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Discussion Starter · #1 ·
Hello everyone,

My name is Adam and I've come to this forum with a specific task.

I love Lotus's, and I hope to own one some day, but right now I drive a Scion FR-S. It's a fun little car and does well at the track for what it is. However, with an aftermarket exhaust, the rear bumper tends to act as a parachute and cause unwanted rear end lift. The market for diffusers is still very small (not to mention, expensive) for this new platform, so I've set out on a quest for a DIY solution.

So, my main reason for joining the forum (don't hate me) is to acquire an oem Elise or Exige rear diffuser that I can retrofit onto my car. However, since I'm a new member, I can't PM anyone in the marketplace section, so I'm going to stick around and learn as much as possible about these great cars, and take part in the ongoing conversations.

Best Regards,
Adam.

(shameless plug) If anyone is selling, or knows someone who is, an Elise or Exige diffuser, I would be very interested. Thank you.
 

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More bang for the buck from a rear wing, I would think.

Hello everyone,

My name is Adam and I've come to this forum with a specific task.

I love Lotus's, and I hope to own one some day, but right now I drive a Scion FR-S. It's a fun little car and does well at the track for what it is. However, with an aftermarket exhaust, the rear bumper tends to act as a parachute and cause unwanted rear end lift. The market for diffusers is still very small (not to mention, expensive) for this new platform, so I've set out on a quest for a DIY solution.

So, my main reason for joining the forum (don't hate me) is to acquire an oem Elise or Exige rear diffuser that I can retrofit onto my car. However, since I'm a new member, I can't PM anyone in the marketplace section, so I'm going to stick around and learn as much as possible about these great cars, and take part in the ongoing conversations.

Best Regards,
Adam.

(shameless plug) If anyone is selling, or knows someone who is, an Elise or Exige diffuser, I would be very interested. Thank you.
 

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Discussion Starter · #3 ·
Good point, and it's definitely something I've considered, but decided to go with the lower-cost approach first. Plus, I feel this has the potential to benefit the entire "toyobaru" community, if it functions as desired.
 

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Discussion Starter · #5 ·
Yes, that's a great piece. All the time spent on R&D and quality materials are definitely worth the price. For me, it's mostly the desire to explore other options, "MacGyver" something, analyze the results, and repeat. :)
 

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I came in here to plug the Driveway Labs aka Difflow diffuser from Glen, but voila there is a plug already. :)

No, it's not dirt cheap. But the fact they did CFD is a big cut above typical aftermarket. If you wanted to try to copy it with bend-your-own sheet aluminum from your local metal store or McMaster Carr, it would be a great DIY experience. You might end up finding the total cost [materials plus time] end up being a wash with Glen's extremely well made piece.

That's my 2 pence.
 

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I think that by the time you have modified a Lotus diffuser to fit you toyobaru you would find that you have replaced all three pieces of the three piece diffuser. (Its basically a flat piece of aluminum with a curved "tunnel" riveted to each side)

Start with a large piece of cardboard and build a template for the basic diffuser template and then transfer that to a piece of sheet aluminum.
Keep the angle of attack, or is it retreat on a diffuser, to approximately 14deg. (the stock Lotus config is, hmmm, a bit aggressive)
Make it as long, going as far under the car, as you can (the back of the tubs for the driver/pass seats looks promising).
Study/Copy Difflow's solution as much as you can.
Use many vertical fences to keep the air excited about getting out from under your car in a beneficial way. (adrian newey's thinking on this seems to be vortex generators, but....)
Keep reality in mind. If you install a simple 3ft by 3ft diffuser, and it produces just 1PSI down-force (or negative lift), that sounds like nothing, but.... that would equal 432 pounds of down-force, which would be an AMAZING amount of down-force.

I suspect, but have not spent anytime validating, that without a full belly-pan, your will get the most bang not from the down-force it produces, but by that drag it reduces (you are right, mufflers and bumpers are great parachutes).

I just looked at a picture of your car and it could be much worse. I think you are going in the correct direction.
 

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Discussion Starter · #8 ·
Thanks a lot, Doug! I never thought of trying to fabricate my own, due to the lack of testing equipment (wind tunnels, etc), that's why I was looking for something that was already developed (albeit for a different car). The theory behind it makes sense, so I may just embark on this journey.

What thickness of aluminum would you recommend? I guess the thinner the better, due to weight savings, but want to make sure it doesn't flex. Also, using rivets to attach the vanes would be sufficient?

This forum is full of knowledgeable people. I like this!
 

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This forum is full of knowledgeable people. I like this!
It is pretty amazing sometimes. Artists, engineers, mechanics and maniacs seem to love these cars. They tend to contribute a lot of talent and passion to a relatively small forum.
 

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Discussion Starter · #11 ·
Two books I'd recommend:

Competition Car Aerodynamics: A Practical Handbook, 2nd Edition: Simon McBeath: 9780857330079: Amazon.com: Books

Race Car Aerodynamics: Designing for Speed (Engineering and Performance): J Katz: 9780837601427: Amazon.com: Books

Both of these books have very detailed descriptions of diffuser systems that should enable you to build a working one from principles/theory without needing to do the CFD or wind-tunnel work yourself.
Great, thanks! I've always been intrigued by this topic, and now I have a reason to get educated.
 

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Discussion Starter · #13 ·
You guys make some great stuff, that's for sure! There are a couple of guys on the forum that have custom exhaust systems tucked up high, along with your diffuser setup. Looks mean!

One can use your specific FR-S/BRZ diffuser without re-routing the exhaust, correct?
 

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You guys make some great stuff, that's for sure! There are a couple of guys on the forum that have custom exhaust systems tucked up high, along with your diffuser setup. Looks mean!

One can use your specific FR-S/BRZ diffuser without re-routing the exhaust, correct?
Correct. Our BRZ/FRS/86 diffuser works with most aftermarket exhausts too.
 
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