What are the aerodynamic issues affecting the 4th gen at high speeds (>100MPH)?

I had mine up to 150 once, and did not feel very secure. No movement, but it did get light. Even if you were on a flat deserted highway between Las Vegas and Reno, there comes a speed where the front end or back end get squirrely. Has there been much investigation on this issue?

 

All I know is that the SS spoiler makes a little bit more downforce at speed than the Z28 spoiler.

 

As far as I know, there are two big things that you should do to help the high speed handling of any car (remember hearing this awhile back).

Drop it as low as possible...

Clean up the airflow underneath (think about how aerodynamic the underside of the car is...stock its almost as bad as it can get)

Look at the undersides of F1 cars...completely smooth. Because of the airflow underneath the car, it adds downforce without adding any drag. Someone else could go into it more, but thats all I know right now.

 

Back when i had the 6-speed in the car, I got it up to 148 and it actually felt pretty smooth... didn't feel it get light in the front end or buck around (stock ride height). It was rather loud though, and tunnel vision freaked me out. A good suspension with a lowering kit should make a 4th gen feel pretty good at high speeds. A good tire can make a difference too... i have an el-cheapo "performance" tire on the car now (falken) and it feels worse at 120 than the goodyears i had when running 148.

I quickly discovered in that 148 run that i don't have the testicular fortitude to ever go that fast again.

 

1) Shocks.
Doing anything over 100 in the stock DeCarbons is a death wish.

2) alignment.
More caster and atouch of toe-in will help keep you pointed in the right direction.

3) tires.
High speeds require Z-rated or better tires. Doing high speed runs on drag radials shows a limited thought process.

4) roll cage
The extra weight in the rear isn't such a bad idea, but the main goal is for safety and chasis stiffness. A rear hitch would compliment this as well I suppose.


Until those 4 are all covered, any gains from aero-dynamics is a waste of time.

You could experiment with lowering springs, functional skirts (spring loaded, wear-to-fit units like NASCAR, not the useless vanity skirts people weight down their Integras with... the skirt needs to be at or less than 1 cm off the ground... most data shows benefits maximize around 7mm), rear diffusers (used to keep you striaght and increase down force on the rear wheels), etc...

But again, aero really has little effect at moderate speeds (i.e. 140 mph).

Removing the side mirrors could probably get you about 5 mph near 200... at 140 you'll be lucky to find 2 mph max...

Unless you plan on open road racing this is not where you want to put your money.

 

if this is a street car/daily driver i would not put in a roll cage. having a roll cage just makes the car more dangerous.


brook

 

Is this going to be like your alleged C6 Z06, or do you actually have some evidence to back that up?

My car felt fine at 150. I was on an open road with lots of room, no other cars, and just a slight curve. I could have and would have gone faster, but the "lots of room" was running out. I have 245/50/16 BFG KDWS tires on stock suspension.

I used to have a '93 Civic EX. I could get that thing up to 125 with enough room, but it was a little squirrely at that speed.

 

the rollcage being dangerous has to do with it's proximity to the drivers and passengers head. The main hoop, if not placed back far enough can split your head open in a wreck.

Also of consideration is that if the cross bar for the main hoop is not far enough back and the reclining mechanism in the seat snaps you could potentially be slammed back into the cross bar breaking your neck or spliting your head open.

Saying "I'll put padding on the cage" does nothing for driver safety (on the street) as it's designed for a helmeted head hitting it, even with foam it will split open your head.

The danger to a passenger in the backseat is immense as the bars are right there beside and in front of them. The rear seat should really be removed so the temptation is not even there to have a passenger.



It can be done safely, it does require a custom cage however. Consideration has to be given to keep the main hoop as far back as possible and if you retain reclining seats the cross bar needs to be back far enough that the seat can recline all the way back without the driver touching the crossbar. The sidebars still pose the threat of snapped ribs and broken arms, but those are not generally life threatening. Ideally a non reclining seat would be used and if it's not FIA approved (there's only a couple) then it needs to have a back brace. After seats and a custom 6pt cage with belts your looking at about $2000.


All of the cages I've seen on the mrkt that are not custom made have the hoop too far forward.

 

Ah, okay. Thanks for the info!

 

he basicly summed it up.. except it sounded he was talkign more about roll bars (he only mentioned the main hoop)

a roll cage you have bars going down the a piller and one going across the car above the windshield.

now do you think putting steal bars around your head is a safe thing???

roll cages in race cars are part of a safty system... (roll cage,helmet, harness)
if you dont use part of the system then it makes things more dangerous.

brook

 

Certainly you don't want to take any car above 100 without proper suspension and tires (Z) commensurate with the environment, including air pressure, and wheel alignment.

What I'm seek is there any info on what a occurs in a wind-tunnel, or other measured environment, at high speed for a 4th gen?

Where is the high-lift (directly above the roof, just rear of the pillar), what happens to the rear end (lifts/squats), does the nose drop or rise, does the contact PSI of the tires change? What happens to all the turbulence behind the car (drag).

 

You have got to be kidding. Why the hell would a daily driver be outfitted to run 150+.

I agree that proper restraints, padding, helmets, spacing, etc... is required for high speed runs like this, and the cage is just one part of the safety system as a whole... but what kind of a moron would actually try to outfit a car for these speeds and still consider it a daily driver? Or worse, try to get high speed tuning performed without the nessesary safety items?

Obviously we're talking about a dedicated race car, or a complete moron. I gave him the benefit of the doubt on this one... lets assume its a race car.

 

yes I was talking about a 6pt rear bars, main hoop, a diagonal and crossbar on the main hoop with diagonal bars from the hoop to the footwell. The standard fair one sees most of these guys throw in thier car.


A set of monkey bars is a whole other ball game. Just forget about it on a street car.


Aero really doesn't come into play until you are up there aways. Most of all the tricks have been stated. bring the car LOW to the ground, a slightly raked stance will help, your looking at springs in the 650-750 range and some good shocks (a coilover setup). Swaybars and some adjustable LCAs and PHR to center the rear after you lower it and then make damn sure there is plenty of clearance for the tires in the front and rear. The rear 1/4 will slice it to pieces if there's a big bump.

A bellypan is mostly a waste of time, a rear diffuser helps in the 170 range and up. When you go out to the track using some flexible plastic on the front end so it touches the ground will keep alot of air from getting under the car.


We all know these cars will see 150+ if someone wants to try it, and this is straight out of the lot. head and cam will see 165-170 roughly. As it sits stock though, it's definitly not a good idea at all.


As it's already said 150+ on any street is making yourself a darwin award candidate. It's pretty dangerous even with MKM/USAS.

 

my daily driver was going to trap over 150 in the 1/4.

the cage issue is one of a few reasons why i decided to not finish the project.
if i wanted to drag race it i would need a full cage. if i wanted to daily drive it i cant have a cage.
so i decided to go in a totally different direction lol


brook

 

... you and I both know that trapping 150 is substancially different that cruising at 150 on a regular road surface. Open Road Racing guys have to contend with cornering, heavy sufface imperfections, and praying that the chasis doesn't get unsettled.

Tapping top speed for a few seconds on a perfectly straight stretch of drag strip is aerodynamicly a moot point. Traveling at that speed for say 45 minutes is substancially different and aero effects may well be worth looking into... in drag racing it's enough just to roll up the windows, install the t-tops, and keep the headlights off (assuming you have pop-ups. ).

Frrax has an aero-dynamics forum for high-speed considerations like these. I really wouldn't put this in the daily driver category though... tapping it on a drag strip really needs no aerodynamic changes, but operating above that could use some downforce, a decent rake, and diffuser to keep the rear pointed straight.