Aerodynamic tests and modifications on the MR-2 Spyder

[Autobahnschleicher]

I will look into that, but please consider that the MK1 and MK3 are very different in some regards.
The MK3 has the longest wheelbase of all generations yet is the shortes of them overall.
Due to its short overhangs, the radiator is just about in line with the front of the wheels.
Any ducting to divert air must come from in front of the radiator as there is no space for ducing radiator exaust there.
This is why I consider using the small intakes on the sides of the front bumper for it as the ducting would be significantly less complex.

Edit:
I will also keep the frunk as deleting that would massively reduce the practical capabilities of my car.
It also needs some weight in there or it becomes unballanced.
Wich is not nice as it makes the car understeer at low speed and unstable at high speed.

[freebeard]

This is why I consider using the small intakes on the sides of the front bumper...

If the bumper bar is above the radiator duct as I believe it is, that air plus more from the sides of the radiator duct could mix and flow across the face of a wheel spat. As a converging duct it might be a 5-8mm slot half the height of the tire.

Would you want to preserve the stock fender line?

Wich is not nice as it makes the car understeer at low speed and unstable at high speed.

Tail fins!

[Autobahnschleicher]

There is no radiator duct.
There is a crash bar in front of the radiator and air just spills in from the intake.
Ducting air from a radiator intake duct all the way to the fender liner as an air curtain would be rather complicated as it would need to take quite a sharp bend twice.
In case of the smaller air intakes on the side, it's a pretty straight path, requiring only a small duct from the intakes and a small cutout in the fender liner.
Likely it would even work without the ducting and just cutouts, but not anywhere near as well.

I will take some pics soon, have to do some work there anyway.

[Autobahnschleicher]

Finished my rust removal and prevention work on the Spyder and refueled.
Finaly broke the 40 mpg barrier.
45 ish should be possible as of now if drive a little slower on highways and drive less in the city.
Likely my fuel economy will get even better when I've installed a few more modifications.
50 might even be possible.

[aerohead]

A few years ago, one of the magazines hyper-miled a Porsche 911 GT3.
It was rated EPA 19 mpg highway. They periodically saw over 32-mpg, and predicted that with the optional touring fuel tank that, they'd be able to do 650- miles on a tank.
Driving 50-mph was part of their strategy.

[Autobahnschleicher]

I just noticed today that I hadn't re-installed the underbody plastics of the car.
So there might be some gains with the next tank of gas.
Just installed the front one and will install the two rear ones later.
Rain kind of interrupted the whole operation.
Also noticed that installing a flat undertray under my car will likely be an easy job as I have loads of good monting points and for the most part no exaust system in the way.
Only in the rear end where I could make a smooth transition to the stock plastics.

However unlike most aeromods here, this will need to hold strong at speeds well over 200 km/h.
Likely 230-250 km/h depending on how effective it will be.
Due to the higher maximum loads, I will need to use 3 mm ABS-sheets instead of the popular coroplast and reinforce it a lot.

[freebeard]

Look for Polymetal/Alumapanel/Grimco MaxMetal or equivalent. It would be 3mm of thermoplastic with aluminum skins and a baked enamel finish on both sides. (with some 6mm, one-sided options). Stiffness equals 5/8" plywood. One use is commercial signage, so sign shops become a source of cut-offs.

The samples shown were sheared, rolled and braked on hand tool with an 18" (0.5m ?) lever arm. I think a pneumatic nibbler would be an ideal cut-out tool.

The enameled finish saves a lot of work compared to e.g., fiberglass.

[Autobahnschleicher]

I had to drive it with the ragtop again now.
The difference in aerodynamic drag is quite noticeable.
It coasts noticeably worse than with the modified hardtop.
Where I maintained speed with the hardtop, I'm now slowing down.
And where I slowed down slightly enough to be a ble to compensate by speeding up before, I need to use the engine.

I wouldn't be surprised if the modified hardtop gave me a simmilar CDA to a Gen 1 Insights.
But I'd still need to measure that...

[Autobahnschleicher]

Fitted the rear underbody panels again.
Looked a little more for points to mount the flat undertray as well, it seems like my car is perfect for it.
Will likely use that aluminum/plastic sheet stuff if not all aluminium.

[kach22i]

I'd be more tempted to use the clad sign material than simple aluminum because I don't want to hear every little stone kicked up to the underbelly.

NOTE: If anyone finds a house roof material that is metal on the outside and dampened on the underside (plastic/bituminous) let me know. I want a metal roof but have a large Black Walnut tree out front that drops these rock like projectiles (walnuts) for a month every fall.