printed rear diffuser

[Mr X]

I guess this is Performance Related too but I'll put it here.
I finally got round to doing something I always wanted to do, sort out a rear diffuser. I made it so it would fit if I go back to the standard or quad style exhausts.



The original design was supposed to be fully 3d printed. It fits using the existing holes where the under tray goes and then to the bottom of the bumper. The base part sits level with the under tray and channel walls come down about an 1inch (at the front).



The I decided (at least atm) to make a mould and make the base part out of fibreglass (woven not matted). Printing this part would be cheaper but take a good day or 2. Fibreglass is quick to do, much more expensive but messy as hell. The channels are still printed.



I need to do something to straighten out the exit if the diffuser a little as the fibre has some flex to it (not a lot but it's bolted down).



The channels did come down another inch or so but I was really doubtful they would make a speed bump. They are quite strong but the idea of making them as a separate is to be able to easily replace them if they do take a knock.

Now I need to make a part that bolts onto the front of the diffuser, (using the existing holes and slots into slits made in the under tray) with channels to screw onto the under tray. This should then allow a more smooth transition the air onto the diffuser. Then I need to make sections to channel the air from the sides of the wheels and down where the exhaust(s) exit and spats would be.

[1979scotte]

Always an interesting read.
Looks good.

[shnazzle]

I like it a lot

[Mr X]

Thanks guys. It actually didn't take too long to make once the fibreglass mould was done.
Plus I've been driving around without a nappy and showing my arse for years. Looks loads better now the CAT is covered.

[Mr X]

Something like this, so it slits in part way down the engine under cover


I also just took a few measurements. The bottom of the channel sides are 100mm off the floor at the front (this is about where the wheels are) and 140mm at the rear. If i make it 100mm all the way along (I was hoping to keep them straight as it creates a bigger expansion chamber & increasing the effect), I'm sure it's going to knock speed humps as I come down them. 

[StuC]

Have you completely removed the undertray?

[Mr X]

Have you completely removed the undertray?

The one that is normally around the CAT, I never had on. The one that's under the engine, this will (at least for the moment) be incorporated onto.
The whole floor plan really should be as flat as possible but it's so much work to do that now I've sold my 3D scanner, I doubt I'll get around to doing it.

[StuC]

Agreed you need a fully flat floor for maximum benefit. Ikrana had the closest thing I'd seen to a full installation.

Having the forward one, will deffo help. If you'd removed both I was gonna post about the futility of it. Lol.

Also... seems ages since I have seen any pics of your car!!

[dan944]

I'm hugely interested in aero. If you look up a a youtube channel called Kyle.engineering then you can see his stuff on aero. In his explanations a flat floor is THE best thing you can do at low level aero.
I've been speaking to streetwerks and they're working on this.
But...I have an angle grinder. A four post lift. A lot of cardboard. And threaded bar.
I reckon I can replicate a better version...if a little rough around the edges.
I'm currently snowed under....but progress will be revealed in due course. I

[Mr X]

I've been about but only really fitted a UD sub in the past year. Not done much else to it since... I did make these tho:






and my second version:



The main thing, apart from getting the design done, is trying not to have bolts sticking out (you really are pissing into the wind doing that!;) ) and being able to get the thing on and off.

Driving about without covers really is like having a parachute open so I think that just the back part will have quite a considerable benefit. Ideal would be at least middle of the car back as it will give the air a lot of chance to settle and get back to the same speed as the air going over the top of the car.
I downloaded software that runs airflow and pressure simulations as I want to see how it's effected it but don't have a CAD file (or SLI) of the car.... yet

[Mr X]

Made some new channel walls.



These are a lot longer than the old ones so now they're 100mm from the deck. I've been over speed bumps ok (tho it must be close). They're stronger with 2 sidewalls and print in half the time thanks to some new printer settings (about 3 hours each rather than 6)!



Ready to start printing the bits that go from the undertray and channels from the side of the wheels.

[Mr X]

Think I'm about there with the drawing


I can make the side two run out as they should because the CAT isn't in the way.




From what I've read, this will create more vacuum and again, less drag.

Hopefully I will have time to get it done before I go to sweden in 2 weeks 

[dan944]

These are a thing of beauty!! Love it.

[Nvy]

The design is quite nice and its going to work the way its setup. Just an idea, cant we cut the bumper up and make the curve of the diffuser start a bit earlier. That way the gap between the ground and the ending of the diffuser will be bigger and bonus the fins can be shorter and not getting broke when coming down from a speed bump. It will also work better with bigger gap.

[Mr X]

The design is quite nice and its going to work the way its setup. Just an idea, cant we cut the bumper up and make the curve of the diffuser start a bit earlier. That way the gap between the ground and the ending of the diffuser will be bigger and bonus the fins can be shorter and not getting broke when coming down from a speed bump. It will also work better with bigger gap.

Thanks for the input guys.
I wanted to start it where it bolts onto the 2 rear under-tray bolts (on the sub-frame) so I could take it on and off easily and fit these with as little modification to the original as possible without gimping what I'm trying to do. From what I read if the exit angle is too great you're going to increase drag and then we're looking at about 70 odd deg over a fair few inches.

https://ac.els-cdn.com/S1875389211006924/1-s2.0-S1875389211006924-main.pdf?_tid=7914888a-b906-435b-9ba6-ce36bd368c04&acdnat=1531213775_10cf6186b46c3cc2a20dc877035997cc

I know the case will be different as the Mr2 has a different aerodynamic profile. I really need to look at the simulation programme I downloaded!

So doing this could defeat the object. I'd have liked to have a rake on the centre section but that would mean the original CAT wouldn't fit. I wanted to keep it so it could fit with the standard exhaust setup.

I'm no expert with designing these things, I'm just going on what I've read. That's was what I had before. At the start, 100mm from the floor and at the exit 140mm. Again, in an ideal world the air needs to be kept as uniform as possible reducing as much turbulence as possible. Having it leave the diffuser half way down it (because the angle is raked) could mean it creates turbulence. Again, I would need to run some simulations to test.. It's now 100mm and 100mm. I've been over quite a few speed bumps over the past few days, all good so far!

[lamcote]

The YouTuber Kyle.engineer said a good generic roadcar aero setup was to have a flat floor with 25mm rake from front to back wheels and then to have a diffuser angled up at about 10 degrees.

If you don't know him he has now closed his YouTube channel because he got an aerodynamicist job at the AMG Mercedes F1 team so I think he knows what he's talking about!

[dan944]

The YouTuber Kyle.engineer said a good generic roadcar aero setup was to have a flat floor with 25mm rake from front to back wheels and then to have a diffuser angled up at about 10 degrees.

If you don't know him he has now closed his YouTube channel because he got an aerodynamicist job at the AMG Mercedes F1 team so I think he knows what he's talking about!

I watch his stuff.

Realistically I think a flat floor will give the biggest benefit to our cars due to speeds etc. And a splitter or air dam at least.

Someone is making these on the FB page but I cannot remember who. Believe it may be Meguillian motorsport?

[Nvy]

The YouTuber Kyle.engineer said a good generic roadcar aero setup was to have a flat floor with 25mm rake from front to back wheels and then to have a diffuser angled up at about 10 degrees.

If you don't know him he has now closed his YouTube channel because he got an aerodynamicist job at the AMG Mercedes F1 team so I think he knows what he's talking about!

I watch his stuff.

Realistically I think a flat floor will give the biggest benefit to our cars due to speeds etc. And a splitter or air dam at least.

Someone is making these on the FB page but I cannot remember who. Believe it may be Meguillian motorsport?

Id love to have flat floor and lowered to the ground car but lifting kits are rly expensive so i wont be able to go on speed bumps Other than that, i would like to get in the line for a diffuser:)

[Mr X]

I went bump hunting again on thurs, no issues still. I wouldn't want to go over the smaller type (that are in pairs) but I had to drive in-between them already anyway so no biggy!
The first set of sides are printed and test fit ok! I took some pics before I paint them so you can see the curve a bit better. The outer ones are coming out now. I've made these in black as I assume they're going to see some grit from the wheels. That way I don't need to keep re-painting them








I actually went into a plastics place where I brought sheets for my 3d printer and asked if they had any ABS. They had a sheet of 2mm. It was expensive (weight for weight) compared to what I print with but it saves massive amounts of time doing flat surfaces. I wish I'd have gone in there before I started because I'd have done the main body in this rather than messing about with fibreglass!

I might actually have enough left from this sheet to make a duplicate diffuser so I'm going to give it a try in this too rather than the fibreglass.

[Mr X]

So all was fitted and looking good (car jacked up in the pic)...


But I had a problem...

once it's jacked up the diffuser clashes with suspension components (:< >

I removed the outer section and made the brackets to hold up the front.




I've kept the outer channels and the plan now is to either start to font of the outer channels later or slot the diffuser so the suspension components can down down when the car is jacked up.

I don't think I'll be able to get this done before I go on holiday now.... I had a big box delivered today with my new side-skirts in  I don't really want them hogging up all the space in the shed while I'm away when they should be on the car.

*edit looking at the pictures I think the car actually looks better without the outer channels.

[1979scotte]

Agreed looks better.
Good work.

[dan944]

Same. If you get some rear seats on there it would blend in lovely but I think would be counterproductive to the aero.

[Call the midlife!]

Same. If you get some rear seats on there it would blend in lovely but I think would be counterproductive to the aero.

Assuming you mean "spats" I was thinking the same, diffuser looks lovely but just missing that finishing edge like spats.


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[dan944]

Same. If you get some rear seats on there it would blend in lovely but I think would be counterproductive to the aero.

Assuming you mean "spats" I was thinking the same, diffuser looks lovely but just missing that finishing edge like spats.


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Yes...yes I did haha

[Call the midlife!]

Same. If you get some rear seats on there it would blend in lovely but I think would be counterproductive to the aero.

Assuming you mean "spats" I was thinking the same, diffuser looks lovely but just missing that finishing edge like spats.


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Yes...yes I did haha

Although you're right, some seats on there would really mess with the aero.[emoji23]


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