How to make your own air box lid pre-filter (step by step)

[maxfior]

NOTE: This was first posted in the 400EX section, but I had some people over they mention that I should post it here for everyone else to see. Also, I'm sure this will work for other quads, not just the 400EX, you just have to see if EHS makes the filter and then order it. Make sure you tell them that you just want standard shipping, so that will save you a little bit more. Take your time and you'll be fine. Thanks for reading this. Any questions, please ask!

Max


I'm cheap. I don't like to spend money on stuff unless I really have to. So, when I saw the EHS air box pre-filter I thought I could make one myself. I ordered the filter from EHS (since that is the hard part to try and make a filter) and then went to work. If you are handy you should be able to do this with out much problem. Just take your time and be careful. The only thing that I needed on hand was a sheet of thin aluminum and some bolts, washers and lock-washers. The filter from EHS only cost $17.00 for regular mail.

NOTE: Here is a link to a .PDF that I made of my template, so now all you need to do is print it out and cut it carefully.
---LINK---
http://www.maxfior.com/atv/400EX/MODS/AIRBOX/400EX_template.pdf (right click as save it to your desktop or where ever)
---LINK---
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http://www.maxfior.com/atv/400EX/MODS/AIRBOX/DSC05235.JPG
Here is the sheet that I used, you want to make sure that it is the right size.
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http://www.maxfior.com/atv/400EX/MODS/AIRBOX/DSC05237.JPG
Filter looks like it'll fit nice. Now it's time to make a template, I used an old folder that I found lying around. Just take your time with this.
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http://www.maxfior.com/atv/400EX/MODS/AIRBOX/DSC05242.JPG
Looks good, now it's time to cut the middle out...
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http://www.maxfior.com/atv/400EX/MODS/AIRBOX/DSC05245.JPG
When using trusty razor blade make sure you be careful... You don't want to cut your fingers or face off... Then you won't be able to pull wicked hole shots in the summer time! :p
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http://www.maxfior.com/atv/400EX/MODS/AIRBOX/DSC05246.JPG
Now with the middle out you can work on tracing to the metal sheet. Tape it in place and then get out the marker.
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http://www.maxfior.com/atv/400EX/MODS/AIRBOX/DSC05249.JPG
Trace away...
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http://www.maxfior.com/atv/400EX/MODS/AIRBOX/DSC05251.JPG
After the trace job, clamp that sucker down and get out a 1/4 inch drill bit for making the holes. You'll also want to pop a hole at an edge for getting the scroll saw started...
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http://www.maxfior.com/atv/400EX/MODS/AIRBOX/DSC05253.JPG
Holes drilled.
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http://www.maxfior.com/atv/400EX/MODS/AIRBOX/DSC05254.JPG
Hole to start the middle cut with your scroll saw.
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http://www.maxfior.com/atv/400EX/MODS/AIRBOX/DSC05255.JPG
Middle cut out, now it's time for the sides...
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http://www.maxfior.com/atv/400EX/MODS/AIRBOX/DSC05257.JPG
Take your time when cutting out the rest... Make sure to re-position everything when cutting and clamp it down really well so that vibration is kept to a minimum.
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http://www.maxfior.com/atv/400EX/MODS/AIRBOX/DSC05258.JPG
The cutting is finished and then I made sure to clean any sharp edges off... Don't want to cut anything...
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http://www.maxfior.com/atv/400EX/MODS/AIRBOX/DSC05259.JPG
After the sharp edges were removed I then clamped the metal to the air box so that I could punch 1/4 holes properly.
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http://www.maxfior.com/atv/400EX/MODS/AIRBOX/DSC05260.JPG
I also made a hole in the middle to start the saw... Now I carefully cut out the middle. Taking my time...
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http://www.maxfior.com/atv/400EX/MODS/AIRBOX/DSC05261.JPG
Now that the middle is removed I clean the burrs off and get ready to assemble everything. Make sure that you use good bolts with washers on each side with a lock washer on the inside before the nut.
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http://www.maxfior.com/atv/400EX/MODS/AIRBOX/DSC05263.JPG
Finished product... Looks pretty okay if I do say so myself... Now with the money I saved I can go buy some lunch, I'm hungry...
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http://www.maxfior.com/atv/400EX/MODS/AIRBOX/DSC05264.JPG
Bottom view.
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http://www.maxfior.com/atv/400EX/MODS/AIRBOX/DSC05266.JPG
Ready for action! :)
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Any questions, please ask! This might not be for everyone, but I like to make things when I can. Good luck!

Max

[hornetgod13]

This is a great "how to" and an excellent way to significantly increase airflow to the motor at a fraction of the cost of an aftermarket airbox lid. I would recommend bumping the pilot and main jet up one size. This would go perfectly with an aftermarket exhaust mod to really maximize airflow and increase performance.

[maxfior]

Originally posted by hornetgod13
This is a great "how to" and an excellent way to significantly increase airflow to the motor at a fraction of the cost of an aftermarket airbox lid. I would recommend bumping the pilot and main jet up one size. This would go perfectly with an aftermarket exhaust mod to really maximize airflow and increase performance.

Thanks for spreading the word! :D

Max

[djguestone]

Looking good! Are you still running the filter inside the box?

[maxfior]

Originally posted by djguestone
Looking good! Are you still running the filter inside the box?

Yeah, I have the pre-filter, then my Uni or it might be a Twin-Air (one of them was dirty and I swapped out) in the box. I think I might get a K&N though in the future and do away with the metal inner filter... Then I'll just clamp the K&N. The prefilter works good thoug and came out decent. If I had a stationary bandsaw, I could have make the cuts look better, so if you have one of those I'd use it. There is another member on here that is going to make a pre-filter as I did, so keep looking back at this thread.

Max

[Brauap]

You might remember me from the 400EX thread you made, well anyways, I decided this to be my next project. Could you please send me the E-mail or anything on how you asked them for just the filter. Thanks!

[maxfior]

Originally posted by Brauap
You might remember me from the 400EX thread you made, well anyways, I decided this to be my next project. Could you please send me the E-mail or anything on how you asked them for just the filter. Thanks!

Hey man! First, go to this section of their site:

http://www.ehsracing.com/catalog/index.php?cPath=21_28_29

Get the filter that you want and then buy it, but in the notes section you can tell them that you want the cheapest shipping available and they will cut you a better deal. Let us know. Thanks!

Max

[Brauap]

Thanks!!!!

[j.fort 8]

couldnt you use just very fine netting then make a template for that and then install, cause i have a predator 500 and they dont make a pre-filter for it.

jake

[j.fort 8]

couldnt you use just very fine netting then make a template for that and then install, cause i have a predator 500 and they dont make a pre-filter for it.

jake

[maxfior]

Originally posted by j.fort 8
couldnt you use just very fine netting then make a template for that and then install, cause i have a predator 500 and they dont make a pre-filter for it.

jake

Jake,

I don't see what you couldn't use a really fine net of some sort, that would help with large chunks but not water. The EHS filter can take a few splashes and such. You might want to take some measurements and see what filter of theirs is a close fit and then you can start making the template and hacking up your air box! Just make sure you rejet too, you'll see a nice performance boost. I know I did with my 400, it was like a new quad!

Max

[f4istunna]

Good idea and nice write up. I was planning on a lid, but i think im going to try this. Im down to save some $$ whenever i can, can use it for other parts/mods

[j.fort 8]

Originally posted by j.fort 8
couldnt you use just very fine netting then make a template for that and then install, cause i have a predator 500 and they dont make a pre-filter for it.

jake

ya i would definatley rejet but i dont no what size's to bump up to.

[maxfior]

Originally posted by j.fort 8
ya i would definatley rejet but i dont no what size's to bump up to.

Well, a good place to start would be 1 or 2 sizes up from where your stock settings are at. I'll use my EX as an example. I went from a #138 main to a #142 main and I went from a #38 pilot to a #42 pilot. I also made sure to have some different sizes on hand to and just things if need be. So... You will want to find out your stock settings and go up a little bit. You will want to do this too with a slip on or full system, then you'll really see nice gains. Your local dealer should have the correct jets and they are fairly easy to install. It just takes a little time.

Max

[j.fort 8]

thank you.

[Brauap]

I just got my prefilter!!!!!

[maxfior]

Originally posted by Brauap
I just got my prefilter!!!!!

Good deal man! Now GET TO WORK!!! :D Just take your time and I'm sure it'll come out good! Can't wait to see how it works out for you!

Max

[Brauap]

Well, I am having my dad's buddy making me an aluminum airbox for free, so I am going to fit it on an aluminum lids, thats going to be the only difference.

[maxfior]

...sounds good. I'm sure it'll work good for you. Post some pictures when you have it all completed

M.

[Brauap]

Hey, I just got mine done! Here it is! Tell me whacha think!

http://i197.photobucket.com/albums/aa283/braaup/100_1915.jpg

http://i197.photobucket.com/albums/aa283/braaup/100_1916.jpg

http://i197.photobucket.com/albums/aa283/braaup/100_1914.jpg

Your print out, was x-tremly helpful! Thanks!

[maxfior]

Looks pretty dang good to me! Nice and tuff looking, I'm sure it can take a good beating! Nice work... Glad the template worked out for ya, isn't it nice when you can make your own stuff! I can't wait to get my EX out and roost! Good going!

Max

[Speedy 400ex]

Great idea! that is a big price diffrince! How thick is the aluminum sheet you used?

[maxfior]

Originally posted by Speedy 400ex
Great idea! that is a big price diffrince! How thick is the aluminum sheet you used?

If memory serves, I think it was 16 gauge or .080 (don't quote me though ;) ) or you can make it out of something thinner, you just want to make sure it won't be all flip-floppy, Good luck!

Max

[Speedy 400ex]

cool thanks!

[Speedy 400ex]

here is how mine turned out! I ended up using two peaces of 22 sheet steel and sanwitched two peaces togather and glued them togather and then painted them black.

[maxfior]

That looks REALLY good man! Very clean looking, best part is, you did it your self and save some cash! Looks really good dude!

Max

[Speedy 400ex]

i just chainged the piloit jet from a 40 to a 42 to get rid of the bog and it seems to be running good, but that is just from reving it in the driveway. so im wondering if i should change the main jet to the next size up(it is a 155 right now)?

[maxfior]

Originally posted by Speedy 400ex
i just chainged the piloit jet from a 40 to a 42 to get rid of the bog and it seems to be running good, but that is just from reving it in the driveway. so im wondering if i should change the main jet to the next size up(it is a 155 right now)?

It wouldn't hurt to test it out first under load aka, WOT! It's a good thing that the jets in the carb are fairly easy to change. For me, the #42 can be hard to start when it's really warm out, but my main seems to work good (#155). You might have to play around a little bit, but I'm sure you'll find a combo that works for you. Just make sure you check the plug. Good luck!

Max

[Speedy 400ex]

how do u get the plug out? none of my sockets fit in cavity.

[maxfior]

Originally posted by Speedy 400ex
how do u get the plug out? none of my sockets fit in cavity.

Do you have the OEM plug tool that came with your tool kit? I take it you don't... That is what you want, otherwise you'll need to get a thin-walled socket to fit, I've heard some people get a normal socket and then grind down the sides so it'll fit. The Honda tool is the best bet, I was lucky I had an old one from a XR250 and it fit my 400EX too. I forget the exact plug size, 17mm maybe? Good luck!

Max

[Brauap]

(SIDE NOTE: ANYONE WHO TRAIL RIDES, THIS IS A HORRIBLE INVESTMENT (OUTERWEARS) !!! STOPS VERY LITTLE WATER!!! HAD THIS OUTERWEARS OUTERWEARS ON MY K&N AND MY K&N GOT DRIPPING WET!!! :THUMBSDOWN::grr: :cuss: :mad: :grr: :cuss:

Originally posted by Brauap
(SIDE NOTE: ANYONE WHO TRAIL RIDES, THIS IS A HORRIBLE INVESTMENT (OUTERWEARS) !!! STOPS VERY LITTLE WATER!!! HAD THIS OUTERWEARS OUTERWEARS ON MY K&N AND MY K&N GOT DRIPPING WET!!! :THUMBSDOWN::grr: :cuss: :mad: :grr: :cuss:

hmm it worked fo me, i was smashing through puddles and I even went into one fast as i tried to turn to save it because i figured it was deep and it was, i ended up holding my quad up from the water half way underneath it chest high in water until my friends came to help lol Good thing part of it was on the bank from when i turned because no lie this water in this rut was chest high I couldnt believe it. Anyways no water on my filter, most went down through the drain hole and the other drops beaded and rolled off my outerwear on my air filter. Now I have both outerwears and I have nothing to fear now unless i sink the quad.

[Brauap]

I ramed a creek and my quad started to sputter then die, do I looked in the air box, the outerwears was clogged with water so I had to take it off, then I looked up into the black thing.. I can't remember the name, and it was all wet and it took off the oil on my filter.. and around here I was riding then at the end of the day I went to clean it and it was clogged with dust! IT WAS THE WORST AMOUNT OF MONEY EVER SPENT!!!!!!!!!!!!!!!!!!!:grr: :grr: :grr:

[maxfior]

Originally posted by Brauap
I ramed a creek and my quad started to sputter then die, do I looked in the air box, the outerwears was clogged with water so I had to take it off, then I looked up into the black thing.. I can't remember the name, and it was all wet and it took off the oil on my filter.. and around here I was riding then at the end of the day I went to clean it and it was clogged with dust! IT WAS THE WORST AMOUNT OF MONEY EVER SPENT!!!!!!!!!!!!!!!!!!!:grr: :grr: :grr:

Too bad about what happened. I've had no issues with mine, I don't run a K&N filter though... My outerwear has been fine. Maybe the water came in through the side of the filter, mine fits tightly on the lid, but it might be a good idea to get some RTV or some other type of sealer. If you are going to play swamp boss, you might want to get a stock lid, an open lid with a pre-filter is still going to allow water to come in. I hope you didn't suck in water... :(

Max

[Elite07trx]

could u put the aluminum on the underside of the lid, so you dont see it just the bolts?

[Speedy 400ex]

I dont see why not. you will just have to make it flat on the underside.

[maxfior]

Yeah, it should work, might take a little more messing around with, I belive there are plastic ribs on the bottom that may get in the way, but I'm sure you could figure something out...

Max

[mojavedude]

i made my own lid for a kfx400 because the quad didnt come with a lid at all. i made it out of 2 clipboards (masonite sp?) and used 2 layers of ac duct foam filter and a screen to make it look nice. i just wanted to keep big pieces out of my airbox.

id say make it out of beter material tho, some of the masonite broke off, it it still works.

http://i12.photobucket.com/albums/a244/mojavedude250/kfx/munkluie001.jpg
http://i12.photobucket.com/albums/a244/mojavedude250/kfx/munkluie002.jpg

[maxfior]

Originally posted by mojavedude
i made my own lid for a kfx400 because the quad didnt come with a lid at all. i made it out of 2 clipboards (masonite sp?) and used 2 layers of ac duct foam filter and a screen to make it look nice. i just wanted to keep big pieces out of my airbox.

id say make it out of beter material tho, some of the masonite broke off, it it still works.

http://i12.photobucket.com/albums/a244/mojavedude250/kfx/munkluie001.jpg
http://i12.photobucket.com/albums/a244/mojavedude250/kfx/munkluie002.jpg

That looks really good man! It's nice to be able to make performance mods like this... They really are quite simple if you just take your time. After a rejet I'm sure your quad woke up nicely! :)

M.

[Speedy 400ex]

it still bogs off idle even with the 42 pilot. so im confused in what i need to do to fix it. also the thing heats up really fast.

[maxfior]

Originally posted by Speedy 400ex
it still bogs off idle even with the 42 pilot. so im confused in what i need to do to fix it. also the thing heats up really fast.

• What is the needle position?
• What main do you have installed?
• Is filter clean and oiled properly?
• What did you set for fuel/air screw? 2 1/2 turns out to start?

The engine should heat up pretty quickly, esp. in the summer time; my engine gets HOT to the touch (middle part of the jug) within 1.5 minutes sometime less… Do you have a after market pipe installed? You won’t have to jet too much from stock if you have the OEM pipe on. Let me know.


EDIT: I see you have a slip on. #155 and #40 or #42 should work with your pipe. How is your plug? Does it run okay past idle? How is WOT?


Max

[Speedy 400ex]

I dont know about the needle position, where do i chainge that? i have a 155 main in there. it idles well but it bogs when i punch it but if i roll in to it I can get to WOT which feals good. i dident tuch the fuel air screw. Im going to go get a socket that fits today.

[maxfior]

Originally posted by Speedy 400ex
I dont know about the needle position, where do i chainge that? i have a 155 main in there. it idles well but it bogs when i punch it but if i roll in to it I can get to WOT which feals good. i dident tuch the fuel air screw. Im going to go get a socket that fits today.

Sounds like you have a pretty good attack plan. Check the plug and also check the fuel screw out. You'll have to pull the carb or move it to the side to get access to it. Turn it all the way in (tighten lightly) then back it out 2 and 1/2. After that, you can check the needle; it's at the top, where the slide is. You'll have to pull the top of the carb and get access to the needle. Then you can make sure it's in the middle (if memory serves there are 5 steps, so you'll want to be in the middle. I know my 2005 has a fixed needle. I'm pretty sure stock should be in the middle. I'd check your fuel air screw before you rip in the carb more as it might be your issue. WOT feels good, so that means that your main jet is good. If the fuel air screw does not help you might want to try a different pilot jet. Let me know what happens.

Max

[Speedy 400ex]

well i just took the plug out and from looking in my clymer the plug is carbon fouled and one of causes was a rich fuel mixture. Is this just a matter of changing the fuel air mix?

[Speedy 400ex]

ok well i got it now i think. thanks for the help

[maxfior]

It looks like you are on the right track... dark plug could be air/fuel I would check the screw first, try 2 1/2 turns out. I believe that's what I'm running on my 05. Jetting sure can be a pain in the ares!

Max

[08Outlaw]

Want to thank Max for a great tip on the airbox!! I too love to save some $ and make my own parts! Take a look at the results on my 08 Outlaw 525s- and the resulting performance is awesome- the beast can finally breathe!!!

[08Outlaw]

more.....

[08Outlaw]

yet another....

[maxfior]

Originally posted by 08Outlaw
more.....

THAT looks REALLY nice man! Good work! It is a good feeling when you can make some stuff your self and save a few bones for other items, plus, stabbing the throttle and feeling the extra gained power is nice too!!! :D

M.

[maxfior]

Originally posted by 08Outlaw
yet another....

Looks really good! I'm sure you've noticed a pretty decent gain in performance... It really amazed me how much more power I got out of this simple and cheap mod!

M.

[08Outlaw]

Absolutely- I first installed the FMF exhaust, and was impressed with that gain, I then modified the air box and got just as significant gain, but started to sputter @ wot. I couldn't believe that I was able to gain as much low and mid range umpf with a $20 mod versus a $500 mod. Now that I have completed those, all that's left is to re-jet and solve that wot sputter.
Again thanks to you for such an awesome tip- one of the Outlaw's few shortcomings was the airbox design due to cramped space from rear suspension and this helps tremendously!
And I will save even more $ in the long run cuz I will never have to replace the front tires!!!! LOL

[maxfior]

Originally posted by 08Outlaw
Absolutely- I first installed the FMF exhaust, and was impressed with that gain, I then modified the air box and got just as significant gain, but started to sputter @ wot. I couldn't believe that I was able to gain as much low and mid range umpf with a $20 mod versus a $500 mod. Now that I have completed those, all that's left is to re-jet and solve that wot sputter.
Again thanks to you for such an awesome tip- one of the Outlaw's few shortcomings was the airbox design due to cramped space from rear suspension and this helps tremendously!
And I will save even more $ in the long run cuz I will never have to replace the front tires!!!! LOL

LOL @ the never have to replace the front tires! Yeah, bump your jets a few sizes and I'm sure you'll be good to go!

M.

[josh burden]

h

[08Outlaw]

Finally got the carb jetted how I wanted it. Went out riding this past weekend for the first chance to really open her up since the airbox and carb jetting. Wow, was I impressed. Great powerband improvement throughout- was on a 300' dirt dragstrip and went up against and beat the following: 700 Raptor with HMF pipe, 07 Outlaw, CanAm 800 Renegade, Honda CRF450x bike, and a new Yamaha YFZ450 with ice cube big bore kit.
Man, am I happy now!!

[maxfior]

Originally posted by 08Outlaw
Finally got the carb jetted how I wanted it. Went out riding this past weekend for the first chance to really open her up since the airbox and carb jetting. Wow, was I impressed. Great powerband improvement throughout- was on a 300' dirt dragstrip and went up against and beat the following: 700 Raptor with HMF pipe, 07 Outlaw, CanAm 800 Renegade, Honda CRF450x bike, and a new Yamaha YFZ450 with ice cube big bore kit.
Man, am I happy now!!

Glad to hear it man! letting your baby breath makes a BIG difference!

[Hunley]

Thats a pretty good looking lid.. Thinking this could be my next project also

[maxfior]

Originally posted by Hunley
Thats a pretty good looking lid.. Thinking this could be my next project also

What's holding you back! Go for it! :D Your quad will be happy that you did it. After you get all the materials, and, assuming that you have the tools, this job should not take more then 2 hours tops. Good luck!

Max

[IRISH-RACER-14]

where can i get one of those pre filter thingys???

[maxfior]

Originally posted by kdigginz
where can i get one of those pre filter thingys???

http://www.ehsracing.com/products/air_box_covers.htm

Talk to them and just tell 'em you want the filter, nothing else. Then you can make the bracket for your air box, and you're good to go!

Max

[07ltz400]

anyone running one of these on a ltz400. im really intrested in doing this. looks simple and seems to have very nice end results. i'll just wait until my pipe and jet kit come in before i begin my work

[ballerchaos]

wow looks awsome, i am going to have to try this on my 400ex once i save up the money to buy my exhuast so i only have to jet and tune the carb once. Looks easy, and a nice piece ove diamond plate and some stainless steel hardware, will make it sweet. Just a question, are you useing a gasket of any type.

[ballerchaos]

also, what about cutting out other areas of the airbox and doing this same idea? i was looking at mine and the left side looks like it has a flat decent size surface, you think there would be to much air or any issues if i attempted ot do this??

[08Outlaw]

I did not use any gasket, just a little RTV sealant between both the pre-filter and box surface and bracket and pre-filter. As far as other mounting surfaces, I would just make sure that it's in a location least likely to get alot of water. Since the Outlaw already had a small intake opening on top of the box, that is naturally the best place for the cutout

[ballerchaos]

i got yah, i already bought the diamond plate to make the mod, waiting to save up the money for my exhuast, so i only have to tune my baby once. ill post pics ASAP

[Thumpin440ex]

I just ordered the k&N cover fri, am going to be doing this. I will post pics up when I am finished.. Def better then buying there kit for 50+ buks, well if you can do it yourself... Nice write up


John

[j0sh]

Thanks for this! I have a buddy at a body shop that is cutting me a flat piece of plastic from a bumper. I will cut it to fit and either bolt it or rivet it on.

[j0sh]

quick shot of mine. just finished

http://i27.photobucket.com/albums/c169/element_dc5/400ex/photo.jpg

[08Outlaw]

Nice job, Josh- looks great

[j0sh]

could have been a little better, but I'm happy. The filter opening was a little different shape than the template. That's why the inside looks like the cut is off.