Sorry guys, I don't come into the drag forum much (autocrosser here, not set up for drag)...so apologies if this is either a stupid idea or something discussed before.

In any case, was out smoking a cig looking at the car, and for some reason I was thinking about reducing drag on the car (for me, for road course racing)...one of the most obvious drag item I noticed was the wipers and inset area where they attach. Was thinking perhaps a plastic/fiberglass/rubber piece that would cover up this area/the wipers - essentially it would attach at the lip of the hood and pretty much sit up against the windshield at an angle (angle between the hood angle and windshield angle)....to deflect air.

I couldn't use that for road racing (since sometimes we need to use our wipers/washers during races), but could be useful for drag

anyhow, just throwing it out there, apologies if it's "nothing new"

another one: on 5th gens, at least, the fog lights sit "in" from the bumper...drag drag drag. fabricate some kind of molded cover that would "flow" flush with the bumper so air could not get caught up in the fog light holes.

 

Thats actually a good idea. What about items on the underbody as well?

 

on the underbody, there are pieces known as "splitters" (and by other names) that cover everything up with flat/smooth panels. The purpose of these are to cause more downforce for road racing at higher speeds, by changing the air pressure/resistance below the car as opposed to above the car.

I'm not so sure that this would be helpful for drag racing, though - downforce might be counterproductive for straight line speed.

 

Most people don't get going fast enough in the 1/4 mile for it to make any noticeable difference. I can change the CD in cartest to something insane like .28, as good or better than almost any supercar on the road, and the trapspeed goes up like... .3mph.

A good idea in theory but in practice you wouldn't notice a difference on your timeslip.

 

yeah, im always up for ideas. never hurts to think ya know.

 

I have thought of this before, adding some light sheeting underneath to seal up and reduce turbulent areas... but like Neal said, it's not worth it at 1/4 mi speeds. If you look at the loss curves and 1/4mi times in a program such as CarTest it becomes apparent.

 

yeah i wonder about the sarona rear bumper acting as a parachute as im racing down the strip, lol ! but doesnt seem to be hurting much.

 

yeah, I didn't figure it to be worth much...my focus personally is more on road course racing, where reducing drag in straights could be worth a few seconds on lap times...just figured I'd mention it to the 1/4-mile guys. Every little tiny bit adds up....like the guys who take out their back seats to get rid of 10lbs of weight - not much by itself, but each pound adds up if you keep on removing small weights one by one!

 

ive been thinking like this about my spoiler. taking it off would serve as a weight reduction, and maybe less drag too. i mean...its just in the way.
but...its all in my mind (the drag) is waht i tell myself.

 

The spoiler does not serve its purpose unless you're doin a buck twenty. other than It does not bother the drag coefficient of the car because it sits too low to disrupt the laminar flow under 75 mph. try a google search on the coefficient of drag on a maxima gxe (no spoiler) and a maxima se and see what comes up. as far as weight reduction is concerned, every pound shedded counts. Good luck bro

 

I know it doesn't serve a purpose for the most part. Plus I kinda like how it looks without it.
Do kits cause what ceasar is saying, parachute action?
Thanks for the info.

 

I think the biggest concern with a body kit is weight, not drag. Like they said, coefficient of drag has very little impact on times, but weight does.

 

How about the .26 cd for my G35 sedan the Aero Package that includees undercar diffusers and rear wing It may be even better with the 1" lower ride height it has now. Of course the increased rear camber is has probably offset anything.

During my last outing at the track, my friend had his B18 turbo 95 Civic sedan at the track. It looks bonestock on the outside and inside except for the larger normal non-ricer muffler and the slicks in the front. He was running low 11s@125mph all day. Just for fun we decided to yank the rear bumper cover and the car started going 10.8-10.9@127mph. 60 foots didn't change and neither did the boost. I can't be certain, but it sure seemed like his rear bumper was acting like a parachute.

 

There was a thread in the 4th gen Forum about a front splitter.

 

Here is a 2 part article from AutoSpeed on airflow. I have been debating on whether to do this or not using some 1/8" lexan. My front covers are getting pretty beat up and with the lexan I can see through it which would help at times. My main concern was the rear bumper catching all that wind and I am working on something for it. I see a lot of guys at the track cutting like 2-3" holes in the bumper to let the air out but I really don't want to change the outer appearance so I am going to work on some sort of deflector for the rear.

I had to put these articles on my site so you can read them they aren't accessible without a subscription to Autospeed. Some real interesting stuff in their old articles.

http://jime.homeip.net/maximase/Airf...1/article.html
http://jime.homeip.net/maximase/Airf...2/article.html

 

Good read! Thanks Jim.

 

IF anyone wants some more good reading on what all this stuff does to temperatures etc checkout this 3 Part Article on Undertrays, Spoilers & Bonnet Vents.

http://www.furl.net/members/Jime10

 

Dave B - after reading Jime's articles, and your comments about the "rear bumper mod", I went out and eyeballed my '99 Max. It would take a 5ft-by-2ft piece of 1/8" ABS for the front and 5ft-by-4ft section for the rear, but I think I can cut and mold covers for both ends of the car, following suggestions in Jime's articles. I know from building large showbots for several hospitals in the 80s how to cut, drill and shape the ABS, which is great stuff, so molding a piece to cover the front of the gas tank extending back to the rear bumper and a front cover extending back to the front wheels looks complicated but doable. The front should be easier.

I think I'm going to go to the local Cope Plastics distributor and get a couple of 4'x8' 1/8" pieces of black ABS and stare at them for a while...

 

It's worth a shot. My G35 has zero lift aerodynamics which includes a plastic cover from the front of the bumper to the rear of the engine, rear air diffuser plates (they sit just in front of the rear A-arm), plastic cover at the rear (passenger side) covering the fuel tank charcoal cansister, a mostly flat muffler, and even the central exhaust resonator is flat. I can see how making some panels could potentially help things. I personally think the G's slippery shape (0.26) is some of the reason why the car performs so well. At highway speed and speeds well over 90mph, the car feels rock solid and I think it has a lot to do with the flat undercarriage.

I'll tell you what though, it's a pain to change the oil in the car though. I've got remove 17 bolts (no joke) in order to remove the front panl to gain access to the filter

 

"the G's slippery shape (0.26)" That's a slick car! (pun intended) Does the G's front deflector do anything about deflecting air flow from the front tires, as mentioned in one of Jime's articles ??

Would you consider taking off all the underbody covers and trying the car again on the highway? - OK - just kidding, but it sounds like a good hard look under a G and maybe the new 350Z might be an education in directed air flow... Thanks for the feedback.

I was talking to folks about the idea, and got put down a couple of times, but when you ask them if they ever drove down the highway at 100MPH and stuck their hand out the window and felt the pressure, they shut up...

Can you imagine sticking a rear bumper shell out the window at 100MPH?? OK, maybe that's not realistic.

One last thought, thanks to you - if a complete front deflector can be shaped and installed on my '99, it wouldn't be difficult to make a removable panel to get to the filter and drain plug. Six self-tapping screws would do the job. FYI, the ABS plastic is tough, hard, and can be machined or tapped easily, and the stuff is dimensionally stable. (screws wouldn't fall out).

 

I think the G35 sedan is one of the more slippery cars on the road. With and without the wing it's rated at 0.26/0.27, respectively. The coupe and 350Z are in the 0.28-0.29 range which is still really good. I think all the cars employee zero lift aerodynamics though. The front deflector is cut around the suspension and doesn't appear to direct any air from the front tires.

Now I know the G35 has a lot more sound deadening and a stiffer structure than the 4th gen Maxima; however, I think the undercar aerodynamics are somewhat responsible for the very quiet ride at all speeds. My G is lowered about 1" all around and it sits only about 5" off the ground. You'd think with that ride height you'd get a lot more road hiss.



I'd think with some self tapping screws, maybe a little epoxied metal for internal support on large panels, it would easily work. My guess is the biggest gain would come from cleaning up the rear of the car because I think that's where most of the drag and lift occurs. The set up doesn't have to be completely smooth either. After looking under my G for a while, it appears the goal is to cover any deep voids to reduce air build up and to stream line the undercarriage supports and parts in a length-wise fashion where practical.

 

After looking up the skirts of my '99 in the front, a full-width panel with tire deflectors looks pretty easy - about 5 1/2 ft wide, and it can mount to the existing underbody panel mount holes. An access panel for oil changes still looks easy to do. If the front is shaped downwards, I think the Jbars front mounts will also clear inside the panel..

The rear looks more complicated at first, but one flat sheet from the rear bumper lip up to the rear axle would work, I think, and then roll up the forward lip just even with the rear axle to close off that space. This would give a flat air shield from axle to bumper. The panel can also attach to existing mounting points for bumper and fender wells, it appears.

You know, this really does look doable. Now whether it will have any gains, well, only some track time will tell, but if it's a big deal to use teeny rear tires and changing windshield wipers to reduce rolling resistance, then a couple of underpanels to reduce rolling wind resistance seems to make sense.

Off to Harbour Freight for a larger heat gun!

 

I'd imagine it would be hard to reduce drag reduction by much considering that it mostly deals with the overall shape of the upper portion of the car and body.

I think the best bet would be to improve aerodynamic efficiency with underbody diffusers. You get improved downforce of a heavy car without the contribution of extra weight.

 

Could you explain the idea of "underbody diffusers" ?? I dont see why we would want more downforce - that would increase rolling friction, I think. ???

Since the upper body design is already set by the manufacturer, we can't do too much there, except maybe a big wing on the tail.

After hearing from folk here about how several later "slippery" cars from Toyota and Infiniti have used underbody panels to clean up their underneaths, I think it's worth a shot. Flat panels in the rear section are becoming more common, and careful attention to a front underbody panel could clean up airflow for the tires as well as the area just behind the bumper. Now i'm wondering about the factory wind deflector in front of the sunroof?

 

rolling friction will not increase in any measureable amount on a street car simply by reducing lift with aerodynamic aids

 

OK .... but the point of underbody panels like we have been discussing is to reduce the resistance of air flow under the car, not create upforce or downforce for the car. Shaping airflow reduces turbulence which reduces drag caused by messy airflow.

Others here have mentioned high-performance or high-MPG cars that use underbody panels to "slick up" airflow under the car. The top of most late-model cars have been built to help meet Federal MPG requirements, and now the undersides are getting the same attention.

It seems that we can make some improvements to the bottom of our cars, shaping the front panel to manage airflow around the front tires, and add rear panels or a panel to smooth air underneath the rear parts of the car.

D*mn, that sounds stuffy - sorry. Look under the rear of a 4th Gen Max - there are lots of places where fast-moving air is gonna get swirled around - in front of the gas tank, in front of the rear bumper, and around the wheels.

Does it matter? Maybe. The Toyota Prius got 10% better fuel mileage with a shaped front panel - it already had a rear panel from the factory.

 

when you reduce the resistance of airflow underneath the car, you speed up air flow velocity because there is less turbulence..... therefore creating downforce without the exacerbating effects of extra weight or drag because the slower moving air above the vehicle will create downforce

Bernoulli's Equation
"In order to discuss lift and downforce, it may be helpful to provide an additional explanation of the relationship that occurs with the above form of Bernoulli's equation.If a fluid flows around an object at different speeds, the slower moving fluid will exert more pressure on the object than the faster moving fluid.The object will then be forced toward the faster moving fluid.8A product of this event is either lift or downforce, each of which is dependent upon the positioning of the wing's longer chord length.Lift occurs when the longer chord length is upward and downforce occurs when it is downward."

http://www.f1-country.com/f1-enginee...odynamics.html

 

OK - so you agree that reducing turbulence under the car is a Good Thing ??

And doing this will create more downforce, which is a Bad Thing ??


???

 

I don't think it will change downforce much.. the longer flow path is still over the top of the car body.

If you look at the articles Jim posted you'll notice front lift usually increased (ie negative downforce) due to upward pressure on the deflectors that were made (depending on dimensions, angles etc). The overall loss of drag was worth any slight change in lift or downforce provided stability was maintained.

 

The Lotus Elise has great underbody diffusers if you can find one easily. I believe creating additional downforce also adds drag. In the case of the Elise it has huge downforce but at the expense of a .3 or even .4CD.

 

Larrio's F1-Engineer link contained the first quantification of horsepower loss caused by drag of a flat surface I have seen (quoting from the article):


DRAG FORCE ON A ONE-SQUARE FOOT SQUARE PLATE

Speed................Drag Force.......Horsepower required to overcome drag

100mph................33lbs...............9 hp

An extra 9 HP at 100 MPH by removing one square foot of flat area... I'll take a half-dozen of those, please.

If the loss is linear, that's 4 1/2 HP at 50 MPH. Looking under my '99 again, I can see a square foot of frontal area between both front tires, which could be deflected. In the back, there's several square feet of flat area near the bumper, gas tank, and around the rear axle area. One flat plate could cover most of the flat areas, and conservatively cover three square feet of flat surface. And there is the nose of the car - fog lights, etc.

This sounds better and better.

 

For what it's worth, this site http://www.internetautoguide.com/car...ons/index.html
shows the '99 max as having a "slippery rating" of 0.31:

"1999 Nissan Maxima Exterior & Aerodynamics Standard Features
-Body color body side molding
-Front and rear body color bumpers
-Chrome/bright trim around side windows
-Coefficient of drag: 0.31
-Driver and passenger power body color door mirrors
-External dimensions: overall length (mm): 4,811, overall width (mm): 1,770, overall height (mm): 1,415, wheelbase (mm): 2,700, front track (mm): 1,529, rear track (mm): 1,509 and curb to curb turning circle (mm): 10,607
-Complex surface lens halogen bulb single headlights
-Metallic paint , black paint , gloss paint , pearl paint
-Rear window
-Tinted glass
-Weights: gross vehicle weight rating (kg) 1,938 and curb weight (kg) 1,366
-Windshield wipers with fixed intermittent wipe "


and a 2006 350Z as being 0.3 :

"2006 Nissan 350Z Exterior & Aerodynamics Standard Features
-Body color front and rear bumpers
-Coefficient of drag: 0.3
-Driver and passenger power heated body color door mirrors
-External dimensions: overall length (inches): 169.4, overall width (inches): 71.5, overall height (inches): 51.9, wheelbase (inches): 104.3, front track (inches): 60.4, rear track (inches): 60.6 and curb to curb turning circle (feet): 35.4
-Projector beam lens Bi-Xenon headlights
-Luxury trim alloy & leather on gearknob
-Pearl paint
-Fixed rear window with defogger and intermittent
-Tinted glass on cabin
-Weights: curb weight (lbs) 3,212
-Windshield wipers with automatic intermittent wipe "

and the 2006 G35 is shown as being 0.29 :

"2006 Infiniti G35 Exterior & Aerodynamics Standard Features
-Body color front and rear bumpers
-Coefficient of drag: 0.29
-Driver and passenger power heated body color door mirrors
-External dimensions: overall length (inches): 182.2, overall width (inches): 71.5, overall height (inches): 54.8, wheelbase (inches): 112.2, front track (inches): 60.4, rear track (inches): 60.6 and curb to curb turning circle (feet): 37.4
-Front fog lights
-Bi-Xenon headlights
-Heat reflective glass
-Luxury trim alloy & leather on gearknob, alloy on doors and alloy on dashboard
-Pearl paint
-Fixed rear window with defogger
-Tinted glass on cabin
-Weights: curb weight (lbs) 3,486
-Windshield wipers with automatic intermittent wipe "



Guess the old 4th Gen isn't too bad, eh? Add a few deflection panels and the old cars might still look good.

 

Don't get too excited. The drag and lift coefficients are not linear, but exponential. So at 50mph you'd need 2.25hp, 100mph is then 9hp, and 150mph needs 18hp.

 

when did i say downforce is a bad thing?

 

Taken directly from Infiniti http://www.infinitihelp.com/Infiniti...escription.htm

 

You are correct. I know from experience that the spoiler will produce enough downforce to latch the deck-lid at 110-120mph. Before that it won't on flat ground.

 

cut holes in your rear bumper? my old school racing buddy told me about that. dont know if its true or not but you can pretty much tell it acts like a parachute

 

Incorrect.
The REAL reason that some Honda Civic drivers do that is because they've removed their rear bumper supports. When the bumper support is removed the bumper flaps in the wind and then causes a little more drag. The holes are drilled to alleviate flapping.

Most cars you see with holes drilled in their bumpers is because they saw someone else do it and though it was 'cool'. Most of these people have absolutely NO idea what the real reason for the holes is.

 

This topic has been on my mind for a long time now. May have began when I saw a Lexus ad boasting about their underbody, or when I was changing my oil.

Nice to see others also thinking about it. Those whom I asked played it down as a dumb/pointless idea.

At first I thought the added weight may be worse than the drag reduced. But also, what about all the air entering the engine bay. If we block out too much underneath, won't we be causing a lot of pressure in the front????

And has anyone considered our body kits?? are we not totally changing the coefficent of friction drastically up front????

So what material would be light and easy enough to work with yet durable enough to install down there? I like the idea of something clear. And it would have to be simple to take off for oil changes and other work.

how about some exit only vents to let out air? _____ \_____

And it also crossed my mind if rear bumpers (especially kits) trap air. Seeing how big my rear is and that Sarona made it even bigger, yet install three vertical vents.... Are they possibly functional??

(btw 6th gen is rated at .30 with the oem spoiler, .28)

 

Nismomax80

I like the idea of air vents like that.

The Stillen front spoiler seems to be a nice way to change the drag coefficient. As for your question on what would be light and durable, I think that Sheet Metal would be a good bet. To be able to mold ABS would be a disaster and expensive.

Sheet metal would be easy to remove, just clearcoat it to prevent rust.

Who's with me?