'00 Civic Custom Rear Diffuser, pics inside.

[M@]

Finished it up this morning, came out pretty freaking clean, in my opinion. One of the holes is slightly out of perfect round because my holesaw bit came loose while I was cutting it, but oh well. Close enough. Don't mind the messy garage, I'm in the middle of 100 projects right now.

http://i109.photobucket.com/albums/n67/eyeheartboost/diffuser2.jpg

[Eric]

Ricer mod :P but, nice license plate.

[M@]

Rice on most applications, not rice on a drag car that will be trapping 120+ mph.

[orbit77]

good job, half the time i see people mess it up and its all crooked.

[M@]

Thanks... I might re-make it since the one hole is kind of noticeably bigger than the others, but we'll see.

[J.Dub]

Looks good man!

[M@]

Thanks... :rofl: @ your sig... oh man

[Eric]

The rice bit was a joke. Is there a piece of aluminum on the inside as well or just the outside?

[way2slow]

YEAH LOOKING GOOD!!

[99GunMetalSi]

looks great

[cybergreencivic]

Good job. No 2g1c on the plates? That ones pretty good as well though.

[Brandon]

Looks to me like you're trying to create air turbulence and thus more drag, yes? Looks good.

[M@]

The rice bit was a joke. Is there a piece of aluminum on the inside as well or just the outside?

Nope, just drilled the holes to exact size of the rivets, and used the same size washers on the back side.

Good job. No 2g1c on the plates? That ones pretty good as well though.

:D I figured the plates I chopped on were mo bettuh.

Looks to me like you're trying to create air turbulence and thus more drag, yes? Looks good.

Apparently on Civics the back end acts like a big air brake, and the holes are supposed to allow the air to escape from back there thus eliminating any drag. Seems to me there are some pretty smart folks out there doing it.

Sam Park's new race car:
http://importsports.net/img/sampark/052504/finrace4.jpg

Chris Bowes:
http://a466.ac-images.myspacecdn.com/images01/128/l_4c4b83e29943f8de63c5efac9c1f7e01.jpg

Etc. All the research I did on it before making it and hacking up my bumper showed there were only beneficial results when using the car for drag racing.

[Skaterkid]

Its not a diffuser. At least not in the technical sense.

[Brandon]

Unless that research included wind tunnel testing, I would bet that the holes created drag. Without the holes, there's most likely a pocket of stale air and the air that's moving under the car goes right under. Think of a golf ball, they have dimples that create pockets of air because air on air is less drag than air on a smooth golf ball. Now that there's holes in the bumper air is going to flow through that pocket and it's going to be like a parachute.

A streamlined under carriage might've been a better idea (of course that wouldn't look as cool either). Look at real race cars that do wind tunnel testing, they don't have holes in the rear bumpers of NASSSSSSSSCARs or top fuel cars.

[M@]

Nascar cars are also slammed on their nuts with super flat under carriages, too. Cars like this have to be rather high in the air to allow the fitment of bigger tires up front which allows air to go underneath the vehicle. Many people have tested this and picked up .1-.3 in their times, and 1-3 mph in trap speeds from what I've found. Either way, the bumper already had holes in it from the battery charging posts that Tobi had on there before, which I personally didn't like, so even if this does slow me down, I can simply replace it which I would have needed to do anyways.

[aQuarius26]

Looks good! Hope it helps too...

[Evil_SpeedRacer]

Looks good man, I can't wait to see it run. Its getting closer and closer......

[M@]

Boost coming in 7 days. http://smiliesftw.com/x/ninja.gif

[Evil_SpeedRacer]

werdly werd. I would like to come check it out, and that kickass truck of yours.

[M@]

Word, just give me a call on the ol cellular. Maybe I can grab my jackstands from ya' too. :D

[Evil_SpeedRacer]

Yeah, I went to go put the wheels on it the other day and realized the rear axle is missing...LOLz I forgot pretty quick there! Any word on that?

[M@]

Need to get it rebuilt stillz. >_< I'll try to drop it by RM Driveline in the next week or so.

[Evil_SpeedRacer]

Sweet, I start the yanking process this weekend. I can't wait to feel the turbocharged goodness once again....LOLz

[M@]

Sweet, I start the yanking process this weekend.

:spit::spit::spit:

[Evil_SpeedRacer]

oooo...you got me good fucker! :rofl:

[99GunMetalSi]

i think thats Sam's old race car from a few years ago?

Sam Park's new race car:
http://importsports.net/img/sampark/052504/finrace4.jpg

[Evil_SpeedRacer]

Try again, it was a race car from a shop...but not that one. I'm pretty sure that was Tobi's car for a while as a test mule.

[ryanman]

Looks good.

[99GunMetalSi]

either way it still has the diffuser

[M@]

i think thats Sam's old race car from a few years ago?

Sam Park's new race car:
http://importsports.net/img/sampark/052504/finrace4.jpg

No, that's not Tobi's old race car... MY car is Tobi's old race car. And Sam's could be and old car. I'm not sure... it's listed on Import Sports' website as his new racecar. I dunno.

[Skaterkid]

either way it still has the diffuser
It's not a diffuser.

[99GunMetalSi]

Sam's running a white 95 hatch if I'm not mistaken.

[M@]

It's not a diffuser.

Shut the hell up already, no one cares.

Sam's running a white 95 hatch if I'm not mistaken.

He was last season, I'm just wondering if he switched to this car. Who knows.

[M@]

Also, diffuser is defined as:

"Diffuser can refer to any device that diffuses in some manner such as:

* Diffuser (automotive), a shaped section of a car's underbody which improves the car's aerodynamic properties"

http://en.wikipedia.org/wiki/Diffuser

Therefore, until you can provide some evidence that it does NOT improve the car's aero, who are you to say that it's not a diffuser?

[Evil_SpeedRacer]

No, that's not Tobi's old race car... MY car is Tobi's old race car. And Sam's could be and old car. I'm not sure... it's listed on Import Sports' website as his new racecar. I dunno.

Thats what I was trying to say. That your car was Tobi's at one time...LOLz

[Eric]

Nope, just drilled the holes to exact size of the rivets, and used the same size washers on the back side.


Ah, gg.

[john]

I always knew you were a ricer, M@.

[M@]

Dammit, John... if I was about 5 years younger, I would have had to find and add your daughter on myspace for that one! Jerk. :cry:

[jackmode9316]

Do it anyways.
In other news.
Terry is trying to proposition me on myspace.

[dcsportsciv]

Its crazy how everyone is very unsure about how a diffuser acts. If M@ was to add a plate to the undercarage in the rear, Yes that would work, but that take more time and money to mount a piece of sheet metal under there, also carries more weight to the car. The way hondas are set up, the rear bumper does act as a parachute, so having a diffuser does help. and all it is, is cutting out the bumper and just adding a piece of sheet metal on there to clean it up from the cutting.

All the pros used diffusers when they were running their hondas back in the day now their cars are set up where they dont need them. Gary Gardella used a diffuser on his hatch also.
http://www.turbomagazine.com/features/0206tur_custom_honda_civic_drag_race_car/photo_02.html
Its not rice, and ill have sex with your mom........Im done ;)

[M@]

Chris has spoken.

[jackmode9316]

People hate what they don't understand.

[ryanman]

:werd:

[Jake Fear]

RICE!

But only on M@'s car.

On everyone else's car it helps. Neons are the same as Civics in this instance, our rear bumper acts as a huge parachute at anything over 100mph. I picked up 4 mph after adding my "speed holes" to the Neon. Barnett had roughly the same effect.

[HONDA GHANDI]

Maybe I should add some speed holes to the Hellement. I could use another .1 or 1-3 mph. Or maybe I could put my powertrain into something that doesnt weigh 3500 lbs and go 11s like Chris.

[Kwando]

looks nice and functional M@. if the bumper creates that much drag why not run without one?

[M@]

:rofl: Yeah, I'll just pull off my side skirts, fenders, and hood while I'm at it! :p

[dcsportsciv]

Maybe I should add some speed holes to the Hellement. I could use another .1 or 1-3 mph. Or maybe I could put my powertrain into something that doesnt weigh 3500 lbs and go 11s like Chris.


If you took that set up and put it in something else you would run faster and i would hate you for that haha but love it at the same time.

[C90slpR-Xprmnt]

thumbs up!!s what going into that thatll make it a 120+ honda

[M@]

Wouldn't you like to know? ;)

[HondaPower]

Looks good, got pics of interior? I'm curious on how the inside looks.

[M@]

Nope.

[HondaPower]

What does the car weights? is it all gutted?

[Kwando]

:rofl: Yeah, I'll just pull off my side skirts, fenders, and hood while I'm at it! :p

No one said anything about the side skirts, fenders, and hood creating drag so why would you do that?

if your side skirts, fenders, and hood do create drag are you going to drill holes in those also? Or are you going to wait until someone else does it first.

seriously, if the back bumper creates that much drag like a parachute why not remove it. Does Bandimere require bumpers to race?

[M@]

Uh, because it would look absolutely fucking retarded...........

[HONDA GHANDI]

If you took that set up and put it in something else you would run faster and i would hate you for that haha but love it at the same time.

I do have a CRX shell here just chillin.....

[dcsportsciv]

I do have a CRX shell here just chillin.....

OHHH tobi is going to take over the world!!!! need to clean that thing up and do it ;)

[M@]

Bwuahahahahaha! That would be a helluvafast car.

[nrich]

Looks pretty good. Not my personel style but as long as it makes you happy. You say your trapping 120+ wat are you pushing for ponies

[myshtern]

Its not a diffuser. At least not in the technical sense.
What's a diffuser in the technical sense?

I never really understood how these hole mods did anything on civics but maybe I'm wrong

[M@]

Looks pretty good. Not my personel style but as long as it makes you happy. You say your trapping 120+ wat are you pushing for ponies

465hp/350tq spinning on the dyno. 127 mph trap speed finishing in 5th on tiny slicks.

[M@]

What's a diffuser in the technical sense?

I never really understood how these hole mods did anything on civics but maybe I'm wrong

Read the freaking thread, dude.

[RiceNwateR]

What's a diffuser in the technical sense?

I never really understood how these hole mods did anything on civics but maybe I'm wrong
here.... pg 3
Also, diffuser is defined as:

"Diffuser can refer to any device that diffuses in some manner such as:

* Diffuser (automotive), a shaped section of a car's underbody which improves the car's aerodynamic properties"

http://en.wikipedia.org/wiki/Diffuser

Therefore, until you can provide some evidence that it does NOT improve the car's aero, who are you to say that it's not a diffuser?

This also includes wings, spoilers, lips, strakes, splitters, vortex generators and such.

[Skaterkid]

What's a diffuser in the technical sense?

I never really understood how these hole mods did anything on civics but maybe I'm wrong

A diffuser, in an automotive context, is usually a shaped section of the car underbody which improves the car's automotive aerodynamics properties by enhancing the transition between the high-velocity airflow underneath the car and the much slower freestream airflow of the ambient atmosphere

This is not a diffuser as it does not help slow the air from the high speed under the car. Diffusers are supposed to help the extraction of air from underneath the car despite there being a negative pressure gradient from under the car to behind the car. In fact, after looking underneath a Civic of the same generation as Matt's, I can't even see a good reason for the "trapping air" arguement. There's a tray or plastic piece that is parallel with the rear crossmember that runs to the rear bumper and is parallel with the rear bumper's bottom edge. That would provide better aerodynamics if it is removable than these holes since there is no smooth transition, the holes would only make for more turbulence, hence more drag. An aluminum undertray that seals off the whole rear of the car past the rear crossmember would be even better, and as far as the weight goes, a sheet of aluminum that size would weigh 20 lbs at most. That's hardly significant at the power Matt's making. If he was really serious about aerodynamics he'd make a front splitter and air dam to help keep air from getting underneath the car helping increase downforce (increasing traction at high speed) and decreasing drag since the underside of the car has a lot of areas that can cause turbulence. Also, it would increase the pressure gradient across the intercooler and radiator meaning cooler intake temps. At the speeds Matt should be hitting at the end of the strip drag overcomes weight as the most significant detractor from acceleration. Finally, .1 to .3 sec is hardly significant since that spread could be caused from different weather or track conditions from day to day or even driver error. Unless there's a significant number of passes made on the same car and same driver before and after (like 15 for each) I'd hardly believe that this "diffuser" actually does anything.

[M@]

Who honestly gives a fuck? It's not your car, so buzz off. :)

[Skaterkid]

Sorry to point out your mod is rice with actual engineering principles rather than Honda-Tech guesses. And why does it matter if I post such? I'm actually giving you some points that would actually make your car faster with minimal investment. After all the money you've spent on your motor, one would think you'd be looking for an advantage to set you apart from the rest of the pack.

[M@]

I want to fuck your skull.

And sorry to point out that people have actually picked up time at the track by doing this. Sorry that track numbers spoke louder than the physics you claim to know so well. :spit:

Fag.

[Skaterkid]

Again, not significant enough without scientific data to back it up. What were track conditions like on pre mod and post mod days? Was the same driver used? How did the 60' times change? How many mph were gained after 1000' pre and post mod? How many passes were made pre and post mod? Like I said before .1-.3 isn't significant enough without many passes pre and post mod to say if it does dick.

[M@]

I am right, you are wrong.

[Skaterkid]

Yet you don't provide any links, background information for your "proof" other than "lots of people have done it!" But hey, if you don't want to actually engage in a debate, that's fine.

[M@]

I really don't care to. Not because I can't provide facts, but it's because I truly don't like you and would rather waste my energy jerking off or drinking an ice cold Coors Light.

[Skaterkid]

Your past three posts say otherwise.

[M@]

Not really, I am indeed drinking an ice cold Coors Light, and I am indeed contemplating jerking off to your baby pictures.

[Skaterkid]

Well that's too bad. I was hoping that I could at least get a semi-rational, fact based, or some type of response that was above the level of a 6th grader. It'd be nice to get some actual tech discussion going on here again.

[M@]

Fine, this is all you're getting out of me though, and it's already been said.

I guess Gary Gardella must not have known what he was doing, huh? :rolleyes:

http://images.turbomagazine.com/features/0206tur_12z+honda_civic_hatchback_drag+right_rear_ view.jpg

[Skaterkid]

Does he have wind tunnel tests or several passes under similar conditions with no other changes to the car to back up that it does reduce times or increase trap speeds? Some people think that trucks have less drag with the tail gate down, but that's not true.

Give me something beyond with actual numbers.

[M@]

I'm not even going to respond to that. Do some research and find out who Gary Gardella is. KTHXBYE!

[Brandon]

No point in arguing with someone that has made up their mind.

It's just like arguing a plane taking off from a treadmill, you can explain the physics, even show it being done and some people still won't believe it's possible.

[Weston-work]

:rofl: Yeah, engineers are silly like that... always limiting themselves to actual facts and the laws of physics.

BTW: Here are some real rear diffusers: http://www.pennon.com/products/diffusers/diffusers.html

[doogie06]

I can't believe this has turned into a fight...1 speed-hole = 10 hp, nuff said.

[Dave_L]

I'm going to put a diffuser on the jeep so I don't get passed by SMART cars. :D

[Weston-work]

I'm going to put a diffuser on the jeep so I don't get passed by SMART cars. :D

People who pay $20k for an economy airline seat mounted on top of an engine that can't even match the fuel mileage of a 20 year old Honda CRX aren't very "smart".

[RiceNwateR]

you don't need a wind tunnel to test something like this, just a magnehelic gauge. You can find whether it builds positive pressure from inside the bumper and the pressures outside. Than cut holes and retest. Simple. If the pressures underneath are in fact positive, the rear is creating drag and lift. Cut the holes, than see if the pressure drops. If it drops, than you know it's working. Simple. Most drag is created by these small pockets of air lifting the car slightly off the ground.

BTW, creating downforce also creates drag. What one is supposed to do is reduce lift. Than you reduce drag. Simple.

[Skaterkid]

you don't need a wind tunnel to test something like this, just a magnehelic gauge. You can find whether it builds positive pressure from inside the bumper and the pressures outside. Than cut holes and retest. Simple. If the pressures underneath are in fact positive, the rear is creating drag and lift. Cut the holes, than see if the pressure drops. If it drops, than you know it's working. Simple. Most drag is created by these small pockets of air lifting the car slightly off the ground.

BTW, creating downforce also creates drag. What one is supposed to do is reduce lift. Than you reduce drag. Simple.
Creating downforce doesn't create drag. Vacuum cars can create tons of downforce and have reduced drag since they seal against air getting under the car.

While seeing if pressure is reduced is realtively easy, that doesn't address the drag portion since that is created by eddy currents. My whole point is, M@ has no data to back up his "claims" he just did this because a couple of drag racers misguidedly thought this was a good idea.

[RiceNwateR]

Creating downforce doesn't create drag. Vacuum cars can create tons of downforce and have reduced drag since they seal against air getting under the car.

While seeing if pressure is reduced is realtively easy, that doesn't address the drag portion since that is created by eddy currents. My whole point is, M@ has no data to back up his "claims" he just did this because a couple of drag racers misguidedly thought this was a good idea.

Show me an example of a real world production vacuum car that can run fine on the streets. The reason car manufacturers haven't produced any for street use is because it's impractical. Ferrari and the likes have bodies that are shaped like inverted wings. This helps them produce the downforce they need. Not a vaccum car at all. They benefit from reduced drag from being low, having small frontal areas and smooth underbodies. they benefit using the air from under them as well. Not a vacuum indeed.

Yes it deals a lot with the drag portion. The majority of a production cars drag comes from areas like this. Tires, rough underbody, rear flow seperation. It all is a pressure game. The big hole in front of cars is for cooling. Coincidentally it is also a big gaping parachute. It obviously gets vented somewhere (mainly underneath). If not, it would really be a parachute. But manufacturers still make them (make them bigger than they need to be) because gas engines need cooling.
If the rear bumper creates some sort of drag, a pressure gauge can easily identify positive pressure. And if the rear diffuser reduces that pressure build up, it is indeed a diffuser, because it actually is diffusing air, and it would help reduce some drag.
Now would I take this approach? That is a different story, there are better ways of getting better results. This though, is an easy fix.

[HONDA GHANDI]

I think there is one other thing that has not been addressed in this thread. Most of the race cars that began to shop up at tracks (10 years ago) with this modification were strictly race cars. The stock fuel tanks were removed and parts of the floor, mainly the spare tire tub, were also removed and replaced with lighter materials. These two things alone would radically change how air traveled under the body of the car. The bumper which cannot be removed because of strict appearance rules now becomes a giant scoop in the back of the car. Another way of venting this air was to have hinged panels on the back (no one does this anymore, because it was quite weird and ugly) of the bumper that would release air pressure when moving, but swing closed when stopped giving the bumper a stock appearance. Much like NASCAR vents used to keep air from lifting the car in a high speed spin.

Any import team that has the dough to do wind tunnel testing is not going to release this data to the public. On that point, there is far less money in the Import racing world than any other, so even scales wind tests are not existant. It is 50+ years of racing technology recycled for FWD cars, and some innovative ideas specific to the sport. There probably will be no raw data to ever conclude this.

[Skaterkid]

Show me an example of a real world production vacuum car that can run fine on the streets. The reason car manufacturers haven't produced any for street use is because it's impractical. Ferrari and the likes have bodies that are shaped like inverted wings. This helps them produce the downforce they need. Not a vaccum car at all. They benefit from reduced drag from being low, having small frontal areas and smooth underbodies. they benefit using the air from under them as well. Not a vacuum indeed.
You asked for an example of cars that produce downforce without creating extra drag. That is one. And there was a vacuum car created for last years 200X Competition. It was a pretty slick setup. One would only produce a vacuum car for the track since downforce isn't needed on the streets. I know Ferrari, Lotus and the like do wind tunnel testing to create cars with true underbody diffusers to reduce underbody pressure, and force the underbody air to smoothly release behind the car to produce downforce.

Yes it deals a lot with the drag portion. The majority of a production cars drag comes from areas like this. Tires, rough underbody, rear flow seperation. It all is a pressure game. The big hole in front of cars is for cooling. Coincidentally it is also a big gaping parachute. It obviously gets vented somewhere (mainly underneath). If not, it would really be a parachute. But manufacturers still make them (make them bigger than they need to be) because gas engines need cooling.
If the rear bumper creates some sort of drag, a pressure gauge can easily identify positive pressure. And if the rear diffuser reduces that pressure build up, it is indeed a diffuser, because it actually is diffusing air, and it would help reduce some drag.
Now would I take this approach? That is a different story, there are better ways of getting better results. This though, is an easy fix.

I think you are oversimplifying the problem here. Number one, Matt, nor anyone else has provided proof that there actually is air getting trapped under this bumper which has been the core of my arguement the whole time, and second I'd imagine that this situation would be very similar to the air flowing over a truck bed. A pocket of stale air forms in the bed so that the boundary layer does not tumble down off of the cab and into the liftgate, instead the stale air allows the boundary layer to smoothly separate off of the cab and over the liftgate causing lower drag than if the liftgate is down, and that pocket does not form.

Second, if this really is a drag issue, then sealing off the area behind the rear crossmember with some sheet aluminum would be just as easy and prevent the turbulence that is bound to happen when high speed air is exiting those holes, resulting in lower drag than drilling holes or a stock bumper.

Finally, I've checked under an 00 Civic Si and there is a large flat piece that would prevent the bumper from acting like a parachute since this piece is parallell with the rear bumper and covers most of the area behind the rear crossmember.

[Brandon]

Seems like an echo in here, I think I said just about the same thing on page 1. :)

By M@'s argument, Gary Gardella should share his findings with nascar and top fuel because neither of those have realized the effect of bumper holes.

[M@]

Haha.

[Mark_H]

RICE!

But only on M@'s car.

On everyone else's car it helps. Neons are the same as Civics in this instance, our rear bumper acts as a huge parachute at anything over 100mph. I picked up 4 mph after adding my "speed holes" to the Neon. Barnett had roughly the same effect.

^There is some real world results. I'd like to hear what Barnett has to add to the subject. I know 2 guys YEARS ago that got about .2 at Bandimere with these "speed holes". They were only trapping around 100-105mph though, so my uneducated guess is that the same car trapping higher mph could see better then that.

[Mark_H]

I can't edit my posts so^^Whoops, I meant 2mph not .2 secs

[myshtern]

:rofl: Yeah, engineers are silly like that... always limiting themselves to actual facts and the laws of physics.

BTW: Here are some real rear diffusers: http://www.pennon.com/products/diffusers/diffusers.html
Seems like its just you and skaterkid being d-bags just to be d-bags.

Cool mod 'burnout:

[Bruce_Lee]

Some people seem to believe that if there is no formal testing, then it must not and cannot be real. Then again it could just be personal. Which appears more likely the case.

[97CivicNick]

props. came out very clean. and as much as i hate going with the bandwagon.... quite a few of the FAST (under 11sec) civics Ive seen Indeed have these. And i have no degree but the parachute thing makes sense.

in the end who cares? even if it doesnt do shit and M@ just wanted to rice up his car (which i would find hard to beleive), what business of yours is it to come in here talkin shit?

[HONDA GHANDI]

Seems like an echo in here, I think I said just about the same thing on page 1. :)

By M@'s argument, Gary Gardella should share his findings with nascar and top fuel because neither of those have realized the effect of bumper holes.

Never seen the back of a Top Fuel Funny car I guess?
Here is a good example:
http://www.youtube.com/watch?v=PdeGDmQb39U&feature=related
You can see it when they let the body down and again when it launches. The two sections to right and left of the parachutes are painted to look like tailights, but they are in fact flapper doors.

[Brandon]

Well I didn't see anything of the sort but I believe you. Before I said that I briefly googled some images and didn't see any ;)

I never said I didn't think the holes looked cool on M@s car, I just don't believe they're doing more good than harm.

[HONDA GHANDI]

I know, the video is crap, but it the only thing I can find that even remotely shows them. Having been in person, I have seen them up close several times.

[M@]

I saw what you were talking about, Tobi. Pretty cool design, IMO.

[RiceNwateR]

You asked for an example of cars that produce downforce without creating extra drag. That is one. And there was a vacuum car created for last years 200X Competition. It was a pretty slick setup. One would only produce a vacuum car for the track since downforce isn't needed on the streets. I know Ferrari, Lotus and the like do wind tunnel testing to create cars with true underbody diffusers to reduce underbody pressure, and force the underbody air to smoothly release behind the car to produce downforce.
So did a small team of engineers with their Corvette for the GRM $2008 challenge. That is for less than $2008. Granted it was fan powered, but still exactly the same, a vacuum car. I did say production car though.
Lamborgini started their designs without wind tunnel testing. Their designs were a few decades ahead of the competition. Clicking the highest top speeds of the time for a production car.

I think you are oversimplifying the problem here. Number one, Matt, nor anyone else has provided proof that there actually is air getting trapped under this bumper which has been the core of my arguement the whole time, and second I'd imagine that this situation would be very similar to the air flowing over a truck bed. A pocket of stale air forms in the bed so that the boundary layer does not tumble down off of the cab and into the liftgate, instead the stale air allows the boundary layer to smoothly separate off of the cab and over the liftgate causing lower drag than if the liftgate is down, and that pocket does not form.
Maybe so, but it is the most simplist test can prove whether air is getting trapped into the bumper. This test can also prove that there is a pocket of air being trap within the liftgate. As with flow seperation, it is known that the air closest to the body is the slowest. This could prove that it could seperate smoothly from the rear bumper and not into it. My claims on a pressure test is not a simplified fix to a problem, it will prove/disprove that the vice is a trouble area. If this is not satisfying, coast down testing is another option. You think all solar panel race cars are engineered in a wind tunnel, no.
Second, if this really is a drag issue, then sealing off the area behind the rear crossmember with some sheet aluminum would be just as easy and prevent the turbulence that is bound to happen when high speed air is exiting those holes, resulting in lower drag than drilling holes or a stock bumper.
Yes, but if the inner fender wells of the rear bumper are exposed, than air will still get trapped within the bumper as well. The wheel itself is a drag mechanism in it's own design and the rear bumper is right behind it. So that is only part of a solution. Like I said, an easy fix, but likely with minimal gains.

Any import team that has the dough to do wind tunnel testing is not going to release this data to the public. On that point, there is far less money in the Import racing world than any other, so even scales wind tests are not existant. It is 50+ years of racing technology recycled for FWD cars, and some innovative ideas specific to the sport. There probably will be no raw data to ever conclude this. True, everything we think is new to the sport has been used in some form before. Only a few execptions.

[Evil_SpeedRacer]

I noticed at the last test and tune that M@'s rear bumper was not flapping, but we did see 2 other Civics there that were. My son first pointed out the hatch that we saw flapping, right before the traps. I was not too quick with the camera to catch it though...I watched the vids of M@'s car and did not see the same over at least 4 runs. That flapping could be an indicator of air indeed getting trapped in there. Just a thought.

[pontiacrapper]

Well I didn't see anything of the sort but I believe you. Before I said that I briefly googled some images and didn't see any ;)

I never said I didn't think the holes looked cool on M@s car, I just don't believe they're doing more good than harm.

k so where is your scientific proof that they are doing any bad for m@?


btw M@ i think it looks badass

[Brandon]

WTF are you? Study some fluid flow and you'd understand n00b box.

[M@]

WTF are you? Study some fluid flow and you'd understand n00b box.

My fluids look nice as they flow down your chin.

[Conrad]

I say we light Dave's M3 on fire on the highway.... follow me here....

He drives with a coat hanger in the rear catching the trunk on fire.... As soon as smoke is billowing out, M@ follows at a good 90 mph and we attach weston's little pretend racecar camera under M@s car... and we video it from the side. and compare the weston camera vid and side vid and makes lots of money for ricer bumper hole development.

[Brandon]

I didn't follow all that but it sounds pretty cool. Dave will be down.

[M@]

:rofl: I'm down.

[cybergreencivic]

roast marshmallows in the trunk fire when its all over.

[Weston-work]

I say we light Dave's M3 on fire on the highway.... follow me here....

He drives with a coat hanger in the rear catching the trunk on fire.... As soon as smoke is billowing out, M@ follows at a good 90 mph and we attach weston's little pretend racecar camera under M@s car... and we video it from the side. and compare the weston camera vid and side vid and makes lots of money for ricer bumper hole development.

Good idea. I'm sure "ricer Civic crashes into hot dog enthusiast's burning M3" will be a big hit on YouTube. :D

[Dave_L]

I got loan gap coverage. :D

[M@]

Good idea. I'm sure "ricer Civic crashes into hot dog enthusiast's burning M3, slow Porsche owner finally glad he's faster than the ricer Civic" will be a big hit on YouTube. :D

Fixed.

[Weston-work]

Fixed.

YouTube doesn't allow that many characters in a title, noob.

[M@]

:( Dangit.

[Pang]

Its not rocket science.... Take a look underneath the rear and you'll see how the bumper will trap air. The holes allow it to escape.

[Weston]

Its not rocket science.... Take a look underneath the rear and you'll see how the bumper will trap air. The holes allow it to escape.

This has already been covered...

Some people think that trucks have less drag with the tail gate down, but that's not true.

Finally, I've checked under an 00 Civic Si and there is a large flat piece that would prevent the bumper from acting like a parachute since this piece is parallell with the rear bumper and covers most of the area behind the rear crossmember.

[M@]

In my opinion, just because Robbie says so isn't enough evidence for me; call me crazy!

[Weston]

Engineer who knows what he's talking about > Ricer who went to the mysthern school of aerodynamics

[M@]

That was a low blow. That was just downright mean, Weston.

And Robbie hasn't gotten his degree yet, has he? Therefore, he isn't an engineer yet because Stone Cold says so.

[Weston]

That was a low blow. That was just downright mean, Weston.

Ok, you got me there. I went a little too far when I compared you to myshtern. :D

[Skaterkid]

I graduated a year and a half ago, kiddo. So the Colorado School of Mines says I'm an engineer. :D

[Brandon]

Doog and I saw sex and the city this weekend. I would recommend it.

[M@]

I graduated a year and a half ago, kiddo. So the Colorado School of Mines says I'm an engineer. :D
Oh, well congrats... but Stone Cold still says otherwise.

[Pang]

This has already been covered...


I didn't have the time to read all 8 pages of yapping.

[myshtern]

So let's just clarify:
Weston and skaterkid say it isnt so because skaterkid looked underneath the a civic recently
Racers use it commonly and it's fairly common knowledge that it helps drag times. Also backed by 2-3 guys who race imports most often here.

Weston, we offer scholarships for underprivileged kids at myshtern's school of aerodynamics, if you'd like I can send you an application.

[jackmode9316]

Weston, we offer scholarships for underprivileged kids at myshtern's school of aerodynamics, if you'd like I can send you an application.

Sound like a sweet deal there sweet puff.

[Brandon]

So let's just clarify:
Weston and skaterkid say it isnt so because skaterkid looked underneath the a civic recently. And for the sake of my argument, we'll ignore anything intelligent skaterkid might've posted as well as any basic physics concepts that have been brought up.

Racers use it commonly and it's fairly common knowledge that it helps drag times. Also backed by 2-3 guys who race imports most often here.

Weston, we offer scholarships for underprivileged kids at myshtern's school of aerodynamics, if you'd like I can send you an application.

Sounds like you got it.

[myshtern]

You don't exactly have to have a degree to understand the concept that if it's a smooth surface underneath the bumper there isnt any drag created. The point is, something else is going on clearly the rear bumper on civics is stopping the flow or creating bad turbulence at high speeds that skaterkid isnt going to see from just looking at the bottom. How many people does it take to say that they have personal experience with it working to recognize this?

[Skaterkid]

No data has been posted by time slips, threads, coast down to say that this actually does anything. Nothing of value beyond "somebody said..." and nothing beyond a sample size of one, nor is the claimed benefits greater than could be explained away by better weather, better driving, or that the only change on the car between runs was drilling holes in your bumper. Your ignorance shows when you say that a smooth surface creates no drag when moving through air. Everything that moves through air creates drag. And actually, a dimpled surface would have a lower coefficient of drag than a smooth one. I've actually used a wind tunnel in real life, I've helped with aero work on an FSAE car, and I've taken Fluids classes. I've got a good understanding of how air works on a car. Come back when you can add something intelligent here.

[M@]

Once I get tech'd for 10's, I'll do a pass at the track with it unblocked, and try to get a similar pass with it blocked and post up results.

[Skaterkid]

If you can, do two or more in each configuration.

[M@]

I will certainly try. I'm pretty consistent with my 60's, so I think that should be doable. It will be a few weeks, though. I'll bump the thread at that time (that's if you women aren't in here still arguing by then ;)).

[97CivicNick]

soo I was just thinking about the whole parachute effect thing of a civics rear bumper... If that is bullshit like you guys are saying, that it is stale air and doesnt slow you down....

... How does an ACTUAL parachute work?

Im no engineer either. fill me in.

[chris_venturini]

this thread is why I still occasionally read HAI, and also why I dont.

[myshtern]

Once I get tech'd for 10's, I'll do a pass at the track with it unblocked, and try to get a similar pass with it blocked and post up results.

You better not fall through on this :D

[Brandon]

You don't exactly have to have a degree to understand the concept that if it's a smooth surface underneath the bumper there isnt any drag created. The point is, something else is going on clearly the rear bumper on civics is stopping the flow or creating bad turbulence at high speeds that skaterkid isnt going to see from just looking at the bottom. How many people does it take to say that they have personal experience with it working to recognize this?


If you're asking me, personally, based on the method of "analysis" that's been presented I don't care how many people say they gained 2mph in the traps.

The point is, something else is going on clearly the rear bumper on civics is stopping the flow or creating bad turbulence at high speeds

You say this as if it were a fact which it isn't until it's proven and someone saying they are faster in the 1/4 mi because of some holes in the bumper isn't proof IMO.

Maybe some pictures will help us, sorry they're not to scale. The black is the side view of the spare well and the bumper. The dotted black line is about where the wheel might be. The red is obviously air flow.

Here is what I think that some people think is happening and creating a "parachute" and drag:

http://www.highaltitudeimports.com/attachment.php?attachmentid=4341&stc=1&d=1212553763

The problem is the air has to go somewhere, it can't just jam up into the bumper and stay there.


Here is what I believe to be happening:

http://www.highaltitudeimports.com/attachment.php?attachmentid=4342&stc=1&d=1212553763

The air will take the path of least resistance.

[Brandon]

soo I was just thinking about the whole parachute effect thing of a civics rear bumper... If that is bullshit like you guys are saying, that it is stale air and doesnt slow you down....

... How does an ACTUAL parachute work?

Im no engineer either. fill me in.

I doubt you really care based on the bullshit comment but I'll entertain you for a bit with some pictures. ;)

I'm no engineer either nor an expert but this is how I would imagine a parachute might actually work:

http://www.highaltitudeimports.com/attachment.php?attachmentid=4348&stc=1&d=1212555181

This is how some people in this thread might think a parachute works:

http://www.highaltitudeimports.com/attachment.php?attachmentid=4347&stc=1&d=1212555181

Again, I'm not sure where all that air is supposed to go. Maybe it curves up to the top of the chute and then back out the sides which doesn't look like the path of least resistance to me.

And finally here's how the same people might imagine a parachute combined with m@'s bumper would work.

http://www.highaltitudeimports.com/attachment.php?attachmentid=4346&stc=1&d=1212555181

Those people might argue that the air goes up into the pocket, turns around, and exits out the bottom of the chute. You could then cut speed holes in the pocket and therefore make the air flow right on through.

[97CivicNick]

No.. Im serious now.. this turned into a big debate... about wether or not the holes in M@'s bumper reduce drag and allow his car to go faster...


Thinking about a REAL parachute.. if i cut a whole bunch of wholes in it.. I just cant see it working the same... :)

Debate. lol

[Brandon]

Parahutes with holes and rear bumpers with holes aren't comparing apples to apples, more like caulk and cheese. If M@'s car was a board (no depth when view from the front) and you cut holes in it, then yes, I would imagine the car would have less drag. It would have less frontal area although might have a higher coefficient of drag but I don't know about that.

[97CivicNick]

Im not getting your arguement anymore... Various people that race have improved times when they have cut holes in there bumper...

Everyone says the bumper works like a parachute, causing drag...

A real parachute with holes cut in it would run 10's (haha)

I mean.. what else is there to this?

I dont speak tech. so lets use small words. haha



Either way, I dont see how it could make the Drag situation any worse... So what would be the point in NOT doing it?

[Brandon]

Another masterpiece....


I think this is more like M@'s bumper combined with a parachute...kinda. The left hand side is looking up into the chute and all the little holes are chimney type things.

http://www.highaltitudeimports.com/attachment.php?attachmentid=4349&stc=1&d=1212556292

[97CivicNick]

stop drawing pictures. your confusing me... whos side are you on? lol

[M@]

I think B is drawing those while in the nude.

[Brandon]

Im not getting your arguement anymore... Various people that race have improved times when they have cut holes in there bumper...

Everyone says the bumper works like a parachute, causing drag...

A real parachute with holes cut in it would run 10's (haha)

I mean.. what else is there to this?

I dont speak tech. so lets use small words. haha



Either way, I dont see how it could make the Drag situation any worse... So what would be the point in NOT doing it?

Your side of the argument is "he said...she said..." it has no merit. Not everyone says the bumper works like a parachute or this thread would've died 2 weeks ago.

What else is there to this?
Just physics, nothing much.

So what would be the point of NOT doing it?
Um, that's what this whole thread is about. I think that by making the holes is introducing drag. As was suggested earlier, a better option would've been to make a flat bottom car.

[Brandon]

I think B is drawing those while in the nude.

I have my glasses on so I feel smarter.

[97CivicNick]

how would making holes introduce drag?????? thats EXACTLY what this argument is about is that a civic bumper works like a parachute.


PARACHUTES SLOW YOU DOWN...

like you keep drawing pictures and saying shit, and saying how everything you say is based on physics, but your still not explaining ANYTHING

Im just gonna repeat the same thing untill one of you explains how its not the same

Real life parachute slows you from falling to the earth.
Civic Bumper acts as parachute, thus slowing you at highspeeds
Cut wholes in REAL Parachute >>>> Fall real fast.
Cut wholes in Civic Bumper>>>> go Faster

*********Retard voice*** Duh DUh DuhHHHHHhhh

[Brandon]

The drawings make sense to me, sorry.

Fluid Mechanics will answer all your questions. It's offered this fall at UCD. You could also check with Metro.

[97CivicNick]

Cool. I want someone else to come argue with me. You fail at debating.

where is weston at? hes good at arguing.

[Pang]

http://tempestracing.net/images/85_copy.jpg
^Just went 8's on gas.

[Martian]

Forget drag, what about lift? I don't have much knowledge in fluid dynamics, but..........................................

Isn't it possible that this trapped pocket could have a higher pressure then the top of the car, causing the rear to lift? Then if that does indeed happen, cause drag in and of itself?

[cybergreencivic]

Doog and I saw sex and the city this weekend. I would recommend it.

I am not going to take either one of you guys word on this. Wife wants me to see this shit.

I think B is drawing those while in the nude.

M@ asks this of me on occasion. I think he wants picture confirmation of the reply, or maybe just i do.

I have my glasses on so I feel smarter.

[jackmode9316]

I see what brandon is saying about it potentially creating drag. (Not saying that I agree because I don't actually know)
but....
http://www.highaltitudeimports.com/attachment.php?attachmentid=4342&stc=1&d=1212553763

If this picture is actually how it works, then the holes would actually cause the passing air to move through the bumper creating drag on the area in between the holes and on the sides, where as before the stale air would actually hold the passing air down and keep it flowing smoothly. Again im not trying to pick a side, im just answering myshtern's question about how the holes could "potentilly create drag".

[swtvi3txtcboi]

wouldn't the heat of the track at the time also make a difference? the hot asphalt would change the pressure of the ambient air, therefore causing it to push the flowing air and could cause the air trap.

[Boostedcivic]

looks good man

[crteg6]

thats clean i miss my em1 :(

[Mark_H]

bump!


Mods...regulate^.

[Kwando]

fucking st00pid n00bs trying to whore their post counts!

[jackmode9316]

Its like they don't even try to make it legit.

[myshtern]

So does the diffuser work or is it a ricer mod?

[M@]

It's definitely not hurting, so... who cares?

[Maelong]

wont be going fast enough to make them actually work

[M@]

Oh is that so? How "fast" does it need to go to work? :rofl:

[Brandon]

I would estimate at 88mph you're gonna see some serious shit.

[jackmode9316]

What is this "some serious shit"?

[myshtern]

I would estimate at 88mph you're gonna see some serious shit.
:rofl:

[M@]

Bwuahahahahaha!

[J.Lee.M]

it doesn't matter, just looks good. in my opinions.

[jackmode9316]

in my opinions.
How so?

[mx-6er]

How so?

J. Lee is very KDM, with a pretty good accent. I don't he even knows how so.

Edit: I have seen a few different people pick up a few more mph at the end of the track with those speed holes.

[Mark_H]

wont be going fast enough to make them actually work

Oh my god...You have shown us all THE light!!!!!!! Thank you thank you thank you!

[J.Lee.M]

i'm rice so i just like rice, thats how so.

[M@]

J. Lee is very KDM, with a pretty good accent. I don't he even knows how so.

Edit: I have seen a few different people pick up a few more mph at the end of the track with those speed holes.

:thumbup:

[chris_venturini]

you should put a tornado fuel saver in each of the holes, 60% of the time, it gets air out faster every time.

[jackmode9316]

+ 1 on the Tornado. It creates that awesome "Cyclone" Affect. Air will be leaving your bumper so fast, it will basically be propelling you.

[TurboTipeR]

im doing that to my evo 9 mr and my EK lol sike . looks good on your ride bro nice job

[jackmode9316]

Some people think that trucks have less drag with the tail gate down, but that's not true.


I'd imagine that this situation would be very similar to the air flowing over a truck bed. A pocket of stale air forms in the bed so that the boundary layer does not tumble down off of the cab and into the liftgate, instead the stale air allows the boundary layer to smoothly separate off of the cab and over the liftgate causing lower drag than if the liftgate is down, and that pocket does not form.
Myth busters did a test on gas mileage with a tailgate, without a tailgate, with the tailgate down, with hard cover, and with a mesh tailgate. Their thoughts were that best gas mileage would be achieved with a hard cover or with the tailgate up. My guess is that less drag=better mileage, right? One would think that the hardcover and/or tailgate up (for reasons already explained) would result in better gas mileage. Well guess what.....the fucking mesh tailgate got the best mileage. As to why? Who knows.....they didn't "wind tunnel it" to see why, but the physical results were with the mesh. Who would a guessed? As for conditions of testing having an effect? The package the mesh comes in also claims to result in better mileage, so i'm sure there was a little more extensive testing involved by the company(s). Especially since they could be sued for such claims if false.

M@'s speed holes are really not much different then a mesh tailgate in the sense that it could and seemingly would create drag, but in fact does not. Perhaps is creates the stale pocket effect AND releases potential drag *shrugs*

Although my thoughts do rely heavily on the fact that less drag results in better mileage.....but it would make sense right?? Why else would you receive worse mileage with the tailgate down, or removed. Oddly though the hardcover was worse than the tailgate up scenario.

Just a thought to ponder anyways. Maybe one of you Brains can give some more knowledgeable input.