Flat underbody - MR2 Owners Club Message Board
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post #1 of 39 (permalink) Old April 19th, 2012, 11:40 Thread Starter
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Flat underbody

Hi have plans to make the underside of the car completely flat as alot of you have.

I am going to go right to the sills either side and fit skirts to prevent the air going under the car and also a front splitter and rear diffuser.

Im stripping the car in winter to the chassis for shot blasting and as stupid as this sounds, ill be trying to keep the car as stock looking as possible while helping the aero, its not a dedicated track car but I am looking for performance gains.

I have a few issues with cooling...

1) the radiator vents to the underside of the car, how detrimental to the setup is cutting holes in the bottom for the radiator vents? I really dont want to change the bonnet so it vents out of the top but if cutting holes in the bottom will ruin my aero ill have to do it.

2) I have a trunk mounted intercooler which gives me great intake temps, i also have fans pushing the air thorugh it out between my exhausts underneath the car, i have no under engine covers on and fan on the engine lid, this is all to keep overall temps down for intake, not to keep the engine cool.

Has anyone blocked off the underside of the car and measured the temperature change in the engine bay itself?

Not sure what to do about venting my intercooler as the rear diffuser will be there!

Lots of planning but plenty of time

Any advice at all would be great!

Thanks

Graeme
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post #2 of 39 (permalink) Old April 19th, 2012, 11:44
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I feel like your going to be pioneering alot of these ideas. No way to measure less more more effective with out a wind tunnel, its all just theory. and road feel
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post #3 of 39 (permalink) Old April 19th, 2012, 12:48 Thread Starter
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Yeh I completely agree with you, i might see if there are any wind tunnels in the UK, sometimes universities and schools will use your stuff for free in education so I might be able to get a before and after if I can find somewhere, thing is id probably only get that, and wouldnt be able to do multiple testing.

I think holes under the car for venting would harm the setup and possibly make it completely useless, so i might have to work on other ideas to vent the car

Graeme
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post #4 of 39 (permalink) Old April 19th, 2012, 12:53
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I would love to do a flat panel up to the engine bay, I actually had thoughts of welding on a square bar the length of the car that will be tapped. It will make the under panel as flush as can be with the other under body parts thus making the panel removable. The second section will be a diffuser that will somehow connect to the longer section like this ---[---. The rear section will cover from the engine bay to the tail pipe and have an incorporated diffuser. This will allow for the engine to be removed without removing the whole under body off.

As far as the radiator I had thoughts of opening up the wheel splash guards and somehow put two puller fans in there to such the hot air out from the radiator section with some type of tunnels created. This way you can still have the bottom completely sealed and flat, while letting out the hot air. I just dont have the resources to complete such a job.. or the time to do it even if i did..
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post #5 of 39 (permalink) Old April 19th, 2012, 13:08 Thread Starter
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I was thinking of somehow verting the radiator out of the wings and modifying them with grilles, im going to put the car on a ramp and take alot of measurements and pictures and try to come up with a selection of ideas, i dont have a problem chopping and welding the car to make stuff work and fit, I think itll be an interesting project.

I want the entire underside of the car flat to the rear diffuser, im trying to envisage how far the subframe sticks down and if this will get in the way.

I was wondering if there is a risk of flipping the car at high speed if you hit a bump in the road, i regulary do 120-160mph

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post #6 of 39 (permalink) Old April 19th, 2012, 13:43
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we lost a few stock vets at that speed here in NY on the southern state parkway.. in the trees, in a house, off the road due to its flat bottom and high speeds.. So if thats the case on a stocker on a flat parkway.. You are now putting yourself in the realm of being subject to that. I am also sure that the engineers behind the vet put a lot of thought into them and still cant seem to get it right. So i truly wish you luck on the not flipping part. Just make sure you have on a 5 point harness, a helmet and a working airbag when you do testing over 130
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post #7 of 39 (permalink) Old April 19th, 2012, 15:15 Thread Starter
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Yeh i hear you, when i strip the car ill be having a roll cage welded in, i do need some safety now, 8 years of hard driving this car with no accidents must just be luck

I was just thinking, would have a vented bonnet for the radiator give some front end grip?

Graeme
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post #8 of 39 (permalink) Old April 20th, 2012, 16:03
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Quote:
Originally Posted by ^Trickster^
Yeh i hear you, when i strip the car ill be having a roll cage welded in, i do need some safety now, 8 years of hard driving this car with no accidents must just be luck

I was just thinking, would have a vented bonnet for the radiator give some front end grip?

Graeme

that should keep the front down.. and ill be working on a project like that soon as i clear up some of my other projects.. :-)

p.s.

im sure you will be ok, just follow what that MR2 did a few years back at the salt flats.. he didnt flip so im sure you will be fine..

Last edited by eazy2001x; April 20th, 2012 at 16:09.
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post #9 of 39 (permalink) Old April 20th, 2012, 16:59 Thread Starter
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What did that mr2 do? lol educate me

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post #10 of 39 (permalink) Old April 20th, 2012, 20:54
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I would recommend tilting the Radiator forward and venting through the hood, doing this would increase cooling and add down force by having the Rad fins act like many tiny front spoilers. Also From what I have seen on GT full skid plates is that there are vents for heat sensitive parts.
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post #11 of 39 (permalink) Old April 21st, 2012, 08:55 Thread Starter
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Thats interesting, so they arent all completely flat, they do have openings?

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post #12 of 39 (permalink) Old April 21st, 2012, 16:39
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post #13 of 39 (permalink) Old April 21st, 2012, 16:45
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I think you would be crazy to even think of closing the engine bay off
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post #14 of 39 (permalink) Old April 21st, 2012, 17:54 Thread Starter
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Why do you say that?

The engine is water cooled, and im sure the side vents would supply plenty of intake air and air to my trunk mount still, its debatable how much air comes up from underneath.

I run an external oil cooler also, so I think it would be fine to be honest

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post #15 of 39 (permalink) Old April 21st, 2012, 18:31
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I can sort of agree.. If ur unsure about how much air come from underneath, do some tufts testing amd it will show u... Ive driven with my engine lid unhooked on hood pins, after 160kmh its lifted the engine lid up almost 2inch... So i would not underestimate how much airflow come from under and then up....

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post #16 of 39 (permalink) Old April 21st, 2012, 21:59
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The Bernoulli effect will pull a lot of air through the engine bay creating a vacuum under the car causing additional downforce, however this will cause a little more drag than a pure flat bottom, but a cool engine is a happy one, especially in a endurance race.
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post #17 of 39 (permalink) Old April 26th, 2012, 12:13
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I would suggest putting fans on the engine lid to suck air from the side vents. You might want to put an oil cooler in one of the vents if possible. The RX8 pictured above uses a Naca duct, which might be a good idea to blow some air up onto the turbo.

Venting the radiator will give you the best cooling and aero effects. Venting it under the car will nearly, if not completely, negate the benefits of the flat bottom.

For the intercooler, I would suggest venting it straight out the back. Cut holes in the middle plastic thing, put some black grill like material and mount two fans there and you will get the aero benefit of venting your intercooler right into the dead air behind the car. If you want to rice it up, you can put some lights there too.

Another option would be to vent directly above the rear diffuser. I am not sure how that will effect aero performance. To do it right you will need to fabricate a narrow, but long duct. Would be pretty interesting.
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post #18 of 39 (permalink) Old April 28th, 2012, 00:51
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There is a LOT of air that comes up from under through the engine bay and tries (or does) exit out the engine cover. My SC cover has a gas strut prop with no latch and it lifts on its own with the sunroof up (swap car) at 80MPH... closes when you put the sunroof down (very entertaining to observe) when going down the road I'm sure. Scared the crap out of me first time it flew completely open like that. Looked up and all I saw was red and vents! Clearly as was stated, I think you're vastly underestimating how much air comes from under that engine bay to help cool the motor.

As the others said, I'd think doing a flow through angled radiator setup vented out the hood is going to be the only way (shy of canards mixed with maybe a crazy 4-5 inch lipped CF splitter, etc) to hold the front end down on the ground... rear may need more down force too at that point, something to consider anyway. I've been looking at doing this for years... have the metal in the shop for the widebody and flat bottom panels, just haven't gotten to it yet! Best of luck!
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post #19 of 39 (permalink) Old April 28th, 2012, 19:30 Thread Starter
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Thanks for the replies guys, i have a loose engine lid as the latch had to go because of my engine setup , but it has a shroud with fans which must be heavy as it never lifts up even at 160mph

I have an external oil cooler in the side vent already, I think the radiator would have to be vented through the hood, so thats an agreement, i am considering removing the rear quarter windows and turning them into vents into the engine bay.

I had thought of venting the intercooler through the rear between the lights, didnt want to but if thats the only option i will.

Any thoughts on the car flipping?

Graeme
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post #20 of 39 (permalink) Old April 29th, 2012, 11:22
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I have thought of putting a secondary rad in the Black Plastic mesh area between the two lights myself, but you would need to duct air into the drunk from under the car with out causing too much turbulence.

As For the Flipping, Front end down force is your friend. would suggest tilting Rad forward.
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