Aerodynamic tests and modifications on the MR-2 Spyder

[Autobahnschleicher]

Did some repairs on the MR2 again:
The bushings on the fron lower controll arms as well as one of the bolts holding them went bad.
Also did some sandblasting and repainting of some other suspension components while I was in there.
Also checked some other places I've treated before, no rust there.
The treatment with epoxy rust converter and cable grease seems to be effective.
Still need to get that bolt new from the dealership because it is missing some material and seems to have caused some issues under hard braking.

Big downside of sandblasting:
The sand is stuck in my hair now...

[Autobahnschleicher]

Mounted new front controll arms, replaced front brake pads, replaced front rotors and greased the slider pins now.
The car is handling great again and brakes straight as an arrow.
The issue seems to have been with the brakes themselfes not the controll arms as replacing just them and checking the alignment did not fix the issue, but servicing the brakes did.
Did a bit of high speed driving with the tires aired down to 1,6 and 1,8 bar to check the handling, that will affect my fuel economy a bit as it realy guzzles gas at speeds in excess of 200 km/h (125 mph)

Coming up:
3-D laser scan, CFD simulations, modifications of the 3D-model for CFD tests including but not limited to fastback hardtop, spoiler and rear wheel covers

[freebeard]

What software will you use for the CFD?

[kach22i]

Originally Posted by Autobahnschleicher

Coming up:
3-D laser scan, CFD simulations, modifications of the 3D-model for CFD tests including but not limited to fastback hardtop, spoiler and rear wheel covers

Cool, can't wait.

[serialk11r]

Oh hey, someone working with a MR-S. I used to have 2.

The front cooling is definitely a good place to look. Ducting the exhaust might be too much effort but the intake definitely could use some modification. If you can take out the grill, it should be easy to take some plastic sheet and foam and make a smooth duct with a smaller and more efficient opening.

I remember thinking about how to make the exhaust a bit better and my conclusion was that you can remove the stock plastic piece and replace it with a flat plastic panel with a thin slit cut in it and an angled duct above.

As far as the rear, I would just toss on the longest spoiler you can find (if it doesn't need to look really good, this is pretty easy to DIY: https://auroraautodesign.com/product...nb-miata-90-05)

You can try to mess with a diffuser but the lack of OEM paneling suggests to me the results may not be great.

[Autobahnschleicher]

Originally Posted by serialk11r

Oh hey, someone working with a MR-S. I used to have 2.

The front cooling is definitely a good place to look. Ducting the exhaust might be too much effort but the intake definitely could use some modification. If you can take out the grill, it should be easy to take some plastic sheet and foam and make a smooth duct with a smaller and more efficient opening.

I remember thinking about how to make the exhaust a bit better and my conclusion was that you can remove the stock plastic piece and replace it with a flat plastic panel with a thin slit cut in it and an angled duct above.

As far as the rear, I would just toss on the longest spoiler you can find (if it doesn't need to look really good, this is pretty easy to DIY: https://auroraautodesign.com/product...nb-miata-90-05)

You can try to mess with a diffuser but the lack of OEM paneling suggests to me the results may not be great.

As for cooling, at current temperatures I postponed the idea of grille-blocking, but modifications to the ducting (or rather lack there of) are considered for the future, same as a flat underbody.
However due to the complexity involved in that, I won't be doing that now.
(also TÜV is coming up so I'll only do stuff they don't care about untill then)
As for the cooling intake, I am considering to fabricate a fiberglass insert for the bumper as well as some ducting inside.
Exausting it would likely work via the front wheels in that case as hood vents would cost me my trunk.

As for the spoiler, one as large as that would add a lot of drag.
My plans where going more in the direction of a small spoiler for a cleaner flow seperation as well as canceling out rear end lift.

The idea of adding a diffusor is tempting indeed, however due to drivetrain as well as exaust components, this would be complicated.
If the goal of the diffusor was to add significant downforce, it would need to extend quite a bit to the rear.
However my main goal here is drag reduction, so I won't need much of a diffusor.

[aerohead]

Originally Posted by Autobahnschleicher

As for cooling, at current temperatures I postponed the idea of grille-blocking, but modifications to the ducting (or rather lack there of) are considered for the future, same as a flat underbody.
However due to the complexity involved in that, I won't be doing that now.
(also TÜV is coming up so I'll only do stuff they don't care about untill then)
As for the cooling intake, I am considering to fabricate a fiberglass insert for the bumper as well as some ducting inside.
Exausting it would likely work via the front wheels in that case as hood vents would cost me my trunk.

As for the spoiler, one as large as that would add a lot of drag.
My plans where going more in the direction of a small spoiler for a cleaner flow seperation as well as canceling out rear end lift.

The idea of adding a diffusor is tempting indeed, however due to drivetrain as well as exaust components, this would be complicated.
If the goal of the diffusor was to add significant downforce, it would need to extend quite a bit to the rear.
However my main goal here is drag reduction, so I won't need much of a diffusor.

1) The OEM rear spoiler terminates along the AST-III contour. Local streamlines have already 'widened', with lower velocity, and higher pressure. Any extension, unless angled downwards, will only constrict the streamlines, re-accelerate the flow, lower pressure, and increase base drag.
2) If you had a full belly pan, it looks as if an 'all-metal' diffuser, in full contact with the bottom of the tailpipe, would give you a 'slow' diffuser, best known for low drag.
3) Extending the B-Pillars ( the MR-2 doesn't have C-Pillars ) as flying buttresses, with plan-taper, as Ferrari and Lamborghini have used, along with a 'narrowed' rear spoiler could be even better.
These changes helped me get to Cd 0.235

[Autobahnschleicher]

Originally Posted by aerohead

1) The OEM rear spoiler terminates along the AST-III contour. Local streamlines have already 'widened', with lower velocity, and higher pressure. Any extension, unless angled downwards, will only constrict the streamlines, re-accelerate the flow, lower pressure, and increase base drag.
2) If you had a full belly pan, it looks as if an 'all-metal' diffuser, in full contact with the bottom of the tailpipe, would give you a 'slow' diffuser, best known for low drag.
3) Extending the B-Pillars ( the MR-2 doesn't have C-Pillars ) as flying buttresses, with plan-taper, as Ferrari and Lamborghini have used, along with a 'narrowed' rear spoiler could be even better.
These changes helped me get to Cd 0.235

I think you're misstaking my MR2 with a different car:

1. It has no OEM rear spoiler
2. Yes, a mild diffusor might be possible, although that's more of a mildly angled bellypan than a diffusor
3. It does not have B-pillars as it's a convertible

[aerohead]

Originally Posted by Autobahnschleicher

I think you're misstaking my MR2 with a different car:

1. It has no OEM rear spoiler
2. Yes, a mild diffusor might be possible, although that's more of a mildly angled bellypan than a diffusor
3. It does not have B-pillars as it's a convertible

1) Thanks! It could be that only the US-spec MR2 possessed the rear spoiler. I have a blueprint for the 1998 model year. Cd 0.35, with the spoiler.
2) I believe that any upsweep to the final portion of a belly pan is considered a diffuser.
3) Convertible. Okay, got it! My image is for the hardtop. A spoiler wouldn't do any good for a convertible. The flow separates at the top of the windscreen and has no chance for reattachment.

[Autobahnschleicher]

Originally Posted by aerohead

1) 1998 model year. Cd 0.35, with the spoiler.

1998 model year was an entirely different car, the SW-20.
Mine is a 2000 model year, the ZZW-30.

Unrelated, did sparkplugs recently and my fuel efficiency improved a bit despite driving with the ragtop or the roof down. (heatwave here has been pretty bad)
Getting realy close to 45 mpg (US) now.
With more efficient tires, I should be able to beyond that.
Coming up: 4,xx L/100 km