Gotpsi?

iTrader: (5)

I know strait down would be more aerodynamic, but with the stock bumper tilting back it would cause more high pressure on top of the splitter, if you have one. Would it not?

GeneSplicer

iTrader: (14)

It would/will have a splitter - my splitter is currently supported from the bumper support and hangers - nothing to tug/pull down on the bumper cover itself, and that's the way it'd be if I changed bumper covers

No flares? - Well, seeing how I'll have 275/35s on - the tires already do a pretty good job of adding frontal drag - ****, my 225 nto1s + 20mm spacer already stick way out with the oem bumper - was just trying to 'smoothly' deflect the air around better than letting it slam into the front tires - same with the rears too

spoolin2bars

iTrader: (1)

absoultely want to cover those tires. they're worse than drag, exposed spinning tires supposedly create lift. you would want the flares/bumper assembly to cover the entire front/exposed part of the tire.

GeneSplicer

iTrader: (14)

These are the flares I was thinking about molding into another bumper - still wish they were smoother in design... kinda like rharris's N2 flares but stick out more at the bottom instead of curving back in. Someone just needs to come up with a functional aero kit not based on just looks.

Savington

iTrader: (31)

+1. 54% of the drag that an Indy car creates is caused by exposed tires.

Every bit of unshrouded tire below the hub line is not only frontal area, but it's also angled to catch air and funnel it under the tire - the high pressure that creates is going to act to lift the tire up off the ground. Worst yet, MOST of the unshrouded tire on a Miata is under the hub line.

The more you can shroud the front tire, the better.

greeenteeee

Here's my attempt. Still not done, but first time mounting it on the car and driving it on the street.




^ There is a slight gap on pax side only, btwn the lip and splitter. Probably due to the mounting points for the lip, as the driver side does not have a gap. Can fix this by widening the hole to move the mounting point of the lip further back a little bit.



The nut/bolt on the sides are 1 of 3 nut/bolts... it has an aluminum L bracket to block the tire, found in OEM vehicles. It is also supported to a 10mm bolt to the frame. It only extends down 1/4", didn't want to overdo it. These affect drag, and lift (front and rear) with different configurations. On a DIY w/o a wind tunnel, I think it is all a guess... Here is the article I referenced for this:
http://autospeed.com.au/cms/article.html?&A=2456



So the "tire deflector" serves for that purpose, as well as support for the sides of the splitter, and will be incorporated into the tire spats to be added. I will bolt it onto that point and curve up following the contour of the lip/bumper. Probably will make it out of rubber (truck mudguards).



^The view underneath looking straight back. At the very back, it is mounted to the 2x 10mm bolts in front of the subframe, right below the steering rack. I should probably add some spacers btwn the splitter and the sub frame so it does not bow/mushroom the way it does, tho very minimally.



^Here is the inside mounting points. Box aluminum frames extend from a 10mm mounting point to the chassis, M8x1.25 hardware holding the splitter to steel 5" L-bracket, with a box alum running horizontally from front-most of L bracket to each side, for some extra support.



View of the box alum to L bracket through the duct. Will add brake ducts eventually. Take note the clevis pin/bolts for quick release. I need to make the bumper easier to remove first for it to be "quick release" -- it was a PITA to get the car on the ground as it is.



^ Also an aluminum L bracket running fore and aft from the rear to the front, it ties into the box alum that ties both steel L brackets and is lengthened further out front to give some extra support.

1/4" Birch Plywood, no fiberglass, yes I am taking a risk taking it out in the rain. I wanted something thicker, but they had either 1/4" or 1/2"... the 1/2" was pretty heavy, so I went with this for now. It's not as thick as others, which is why I added the extra supports that I did. Though as I was fabbing it up, even if I went with a thicker Ply next time around, I probably would still do the same supports.

Chose not to fiberglass for cost, and I may not use it on the streets anyway. Only sticks out maybe 1 to 1.5" from the GV-style lip. After much research and feedback, my main priority is to reduce drag and have a flat bottom. I can also trim it shorter if need be to further tune it. Already looking to what I can do to smoothen the underside of the car, and finish it off with a simple diffuser.



It is for this car, and I have since raised it to 4.375" front pinch, 4 11/16" rear pinch (about 11.5" F 12.25" R hub to fender)... may need to raise it more as my old lip hits the bowl of Streets of Willow at 4.125" front pinch height, but I don't like wheel gap.

astroboy

iTrader: (18)

I've been thinking a lot about deflectors and how much they should go down. I would go with longer than 1/4 of an inch if you have some power to compensate for drag (I don't think there would be too much to worry about if you went with 1/2").

hustler

iTrader: (6)

My car was really scary over 120mph with the stock bumper, can't use much brake pressure, can't steer at all on the back-stretch at ECR:

With the RB bumper it's much more planted, brakes work, I can steer at 140mph at TWS

I never knew those figures, but it makes sense.

jacob300zx

Good splitter greentee. Now add some aluminium going from the top of the front fender curving down to the splitter, it should follow the outside edge of the tire if you were to look from the front of the car. Off the car it would look like a triangle that had been curved over a 55gal barrel. I'd also ease up on the thickness of your bottom L brackets, it might be a bit over kill using 3/8 alum.

bbundy

That vent in the hood makes a huge difference in lift at speed. At 140 mph the stock hood has so much more pressure on the bottom side of it than the top side it will almost bend with the stock latch trying to hold it down. With a properly placed vent the lift forces go away.

I think my Eribuni hood made a bigger difference than the splitter.

Bob

spoolin2bars

iTrader: (1)

+1 ^^^^ i doubt his bumper made much of a difference at all. any reduction of lift was probably all due to the hood.

hustler

iTrader: (6)

Why must you always come down upon me and pick on me!!!

I'm not sure that hood has a big-enough hump to make a difference but you guys know more than I do. I've considered adding an aluminium foil/flap to increase the pressure differential...not because I need it really, but because Matt's oil temps were so much lower than mine with the same heat exchanger. With all that said, the hood and bumper made a huge difference at speed.

jacob300zx

I wonder if you could put a gurney flap on it.

spoolin2bars

iTrader: (1)

not picking on you. just have gone through that stuff before. bumper probably helps a little since some people report the r lip makes a slight difference, and your rb style bumper is probably a little better than that. the hood that we have is another story. robert made that mold from the carbontrix vents that everyone uses and has reported on making a huge difference. it made a big enough difference on my car that i had to trim down my splitter to compensate for the added grip up front. plus you said at tws that your car was scary on the front straight like you need more downforce. it might be time to bite the bullett and buy a secondary trunk with a spoiler or a small wing, and a splitter. even the little aluminum splitter i had on my car made a big difference above 100mph on the track. when you drove tws you already had your bumper and hood so i wouldn't expect you to know which helped the most. that's kinda the problem i had all last year. i did so many mods throughout the year that i was chasing my tail trying to get back the balance that i had at the end of 2009. my car got faster, but not as much as it should have. sorry, i don't hate.. i educate... besides i like you!

hustler

iTrader: (6)

I'm jacking with you.
Part of my fear may have been never driving my car that fast with others around it; I was able to steer and brake the car pretty well. However compared to the backstreatch at ECR, the car was definitely more planted with the new body parts.
I already have a painted spare trunk in the garage; I would have bought-up Savington's spoiler if I had the money but last year was a hard year. Hell, I have a $4000 tooth, not including the two crowns from last year.
I'm trying to leave the car the same this season and change nothing, but the reality of TTA hit me yesterday.

GeneSplicer

iTrader: (14)

Hey Hustler - I'm in the same boat getting into TT this year and with the passing rules - might as well be racing. Still trying to have Greg tell me what I'll be classing - I can check everything off a list, but when it's turboed, it has a different base weight which only he has some magical/wonderful formula to let you know. He says I could very well end up being TTA - which would suck *** at places like RA. Has he (Greg) been responsive to gettign you classed? I know the man is the freakin national director - but dam, my first event is early march, and hasn't been much help getting started/classed. I'm in for 4, but with check ride should get the provisional license and run TT. It's the ** that kills us - 14pts right there.

Jfornachon

iTrader: (23)

Unfortunatly, Greg is a very buisy man and we too have our first event in march. Hell I have a hard time getting a answres to my questions when I am talking face to face. All year miatas have taken a hit this year.

BTW Gene there are many people that are dealing with his magical formula to fgure out classing and I feel for all of you. I will be going throough it later this year. I honestly think it needs to be a set formula. Welcome to 4I was forced out of 3 by the instructor and am glad that he did so. I have improved so much as a driver its not funny. This class is considered to be a competetive class. So yes it may feel like racing. I dont know how the people out there are, but I have a great group of people that I get to run with. The passing issue for me is a non issue. We are not door to door racing like Spec Miata.

have a gerat day,
Jared

spoolin2bars

iTrader: (1)

that's wierd, i had my tt classing within a week or so of emailing him. less than that on our crx turbo. maybe he's extra busy or you didn't give him the info needed. all you need to tell him is what your whp is (dyno based) tell him what kind of dyno was used (dynojet, or mustang etc..) and what your competition weight will be. (weight of car with you in it after exiting the track) so you might wanna add a few hp and a few lbs. to your actual #'s to make sure you don't come in under weight or over whp due to weather, amount of fuel in tank, etc.. how much does your car weigh? my car with 230whp and 2500lbs comp. weight was classed ttb* in 09. i never ran that much power so i lowered it to 204whp (9psi) and lightened my car to 2400lbs comp. weight and was classed ttc** but after points i'm at the top of ttb.

one other thing, once your base classed, you don't take any points for any power mods or weight reduction. it doesn't matter what you do in regards to those things as long as you don't exceed your stated whp, or go below your stated comp. weight. lmk if you have any questions, i've helped 4 of my friends get their tt classing figured out this past year. or you can go to your regions tt section here: www.nasaforums.com
good luck this year

hustler

iTrader: (6)

I believe Ken Brewer does classing for my regions. It's easy to see if you will be in A or B just how Spoolin said, divide actual weight by actual peak whp, hopefully you're over 10.25, I'm literally 2hp away from TTA. After that, our tires are skinny enough to give lots of head room for mods.

I used a Cat trucker scale so I'm a little concerned with accuracy. I guess I'll class it and hope for the best at the first event. I suppose that I can enter TTB, then find myself in TTA hopefully without a gay penalty.

GeneSplicer

iTrader: (14)

Jared - 4 is like PBOC supersolo - absolutely awesome, keps you focused at what you're doing. I might have pissed off one vette in 3 - I didn't give him a PB for like 3 laps, figuring he'd notice the Nasa4 sticker on the bumper - guess he missed/skipped class and didn't know about it - that's his own dam fault. The instructor was all in my favor when I told him about it!

Last fall at 1/2 tank, I was 2420 comp weight on their cert scales at Nasa. Just got the extinguisher and that weights 16pds - I put a comp weight of 2450. If I have to add ballast or back off the boost, no problem. What I did was fill out the older 2010 form, checked all that apply, make notes to vague mods, - scanned and emailed it to him and also my dyno sheet. That was about a week ago and haven't heard anything back - yet. I still had quesitons before filling out the classer, but just went ahead with it anyway. Maybe we should start a TT miata classifer thread to help us out?

Currently, I'm at 92 mod points. What did he say was your turbo base weight. He did say it will not be the 2182 listed in the rules. My my shady math; my P/W ratio ends up at 10.65:1 - can up the ponies to 239 if the min base weight is 2358 - I "think" that's what he said it was/would be but without his "base weight" calculations, I'm lost.

It'd sure be easier to just run power:weight in TTS/TTU That way I can build the car to whatever is fun as a DE car and not feel like I "have" to stay within certain power and point ranges. Prob 1/2 of my track weekends will be TT - other will be just fun DE days. Hell - if I drop in the 1.8 wanting to make 350 at the wheels - I'll be in TTU - competitively speaking, not a chance at tracks with long straights unless I do something about gearing.