rx7 punk

Im sure everyone has seen them at the track, the civics cut slits or use hole saws to make holes in their rear bumpers for air that flows under the car to escape through, has anyone done this on a 7?
Does it do anything or is it all theory?
Does anyone have any pics for the forum members that think im on crack?

I know JC whittney sells mesh vent inserts for rear bumpers that you bolt onto yout bumper after cutting a hole for it. Ill try to find it.

rx7 punk

like this
http://images.google.com/imgres?imgu...lr%3D%26sa%3DN

or this
http://www.overboost.com/obs/product...=Rear%20Bumper

christaylor

Hey! Did you know if you hang a CD from your rearview mirror radar doesn't work?!?!?!11ond!!

YUou should also paint your rotor houstings RED! +++50HP!

Carl Byck

C'mon Chris,the rear bumpers on the second gen are giant parachutes, I'll bet when I do mine I will pick up a couple MPH on the straight. For something other than a purpose buil track car they are a little silly though.There is almost no rear bumper on a stock car, and most purpose built cars today either lack that rear body work, or it is heavily vented. Carl

christaylor

Meh. If you've got a good front air dam there shouldn't be much air on the rear of the car.

As a matter of fact, on a stock car I fail to see how there can be that much air at the rear of the car. All my cars (and those I work on) have fuel cells, suspension components and exhaust that fill all that up.

Lipstick cam + string sides with me, too.

designfreak

well if you look at all of the JGTC cars, including the amemeya rx7 they either cut their bumpers up in half, ad vents or run massive venturis..or a combination of all of them, s oI wouldnt mind taking the hint from them. Im slicing mine, dont need it for anything anyways.

designfreak

check out the cuts in the ASM track attack s2000...


http://hondatuningmagazine.com/featu...00/index1.html

tims

the air tends to swirl around the rear bumper, so cutting holes in the bumper will make you look fast. but it won't have any performance value. A JGTC car is a purpose built race car that has ground effect type tunnels under the car that need the rear diffuser to produce down force. the stock 2nd gen has none of this. this in my opinion is for looks on any production based race or street car.

Carl Byck

Tim, take a look at the underside of your car(as tyou have a thousand times. It is a freakin parachute. I have a 22 gal cell, and looking rear-ward, I can clearly see where the air will be going. All the cars mentioned have one thing in common, and that is steps towards air flow management. Every step helps, a combination is better, and a complete packeage(JGTC) is best. We are not talking a huge wing/no splitter, or something like that, we are talking about reducing drag, and smothing air flow. Even a rear diffuser on our cars would be very difficult if not impossible to seal. That said, I totally disagree with you and Chris(this I rarely do), but there is a first for everything. the lower lip of the rea bumper has a gap large enough to collect air, not vented this will be drag. Carl

DamonB

In this case it may help on an FC but 9 times out of 10 when it's a matter of monkey see, monkey do you can count on the fact that the monkey do's really have no idea what they are doing

rx7 punk

lol damn, I had no idea air flow was such a touchy topic. So I take it no one has actually done it before on a FC? purpose built or street

christaylor

Aero is a black art, and like an *******, everybody's got their own opinion. There seems to be two regular thoughts; number one is to let the air flow through everything. Most noticeable are the people that have done tricky stuff with holesaws and whatnot to let air out of the cockpit (or on Spec Miata's... cut the strip under the top at the back). The second is to fill the area up with air (cockpit or under the car) so that future waves of air skip past it (ok, ok, I can't explain things I'm not very keen on).

My personal opinion is that when the cockpit or rear of the car fills up with air it keeps more air from coming in. The best example is the cockpit; in my SRX7 going down the straightaway at TWS (long and fast... same principle at Road Atlanta) with nothing to duct air in, there is a ton of air noise. With a NACA duct in the passenger window (I happen to have the double-hose setup) the noise is greatly reduced. Less noise = less buffeting. This is assuming the noise is the air boiling in through the windows (set your window net up loose and watch it dance like a college dropout named Candy).

Again, that's just my opinion, and I probably did a shitty job explaining it. Joseph Katz' book on Aerodynamics is awesome, even for an uneducated punk like me.

tims

my thoughts on this matter are from observation and experience with this particular car over many years of racing. I clean my car before every weekend of racing and every time it gets cleaned again the largest amount of dirt is collected between the decklid "wing" and the bumper cover. this tells me that the air behind the car is swirling or tumbling around depositing dirt and oil onto the rear of the car. If the air was caught under the car I would not see these deposits. The car has about 2" of ground clearance and not much air is comming under the car. Even the street car has very little air going under the car. I did like the lipstick camera and yarm tufts suggestion though. this would add some more data to the equation. I have seen many experiments with cutting holes to "vent" air from places people were sure there was a build up. mostly in the cockpit area. most people have found that the air flows back into the cockpit and chokes them with exhaust gases. Cut away at the bumper but a couple mph down the straight can be equalised with a fast exit from the final turn onto the straight away. Spend your time, money, and energy learning to drive what you have to the maximum. I know in my case I have not reached the maximum speed the car is capable of, so until then I'll keep driving and testing what I have. good luck and get to and on the track as much as possible.

Turbo23

iTrader: (4)

I cant see a negative in doing it. reduces weight (like 4 ounces) haha, and it will let air pass, i guess getting a rear diffuser would do basically the same. Except the diffuser would create some down force. But who has 500 or so to spend on a diffuser, and for me i dont do enough track time. Cutting holes would be cheaper, and work fine. I agree with carl though 100%

Turbo23

iTrader: (4)

i dont think the gain would be huge, but like carl said maybe a few mph on the straight. Ive seen some japanese FD's take out their rear reverse light thingys on the bumper. For the same effect

ArcWelder

Right, the only thing that you can trust is hard data. At the top of the list would be wind tunnel data of drag under both conditions. I might believe some peak speed numbers from the track, but only if conditions were gauranteed to be the same before and after the vents and possibly averaged over many laps or runs. Just because some race team has done it is not good enough. No one has provided a link to any websites with any data, just vendors selling the parts. Without data you're just speculating.