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Author Subject: Rear Diffuser
eddy_gti6

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Post #1
Been looking into making a rear diffuser for my car while its off the road. Been looking this morning to see what i could find for a 306 but there is nothing.
Been thinking of the idea for a little while now to fill in that big gap under the boot where the spare wheel is suppose to be what really just acts like a parachute slowing you down no end. Having a rear diffuser will help smooth the airflow under the car thus increaseing grip levels.

Having a rear diffuser eases high velocity air back to normal velocity and also helps fill in the area behind the car making the whole underbody a more efficient downforce producing device by reducing drag on the car and increasing downforce. The diffuser also imparts upward momentum to the air which further increases downforce.

Closest thing i have seen to something good is the diffuser cherry has on his 106 turbo:


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Posted 26th Apr 2012 at 09:36
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dangti6

aka JKshooter

Location: Taunton, Somerset

Registered: 15 Jun 2006

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Post #2
Don't forget to fold your back seats down also.

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    • Posted 26th Apr 2012 at 09:55
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    eddy_gti6

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    Post #3
    dangti6 wrote:
    Don't forget to fold your back seats down also.


    What back seats? i dont have any Crazy

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    Posted 26th Apr 2012 at 10:21
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    rallye1999

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    Post #4
    if your going to do that you may aswel try and to the floor flat also
    Posted 26th Apr 2012 at 12:48
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    phillipm

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    Post #5
    Waste of time without a flat floor anyway. Really big waste of time if it's as high as the one on that 106 and doesn't extend past the boundary layer on the rear bodywork.

    Especially when someone's stuck an exhaust under it.

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    Posted 26th Apr 2012 at 12:59
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    eddy_gti6

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    Post #6
    I was planning on doing the whole underside of my car. He doesnt have that diffuser no more, he has a new one and thr exhaust has been moved to a side exit aswell so its out of the way. Just realy wanting to know if there is anyone that has put one on a 306 before?

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    Posted 26th Apr 2012 at 14:34
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    dangti6

    aka JKshooter

    Location: Taunton, Somerset

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    Post #7
    Are you going down the High Boost route?

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    • Posted 26th Apr 2012 at 14:43
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    eddy_gti6

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    Post #8
    No i will be going N/A power. Jenvey bodys with a rebuilt engine... Whistle

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    Posted 26th Apr 2012 at 14:47
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    welshpug!

    Capt Pedantic

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    Post #9
    I would imagine Ash might have looked into it for his high boost race car if it was feasible.


    you'd probably benefit more from a proper kitcar spoiler like the 106 and saxo's ran, though to make the most of any mods like this you need to be carrying some serious speed....

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    Posted 26th Apr 2012 at 14:47
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    eliotrw

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    Post #10
    I thought about getting that piece from a 309 or 405 (One of the two cant remember which) But theres a plastic bit that goes from the bumper and under the beam which maybe could help things if it was modified a bit.

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    Posted 26th Apr 2012 at 15:41
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    welshpug!

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    Post #11
    neither had a full rear undertray, but both have a small plastic bit between the fuel tank and the spare wheel, and the MI16's spare wheel carrier has a sheet of metal on the bottom.

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    Posted 26th Apr 2012 at 15:46
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    eliotrw

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    Post #12
    Would be good to see if you could make a flat piece of plastic into a decent shape and fix it to the car somehow

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    Posted 26th Apr 2012 at 15:54
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    stan_306gti6 Forum Admin

    Location: Kent

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    Post #13
    I'm with Welshpug on this...

    Unless you're carrying some real serious speed through fast bends, downforce isn't going to come into it. However, I would be interested to see what your results are if you manage to implement such a thing. Yes

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    Posted 26th Apr 2012 at 16:24
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    welshpug!

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    Post #14
    Maxi's only had the rear wing as they spent a fair bit of time airborne LOL

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    Posted 26th Apr 2012 at 16:34
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    smegal

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    Post #15
    Downforce is not a concern but reducing drag may be.

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    Posted 26th Apr 2012 at 17:05
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    daveyboy

    aka Jim Davey

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    Post #16
    smegal wrote:
    Downforce is not a concern but reducing drag may be.


    +1

    I don't think it's going to save you much, 2-3 mph at the top end maybe, but they look cool and might give a slight increase in rear end stability at speed (Look at the tiny sonic the hedgehog wingleys the put in the roof of recent EVOs)Dunno

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    Posted 26th Apr 2012 at 17:43
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    eliotrw

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    Post #17
    Well allegedly a clio 200 benefits from its diffuser

    Also if air is able to travel faster above the car than below then it could create lift in theory.
    I reckon its worth pursuing a way to stop the parachute effect.

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    Posted 26th Apr 2012 at 18:01
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    eddy_gti6

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    Post #18
    I will draw something up and see what i need and how much parts will cost. Also have been thinking of using some sort of plastic but needs to be hear resistan really as will be right under the exhauat, other thing i could use would be some thin sheet metal of some sort. Not sure how high i would take it so it doesnt look stupid when its fitted.

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    Posted 26th Apr 2012 at 18:48
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    Lowercase

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    Post #19
    you could use composite aluminium. really light and strong. its about 2-3mm thick, aluminium core with a plastic sheet on either side (or the other way around, i didnt take a good look at it). a bit of heat resistant foil or something near the exhaust should stop it melting

    reducing the drag is worth doing, i took my rear arch liners out the other day to stone chip the shell and havent put them back in yet/cant decide if i will, and i can hear the drag thats being caused with the exposed bits now the crud guards gone. so i might cut a few small pannels of comp.aluminium and blank them off. should reduce the wind noise and drag a bit..

    or i could just put the arch liners back in.. Wink

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    Posted 26th Apr 2012 at 19:04
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    atterz

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    Post #20
    It may reduce the noise/corrosion on the back end as well especially with rear seats out!

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    Posted 26th Apr 2012 at 19:11
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    yanni

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    Post #21
    I was thinking of that for some time too. The idea was to use the rear diffuser from a Clio Rs and extend it all the way to the front creating a sleek flat under body.
    What about the exhaust tunnel though? Can you seal the exhaust in the under tray and how? Otherwise what's the point of having everything hanging under thereDunno Plus you need a way to channel the air from the front to the back for the full effect!

    Bear with me i don't agree nor fancy the idea in terms of aesthetics but the benefits sounds good.

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    Posted 26th Apr 2012 at 19:43
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    eddy_gti6

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    Post #22
    I will sort something out. Need to get the underside of the car measured up so i know what i need. Will try find time over the weekend.

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    Posted 26th Apr 2012 at 20:56
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    pugheaven

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    Post #23
    Ideally you would want a box section welded along side the side sill with either riv nuts, captive nuts..
    I was looking to do this to the dimma's rear bumper using the new shape scoobys rear diffuser as that already has the undertray for the boot floor.
    Posted 26th Apr 2012 at 21:51
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    daveyboy

    aka Jim Davey

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    Post #24
    welshpug! wrote:
    I would imagine Ash might have looked into it for his high boost race car if it was feasible.


    you'd probably benefit more from a proper kitcar spoiler like the 106 and saxo's ran, though to make the most of any mods like this you need to be carrying some serious speed....


    Pretty sure flat floors are illegal in DMN or he would probably have done it, he has cut away a large section of rear bumper to lessen the parachute effect though.

    Yo can see a pic of it in the NUR carbon/kevlar thread, but I can't seem to copy the image link.

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    Posted 28th Apr 2012 at 12:09
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    buzzbrightyear

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    Post #25
    the rear bumper since I removed the spare wheel looks like a parachute to me, the differences would be minimum but I reckon if you've got some power, then there will be a benefit, has anybody sen underneath a Ferrari ? I was looking around one and i liked what they had done underneath, the whole underside was smooth, and it had like fins and things, it was the only part of the car that I thought was a work of art. I would love to be able to make something similar out of carbon or something, sadly I don't have the skills.
    Surely it has to do something but unless you have the skills to make it yourself then forget it because you could probably fit a supercharger or turbo for what it would cost.

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    Posted 28th Apr 2012 at 12:12
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