Difflow Lotus Diffuser Installed
 

Just purchased my first Miata, a little over a month ago, getting started on getting some aero parts on it.

This is a 5 element Railer Jr. made by Difflow for the Elise/Exige.

I made two custom brackets to use all the stock lotus mounting points for the diffuser. The top one replaces the rear subframe brace. The bottom one bolts to the inner bumper.

https://www.miataturbo.net/attachmen...ine=1335812290

https://www.miataturbo.net/attachmen...ine=1335812290

But this is what it ends up looking like.

https://www.miataturbo.net/attachmen...ine=1335812290

https://www.miataturbo.net/attachmen...ine=1335812290

https://www.miataturbo.net/attachmen...ine=1335812290

https://www.miataturbo.net/attachmen...ine=1335812290

So, you kept the stock parachute-effect bumper, but added a super expensive diffuser that's not mounted in an effective location.....cool story bro

That's not the only dumb thing he's done judging by the bumper stick on the hardtop. :giggle:

Wrong.

You could be right, he could have bought that splitter with bitcoins.

Looks highly streetable! Like!

FTN,

Looks good, props for your engineering, I am also looking to install an Elise diffuser and was looking for a mounting solution. Not too sure about the angle of the diffuser, according to a thread on Miata the angle needs to be about 7-15 degrees(?) yours doesn't look too far off. There's probably less parachute effect than is thought due to the fact that the majority of the airflow is slowed down from the undercarriage bits, but, anything you can do to keep air from getting on top the diffuser is good. Also, good for leaving a slot between the bumper and the diffuser as an exit for any air that does get there..

Best one I've seen yet, but that's not saying much.

Not a big fan of the recent trend in the scene of every other ricer trying to jump on the rear diffuser band wagon, seemingly mostly motivated by the looks (irony being it looks like ----) rather than the function. Aero is tricky business, so I don't say this in absolute terms, but I think without properly sorted under-body aero from head to tail, the rear diffuser does fcuk-le-all for wake improvements.

I bet it's hammered/broken in 2 weeks of street use.

Needs pulled up around 8-12 inches.

Testing?

How much higher could you actually get this without some really crazy modification? I agree that it could be a bit higher up, but I'm not sure if it would even be possible. (Note: I haven't spent any time at all looking at this on my own car with the bumper off)

Cut the bumper, trim the diffuser, profit.

LOL everyone's an aerodynamicist...

I have absolutely 0 desire to raise the angle of the diffuser.

It's sitting at a stock Elise angle right now, with the leading edge even with the floor of the car. The Center 3 elements are at 10^0, and the outer two are at 20^0.

I got about 60 laps at my local track in the weekend i purchased the car, I'll be back out in the next few weeks to get my take on the diffuser...It will eventually all be a part of a bigger aero package i have in mind.

I agree the diffuser alone does not do magic and create tons of down force, does it do a little probably, can you feel the difference not sure yet.

Think of it this way does a wing work with a hardtop/top up? does it do absolutely nothing with the top down? Similar aero theory at work. Smoothing out air flow will always help, but having turbulence doesn't instantly negate all else.

Don't think you can draw those comparisons in effectiveness between a mostly cosmetic diffuser upgrade, to a wing that will still function regardless of how poorly it may be set up.

Point is, that is a huge, tacky eye-sore of a mod for what could be a negligible improvement in aero/wake. You got to get the under-body aero well sorted for it to be even remotely functional.

It just reminds me of the time at the Zoo.

Oh wait, here it is-
https://www.miataturbo.net/attachmen...ine=1335888216

Well despite some of the usual A-hole reactions....:fawk: (you need a really thick skin here...)

I think it has potential and look forward to seeing and hearing the development as it comes along.

I admit that I would like to see it molded into the bumper to clean it up a bit, but I admire the handywork.

Sounds like form over function is the name of your game, and I think that is the right way to go. What's the rest of the aero setup that you have in mind?

i bet that it creates more drag than it helps being that low...

You just added more drag. The stock bumper is a parachute. You need to cut into the stock bumper and raise the diffuser.

Think this:
https://www.miataturbo.net/attachmen...ine=1335936850

Or this

https://www.miataturbo.net/attachmen...ine=1335942249

Sorry but mounting it completely below the stock bumper, with no other mods, is fail. Trim the bumper and tuck it up in there. More ground clearance and more downforce. Double win.

Thank you mobius for demonstrating with photos what I was trying to convey!

I don't think there's anything wrong with it being lower to the ground, in fact, with the remainder of the under-body aero sorted, it's better to have it as low to the ground as possible to prevent air from being sucked in from the sides. There's plenty of examples of race car aero running similar rear diffuser setups, that strive to get low to the ground as possible. The difference being they have a completely flat underbody leading up to it.

I understand higher is better if the purpose of the diffuser is to replace the parachute effect of the rear bumper, but then you may as well not run a rear bumper at all/cut lower half of bumper off.

You should have put that $600 into a slush account for turbo instead. Just my $0.02.

second. I cant prove that it doesn't work but is really looks silly imo. all you can do is take laptimes with segment info to see whats going on with that thing. if it works it works.

Hey guys, just a thought here. If I remember correctly there have been some discussions by some of our more intellectual minds, on how much actual drag is caused by the stock bumper. Someone was going do do some roll down test if my memory serves me right. It seemed to be undetermined. I'll try to look up some of the posts when I have time later.

I'm not a fan of form over function, and I'm certainly not a guru, but if this kid doesn't want to hack up is bumper, wouldn't all or most of the air entering the "parachute" be eliminated with a proper under tray. Something that could be easily removed if he wanted to return the car to stock to sell it? I'll have to admit it's been quite a while since i've read any of those diy splitter threads, but if the under tray meet up with the diffuser in a smooth transitions wouldn't the lower diffuser actually be better, as long as the AOD was correct?

Flame away if I'm wrong, just thinking out loud.

Edit: Just wanted to add. I realize it's not optimal, but what I'm asking is HOW bad is it if it had a proper underbody? I think most of us here make concessions with our cars. Either because a lack of funds, or wanting to keep it street able. We don't do things the "proper" way, we make it "good enough" for our situation.

I think that's really the most funny thing about the input...

the bumper is hacked, I mounted the diffuser where i wanted it, the leading (front) edge even with the floor of the passenger compartment, and the rear was placed as so the fins would be parallel to the ground, the i cut the bumper as much as i needed to, It's has the cutout for a "dual" exhaust then another 5 inches from the top of the cutout inward, as well as about 2-3 inches along the entire lower edge between the outer elements.

IMO this is the optimal position for this diffuser, it wasn't placed where it is for looks at all. I'm sure it's easy to call anyone that would make this type of modificaion a "ricer" or "form over fuction", i don't think i'm either of those, it's mounted where it should be.

Raising it up would do 1 of two things, or a combination of the both.

1.You can lift the entire diffuser up vertically and there would then be a step from the rear lower arm/diff and the diffuser causing a huge amount of turbulent air just as the air is entering the diffuser.

2. you can raise just the rear of the diffuser, making the fins no longer parallel to the ground. Raising the angle of the diffuser to an un-ideal point. like said before the center sections are at 10 degree and the outer are at 20, raising the rear of the diffuser as high as possible would make those more like 40 and 50, any air going over is going to separate from the diffuser and cause the air coming out of the the back of the car to be as turbulent as not having a diffuser at all.

I think you need to post up some pics of this thing from under the car.

At first glance it does look like you just slapped it underneath the bumper. Showing the details of exactly how its mounted may save your case.

https://www.miataturbo.net/attachmen...ine=1335979182

Mounted on the same height/plane as the floor of the car...this picture's on the first page.

this!

Unless you have the entire bottom of the car sealed at the level of the red line, there's air above it. The pinch panels are below the floor of the car by 1-2", and the transmission tunnel and subframe bracing is another 1-2" above that. What you end up with is a big gap that gathers air above the diffuser and stuffs it into the bumper.

With a diffuser that big, you should be able to feel a big, big effect.

BTW - wings on a Miata do almost nothing without a hardtop. If you don't have smooth airflow to aero features, there's almost no point in having them at all.

the frame rails are lower then the pinch welds, thus if you want a true under panel you'll need to go at least to the frame rails...that's a project for later.

the first picture of a mount is where the lowest part of the diffuser, it's less than 1 inch below the mounting surface of the rear subframe brace brackets. the red line doesn't necessarily depict that point as you can still see some air gap behind the rear tire.

I never push this car on the streets, i can say it feels better, at least i think it does...i'll be back at the track in the next few weeks we'll see how speeds are affected, both in turns and straight speeds from all the drag i created. ;)


anyways no real point to argue this further, it's where it's supposed to be, although i'm sure you're all experts and Adrian Newey has you on speed dial.

Make crappy car modification.

Call everyone haters for disproving it.

keyboard aerodynamicists....call ricer...

Yes, we are all ricers on this board. None of us have track cars or no anything about racing cars at all.

Don't get mad at us. You need to tuck the diffuser higher into the bumper. It can be done easily. I would do it simply so you don't rip that nice diffuser off the car when you go off course or over a speed bump.

yes i don't race at all..........this is my first miata not my first "race" car.

negatively adjust aero work so that you can go over speed bumps, and go off track.

although i think i can go off track just fine as is...

Do you have significant personal experience on-track, testing various aero setups? Or are you just repeating what you've seen/heard/read on the internet?

:inout:

I could spend time discussing why you need to move/change it, but it's clear that you have no interest in actually improving your setup, so I'll just leave you to it.

FTN,

If possible I'd like to see some shots from underneath to see how you mounted it

Well, since this ain't going further, if OP was to panel the bottom of the car at the rails for win, what material would you use and how to cope with exhaust temps should you 'box' it in?

Wrap the exhaust from turbo to tip, use aluminum or CF with a skeletal structure, trans+diff coolers would be 100% required, and you would need to figure out a way to duct cool air to the inner CV boots.

C'mon guys he mounted it exactly how the manufacturer wants it mounted on an Elise. What could possibly be different between an Elise and a Miata?

https://www.miataturbo.net/attachmen...ine=1336000074

Oh, right.

The OP isn't really that far off of where he should be with the diffuser though is he? I mean, his is only a couple inches lower than these cars:
https://www.miataturbo.net/attachmen...ine=1336003107
https://www.miataturbo.net/attachmen...ine=1336003107

It seemed like everyone was talking like he should be hacking the bumper until it looked like this:
http://www.awrracing.com/blog/wp-con...7/DSC04771.jpg

(just bought a used Exige diffuser so this discussion interests me ;))

Yeah, only 8-12 inches off where the 2nd cars is at. What other goodies are sitting under those two cars?

1. The diffuser isn't where the bumper is cut.
2. ~9 inches from the bottom of the bumper is where the crease is. No idea if that's the factory location on Matt's car but it looks close so I doubt his bumper is cut even 8".
I'm aware. That's a completely separate discussion though.

Well, the stopwatch don't lie. Looks like the diffuser is easy enough to remove from the brackets, and if you can get 60 laps in a day at your local track, then you should be able to get some back-to-back tests in. Take some times and post 'em up. "Butt dyno" readings don't count either. :)

The bottom line is even the high-dollar F1 teams have a hard time correlating theoretical and CFD results with on-track performance, so this is all just armchair quarterbacking until you get some hard data.

I dont think you will convince anyone here that it has value with some numbers. in the rear defusers ive seen they dont mount flat they slat up at a significant angle and that leading edge is higher then the lowest point so the car is channeled and control. but Im sure you know this.

also when you do unconventional mods and post pics you gotta be prepared for criticisms. I go all kinds of ---- from people for spraying windshield fluid into my motor 10 years ago. didnt mater what i said right or wrong. now everyone is doing it and you can buy like 10 different kits all the new hotness. I should made a kit and proved it worked but whatever. so if you want to prove us wrong do it. casual talk is not going to do much. just sayin, I dont really care because doing something like that is way off in the distant future. I made a sick tray and diffuser for my RC car and it looks bad ass, no idea if it does anything....anyone want to buy a kyosho GT2 ;)

It is not a separate discussion. Diffusers don't work well without a flat undertray in the first place. Aero pieces should be thought of as a package, because they adding pieces to the front will affect the rear, and vice versa.

Guess even "real" racers don't go everything at once....:dunno:

My turn at armchair aero…


If you're adding a flat bottom later, as you say you are, then I see nothing wrong with the position of that diffuser, assuming the flat bottom will join to the front of the diffuser. Your ground clearance isn't helped much, but if it's a track car then that doesn't matter, and if it's a road car and you're prepared to live with it, then fair play.
I do think you'd still need to cut the bumper out a little more above the diffuser with a flat, sealed bottom, to help suck some air out from the space between the flat bottom and the underside of the car, just to help keep things cool. Assuming, that is, that air can be drawn in to that space from somewhere.

exactly.

https://www.miataturbo.net/attachmen...1&d=1336153649

I was only discussing the height of the diffuser at the time, which is why I said it's a "separate discussion"

Of course aero stuff only works well as a package but I was ignoring that in that reply because a lot of people were criticizing something that wasn't even that far off. The Miata doesn't have that much rear overhang so a 15 degree line from the rear differential area doesn't end up that high on the rear bumper.
Interesting find. Didn't realize Matt didn't have a flat bottom on that car. I assume that "diffuser" was designed differently than one would be for a proper setup then because Andrew Brilliant did the design IIRC.

if the bottom of the bumper was cut do air could travel over the top and the diffuser was left as is how well do you think this would work? would the air doing over the diffuser also help create downforce whilst not creating drag??

like this elise s1 diffuser

https://www.miataturbo.net/attachmen...ine=1336516276

The purpose of the diffuser is to smooth out the remaining airflow, this "remaining" airflow is what's left after a FULL F*CKING FLAT BOTTOM.....like the lotus pictured above, or any supercar photo....

if you have turbulent air on the front 80% of the car, the diffuser is basically nothing else but an aero drag. As now you have introduced another element In which the air flowing underneath the car has two different paths to take.

Yes, cutting holes in the parachute area will help, but think of all the videos of the failed skydivers with their cut/tangled lines. The tangled / cut parachute still slows them down, but not as well as a fully working one.

I.e. moral of the f*ching story here...... Retarded add on of a diffuser on an otherwise stock car will not net any usable..(read worth the effort) difference without supporting mods.


Or another way of thinkin. Would any of you, aside from fae, crank up the boost without adding fuel, or addressing timing? No, because you wouldn't do one without doing the rest.

There is no free lunch. You very rarely create downforce without creating drag (unless you're starting with a very poor design).

That being said, I'd do it. Even after you build a flat bottom I don't see that hurting as it's dead space.

I know that picture wasn't your car, but it's hilarious to see someone put in all that work to put a diffuser on the car and then leave mudflaps on the car. That is the first thing I removed on my car. :rofl:

How has aero suddenly become freakin black and white to some overly angry people on here?

Of course, ideally, a flat bottom would be of benefit to the whole package but some attempt at smoothing the the airflow and air transition at the back of the car CAN help in some small way...

You guys rave on about a package, well a package has to start somewhere....who is to say to you "experts" that a flat tray is the sum total of the package. To an aerodynamicist saying a flat bottom and a diffuser is "the package" is probably as ridiculous to them as this is to you, so where does a package start and stop?

Once again I say good on the OP for the effort and good luck with building the car as it comes along, ignore the haters and keep the rest of us informed.

Hopefully you haven't been scared off by the very angry, opinionated few....

I dont think anyone was angry, something gets lost in translation on the web sometimes. I would like to see some data, perhaps it works perhaps it doesn't. I'm interested and hope it works for its intended purpose.

my definition of a package is this: splitter, undertray, diffuser, wing. One affects the other. Adding only one thing may have adverse affects (i.e. adding a splitter may add rear lift).

Nooo, nothing angry here....

must be the web translation .... :eek5: