bumper, and ducts carrying the air from the side to the rear can hopefully be added. Engine can pull air from a diverted portion of the duct, and cooling air can be provided through a smaller hole. Stock exhaust will need some cutting and rejoining to make this work.

Any more ideas?

[serialk11r]

Okay got around to drawing it.



How much effect would a window mounted spoiler like that help do you guys think? The length it extends back over the windshield will be limited by how much extra space there is in the softtop storage compartment :/

Could probably use a rear spoiler as drawn in the second image, I got the "curve" pretty wrong but the Spyder has very little length behind the passenger compartment and so the flow off the top probably never reattaches to the body, I'm guessing.

[mcrews]

very nice little car.

If you do aq search there is someone w/ areo software that show the affects.

[Sven7]

I think you're going to have trouble attaching, detaching and living with the Kammback ("spoiler") unless you want to keep the top up permanently.

Many new convertibles have a vertical mesh fabric sheet behind the headrests that arrests vortexes in the cabin, reducing noise. I've been considering one for the Rabbit but it's not a high priority. Maybe you'd like to pioneer a DIY version?

[serialk11r]

Originally Posted by Sven7

I think you're going to have trouble attaching, detaching and living with the Kammback ("spoiler") unless you want to keep the top up permanently.

Many new convertibles have a vertical mesh fabric sheet behind the headrests that arrests vortexes in the cabin, reducing noise. I've been considering one for the Rabbit but it's not a high priority. Maybe you'd like to pioneer a DIY version?

I studied the way the top folds, and I believe there should be enough space for a permanently attached Kammback spoiler, though there may be space limitations. Nevertheless, I intend to have the top up on any trip that will exceed 35mph, it's just too noisy. There's also the issue of the trunk (engine cover) not being able to open with something sticking out the window, I haven't thought about that though.

I'm not actually a true "roadster guy", I just got the car because I like its lightweight philosophy, and because it's a great driver's car. If I could snag a hardtop one, I would

I do need to play with the streamline template to figure out how far behind the car I want a spoiler to extend. I really hope it's not necessary as the stock visibility out the rear is just so good, but the rear end is really quite short which sucks for aero.

One of the biggest problems I think is the airflow off the side of the cabin, I think there are probably pretty strong trailing vortices. Not sure about how to make an aesthetically pleasing solution to address that...

[aerohead]

If you extended the B-pillars,as extended buttresses rearward along the 'Template' profile you could capture a 'tailored' vortex inside there.
You would have a blind spot on the passenger side,but could compensate by using mirrors more.
The 1967 Lotus Europa was kinda like this and had Cd 0.29.

[serialk11r]

Originally Posted by aerohead

If you extended the B-pillars,as extended buttresses rearward along the 'Template' profile you could capture a 'tailored' vortex inside there.
You would have a blind spot on the passenger side,but could compensate by using mirrors more.
The 1967 Lotus Europa was kinda like this and had Cd 0.29.

Not concerned about the blind spot right there, I recall it being very difficult to see out the passenger side over the engine cover, with the stock car I need to use the mirrors to see anything on that side anyways.

My concern is retaining the ability to open the engine cover. Ideally the top doesn't need to be stowed to let the engine cover open, so if it's like raining or something and I need to pop the cover, only I get wet, and not the rest of the interior I think I would be okay if the engine cover would only open if the top were stowed, but I definitely want the top to be fully stowable because it's kinda stupid having a softtop that doesn't go down. With the softtop Kammback extension, it may be possible to have said extended buttresses sitting on the engine cover and still be somewhat effective.

Aesthetically, though, I'm not sure how to make it work...

[aerohead]

Originally Posted by serialk11r

Not concerned about the blind spot right there, I recall it being very difficult to see out the passenger side over the engine cover, with the stock car I need to use the mirrors to see anything on that side anyways.

My concern is retaining the ability to open the engine cover. Ideally the top doesn't need to be stowed to let the engine cover open, so if it's like raining or something and I need to pop the cover, only I get wet, and not the rest of the interior I think I would be okay if the engine cover would only open if the top were stowed, but I definitely want the top to be fully stowable because it's kinda stupid having a softtop that doesn't go down. With the softtop Kammback extension, it may be possible to have said extended buttresses sitting on the engine cover and still be somewhat effective.

Aesthetically, though, I'm not sure how to make it work...

Thinking out loud,if the mods were rear-hinged and forward-latched,could you swing the new construction away to the rear,exposing the engine cover for access? A removable pogo stick could support the construction as you service the engine.

[MGB=MPG]

"" Trunk (engine cover) mounted "vanes" to reduce trailing vorticies. No idea how to optimize shape, and no idea how to fabricate, ""

is this what you are talking about?
StolSpeed Aerodynamics - Performance Enhancement for Light Aircraft

[serialk11r]

^^ no, that's not what I'm thinking.

Originally Posted by aerohead

Thinking out loud,if the mods were rear-hinged and forward-latched,could you swing the new construction away to the rear,exposing the engine cover for access? A removable pogo stick could support the construction as you service the engine.

Perhaps! I hadn't thought of that. Opening the engine cover would be extremely awkward though haha, the construction would have to sit over the passenger compartment and lifting it to that position may be difficult depending on how much it weighs. Hinges might need to be pretty strong to not twist.

Took her home today:



Studied the softtop compartment a little more carefully. I think a solid structure is definitely not going to fit, but I think a spoiler that can fold would work. More difficult to construct obviously :/