Leafy

iTrader: (1)

Yes in theory running 2.5 all the way to the plate and transitioning down to 2" with a cone as close to the plate as possible should get you nearly all the flow of the 2.5" with an even higher velocity with the air being forced into the nozzle.

ThePass

iTrader: (3)

If the transition is gradual and maintains laminar flow, you'll get an increase in velocity by a factor equal to the factor of reduction of the area of the hose. If I was trying to accomplish this I'd make a long transition piece out of a composite.

But, if you're choking it down quickly, like with a PVC pipe adapter or something similar, the turbulence created will likely cause more of an obstruction than just running 2" IMO.

-Ryan

Leafy

iTrader: (1)

Even choking it down, if you have a run of that crappy tubing longer than a foot or even have one bend in it there's going to be a significant difference in pressure drop between the 2 and 2.5.

cordycord

iTrader: (2)

Thought you guys might find this interesting. With the stock body configuration and windshield, the Catfish has the same Cd as a Miata with the top down. However, because of the flat bottom it also creates negative lift.

This has been discussed before, but aero work on race cars really depends on the class and what's allowed. Rules for everything from DTM to F1 determine all the funky stuff that gets added onto a race car, and not necessarily the most efficient method of doing so.

You probably don't want to hear my two cents about each piece of aero, but I do find it extremely interesting, especially the balance between wing and splitters.

ThePass

iTrader: (3)

Sexy flat bottom is sexy. ^

cordycord

iTrader: (2)

Sir Mix-a-lot likes his big and round, son.

ThePass

iTrader: (3)

I just re-read it

sixshooter

iTrader: (12)

Catfish has a windshield?

cordycord

iTrader: (2)

Building one now...

billybobster

Good input Leafy and ThePass.

The engineer in me wants to build a test bench to try various configurations of brake ducts.

The sane person in me finally spoke up and said put in the full 2" SCAT run and see what happens. If it stops my rotor cracking, great. If it doesn't or the cracking reappears as I (hopefully) get more pace, do something else then.

NiklasFalk

iTrader: (1)

Starting with the TSE duct, there is nothing preventing a 2.5" hose attachment, if you spend some time making the it. 2" fits all but even with ABS you can make something that will have more area and positioned more center than a round 2".
TSE made something that fit all and could be made at a decent cost.

As mentioned; airflow in the brake duct hose can be one parameter to measure if the pressure is to be lowered in the wheel well. The positive pressure in front can be seen as a constant.

I'm not sure if the airflow could be easier to measure than the absolute pressure difference. Measure whatever swings a cheap meter the most.
Anyone with a spare MAF (that of course can be killed by debris)?
or a Pitot tube attached to a differential manometer?

BEAVIS

Hmm, Miata aero and sir mix alot.... Sounds familiar:

mx5autoxer

iTrader: (1)

So vent the fender on the top slightly ahead of the center of the hub with some louvers and remove some material from the behind the wheel starting at the bottom. That about what we've decided so far? Also, should the rear wheel wells be treated the same?

Keith@FM

iTrader: (1)

Theorized, not decided!

ThePass

iTrader: (3)

Yup, no conclusions at this point.

I've done some pressure testing in my track car's fenders, but that car's airflow is too far removed from a 'typical' miata for data from that car to be relevant to much more than just itself.
I'm hoping to find some time to fully map inner/outer fender pressures of a much more stock NA that I have here soon.

-Ryan

90civichhb

iTrader: (5)

Not trying to necro post but this seemed like a great topic. I currently have my fenders spaced, this was more for wheel fitment rather than aero advantage since autocross car, but, I am in the process of making a front splitter and would like to cut my fenders to accompany. Have you all done anymore testing on the theories proposed here? I have used ThePass's car often as a reference for my build and wanted to mimic his fenders until I read that it requires two sets of fenders to achieve that result. Just not in the budget.

Blackbird

Not sure if you've seen it or not, but the vented fenders on Morpheus use one fender -







Filler panels can be done from FG to reduce cost -






Finished product -

ThePass

iTrader: (3)

Welllll yeah, you used one set of fenders, but then you had to make a new rear section from scratch... it's a great execution and lighter weight but it's also the more complicated option of the two, not the simpler one. The point was you can't just cut up one set of fenders and be done - you've got to either scavenge a back section from a second pair of fenders OR you'd have to make new rear sections from scratch.

That said, plenty of guys HAVE done similar stuff with just one set of fenders that takes only simple cutting and no significant fabriction... they just don't have a rear section

ThePass

iTrader: (3)

On the fender venting subject in general, we have some cool stuff in the works. Nothing ready for public release yet.

Blackbird

Well excuse me, Debbie downer
I was just giving the guy another option...

Got a call this morning asking if we're going to make the filler panels available, and it wasn't the first call I got about them.
If there's enough interest, I can make it happen.