concealer404

iTrader: (3)

Ok well... this kitty says it looks well-constructed, but needs some tweaking to be anything but hardparking poop.

HarryB

BTW, even with a full length flat floor, I would still doubt if it could offer any sort of measurable advantage at that height, without sealing off the sides. Maybe less drag, but that would be mostly due to the (non-existent here) flat floor. Single step-change in inclination and no attempt to move the (numerous) bolts out of the flow (at least by using cap head ones) points to looks over function. At least, there are no (visible) gaps.

FS Performance Engineering

Thank you for the several comments! We were definitely asking for input as there is always room to improve. We want to hear from you.

The V1 and V2 diffusers for the NB were our very,very early attempt at diffusers and were not very popular. The V3 model as shown in the pictures on our thread post represent our most recent production. The V3 does attach to the rear subframe bolts. Attaching our diffuser at this location is sound as we have had no problems at Buttonwillow Raceway. We do in fact use 0.08" (12 gauge in alum.) 5052 aluminum which is very strong/stout.

concealer404

iTrader: (3)

The V3 is close, if you would pretty much make it again, but this time not taking the bumper cover into consideration at all, i would be interested. A diffuser that does something should require at the least, a substantial bumper cut.

thumpetto007

iTrader: (15)

Make V4 like this, please.

concealer404

iTrader: (3)

YES.

10/10 would buy.

brainzata

iTrader: (4)

I would vote towards a diffuser like the black AWR NA diffuser, but wider.

mx5-kiwi

Aren't these last few examples openings too big to create the necessary venturi effect?

Scaxx

I'm pretty sure diffusers are moot if not paired with a flat bottom on our cars, correct me if I'm wrong on that. Also what's the angle like on it, it looks fairly steep in the second picture, too steep and it's just going to seperate. Seeing no real world testing leads me to believe it's not really going to do anything.

matrussell122

iTrader: (1)

I agree with you on both those statements. If i remember right the sweet spot on diffuser angle is around 7°

AlwaysBroken

Could you get a higher angle with vortex generators? Isn't the whole angle limitation to prevent flow separation?

HarryB

7deg is a very rough guideline; depends on a number of factors really, but yeah the main point is to avoid separation. As said, the step transition is not helping. Main issue though, lack of the structure on front of it (flat floor or otherwise) and NO sealing from the sides.

FS Performance Engineering

A sharp angle does in fact lead to flow separation, as does a steep angle. Sealing the sides of the flat portion can definitely be done; it would just bring the diffuser closer to the ground. We plan on doing track testing on this diffuser but it also sounds like we need take into consideration a few more factors while disregarding a few of our initial considerations. From a flow perspective (race perspective) this is what sounds like needs to be done:

• Use a long curved surface (as opposed to a single-step) that outlets at an angle that minimizes drag but maximizes down force. Cutting the bumper may or may not be necessary as an angle too large will create flow separation.
• Minimize the number of flow impediments (the bolt heads).
• Make sure the diffuser extends from tire to tire - air flow under the entirety of the car needs to be captured.
• Seal off the sides of the diffuser from beginning to end to avoid leakage (kind of like something Lotus did back in the day when they decided to drag "skirts" on either side of the car).
• Ignore where standard exhausts lie and do what is most effective - exhausts can be built around the diffuser.

We truly do appreciate the input!

z31maniac

Have you checked out how the guys at Verus Engineering are building their parts?

They even include basic CFD numbers as well.

ThePass

iTrader: (3)

FS Performance Engineering

Their work is beautiful. I will be looking into it. Thank you!

Der_Idiot

iTrader: (2)

Have you considered making a flat bottom for the Miata? Something made out of aluminum with attachment hardware and goes from the front subframe back to the rear brace where your diffuser starts and in semi-modular sections so it's easy to ship / swap out replacement parts. I don't think there's anyone that makes anything readily available like that tbh.

Full_Tilt_Boogie

iTrader: (1)

Ive seen some CFD that shows they are effective even without a flat floor. The flat floor helps a lot, but considering how little a diffuser weighs it still make sense to work one into the car even if you cant legally have a flat floor between wheel center-lines.

AlwaysBroken

This would be neat. Would need to make allowances for exhaust heat and diff/trans cooling.