If the two designs jut the same amount in front of the bumper. The 2nd one will make a lot more downforce while having a bit more drag. It'll make more downforce because it will have a slightly higher pressure above the splitter and because there is just more area on that splitter for the pressure to act on. (pressure is pounds per square inch, have the same pressure but more square inches = more force).

Anyone here use OpenFOAM to benchmark their ideas?

The second one will not "wear" well and will rip the bumper skin off during the first gravel incident.

The second one will have more downforce but also more lift because of the forces pushing upward on the underside of the nose as it protrudes. One of the major shortcomings of the stock bumper design is that the bumper overhangs the lowest portion, giving the pressure a point to "lift" against on the underside of the nose. Aerodynamacists caution against this. The one with a straight surface downward from the foremost point is more efficient. The designer obviously built it with this knowledge.

Never thought of the upward force. BUT, empirically, at least on an NB1 front end the air dam further back yields more net front downforce.

I made this a couple weeks ago:
https://www.miataturbo.net/attachmen...ine=1350411914

Is Craig your stage name?

Wow, thats a cool diffuser, hope you got the angle right.... :giggle:

Scarred bro?

F1 aero is crazy awesome, and also crazy expensive.

That aero is weak lol

But you can use the autoclave to make gumbo.

Which means of course NOLA is the perfect place for a US F1 team to set up base.

Some say, he is writing the world's first cook book on making gourmet dishes using common hand tools, and that his recipe for Gear a l'Orange uses Motul for the sauce. All we know is, he's called The Hustler.

I finally ordered some of this stuff and got it in this past week. Easily the best option I've found for air dam material so far. I was a little worried that it'd be too thin, but now that I've seen it in person I'm not at all worried. A little over $50 for two sheets to my doorstep = win.

I'm definitely buying a roll of that stuff.

Pic of my latest low cost aero. Large front splitter, large front diffusers, canards, side skirts that start forward of the front axle line, fastback and dual element rear wing. The car has no mechanical changes (tyres were 2 meetings old last time, this time they are many track days old), just the aero. I picked up 0.9x seconds, with top speed 9mph faster on the straight, and 10mph faster at turn one, now 110mph.

https://www.miataturbo.net/attachmen...ine=1352886977

Looks great lightyear!

Can you elaborate on these two things? Do you have pics of them? I'm assuming the sideskirts start inwards near the center of the body then curve out to the sides of the car? And by front diffuser do you mean a diffuser shape in the front splitter forward of the front tires?

-Ryan

Yep, the skirts run along the inside of the front wheel, actually part of the splitter/under tray. Then go around the back of the tyre to meet up to the sides. Front under tray is wedge shaped at the front in the middle. So there is a triangle that is level to the ground. The rest of the under tray is curved up. With sides to create tunnels. I have a cardboard model I made. If I get round to it I will take a pic.

I would like to run the front splitter 2" of the ground, the same as the skirts. But I can only just get it on the trailer as is.

What spring rates are you running up front? At the length of craftsman deep sockets (bit over 2 inches) off the ground with 900 lb front springs a splitter that does not extend past the body shape will scrape under braking.

I have a pic under heavy braking going down a hill. I will see how high it is. My splitter sticks out from the bumper about 3". I don't know what spring rates I have. The coil overs are a cheap set of street b.c coil overs (gold) with whatever spring rates they come with. I payed $600 for them 2nd hand.

lol @ using a craftsman deep socket as a measurement unit.

-Ryan

Car one is the far superior design. The easiest way to think of aero for me is to imagine the particular part your building being placed in running water ie like a creek. Now your job is to channel that water so it has the least resistance. I know that sounds silly but others have to have their brain wired like mine :) lol

Superior for what? The second design will likely create more downforce as it looks to have a greater surface area for the splitter. If that is your goal.

Well car 1's design is similar to Crusher. Too bad that car is really slow and never wins any races.

Rear main fail:
https://www.miataturbo.net/attachmen...ine=1350319223

Car one with the apocalypseTM front end has a more effect means of evacuating the air above the splitter, has less drag, and creates less turbulent air for heat exchangers and brake ducting. Both designs have been tested here in Texas up to 150ish mph. Design one on the same car with no other changes has to run a lot smaller splitter to keep the balance the same. The goal is really to create negative lift on the front end which translates to more downforce, the stock miata bumper is a great design on the top 4" ;)

Here is version 1 that we built in the winter of 2010 for JohnZ's car (spoolin2bars)
http://www.speedhunters.com/2011/03/...w_track_miata/

JohnR, ZXTEX car one, took it forward and used a better material and covered the front tires better with out canards. I have several improvments in my head but need a fresh junk bumper and some free time. Spoolin also needs more rear aero before we improve on the front design. Look how small the splitters are on both the straight down designs, they are more effective period.

I agree with you mostly. I think it would be interesting to quantify the differences via CFD.

Look at spoolin2bars birch splitter we made in the post below, it was like a 6" splitter. No other changes but added the apocalypse front end and the splitter had to be trimmed down to 2" to keep the balance the same. I believe ZXTEX had the same experience as us on splitter length once you go to the flat front end.

https://www.miataturbo.net/race-prep...r-52759/page4/

I also believe spoolin picked up some mph on several straight's here on local tracks.

I'd like to see what a large front splitter with a flat front air dam would do. Judging from your experience and others you've referenced it would unnecessarily shift the aero balance forward.

There is some interesting stuff in that thread. Like the structural adhesive tape idea.

I'll be running a front air dam and splitter but I'll be going topless. What is the best way to balance out the effects of the front splitter to get rear downforce ? The car will be PT/IT/TT

Depends what your goals are. Personally I think air dams and/or splitters should be used to correct aerodynamic balance after adjusting or changing a rear wing (assuming a diffuser that works is already on the vehicle). The correcting of aerodynamic balance will also add downforce. Also, a decrease in drag can usually be gained by the addition of either a splitter or air dam.

I have simulated both of these types of setups in cfd. If interested, check it out.

https://dl.dropbox.com/u/105015076/a...ata_122612.pdf

Thanks for the response. I definitely need the front down force. I am running with NO hartop and I need a little help figuring the location of the rear wing to help balance out the front. With no top your model is not effective.I don't need to be spinning,chasing my tail due to lack of rear down force. Miatas need all the downforce they can get.

With no top, the air over the car is a swirling chaotic mess. It's a huge oversimplification, but your wing needs to be as high in the air as possible to have a chance at getting some clear air to cut. Fastback>hardtop>open top for aero.

From what I've heard, on the spoiler cars make more rear downforce running a tonneau cover compared to just a straight open top.

I've been told the hardtop is worth 5 mph at 120 ??? dunno but I need the head space and the roll cage will not fit under the hardtop. I can go 6" ( maybe 8" ) above the front windshield height. I'm just looking for any help you guys might have to offer. Thanks

Thought this deserved a spot in this thread

I really like how he did those front fenders. Is there any more info on them in particular?

What materials are people using for flat underbody's?

Im about to put a front end on an NA the same as the blue car with the big Hoosier sticker, and I have a diffuser to put on the back, I was considering just riveting aluminium angle to the pinch welds and screwing an alumalite panel to it with perhaps a few alluminium angle's running across it for stiffness, and of course the whole exhaust will need to be wrapped.

Is there a foolproof option that wont melt? 1/4 birch seems heavy for an entire undertray.

Dann

ABS if you can get it

I would not use wood anywhere near the exhaust system

I can get anything I want locally, however went I went in and spoke to the materials expert we talked about some things and came to the conclusion that PVC would be the best for the front bar for example.

Also is ABS just going to melt and sag under the exhaust?

Dann

Yes it is! Haha. Ask me how I know...

I'm currently remaking my flat bottom out of aluminum.

-Ryan

How thick is the AL you are using? Are you using straight AL sheeting, or a corrugated product like Alumalite? That could get expensive fast.

Volcanic I checked out your fab thread on CR.net. Nice DIY fab work!

This is what Im wondering.

Alumalite has a plastic core.

I think thin ply with a reflective material on it and a fully wrapped exhaust would do the job just fine.

The below pic is a cross section of the MX5 tub. You can see the trans tunnel in the middle, the pinch welds are the vertical lines at the outside and inside them is the frame rails.

https://www.miataturbo.net/attachmen...ine=1356757138

The pink represents aluminium angle, the blue is 1/4" ply sheet, and the red are fasteners.

Looks ok?

Anyone think exhaust heat wrap and reflective tape cannot save the timber?

Dann

Hmm i thought i was subbed here.

A couple things -

First off, don't wrap your exhaust. The header is one thing, but under the car can easily get soaked with oils if you develop a leak since it is downstream of the engine/trans, and then instant fire. This has happened to people before. Whatever you make the undertray out of needs to be able to handle the heat without needing to add exhaust wrap.

As for my particular design, I'm not using alumalite. I have alumalite in the garage, but after my first version which was made from ABS, I have seen how much heat is under there, and I feel that the core of the alumalite will quickly be compromised by the heat just like the ABS was. I am making version 2 from .030" aluminum, which by itself is quite flimsy, but it's being reinforced with a gridwork of small aluminum angle, and I've worked out a permanent and lightweight way to bond the angle to the sheet.

-Ryan

Bonding the angle with urethane?

Im pretty sure ply with alluminium glued to it along the exhaust path will work fine.

Only one way to find out.

Also Lightbulb moment.

Ill fasten everything to the car with rivnuts (also known as nutserts).

Dann

Forget the nutcerts, dezues fasteners.

For an undertray I would rather use rivnuts than Dzus fasteners. If everything under the car is built well, then the undertray will not have to come off often, maybe once a year, and rivnuts/bolts will be a lot stronger.

I haven't used rivnuts, but Dzus fasteners suck

From a fabrication standpoint, the rivnuts would be a much easier install to boot. You could just drill holes in the frame rails to mount the rivnuts, whereas with dzus fasteners you'd be forced to install dzus plates anywhere you want to install, since you can't access the backside of anything to locate the springs.

I've seen this said numerous times but I've had 0 problems with them on 2 different cars now. What kind of problems did you have?

I would make the blue line (floor) a lot wider than just to the pinch welds. The air will be sucked in from the sides. At least go a couple of inches past either side.

I used them to attach bodywork on road racing motorcycles. The damn things would always come undone. We had to cover them with duct tape to hold them in place.

My rear diffuser is aluminum and going with aluminum underbody after birch splitter. Currently not turbo, but I imagine if it actually got hot enough to melt it then you can just line the top side of the tunnel to insulate. My 2 cents.

Weld-nuts are better than Riv-nuts. Riv-nuts are great until they come loose, then you can't get your bolt out because the riv-nut is just spinning in its hole, so you have to cut the bolt head off. Weld-nuts won't do this to you.
-Ryan

Wood is also a bad material for under the car due to oil soak/fire danger. This is why any wood or ply splitter should get a layer of fiberglass laid over the top so it can't absorb oils.