Aerodynamic tests and modifications on the MR-2 Spyder
 

As I plan on improving the aerodynamics of my car I'm making a thread with my tests and modifications.
Maybe someone will find this interesting or usefull, maybe someone will have suggestions.

In my first test, I have use wool, tape and an action cam to visualize the flow on and around the rear window.
As you can see seperation is occuring in the center, but flow is staying attached to large portions of the rear window.
Therefore I'm going to mount vortex genertors near the center above the window to get flow attachment in the center section.

rear window flow
 

Is the car a BMW X4?

As I said in the title it's a Toyota MR2 Spyder, a small japanese convertible.
However the distortion of the fisheye lens does indeed make it look rather weird...

MR2
 

Sorry! You clearly described the car in the header to the thread.
The rear window is extremely steep! I can see why you are thinking about vortex generators.
Does your car have the rear spoiler?

My car does not have a rear spoiler or wing, but I plan on mounting a small lip spoiler on top of the rear bumper to get a cleaner flow seperation.

Cd 0.31 ?
 

I found your car here at EcoModder.com's drag list at the top of the forum.
It shows Cd 0.31, however, I don't know if that required the rear spoiler.
The 1st-gen MR2 spoiler was good for a 10-count drag reduction.
The blueprint for your car shows attention to roof sides camber into the C-pillars. They may already be optimized as they are.
Turbulence and vorticity can rob energy, so VGs, reducing the actual volume of disturbed flow might mitigate some of that to the good, even after accounting for the permanent drag due to the VGs themselves. It's hard to tell without a laboratory environment.

Are you sure you have looked at the right car?
My car has no C-pillars, it's a convertible wich only kind of has B pillars and no spoiler.
Could you maybe have confused it with the MR2 MK-2?

Anyway, getting the flow to stick would siglificantly reduce the size of the low pressure area behind the car, wasting less energy in the wake.
Alternatively I would need to fabricate a kammback-extension over the engine bay to reduce the angle.

C-Pillars
 

Please forgive the steady stupidity.
Your removeable hardtop obviously has no C-Pillars at all, and only the appearance of B-Pillars, since there's no actual structure under the roof.
So, correcting for my blindness, Toyota seems to have paid attention to the faux- B-Pillar area, allowing the air to flow around the sides of the roof and vector inwards, at least limiting the wake behind the roof at those locations. A good thing.
If the flow reattaches onto the boot, you'll have a separation bubble which travels with the car, and it's low pressure will be isolated from the actual wake behind the car.
A Kamm- back would sure help with pressure recovery and higher base pressure, cutting drag. As long as it didn't interfere with mid-engine operation (I'm unsure what the 'grille' openings are for on the rear decklid ).

Yea, the airflow does indeed come around from the sides and helps it staying attached, wich is some good engineering from Toyota.
However a section in the middle has a tubulence, in my video I saw the strings there pointing to the front of the vehicle.
If I can get the flow to attach there, I can reduce the size of the wake significantly with little modifications the TÜV can overlook.
But I'll see if it works, ordered the vortex generators allready so might as well give it a try.

Looking forward to your testing !
Since it has a removable hardtop, you have the opportunity to create a nice top that you can replace when you want.
Since the car is rear engine, I would guess that some ventilation would be needed in the design.
With the airflow being pulled onto the back of the car, this might even help the airflow stay attached, and that is a real plus in your efforts.

Did I miss the year if your car ? I didn't see it.
Looking at the photo though, I'm guessing this may be the design of your car. https://ecomodder.com/forum/attachme...1&d=1618440476


You may find this hardtop Miata interesting.
You could do something similar. ( And it actually would look cool too ! )
Click the video link :
https://youtu.be/ymvI_h1VwgI

Yea, you got the car right.
It's a pre-facelift MR2 Spyder from '00.
That roof in the video is what I was refering to when talking about a Kammback. (Or ar they called fastbacks?)
Anyway, cooling air flows from the sidescoops into the engine bay and out of bottom or rear bumper.
That grille only realy helps reducing heat soak while after shutting the car down and there is even a panel below it, so not realy much happening there.

Main issue with such a top is that it is a lot of work with fiberglass and styrofoam while the vortex generators where 10€ shipped.
Don't get me wrong, I'll probably build something like that eventualy, but first I'll need to do a few mockups and make more tufts and find the time for it.
That's a larger project for a later point.
But if I can build molds from it and fabricate good hardtops, maybe I can recoup my investments by selling them.
OEM hardtops are drying up and where never sold in some markets...

I saw this once on google maps, don't do this. Attachment 30488

Well, that's one way of getting the engine bay temps down..
But that wing placement is just absolutely dumb.
Not only is it sitting right in the turbulence behind the roof, wich is probably worse due to the softtop, it is also sitting WAY too close to the cars body.
That thing just adds way too much pointless drag and likely produces 0 downforce.

Unrelated:
Raised my tire pressures further from 2,0/2,2 bar to 3,5/4,0 bar. (0,5 above sidewall pressure)
Rolling resistance decreased noticeably, I can now coast down parts in neutral where I had to stay on the throttle before.

I performed another wool tuft test to see if the airflow on top of the roof is flowing inline with the car.
This had to be done to ensure proper placement of the VGs at a 15° angle
As we can see, the airflow ontop of the roof is flowing straight, so I can install the VGs with a simple template.
First location will be 5cm upstream of the rear window, spaced 100 mm at 15°.
If that doesn't work, I'll place them 5cm downstream of the front edge of the hardtop.

Ended up mounting them a little forward and had to change the spacing ever so slightly because of trim lines.
Wool tufts are sticked on as well now, will test tomorrow because it's dark now.

I just performed the test.
Airflow is mostly attached to the rear window now, but it's still not as attached as it should be.
Will run that setup for a while and maybe try smaller but more vortex generators further rear.

If you tuft the deck lid, you may find there is re-attachment aft of a bubble.

Completely agree with Freebeard.
From the look of the photos, the tuft that you can see on the decklid appears to be attached, but I can't tell very well with just the one tuft showing.

Where can we see the video of the tests ?

I will have to run more tuft tests, but I agree with both of you, the flow should reattach to the engine bay.
I haven't uploaded the videos anywhere yet, but will perform a tuft test on the engine bay tomorrow.
Still, there is significant room for improvement.

I noticed something interesting:
When driving through rain, the rear window now stays completely dry.
Also I feel like it coasts slightly longer now and wind noises have been reduced.
Will probably mock up a kammback/fastback from depron soon.

When I did some maintainance on my car, I noticed a point where drag could be reduced:
The cooling system.
My car doesn't have a ducted radiator, wich implies I have more cooling drag than I need to.
As it is mid engined, I have the space in the front to add some ducting and the front bumper does have a nice shape to implement a grille block or intake duct.
Idealy I could take some inspirations from the Porsche 911 (996) and use the cooling air as air curtains around the front wheels.
But I will have to look a bit more closely at how I can route the airflow from the radiator.

I've taken a look at the CDA in the wiki:
Even though my cars CD is not that good at 0.31 (softtop), the CDA of 5.68 (soft top) is not that bad.
A gen 1 Insight has a CDA 5.00, to match it I only need to go from a CD 0.31 to down to 0.273.
I haven't done any measurements yet, but the hardtop alone certainly makes a difference and so does my VG mod.
With a flat undertray, ducted radiator and a fastback, I think I could beat an Insights CDA.
After all, I only need a 12% drag reduction to do so and that's based on a softtop.

Only concern with flat floor/undertray/diffuser on mid engined and rear engined cars is the gearbox/differential temperatures and exhaust heat. There may be enough cooling already through the rear vents but it is something to think about. https://classicsworld.co.uk/wp-conte...S-GUIDE-02.jpg

The transaxle shouldn't produce much heat, it's a 5-speed manual running good synthetic oil and the engine only has 100kW.
The exaust is mostly behind a heatshield and airflow in there is from front to back via the sidescoops.
Besides, there are plastic panels under there anyway, but they aren't at all aerodynamic.
They act more lile a parachute, wich is why I didn't mount them again after doing some engine work.

It wasn't that the transaxle produces heat, more that it could be heated by the exhaust. But if there is high airflow through the engine bay anyway, you should be okay.

Just for any non-EU Spyder drivers reading this:
DON'T reduce the airflow around the oilpan.
The 1ZZ runs its oil notoriously hot, especialy in the Spyder.
This causes serious issues and is part of the reason why they don't last.
Only EU models have an oilcooler.
If yours doesn't have one, I seriously suggest you get an aftermarket one.

When looking from the front I'm questioning how much drag reduction a full grille block would yield.
The air intake on this car is quite massive, I don't need that much cooling and with over 10L of coolant, I likely don't need any cooling at all on many trips.
These side-vents next to the radiator don't seem to do anything, so taping them shut with duct-tape would't have any downsides.
But with such a blunt grille block I'm not quite sure if the stagnation in front of the car might even get worse

Well, only one way to find out...

stagnation.............. worse
 

In 1986, FIAT ( SAE Paper 860212 ) did a wind tunnel examination of a large-scale model under many different configurations.
This car's cooling system drag was measured @ Cd 0.017. However, with a 100% grille-block, drag was only reduced by Cd 0.003.
By closing off the grille, upper-body drag was increased for this particular vehicle, limiting drag reduction witnessed on different vehicles.
Which brings us back to the argument about case-specific dynamics. There's just no way in advance, that one could anticipate what any given modification might do to the drag.

Sometimes forcing more air over the bonnet is a bad thing, sometimes forcing more air under the car is a bad thing. sometimes reducing air flowing out the wheels is a bad thing. You may reduce the cooling inlet drag, but lose the drag reduction caused by where the flow exits, or force more air under the car causing more drag there.

completely agree^ , although you can guess based on past examples, but even then it is not always useful if you overlook a critical difference between your car and the previous example's car.

I just had a look under the car in the front-section.
There is absolutely no ducting in front or behind the radiator, the air just spills on and around it and below the car.
Sadly there is no space to make Porsche 996 style air-curtains as the radiator ends about where the wheels start.
There are also some components in the way.
The small vents in the bumper don't actualy do anything and could as well be taped off (or re-purposed for air-curtains)

Possible modifications to the radiator air routing:
-intake duct and smaller intake cross-section
-exit ducting from the fan-shrouds to the wheels
-fully closed flat undertray from the front bumper to the rear end (black ABS plastic untill engine, aluminium sheet metal near the engine and exaust)

Allthough idealy I would design a whole new bumper, the current one has large flat surfaces at the front, wich are less than ideal.
I haven't yet been able to measure pressures there, but a rounder one would certainly be better.

Graysgarge used to post on Ecomodder, before he went to work for Lucent. He has a first-gen MR2 project car.

MR2 Radiator Ducting - Gray's Garage at Gray's Garage

http://graysgarage.ca/wp-content/upl...MG-243x300.jpg

It looks like there is nothing but a bumper bar behind the front fascia. Pull air from the sides of the radiator intake into your air curtains.

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.

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?

Tail fins!

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.

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.

a little slower
 

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.

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.

https://ecomodder.com/forum/member-f...1-100-0866.jpg

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.

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...

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.

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.