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Old 01-30-2021, 09:02 PM   #1
Stiggy Pop
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Default 240 flat undertray examples

Does anyone have on their car, or pictures available of a 240 with flat undertray panels? I know, "it's a flat sheet", but curious if anyone with some experience did anything interesting I can draw ideas from. Not finding much with the goog.

I'm looking to increase high speed stability without adding any heavy visual aerodynamics, I thought this might be a place to start. Would have to figure out appropriate rear treatment without going all time-attack diffuser.

Also thought rather than dealing with a bunch of sharp aluminum, maybe I could make panels out of kydex and hang them with something like a dzus fastener for easy removal.

this kinda thing
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Old 01-30-2021, 09:15 PM   #2
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Kydex or poly would be simplest and similar to the ABS used by many OEMs for the same purpose.

IMO it seems unlikely to solve a problem, though. Assume you've looked at tires, alignment, bushings, tie rods, rake, and the like?
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Old 01-30-2021, 09:57 PM   #3
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Originally Posted by PaddyGarcia View Post
Kydex or poly would be simplest and similar to the ABS used by many OEMs for the same purpose.

IMO it seems unlikely to solve a problem, though. Assume you've looked at tires, alignment, bushings, tie rods, rake, and the like?
Yeah I’ve gone through it a few times, but trying to find ways to be more comfortable up top without compromising a great street setup in terms of the alignment. I do need to try dropping the rear more but it requires shortening the trailing arms. It feels a little twitchy at ~130 so I barely get to push it in 5th

Edit:
Think my last alignment was ~ -2° camber, +4° caster, and ~1/8” toe in. Tires are Dunlop zii

Last edited by Stiggy Pop; 01-30-2021 at 10:05 PM..
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Old 01-30-2021, 10:01 PM   #4
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Originally Posted by Stiggy Pop View Post
without going all time-attack diffuser.
Why not go full time-attack diffuser?

I googled kydex and it said "Maximum recommended service temperature is approx. 180 – 195°F" so you'd probably have to figure something out around the exhaust. Hater pipe out the hood, maybe?
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Old 01-30-2021, 10:30 PM   #5
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why and where you drivin130
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Old 01-30-2021, 10:34 PM   #6
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Why not go full time-attack diffuser?

I googled kydex and it said "Maximum recommended service temperature is approx. 180 – 195°F" so you'd probably have to figure something out around the exhaust. Hater pipe out the hood, maybe?
With the exhaust and driveline I’d probably have to run two panels down the floors and leave the tunnel open. Then try to box out behind the axle/around the tank.
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Old 01-30-2021, 10:40 PM   #7
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why and where you drivin130
Lime Rock, of course.

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Old 01-30-2021, 10:41 PM   #8
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I just replaced my bensin tank, I was looking at that big hole where the rear muffler used to be end was trying to figure out some kind of diffuser to stick in there to make some down force.
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Old 01-31-2021, 12:17 AM   #9
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My car certainly doesn't feel stable above 120mph or so but I kinda just uhh, go with it. Adds a little extra sense of fun. Or danger. I can't tell.
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Old 01-31-2021, 12:26 AM   #10
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I don't have anything to offer, but I'm going to follow this to see where it goes. Twitchy in the front or rear? Are you looking to do full undertray? Do you want to retrofit some OE piece or fab your own?
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Old 01-31-2021, 12:26 AM   #11
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The rear lift is very apparent on gravel over about 70mph.
The rally car uses a 4x8 sheet of LDPE split down the middle to keep the tunnel free. No issues with melting at all. The flaps extended to just a foot or so in front of the rear axle.

With your car being low, could a flat panel go from the floor to the gas tank without fouling on the rear axle?
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Old 01-31-2021, 03:28 AM   #12
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This guy on YouTube has couple of videos about making them. There might be better.
https://youtu.be/L9WCVlWPcys
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Old 01-31-2021, 07:34 AM   #13
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Originally Posted by Stiggy Pop View Post
Does anyone have on their car, or pictures available of a 240 with flat undertray panels? I know, "it's a flat sheet", but curious if anyone with some experience did anything interesting I can draw ideas from. Not finding much with the goog.
Check Lankku and his 245.
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Old 01-31-2021, 09:49 AM   #14
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Look at hypermileing 240s on google. There’s been a few.

Aero stuff makes a difference above 30 mph

the way the panels fit makes a huge difference. Your biggest gains will come from under the engine and smoothing out area behind the axle
Also the less holes in front of car the better ... ie gaps between headlights and turn signals (Look at a 240 vs 850 and then look up their drag coefficient all little things add up)

When you start modifying for aero your car will loose a lot of wind noise
One of the worse things on early cars are the roof drains.

Here’s some simple equations for aero stuff. Found this at my old school F1 engine builders shop

https://imgur.com/a/vwO72Yy?s=sms
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Old 01-31-2021, 09:53 AM   #15
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Quote:
Originally Posted by shoestring View Post
I don't have anything to offer, but I'm going to follow this to see where it goes. Twitchy in the front or rear? Are you looking to do full undertray? Do you want to retrofit some OE piece or fab your own?
- I mostly feel it lift in the rear, which is why it feels a little hairy.
- I thought I'd try to make something from the front lip down the actual floors, then make a tray behind the axle/covering the tank.
- I'll make my own, probably be more fun that way. Even if it doesn't help I just kinda want to do it, if nothing else it will protect my paint job on the underbody!

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Originally Posted by culberro View Post
The rear lift is very apparent on gravel over about 70mph.
The rally car uses a 4x8 sheet of LDPE split down the middle to keep the tunnel free. No issues with melting at all. The flaps extended to just a foot or so in front of the rear axle.

With your car being low, could a flat panel go from the floor to the gas tank without fouling on the rear axle?
LDPE is a good idea. Not sure what I can clear on the axle, will have to check. The exhaust runs under it... feel like the spring perches are low, though.

You'll notice I only make threads like these in the winter time, when it's single-digit weather here and I'm stuck inside lazy and bored looking for ideas.

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Check Lankku and his 245.
thanks for the suggestion. Found pics of a front tray he made. Looks like he's got a low lip on the car.

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Old 01-31-2021, 09:55 AM   #16
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Quote:
Originally Posted by Jack View Post
Look at hypermileing 240s on google. There’s been a few.

Aero stuff makes a difference above 30 mph

the way the panels fit makes a huge difference. Your biggest gains will come from under the engine and smoothing out area behind the axle

One of the worse things on early cars are the roof drains.

Here’s some simple equations for aero stuff. Found this at my old school F1 engine builders shop

https://imgur.com/a/vwO72Yy?s=sms
Thanks, I thought the same on the the engine and around the rear of the car. I had not considered the drip rails, interesting.
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Old 01-31-2021, 10:11 AM   #17
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Originally Posted by Stiggy Pop View Post
Thanks, I thought the same on the the engine and around the rear of the car. I had not considered the drip rails, interesting.
Good example of bad design is the 240 ipd engine “skid” plate

Oem ones have more round corners where the ipd one has sharp corners and then a stupid logo hole. Adds noise and turbulence

I’m working on a few small aero stuff on my 850 but will be moving on to my 240 at some point

The hyper mile crowd tends to just stick stuff on without worrying about accessing anything...
to me that’s the challenge, you can “easily” cover the underbody but making it easily removable and not cobbled together is the hard part. The older the vehicle design the harder it gets
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Old 01-31-2021, 05:20 PM   #18
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thanks for the suggestion. Found pics of a front tray he made. Looks like he's got a low lip on the car.
Lip itself is enough for stabilizing the whole car, didn't notice a big difference with the tray. Made the lip mostly for standing mile/track use. Also wagon roofline might be better for airflow behind the car?

Can't say it feels unstable without the lip up to 156mph(250km/h). Gradual turn on a local track on WOT ~130mph isn't a problem. And with 215/225 semi slicks.
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Old 01-31-2021, 07:12 PM   #19
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Lip itself is enough for stabilizing the whole car, didn't notice a big difference with the tray. Made the lip mostly for standing mile/track use. Also wagon roofline might be better for airflow behind the car?

Can't say it feels unstable without the lip up to 156mph(250km/h). Gradual turn on a local track on WOT ~130mph isn't a problem. And with 215/225 semi slicks.
Pics????
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Old 02-01-2021, 12:46 AM   #20
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On a very remote road, with a two mile line of sight, we saw 110 before I backed off. It was getting “uncomfortable.” I’d sure like to tighten things up.
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Old 02-01-2021, 02:08 AM   #21
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Pics????

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Old 02-01-2021, 02:54 AM   #22
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Subbed. More to shut it up at high speeds but reducing ass end lift would also be good.
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Old 02-01-2021, 07:17 PM   #23
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Pics????



It's not that low, around the same level as crossmember. The rideheight overall means that the lip does scrape sometimes. Doesn't limit where I drive though.

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Old 02-01-2021, 08:35 PM   #24
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Dayuum.

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Old 02-01-2021, 08:38 PM   #25
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Chicks dig Porsche's...


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