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2mAn
2mAn New Reader
1/14/21 10:19 p.m.

Started asking questions in another thread, but didnt want to take it over, so Im starting my own.

2 Simple Goals for the MR2

#1 - Flat bottom into a functional diffuser

#2 - Rear wing thats also functional

A few pics of the car in the garage

2mAn
2mAn New Reader
1/14/21 10:20 p.m.

Questions

How can I determine the best height of these uprights? Here it's sitting on the engine lid about where the bottom of the uprights would be. My guestimates are around 8-10" above the lid.

I also plan to mount the uprights to that center support bar between the shock towers, though it won't put the wing all the way at the back of the car.

Is my thinking right or wrong that it's better being mounted to the chassis directly versus having it as far back as possible?

The other phase is the bottom of the car, as I plan to smooth it out as much as possible and try to adapt a Lotus Elise rear diffuser. The front bumper area actually looks fairly well designed but under the cabin looks like it needs some help. I have a huge section of plywood I was going to try and flatten the center section to prep the rear for the diffuser.


Is this area "flat" enough or does the belly pan brace ruin it? 
Notice how it's a pocket, sort of?

Do I Extend skirts on those edges, or just flatten that whole area?

 

NOT A TA said:

(1) If the engine cover/trunk lid is strong in the area where the bumpers are (won't flex much) you could move the supports back to that area and attach to the lid directly instead of the structure between the shock towers? Then you could open/close more easily.

(2) 8" seems like it might be kinda low causing the wing and rear spoiler to work against one another. Do you know others with a similar car with wing set ups? Any CFD studies done on similar cars?

(3) If you use your plywood mounted flat up to the bottom of the frame rails would the braces interfere? Hard to tell in pic. Is the plywood wide enough to stick out on the sides by the rockers?

(4) If you are able to mount plywood to bottom of the rails would you be able to transition to the Elise diffuser cleanly?

(5) Will the plywood/diffuser restrict engine cooling? I've seen that the Lotus use NACA ducts in the flat area ahead of the diffuser for some reason.

(6) Can you install the Lotus diffuser so it's at a similar angle as it is on an Elise? Need to cut out a section of the rear bumper cover?

(7) This guy is the only one I've seen in the aero forum sections around the Internet that has done similar things to what you want to do https://www.trackhq.com/forum/the-equipment/aerodynamics/7120-i-finally-got-a-wing-results-inside

https://www.trackhq.com/forum/the-equipment/aerodynamics/7042-home-brewed-ground-effects

 

I numbered your questions to try and keep it inline, hope it helps...

(1) Definitely an option, and much more logical 

(2) I've watched some of that Julian guys' aero videos and 8" seems to be a mix of high but not too high. I also found this video, which seems to be helpful https://youtu.be/vB1iAnpuHR4

(3) It wouldn't interfere, the bottom of the brace is just shy of the bottom of the frame rails, in height/ depth

(4) That's the plan, to have it totally smooth all the way beginning of the diffuser.

(5) I've also seen the NACA ducts, but also don't know what it's for. Possibly the oil cooler that the Elise have for the 2ZZ which Toyota doesn't have for its own 2ZZ

(6) The angle will be identical and whatever needs to be cut will be cut (bumper or whatever else is in the way)

(7) He is also on Spyderchat, though the linked forum seems like a fun place to be. Might have to sign up there too haha 

 

It almost seems like the flat underbody would be a larger benefit than the Wing. That's why Im here doing "research" before I start hacking body panels. I'll be at Streets of Willow this weekend for the AROSC driver school. I've done it in the past and figure I'm ready for the Intermediate group but no roll bar means I'm with the rookies/ newbies. All good, first time on track with this car and it's my first mid-engine car so why not start from scratch 

2mAn
2mAn New Reader
1/14/21 10:28 p.m.
NOT A TA said:

If you can attach to the bottom of the frame rails and to the brace (using spacers) it should be pretty easy to create a flat bottom.

Will you have a splitter up front? Does the car under steer at speed without any aero modifications? Find out this weekend!!!  If so, reducing lift/creating down force at the rear may make it worse unless changes are made at the front to reduce lift. Gotta keep your balance! The stock Lotus rear diffuser and under tray were designed by folks waaay more knowledgeable than we are and engineered knowing where they wanted the center of pressure to achieve the balance they were designing for on that car.

I would investigate what the NACA ducts were for on the Lotus to hopefully prevent issues resulting from your under tray/diffuser installation potentially limiting cooling. You may need to install a similar oil cooler?

That forum where I linked the MR2 aero project is kinda quiet now. Several years ago it was one of very few forums with an aero section. My project is posted there and I keep saying I'm going to post it here but haven't done it yet because it'll take hours to move and bring up to date. https://www.trackhq.com/forum/the-equipment/aerodynamics/9416-very-old-bird-gets-updated-aero

I mentioned the flat bottom sticking beyond the rockers because the rounded rockers will probably let air roll under the side of the car, possibly reducing the effectiveness of the flat floor to some degree

 

 

I took some measurements of the plywood I have. Its a 48" x 60" section which seems to be enough to go beyond the frame rails and go all the way out to the rockers.

Plan would be to attach the panel along the frame rails and along the belly plan brace too so it is nice and sturdy, can probably go back to Home Depot Racing and get some skirts that can keep the air in that would normally escape from the rockers. 

I have another 48" x 19" section that I can use up front. The Cusco front brace is an open area behind the stuff going on up front. I think Step 1 will be to isolate the middle. Step 2 will be to clean up the front area, its not too bad but certainly isnt complete. And finally will be Step 3 where I hope to adapt the Elise Diffuser...

 

Stay tuned, and by all means chime in on my stupid idea

jimbob_racing
jimbob_racing Dork
1/15/21 5:41 a.m.

Wow. This is my kind of project. 

Kubotai
Kubotai New Reader
1/15/21 7:22 a.m.
2mAn said:

Questions

How can I determine the best height of these uprights?

 

In his book Race Car Aerodynamics, Katz describes tests with a 'generic sedan-based race car' aimed at measuring lift coefficient vs. height of the wing above the rear deck lid.  The lift coefficient was significantly higher when the wing was in the range of 0.7 to 1.5 times the chord width above the lid.  So if you have an 8" chord, the peak would be in the range of 6 to 12" above the lid.  The coefficient of lift dropped off slowly as you went higher but fell like a rock as you went lower.  So I would err on the side of being a little high and would pick something like 1.2 x the chord.  The peak coefficient he found was more than twice the value for sticking the wing way up in the air (more than 3x the chord) so there is a lot to be gained by getting it right.  Of course, his data was for a 'generic sedan' and you might get a somewhat different answer with your MR2.  

jfryjfry (FS)
jfryjfry (FS) Dork
1/15/21 8:10 a.m.

The wing looks a little narrow....   the wider it is the larger the effect. Most classes limit the width of the wing to the width of the body but it doesn't sound like you are going to follow any classes.  
 

 

iansane
iansane Reader
1/15/21 9:15 a.m.

I think all of your mods should be tempered with, "will it affect resale value?" laugh

Welcome, Simon.

NOT A TA
NOT A TA SuperDork
1/15/21 9:36 p.m.
2mAn said: I took some measurements of the plywood I have. Its a 48" x 60" section which seems to be enough to go beyond the frame rails and go all the way out to the rockers.

Plan would be to attach the panel along the frame rails and along the belly plan brace too so it is nice and sturdy, can probably go back to Home Depot Racing and get some skirts that can keep the air in that would normally escape from the rockers. 

I have another 48" x 19" section that I can use up front. The Cusco front brace is an open area behind the stuff going on up front. I think Step 1 will be to isolate the middle. Step 2 will be to clean up the front area, its not too bad but certainly isnt complete. And finally will be Step 3 where I hope to adapt the Elise Diffuser...

 

Stay tuned, and by all means chime in on my stupid idea

The idea of the rocker skirts is usually to keep air on the sides of the car out rather than get sucked into the low pressure area (fast moving air) under the car although in some cases the vortices created by the skirts are used by those who know more than I.

Carbon (Forum Supporter)
Carbon (Forum Supporter) UltraDork
1/20/21 6:53 p.m.

Ings+1 for a frisbee. Hoping the lack of windshield will make for some clean(ish) air for it to bathe in. Who knows what effect the gaping hole that is the interior and the turbulence that the seats, me, etc. will have on the aero.

Carbon (Forum Supporter)
Carbon (Forum Supporter) UltraDork
1/20/21 6:57 p.m.

i would like to fabricate a small (3"?) carbon and or polycarbonate windscreen to kick air up over the passenger compartment but we'll see. 

2mAn
2mAn New Reader
3/4/21 11:59 a.m.

Not a dead-in-the-water project, just slightly derailed by life...

Here we are with bumper off, and cracked flimsy OEM under tray removed. I tried to get my hands on the OEM front fender liners, as one was hacked and the other was ok but those circumstances have also changed and I've decided to remove all the OEM plastic. 

As you can see the radiator is vented out of the bottom so until I can vent it up top I will need to incorporate some venting out the bottom. I might just cut that portion in the middle and reuse that.

Im hoping to finalize the deal on an Elise rear diffuser so I can really get this moving.

Questions for the peanut gallery:

(1) Suggestions for the venting while it's coming out the bottom?

(2) Suggestions on how to mount up the center section? 

(3) Thoughts on the front section, should it start at the bumper or poke out a little in front? All across the front? Poking out on the sides? None at all , all underneath?

This is all fairly early on in the process, so hoping to take my time and do it right and I'd love any and all advice

BarryNorman
BarryNorman Reader
3/16/21 7:42 p.m.

In reply to 2mAn :

my .02s

3. Lowest point  between your front wheels extending forward and level.

2. How low is any bracing up front?

1. By adding a level front under tray your probably exiting the radiator out of the wheel wells. Until you vent upward.

NOT A TA
NOT A TA SuperDork
3/16/21 8:59 p.m.

I'd attach a long string to the rear of a frame rail. Then with the car on the ground with the shocks settled pull the string taught at the front of the car and raise it till it touches the front of the frame rail. This will give you an idea of things in the front that might be lower and give you an idea of how high off the ground the splitter might be if you had a flat under tray bolted to the rails leading forward to the splitter. 

Then if you can set up a simple way to measure dive & rear lift under threshold braking you could guesstimate how high the splitter needs to be depending how far forward it sticks out and determine what you can do before it chokes out due to the splitter getting too close to the ground.

The original front plastic tray does appear to have been designed to allow warm air from the radiator to escape into a low pressure area under the car.  As long as you maintain the correct pressure difference in front and behind the radiator you may not need to have it go out under the car. Are you opposed to hood or fender vents?

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