brian6speed

iTrader: (5)

I wanted to ask your opinion on what to do with my rear bumper. I am planning on changing my exhaust to a single 3". The problem is I do not want 2 exhaust cut-outs in the rear bumper.

I should also point out if you do not know already, I am building my car for auto-x and eventually track duty. I also still drive it on the street so everything is kind of a compromise.

I will either run one muffler on passenger side, or a dump down in the middle of the car. I think I prefer the one muffler idea and it should sound better. I will be using a race muffler that weighs less than 3 lbs. so not a big weight penalty.

I am undecided if I want to use a rear diffuser or not. I have seen multiple fwd track cars that are very fast without rear diffusers.

If I decide to run a rear diffuser I will probably have this company make one for me or atleast the curved middle section. I can always DIY the side sections.
https://www.facebook.com/media/set/?...4826698&type=1

Option 1: Don't cut the bumper you idiot.

Option 2: Cut the bumper pretty much straight across like the following vehicles. The fwing is the fastest fwd track car ever and doesn't have a rear diffuser. This rsx is also fast without a rear diffuser. I really like how aggressive these look with rear tires exposed.

Here is the fwing 2.0 rear


RSX rear



Here is a link to the rsx in hondatuning
http://www.hondatuningmagazine.com/f...ra_rsx_type_s/

Option 3: Cut only the middle section like a lot of mazda miata owners do.


This would remove the exhaust cut-outs while still being most stock looking.

Option 4: Cut only the sides like villo did to his 3rd gen tl. I think this would require a diffuser to look good.

brian6speed

iTrader: (5)

Here is a bigger pic of the rsx.

justnspace

iTrader: (1)

diffusers only help if they're engineered to help.
so, when you mention some of the fastest fwd vehicles that dont have a diffuser, because either A) it didnt help. B) It didnt help.

I'm assuming the diffuser company would need time with your car in a wind tunnel to design a proper diffuser that decreased time around a track.

gnuts

iTrader: (1)

pardon my ignorance, but what is the point of those cars cutting it right across like option 2?

Is there an option 5 to fill the second exhaust cutout?

Out of the options above i like #3.

Stephen00TL

I agree with gnuts.

brian6speed

iTrader: (5)

You do not need a wind tunnel to design a diffuser. A wind tunnel would help in fully optimizing it tho.

I was just pointing out that if the fastest fwd track car ever built doesn't have one then I definitely don't need one.

Someone tell villo to rip off his front splitter, underbody panel, rear diffuser, and rear wing because it wasn't designed and setup in a wind tunnel.

The bumper creates drag. Have you ever noticed when washing the car how all the rocks and debree get stuck in the bottom of the bumper. Cutting it would allow that air to flow thru. The bumper is almost like a parachute how it is stock.

You mean how I have it now? A single exhaust will reduce weight by 20-30 lbs and not decrease power. I think I am pretty set on a single 3".

Yea i expected everyone to pick 1 or 3. Will wait and see.

AustinTaper

#3, based on appearance, but for performance/weight reduction

Cocoa

iTrader: (2)

First off, that scion is pretty darn sick in person. I have seen it run multiple times here in socal during redline time attack sessions over the past few years. Key things to point out. A) the guy is a millionaire and built the worlds fastest drag scion with 1000fwhp. B) he was bored, threw the front spoiler on, redid the suspension, and blew away all fwd contenders by detuning the draq car down to about 700fwhp. Regardless of making it any more aerodynamic, no one could touch him in the fwd class. I honestly have not seen the car on the track here in socal for about a year now though, unless he's competing in a different event.

As for the diffuser, it works on any platform. It will not work without a front splitter for the very least (it'll make it about 30% effective) but in addition to the front splitter adding the under body panel, you'll get the full effect. It'll create a form of "suction" to the ground, essentially downforce using Bernoulli's principle (this is not the same form of downforce as a front splitter creates). It'll reduce under body air pressure, reduce drag, and accelerate the air from the underbody front of the car to the rear. Essentially the whole point of the thing is to have the atmospheric air flow at the same rate as the air velocity created under the car at higher speeds.

Personally I went this route because I did not care to pay 1500 for a gt wing unless it is completely necessary. Plus I've always liked the way diffusers looked.

Just make sure all 3 parts are leveled evenly to one another, otherwise it will not function properly. You can create the under body panel using alumilite from N. Glantz n Sons. It'll run you about $150 for a 4'x10' panel roughly 6-8mm thick. Its the perfect solution for the front splitter as well, as on the track you'll be going through those pretty frequently as well lol. Its why you rarely see track cars with purty APR ones, unless you're rich I guess.

https://www.nglantz.com/storefrontCommerce/

Cutting the rear bumper is the economical way to reduce drag in the rear, but doesnt do squat about the air velocity, the low air pressure that's in the front, or even handling (think of the suction effect).

Hope that helps.

Cocoa

iTrader: (2)

Forgot to mention, the rear diffuser was bought from warhorse performance, as theirs have been tuft tested therefore are aerodynamically functional. It can be incorporated to any car, but at your expense. It's not car specific persay. Also, it is not listed for sale on there website, just contact the owner in regards to it. You will however find pictures of it on the website. I believe it ran me roughly $360 shipped, much less than the cosmetic ones you find for sale everywhere online for nearly twice the price lol.


http://www.warhorseperformance.com/

brian6speed

iTrader: (5)

Nice informative post cocoa.

I actually posted the warhorse performance link in the first post of this thread.

I understand what you are saying about the aerodynamics. I am just debating how far to take it for a car still street driven. I would need an easily removable front splitter. Not sure if a full underbody panel is a good idea. Rear diffuser would be doable but would get damaged if I ever need to get car towed.

As for the fwing 2.0, that is one of my favorite builds. Last I saw someone else besides chris rado was piloting it. From my understanding they were using the fwd car as a test bed to make an awd car to try and beat everyone. I think the fwing is pretty much dead.

I will be mainly doing competitive auto-x and just some track days for fun. No competition track stuff for a few more years probably. So I have to keep that in mind. For example if I wanted to make canards I have to worry about them getting damaged if I hit cones. Everything would need to be easily removable.

kingofdust

Cut the middle and then run a blast pipe like set up, with a full 3 inch exhaust running to 2, 3 inch pipe angle cut jutting out at a slight angle, that setup would look like pure sex on the CL and would sound so nice if you throw in the muffler before the exit pipes. Just my opinion.

Cocoa

iTrader: (2)

yea pretty much that scion has set some damn hard fwd times to beat that is competitive with some of the best times in the rwd/awd unlimited classes. Essentially its about a 10 second difference between that car and the previous fwd records in buttonwillow raceway. He honestly had no competition. The scion was just 6 seconds off from the cricket's nsx (better known as fxmd's nsx) fastest overall record at buttonwillow that beat hks's carbon evo previous overall record. I've been lucky to have seen these events/records occur live in person. You just get to see it all on the racetrack, i love it.

There's nothing like watching the small shops coming in and beating the multi-million dollar company race cars, thats just another excitement in itself. Everyone sure did know who fxmd was after that year. The record was in 2012, but if i'm not mistaken we have seen them around racing in socal for 2 yrs before that record was set. Small time shop out in vegas. Thats the only reason why I remember it as the cricket nsx (they had in big letters the word CRICKET alongside of the car prior to 2012).

As for the diffuser, yea I suppose having to deal with the whole shebang would get old quick street driven everyday. I'm not much of a naysayer so taking my advice usually only heads in one direction (water boy quote anyone "you can do it")

brian6speed

iTrader: (5)

I wanted to talk a bit more about the "you need a wind tunnel" comment. If you watch the world racing webcasts for the fwing you will see them putting done type of oil on the car, then they drive it around the track. They visually inspect where the oil flowed and make aero adjustments based on that. They say it is the cheapest wind tunnel.

I am not quite sure what you mean. Can you clarify?

I am jealous you got to see those cars in person. Only videos and pics for me. I guess I can cut the middle section and see how I like it and work from there. I might just make a flat or curved aluminum panel. Not sure if I want fins yet.

brian6speed

iTrader: (5)

Cocoa how did you measure and send specs to warhorse performance?

I can go take measurements, but without having the car or a mocked up piece I would think it would be off and need a good amount of adjustment/custom work.

brian6speed

iTrader: (5)

I took your guys advice and just cut the middle section. Took me a week to get the nerve to hack it up. I must say I think it looks amazing and better than stock.

Cutting plastic sucks. The little chunks stick to everything and are hard to clean up. My clothes, face, hair, etc is covered in it. The ones in my hair were soft/melted when they attached, then they hardened up and stuck to my hair.

Here is what my ventilator looked like after cutting.


I used my dremel with a plastic cutting wheel and a sanding disc. I still need to do the final sanding before I remove tape.

Here is what I cut off.


I am going to keep the metal brackets that the bottom of the bumper used to attach to. I might use them to hold the rear diffuser if I decide to use one.

Here are pics of the cutout.

Cocoa

iTrader: (2)

warhorse makes that diffuser specifically for the miata, but provide the specs/dimensions online of said product. They do not make them car specific for any other car. I took the specs and calculated whether or not it would be plausible to fit my car.

Its been incorporated into many other cars such as civics, rsx, nsx, s2k, etc. This portion of the job is done by you, as the buyer (or the shop you take it to of course).

My diffuser (5.5 hrs of labor + hardware) is attached to the bumper, spare tire housing, and the chassis. Side boxes set at 0 degrees giving the center section 13 degrees of curvature from the center edge of the rear. I can get more aggressive by cutting the bumper and take the side boxes to a max of 3 degrees giving the center section a max of 22 degrees of curvature from the center edge of the rear. I also had to reroute my exhaust muffler ($35) in order for the diffuser to be installed properly.

In addition to this work, the car was also cornered balanced which gave it a cross weight distribution of 50% (8hrs of labor which included retuning suspension components and exchange of springs for desired spring rates recommended by tuner to help give desired effects wanted by driver.......for instance I asked my car be given slight oversteer during high speed cornering, this has 0 affect on weight distribution, but it changes the RATE of the weight distribution). This by far, was the absolute best mod I have ever done. It drives and handles perfectly. The car will react to understeer/oversteer significantly upon the mistakes done by driver. What I'm trying to say, the car is completely neutral, if you suck at driving or take the wrong line, the car will tell you and react accordingly. This is exactly what a cross weight distribution of 50% does, makes the car feel neutral upon cornering. The car was raised 25mm upon corner balancing as well, just fyi, and weighed in at 2600lbs. I highly recommend you do this before anything else, as it greatly improves driveability on the streets which is a huge plus for you.

gnuts

iTrader: (1)

looks great! will you have to put anything on the part you cut? Do you still plan to use the RJ kit?

brian6speed

iTrader: (5)

Ah so you just bought the diffuser and modified it to fit. That is what I was thinking would have to be done. I don't need a shop to modify it, I can do it myself. I just need to make my mind up on exhaust setup. I saw the dimensions on their facebook page. I still need to take more measurements and see.

What is the max angle you want that curved middle section at? Looking at my car it might need to be at 20-30 degrees.

Do you have a pic of your setup you wouldn't mind posting, and how did you route the exhaust? I think having the pipe exit out of the passenger side of the rear bumper would be possible. I would just need to make a heat shield for the bumper.

As for corner balancing that is something I want to do just haven't gotten to that point yet. I am still trying to figure out a clunk in my rear suspension. I ordered all new arms and am going to ditch my ingalls arms and make some custom arms(with camber and toe adjustments) with either oem bushings or something like spherical.

I should figure out what I need and get my coils re-dampened and sprung. I was thinking about ordering some custom koni 3011 or 2812 shocks, but they want me to make all the calculations for spring rate frequencies, etc. I need to get the car weighed, etc. before I can do that. Then if I am gonna spend that much money on suspension do I really want to use the stock mounting positions?

Thnx. I do not need to put anything on the part I cut. I made the cut angle upwards to hide the black plastic lip. The only way you would see it is if you lie on the ground looking up. The only part you might see it is at the curved edge at the very bottom by the muffler but that does not bother me. You could add some edge trim or use touch up paint but I am not gonna bother.

I will probably make 2 attachment points to the bumper beam behind the license plate to make it more secure. They will not be seen with license plate on.

I plan on using the front lip of the ron jon kit. I like how it looks and think it aids in aerodynamics and would make mounting a splitter easier. I am undecided yet if I will use the side skirts. I might just use/make my own side skirt extensions instead. I don't plan on using the rear part of the kit. I will just leave it how it is or add a rear diffuser maybe. I will sell the rear if anyone wants it.

brian6speed

iTrader: (5)

Here it is after final sanding, tape removal, and cleanup from 2 different angles.

gnuts

iTrader: (1)

looks great! You have a steady hand my friend. If i didn't know any better i wouldn't have guessed you cut the bumper.

brian6speed

iTrader: (5)

Thnx. I have a lot of practice with a dremel by now. I also have always been into drawing and painting. I did go to art college.

Using the tape as a guide helps also. I put on multiple layers. Then I put a box under the car and used that to steady my hand against.

I made sure to measure both sides multiple times and make sure they matched.

kingofdust

Looks great man! Awesome to see that you went a head and did it!

This is what I am talking about, thinking about it now, you will probably hate it lol but it doesn't hurt to throw my opinion out there!

fsttyms1

Personally i would have just plastic welded the drivers side exhaust opening closed and just had the one opening but on the work.

brian6speed

iTrader: (5)

Ah ok, I see what you mean. That would probably look nice but the extra weight is setting off red flags in my head.

I did think about that option and do have a plastic welder. I was just not sure how good it would have turned out and it would also require paint. I think the cutout looks good and it will work better than stock with a diffuser. I never really liked the bottom stock section of the bumper with that lip section with the holes thru it. You could always see that from behind and it just stood out to me(in a bad way). I tend to like more aggressive styling also.

I am thinking about cutting this section out that I taped off. It gets battered by rocks and kind of blocks airflow. I would still keep the lip edge for structural support.


Here is another diffuser that might work besides the warhorse one. It is made by APR for the evo 8 evil-R widebody. It looks like it would be a perfect fit for the cutout, the exhaust is exactly where I want it, and it has a cutout for that hump in the middle that our car also has.

DuwayneWebPro

thats fresh! i voted before i saw your pictures and all i can say is... fresh!

brian6speed

iTrader: (5)

Here are some links to interesting articles on corner weights and setting up fwd cars.

http://grassrootsmotorsports.com/art...orner-weights/

http://grassrootsmotorsports.com/for...ng/4605/page1/

http://farnorthracing.com/autocross_secrets10.html

http://farnorthracing.com/autocross_secrets11.html

brian6speed

iTrader: (5)

I never posted these before so thought I would.

I used 2 aluminum spacers between the bumper support and bumper. I used cable ties to hold the bumper down for better support. I drilled the holes for the cable ties behind license plate.


I also cut out this section on both sides for the hell of it. I was thinking less air resistance behind the rear tires is better.

twigglius

iTrader: (6)

Nice work. You're car looks amazing in person.

brian6speed

iTrader: (5)

Thnx. It was nice meeting you. I had a great time during the meet weekend like always. I am already looking forward to next year.

Btw I love the pics you posted of my car. I think that front pic is my new favorite pic of my car.

KR3J//

Your bumper looks really good man. Aftermarket looks for free!