PaulFitzwarryne

The fastest top speed of a stock gen 1 was 145MPH. Mazda wind tested to 150mph and found the Gen 1 shape was aerodynamically stable at that speed. A small rear spoiler marginally reduced drag, but a front spoiler increased it. TWR in 1981 found with lowered suspension and a flat race track, front and back spoilers with side skirts were an advantage due to ground effects for high speed race circuits. Both the RX-7 types 252 and 254 used spoilers and wide bodies in low road cleaance configuration. However, below 110 mph drag performance was lower. This might explain why the typical IMSA car being continually driven fast on a high speed oval track, ended up as a different shape to the RX-7s being raced on European style chicane circuits with low speed corners.

My question relates to road going daily drivers. Most authorities impose a minimum road clearance which does not allow the benefit of frontal bent airflow having a low pressure ground effect. For such a car driven below 90mph, it appears a front air dam reduces performance. A rear spoiler improves performance above 65mph depending on shape. Perhaps above 120mph a chin spoiler will create down force and improve steering. My stock front end feels lighter than I would like on 120mph + straight line speed tests when the road surface is poor.

So is there any practical reason for adding a front spoiler to a SA/FB which is rarely driven at 100mph+ speeds? What are the dynamics, and drag effects at normal street use speeds?

DriftFB

This is assuming that you are going to have a identical or close to identical front spoiler as the ones tested.

boog

OK I JUST fabbed up a chin spoiler that only goes the width of the protective tray under the radiator.....it goesd down maybe 2 1/2"(it comes straight down about an inch and then there is an abrupt 45 degree angle for about an inch-like a mini dump truck but angular and not round), about the same as the stock little plastic thingy that runs across the lower front(i thought i needed a change and took it off)

anyways, i wanted to keep it very subtle and i dont want imsa bumpers cause i like the beak nose front...for my final design ill do a whole front wraparound going down maybe close to 3 inches from top of underbody protective tray.......my main goal was to try and force more air up towards the radiato for better cooling when traveling 45 and up (i figured it couldnt hurt since i took the stock piece off anyways so maybe i am at least fixing what i did when i removed it....if it could also cause downfoce: by disturbing the undercar flow and making the overcar flow faster than the under flow: than that would be an added bonus...

My dad and i have debated much over the whole idea...obviously mazda tested it out and found a happy medium...my dad suggested maybe there is a vacume that sucks air up towards the radiator without any spoilers or large air dams: it makes sense if you think about it, the air could be drawn(sucked) towards the radiator because that boxed in area is at a lower pressure than the surrounding swirling air (figuring flowing air is :drawn" to the easiest possible place to flow to/through


I tested it out going as fast as 90 (too fast, but its science right... ; ) on the freeway...the highways are not that nice really in most spots and full of grooves....once i got going it did seem like my car was staying at a better temp. then before with not even the stock airdam....and i feel that my front end was not quite as squirrely/ or hovering feeling (i could make movemnts in the steering that didnt feel stable before)....so maybe it kinda works but it could all be my mind too......ill do the taped pieces of yarn with 200mph leaf blower sometime too.............

iF IT is having an affect, it could have a slight affect in my 0-60 times with the increased drag, but it would be so minimal......the new revamped lotus elise "race track like package" comes with lots of downforce goodies that gave it crazy amounts of downforce at HIGH SPEED over the last car and also at High spped it had less drag i think....but the 0-60 and 1/4 mile times were actually slower than the other elise....


I was also think about doing some canards in the front and experiment with that....but i was woried about my front having considerably more traction/downforce than the rear(no spoiler) at high speeds


also a spoiler "spoils" the airflow right?...so it should create considerably more drag than usable downforce at low speeds also.....if by down force you think of the air flowing faster over the car than under: than a spoiler would be sowing the overcar airflow creating drag, and a little less downforce right? but at high speeds the spoiler would be needed for stability.....im over my head now....these are just my thoughts, so dont nobody (good grammar) get offended if i say something wrong



No matter what, at least this is fun and we are trying to use our brains!! instead of doing something lame like going on the computer...... j/k

13b4me

Front spoilers don't actually have as much affect on aerodynamics as they do on cooling... That's what they're really there for... To shovel air into the radiator/intercooler/oil cooler/etc...

RustyRotary

iTrader: (2)

I can see your points, but visualizing your front spoiler configuration is a bit difficult. I'd like to see some pics.

Also, the previous post makes sense. You can get a lot of cooling by pushing air up into the engine bay/radiator. But if you were being efficient with it, it should provide good front-end downforce, right? Though in my experience, RX-7s have pretty good front traction to begin with, but the cooling isn't too good considering the rotary engine's thermal properties. So instead of focusing on a front spoiler to improve on downforce/cooling, why not focus on a hood with an opening that creates a low pressure zone and pulls heat off the engine?

If you look at typical suspension setups, the rear traction is what is usually a problem, so it would seem that you could have more leeway in the front to work with cooling etc.

aussiesmg

iTrader: (1)

A well designed front airdam can improve your front end mechanical grip thereby allowing higher cornering speeds, this is the usual reason for adding a airdam, along with directing the airflow onto brakes, rad etc.

Lt. Dan

I've had the FB on the track at over 120mph both with, and without a front spoiler. With an IMSA style spoiler, the front end definitely felt more planted at speed, but not enough that I wanted to keep it on there... It just was too much of a hassle in day-to-day driving.... I will be trying a wraparound style spoiler on the rear though...

Dan

79rx_7

What did the Racing Beat speed record cars have on the car to achieve 184 mph and still be stable? In the pics it didnt look like there was anything different about the front and a small spoiler in the back.

Kentetsu

I was going to add a front spoiler (and still will eventually) to assist with high speed stability. However, after adding the Illumina shocks/struts and RB springs, it is already greatly improved (a lot more than I expected)...

82RXSOARER

If you want to maximize front end down force, i would encorporate a front splitter to the underside of the air dam you created... Something flat that will run parallel with the ground. The air running under the splitter speeds up when it has to squeeze between the road and the splitter causing it to have lower pressure. This in conjuction with the high pressure of the air dam will cause downforce. Another way to increase downforce would be to create a smooth belly pan under the length of the car, with a slight upwards rake towards the rear. This would help to remove the air from under the car, and again cause an increase in downforce. But be cautios of the rear differential. blocking all the air can increase the heat on the gears and that would only cause problems.

With the underside of the car sealed up, it would be important to turn your attention to the hood. If the air has no way to escape from underneath, you would nead vents to aid in cooling.

For the rear... I would say that with the downward slope of the rear hatch, a rear diffuser with directional vanes would be the best bet to lower drag. Just a little something to help the air under the car and the air running over the top of the car to meet at a clean point.

Now keep in mind that all of these modifications would only come into effect if the car was running at a high speed. For a daily driver, these mods would probably be overkill, and not be more than added weight.

For aerodynamic questions, i would recomend you visit this forum... www.eng-tips.com ... Click on the automotive engineering or aeronautic engineering link.
Most of these guys are very knowledgeable regarding just about anything you could ask. They could help with front spoiler designs to rear diffuser rakes.

If i mistated anything, i apologize. Most of this stuff i have learned from reading and some personal fabrication. The guys the eng. forum would probably be able to help you more.

Thanks, stephen

13b4me

Why not both?

boog

this is so great, i love this stuff..........i like the idea of a front splitter, would it just be like lowering the car further in a way or is it like a tray or something, could you draw a picture so i could understand better? Would it be good to do a splitter at the front and maybe attach one to the bottom of the gas tank too?

What if you just tried to clean up the underneath of the car the best you could with some sort of light sheet metal (better be welded probably) but left ample space around critical moving or hot parts like the diff/driveshaft and exhaust?...might be cool to try


I am still wandering about canards tho, are those just for show when there on the small side or could they be useful

maybe for a rear spoiler someone should make one like on old camaros and firebirds where it was just like at the last edge of the body and shot at like a 45 degree angle off in the direction away from the car (behind).............but very slight and not huge, it would also have to be very angular looking to match the lines of the car.....it pretty much be a wrap around with just the back part.........still is functional but would now be cleaned up and would make less drag...?

thanks for the website SOARER im gonna check it out, fo sho!

aussiesmg

iTrader: (1)

Great info on the undertray, I ran one on my old Rx3 race car and it made a big difference in cornering stability, aerodynamics aren't an RX3 strong point anyway...lol

Canards definately work they were used in Aussie V8Supercars when the Fords had a disadvantage in their package to help even the field. Oh and a little groupd called Formula One has used them for many years, however good luck getting the best out of them without a windtunnel.

82RXSOARER

Well, the air dam would be what would get it lower... The splitter is just a flat piece about 1/4 to 1/2 inch thick. You can buy them from most dealers that sell bodykits. They may look a little ricey but they are very functional. But you have to run some pretty low ground clearance for the full effect. I actually made my own (didn't want to spend 300 dollars) out of (i think 1/2 inch) ABS and then another from fiberglass. For the pattern you just set the air dam on the ABS, draw your pattern, cut it out, and bolt it up. Not the most technical design, but functional none the less.

For the underbody, i would try fiberglass. I checked into the cost of a large piece of sheet metal, and it aint cheap.

I'm a mechanic for dodge, and i see vipers all the time. The underside of them is virtually smooth. But this is accomplished through one long plate which bolts up. I wouldn't weld or you wouldn't be able to do any repairs underneath. They also have a type of inverted scoop that allows air to flow upwards toward the rear diff. The SRT guys knew what to do there. So i would just follow there lead.

Rear spoiler is a really large field. The JGTC cars and circuit cars run large wings. While some autoXers run smaller "lips" across the rear. I'd say unless your runnin some really fast numbers on the track... It probably wouldn't make a whole lot of difference.

I'm not a big fan of canards... They look a little ricey, and end up bending the fender panel and cracking the paint. But i'm sure they have there place, or the pro's wouldn't be using them.

Also, you should look into vortex generators... Like on the Lancer Evo 7... Mitsu has a downloadable write up which i'm sure you could find if you google it.

Check out the pictures i posted with the Front splitters...

boog

this is great info...and the stuff in the pics looks awesome....even if i never made anything that functional or improving this is still fun...where did you learn about all this stuff, i have been trying to find info everywhere


ok here is my first mock up experimental design (that's my disclaimer for people who want to say it looks stupid).....

82RXSOARER

Well, what you designed there is exactly what i ment by splitter. Probably works as a functional lower air scoop to help cool the rad and what not.

When i'm talkin about a splitter you generally need a lower bumper to attach it to. Stock FB nose is too curved to have a splitter attached parrallel to the ground.

But your design isn't stupid... just probably wont do a whole lot for aerodynamics.

Aero is my passion... I'm gettin ready to start school for mechanical engineering and aerodynamics. Hopefully I'll get to bang on race cars all day long... Maybe...

The stuff I know i just learned from reading online and books in the place nobody goes to anymore... the library. One magazine that is really helpfull is Racecar Tech... I think that the name of it.... I'll check later.

If you wanna do an online search for this stuff, google CFD or computational fluid dynamics. But be warned, it can be a little intimidating. But all in all it's just glorified math problems.

But as for your design, not a bad start... Just try lookin at other peoples stuff. (example...JGTC) Thats were I got start into all this.

FirebirdSlayer666

iTrader: (3)

Definitely seems like a good start. From other's experience I've noticed the stock FB nose will actually begin to lift after 110MPH. A spoiler or air dam would be an increase in not only cooling but downforce on the nose. Even for daily driving a spoiler is beneficiary to cooling.

KeloidJonesJr.

iTrader: (8)

Downforce and cooling purposes.

LongDuck

Part of the 'floaty' feeling on the SA/FB has to do with worn out struts, so give that a look as well to see if they're contributing to the problem, possibly also combined with a steering box that's wearing out and has a long of on-center slack. Both of these are fixable with some knowledge and shop tools, and could go a long way to restoring high speed stability on your car.

As to street-driven aerodynamics, the only limit to the front end is from ground clearance. I chose to go with a Kaminari designed front-spoiler, and added my own kydex sheet splitter parallel to the ground. I'm a pilot and like to play around with aerodynamic designs in my spare time that are both functional and durable. Here's a recent picture from a recent RCCAZ RX7 car club event:



In this picture, you can see the front air dam and splitter. I feel that these are effective at shoveling more air into the front end to assist with A/C condenser cooling (I live in AZ), and radiator cooling. This is important on a car that will run A/C all summer long and you definitely want enough air going through to cool the condenser or pressures will go high enough to burst the plumbing. I've never had a problem with cooling at idle or freeway speeds, and am planning to build a closed duct with more Kydez (plastic) that will force the air straight through the radiator - right now there's still a gap below that allows the air to bypass the core.

I have measured MPG with the aero mods and have lost about 1-2mpg in city/highway mixed driving, so there is definitely more drag induced through front and rear spoilers - along with my rear hatch, which causes a lot of turbulence at the rear, compared to stock glass. The hatch alone was about 1/2 of the MPG loss. HTH,

RustyRotary

iTrader: (2)

Right idea, though that design would probably disrupt airflow more than it would guide it.

A front splitter can definitely be made to work on the stock bumper though. I wouldn't bother spending money on a premade one. A lot of amatuer auto-x/track cars have home-made sheet metal or plywood ones. You'd be suprised how well the plywood works. Though with sheetmetal you would have the benefit of adjustable angle using turnbuckles as support.

boog

the front splitter you drew is exactly what i was going to make first (even the damper/turn buckle thingys i had thought of too) but i strayed away from it to start off simple....i think that is roughly the best design idea for front spoiler/splitter i have seen so far...my favorite part is it keeps the beak nose..

So is it better to make a flate plain that is parallel with the ground than having a "scoop" style spoiler..if i made a splitter how far back could i go with the sheet metal (could i go behind the front wheels?) would it be pointless to have a splitter of some type at either end of the car and have nothing really streamlined in the center?

The diffuser i would have no interest in even thinking about because how much money/time/and troubleshooting you would have to do for just a street car.......
---the row of fins on the rear roof of an EVO MR edition, are they used as a diffuser?

hey "soarer" what school are you going too? thanks so much for all your valuable info, if you ever get locked into racing aerodynamics hit me up on here and tell me all about it......i love designing/engineering (but im honestly afraid of math, it is pure evil) and im going to UNLV right now as an art major

RustyRotary

iTrader: (2)

It may not be as difficult as it seems. It's basically just a series of triangles welded to a curved piece of metal.



The diffuser basically guides the air out of the back, slowing it down from the high-speed zone under the car.

There is much to be gained by making this whole set-up. When used in conjunction with a flat underbody and front splitter, it greatly increases the downforce created by the entire underbody, including the front splitter. The peaks of the downforce are at the front splitter and the beginning of the diffuser fins, but everywhere inbetween is a lowpressure zone as well.

Also, the diffuser will reduce drag on the rear of the car. If you're using a rear spoiler, this will further improve the effects of the diffuser as well.

TheOnesAndTwos

All good ideas and designs, but I think we've gotten away from the original question which was affects under 100mph. Being an areospace engineer I deal with a lot of areodynamics, In my opinion the affects would be negligable at speeds under 100mph. Not to mention when assessing the effects that the front air dam has there are many variables to account for; such as road surface, or even the proximity of the car ahead of you. I don't think that there is much of an effect at such low speeds.

wecycle

http://www.bgsoflex.com/aero.html
Cool site by the guys that developed Megasquirt
Has anyone found good data on the Cd resulting from various air dams?

boog

it seemed to me that splitters/underbody trays/and diffusers would speed up the air moving under the car because it is trying to squeeze its way out...guess im wrong, but why..

Also, if someone made all the underbody stuff wouldn't they need sideskirts of some sort so the air would not be trying to escape out the side at all...