MADDesign rear diffuser

The Oily Bits S1 Specific Topics
1

Hi All,

One of my little projects was to design and build a new rear diffuser for my S1. Now, getting a LotusPower/Edwards item over to NZ was going to be rather uneconomical… the shipping cost would have been more than the item!

Now, with the Edwards’ blessing I was given permission to measure up one of their items to use as a starting point and thanks to Ashley (Acestes on here) who kindly took some measurements for me and my donor S1 OEM rear diffuser I managed to 3-D model up a new diffuser design.

I’ve just had it lasercut and folded and will send it away in a few days for anodising (black). Just test-fitted the fins and they fit PERFECTLY. The design is a little flimsy without the fins in it, but when the fins are bonded in, it’ll stiffen up nicely and looks like it’ll do the job just perfectly.

I’ve stripped the sheet thickness down to 1.2mm and am hoping this’ll be enough… this one will be a test and may make another if it needs thickening up.

The fins are bonded on from above with a high-temp black RTV adhesive (like sikaflex) as opposed to the standard design. The advantages of this are twofold: The fins cannot fall out and get lost, and this presents a cleaner underside for airflow.

Have mucked around for a while but now can’t wait to get it finished and on the car!

And without any further ado… the pics!

[image]http://www.jsr.com/~dinks/Misc/George/Sexige/Tech/MADDesign%20Diffuser%2001.JPG[/image]

[image]http://www.jsr.com/~dinks/Misc/George/Sexige/Tech/MADDesign%20Diffuser%2002.JPG[/image]

[image]http://www.jsr.com/~dinks/Misc/George/Sexige/Tech/MADDesign%20Diffuser%2003.JPG[/image]

2

That looks really impressive - it looks like the tabs have to be folded over after fitting through the slot, is that correct?

3

it looks like the tabs have to be folded over after fitting through the slot, is that correct?

Or just push the fins through from above ???

4

it looks like the tabs have to be folded over after fitting through the slot, is that correct?

Or just push the fins through from above ???

Indeed, They’re designed so that the fins go through on an angle and then lock in at one end in position. To fix them in permanently (after anodising) I’ll probably Sikaflex them in, but alternatively I could use rivets in the conventional manner.

Depending on how the design works on the car, I may shorten the fin slots a bit and increase the “tail” on the actual fin. That way, when you look at the diffuser from above (the bit that sticks out the back of the car), you’ll see no evidence of the fins at all.

The idea was that this design should transition pretty well to carbon later if I so choose to do so, but the ally version should do fine for starters

5

[quotebut alternatively I could use rivets in the conventional manner.[/quote]

I’d counter against using the rivets - in the smaller sizes they just aren’t man enough and the larger sizes are just OTT and ugly. I ended up replacing the rivets on mine with some small bolts after the rivets failed for the second time. To be honest your Silaflex solution sounds the best short of spot welding or tacking.

6

Steve, yeah well the Sikaflex is the likely solution. It’s not resisting the weight force and they’re keyed in so as long as it holds the fins in shear it’ll be good. The large bond-area should help to stiffen the diffuser as well. It’ll also be the most “tidy” solution as a nice clean bonded-joint should be pretty much invisible

7

Looks good! Glad to have been of assistance

8

Looks a great solution !

Managed to lose a fin off mine, so those slot from above fins should be better !

9

I got the design off george and have got another Lotus owner involved who has contacts in sheetmetal and we are taking delivery of our first batch of 2 next week - looks good. A real global design!

10

I got the design off george and have got another Lotus owner involved who has contacts in sheetmetal and we are taking delivery of our first batch of 2 next week - looks good. A real global design!

Any thoughts of an Elise variant (ie slightly shorter) ?

11

I will most likely, out of courtesy offer the design back to the Edwards guys and see if they want to offer this as an option if it actually proves to be a success (might not actually work yet!). But as JJ knows, there’s still one or two bugs in the design to work out first (get that dremel handy mate! )

12

If the fins drop in from above, is there any risk that a hit from below will push the fin into something fragile?

Mark

13

If the fins drop in from above, is there any risk that a hit from below will push the fin into something fragile?

Mark

Like your meat & two veg?

14

If the fins drop in from above, is there any risk that a hit from below will push the fin into something fragile?

Mark

Shouldn’t be, I guess the only thing fragile is the lip of the clam. The gauge of the ally is so light though it’d most likely bend the fin before it’d break the adhsive and come free.

15

Does not look much like a Mussel opening machine which you were supposed to be working on night and day !!!1
Glad to see you have your priorities right then!

Ask Richard about the Taupo sprint …it was fantastic fun and verging on a 5 lap race.
when I suggested the format to our local motorclub they nearly had a fit. …NO NO NO this is England we dont allow motoring FUN…UGH

16

I heard Richard had done rather well in that. I want to do a few of them once the Exige is sorted next season… will have to see how work/cashflow goes first.

Shame I didn’t see you when you were here, but got your note at Pukekohe. SEXIGE was looking a bit forlorn that day, parked next to the exit it was buried under dust!