How to Build An EPIC Diffuser For $100! (Full Parts List Included)

[@loganalbritton1441]

buying home depot stocks now before miata nation descends on the aisles

[@ianfairbanks1318]

LMFAO. truth.

[@byGodspeed]

STONKS

[@juanestrada_]

Not only miata dad helps us make our miatas fast but he also helps us get that street cred

[@FlyingTofu]

I cant wait to make this diffuser for my gaming chair

[@PANTYEATR1]

great video Greg, there's a few things i will add tho...instead of ABS plastic, I'll be going with 3/8" thick high density polyethylene. this stuff can bend in a complete "V" and not spider crack. it's UV resistant and has memory. it will always go back to its original shape should you hit something or bend it...i would use washers on your oval holes, it will help with clamping force. lastly, when i build mine, I'll take it back apart to have each piece hydro dipped in carbon fiber. I'll be using some of these techniques when i build a diffuser and splitter for my mustang 💪

[@kwbalance108]

Good to know man, thanks for the heads up!

[@itz-amemario426]

Actually ABS is way better for that purpose than PE.

[@PANTYEATR1]

@@itz-amemario426 oh wow really? I'm not an expert, but i liked the properties of PE. can you explain why it's not good for street cars and race cars? thanks

[@itz-amemario426]

@@PANTYEATR1 It isn't bad, It just wouldn't be my first choice. ABS is stiffer and tougher, it has decent heat resistance and you can easily glue and weld it. You can form ABS using heat. PE is softer, it deforms permanently. PE is good for stuff like paddings, bushings, gaskets, or non stick surfaces, so food processing or linings. That being said I wouldn't bother with either and go straight to aluminium or alumalite.

[@PANTYEATR1]

@@itz-amemario426 thanks for your reply. i choose the PE cause it has impact resistance and it returns to the original form if a parking curb or speed bump was hit. in cold/hot weather temps, i don't know if ABS could handle those issues without chipping. since this will be on a street car, i wanted something that could handle the imperfect habitat of the streets. if it was a race car only, aluminum or alumalite would be an option. i don't recall the thickness of the ABS used in the video, but I'll be using 3/8" thick PE. I'll run the information mentioned through the plastic store expert and see what they say. if ABS is good enough, I'll buy that. i know it's definitely cheaper.

[@ch_chone]

Nerdy comment about using 1 fin for tracing all other fins vs tracing each fin off of its predecessor; that's a brilliant example of error propagation! 1% error on tracing and cutting each fin successively = 1.01*7 = 1.07, or 7% error by the time you've cut out fin #8. Compare that with 1% error if you were to trace fins 2-8 directly from fin #1. Pretty neat!

[@haydentakara4369]

That’s why you use the same fin for each tracing Edit: well actually you literally just said that so lmao

[@yo_its_devo]

It's like the fabricators version of the telephone game lol

[@user-sd1ry6jw3u]

That "steel" you have there certainly has the thickest aluminization I've ever seen...

[@filibertodelacruz727]

Whenever I have a bad day I watch the Car Passion Channel... Then Happiness

[@carlosarmero594]

First off thank you for taking the time from your everyday life and dropping all the legit content you put out. I admire your passion for the MX5 , much respect for what you do.

[@InfiniteCheeseCrates]

@11:32 The word you are looking for is aluminum flat bar

[@josuedavid6584]

subscriber since the old 1.6, i'm amazed by how much this mx5 has evolved, inspired me to get my own and work on it, miata dad is the f goat.

[@daleabono3616]

Completely off topic: from the looks of the back tires, you are having a lot of fun with the car. Yay!

[@38tech]

He did this vid before going to the track. His track video had the diffuser on the car already.

[@daleabono3616]

Be that as it may, its a "getinsitdownshutupholdon" kinda car that makes it so awesome.

[@yo_its_devo]

Tip: run a finger along the length of the fin to even out the bead of silicone. Best way to get a nice even finish. Learned that from home renovations. I looked for a good tool for a bit the first time I did caulking and then I saw a couple videos and realized the best tool was attached to my body already :)

[@evannoriega-thomas371]

Great job Greg! Adds an amazing look. Me personally, if I ever do this, I would give the hardware a quick spray of black paint because I don’t like the “studded” look the hardware gives being silver. But hey, none the less, this is an AWESOME template that people are going to be able to use to make their own, perfect to them, diffuser. Thanks for bringing the knowledge and showcasing it for us.

[@Criam]

Saaaaame

[@revlimiternet]

Beautiful work sir! Such diffuse. Very airflow. Wow.

[@whitebear96]

one thing I would change immediately in my build are the screws. first off black screws (optional), but most importantly I would use the sleeved type of screw/nut combo with flat head that screw into each other and you end up with two flatheads on both sides with nothing sticking out. Rivets would do the same job, but then its harder to adjust or pull apart/replace damaged fin. other than that sweet vid, thanks :)

[@berniehayhurst1811]

They are called "Rivnuts" in aviation.

[@whitebear96]

@@berniehayhurst1811 oh, didnt mean rivnuts, did a quick search for those im thinking of and funnily enough, they are called sex bolts or chicago screws :)

[@soggysweatsocks]

This feels like an architecture project, fun stuff greg, great video!

[@FDB77]

Finally the diffuser vid!

[@captianknuckles]

Is that parking lot at the end the same one from the “stolen” hardtop video?

[@ThatoneFRC]

Just want to say google brought me here and Im super happy it did. Thank you!

[@spoolin2bars]

Looks a lot like the one I made for my time trial/ time attack turbo ‘95 Miata back in 2010. I used aluminum. Made a template out of cardboard. Used the same mounting points even. I made the same rear L shaped mount but made it shorter and bolted straight to the same bolts holding the tow hooks. Then I used a small piece of “all thread” which is just a rod that with threads end to end. I think it was 5/16”. Then used nuts and washers to hold it to the L bracket which allows me to adjust the height. Using aluminum allowed me to just have the 2 chassis brace points on the forward edge, and the 2 rear points and it was solid as hell and I could install and remove it in a couple minutes without jacking up the car. Also used way less hardware to hold on the strakes with the better materiel. Not to mention aluminum doesn’t melt from your exhaust.

[@gunnarnordstrom2515]

Tip, about the silicon instead of using the screwdriver. Take some soap water dip your finger and just smooth it out, will not stick to the skin and looks better.

[@TC_10000]

Why not use shorter screws so they don’t stick out sideways?

[@mixalisstathis274]

Rivets!

[@winguard96]

@@mixalisstathis274 my thoughts exactly!

[@VintageTechRepairs]

@@winguard96 if it gets damaged bolts make it easier to fix ;) but saying that i do like the sound of Rivets

[@zeppie2002]

Nice project! I agree that some rough edges and no smooth silicone kit gives it a nice racing-touch. A lot of work, but: Well done. 😮

[@zokusharuuku1091]

Ok I get it I don’t have any friends thank you for reminding me. Also I recommend aluminum composite, it’s more stiff and rigid and holds bends and won’t flex plus you can make it thinner for less weight. My diffuser in 1/8 inch thick.

[@machtmonk]

Would love a vid with some A/B testing to see if this thing works. I guess there is no easy way to see if it prdouces some downforce, but maybe some 100 - 200 kph pulls to see if drag is reduced.

[@777MAV]

Great DIY! I strongly advise you to add some kind of rigid brace joining two rear mounting points and connect central section of the diffuser to that brace. Aluminium angle or square tube is first thing that comes in mind for this. Because it seems that it might not hold for too long if it really works and will be able produce any significant downforce. Ant it looks like it really can! ;) Shape of the diffuser definitely provides some rigidity, but abs+exhaust heat+force applied will probably bent it out of shape over time. Ideally you can use fins mounting bolts to hook central section to the brace.

[@johnnycashh7148]

Wrapping your muffler with manifold tape would have looked bad ass too. 🔥🔥🔥

[@mrmidnight32]

Can’t wait to see every lowered Miata with one of these now 😂

[@andrewf8486]

Looks good, I have thought about doing this but I am too afraid to do a bumper cut. Looking at the process you guys used I think you could have made your life a little easier if you would have used a heat gun to relax the plastic.

[@TheEverWickedWonder]

Use a woodburning tool and abs zip tues to platicweld it instead. Do it outside or with good ventilation.

[@christianzinn7636]

It looks OUTSTANDING!!!!!!!!!!!!!!!! I'm Not a fan of cut bumpers, so this finishes your car Very Nicely. Great work!!! It would be interesting to know how it changes your seat of the paints feel when driving hard. Perhaps a LRB Speed type of front under tray for the front???

[@thebrowntown1337]

Saving dis for summer time

[@yevier7898]

That transmission getting caught on the intro tho!! 😅 all jokes aside, good job guys! 👍🏼

[@gsh3159]

Just a thought but I'd be swapping the bolts and nuts holding the fins for rivets. Some black ones would be much less visible

[@goretro77hobbies]

I was waiting for this vid! Hats off and respect to the Miata guys dong this rear DIY diffuser. I'm sure its functional and looks tasteful in my eyes.

[@trix4rix]

Huge fan of these DIY's, keep them coming!

[@hoonata_209]

Pretty solid. Came out nice. Going to attempt to make one for my 17 Hyundai Sonata Sport 2.0T

[@scmiata99]

Brother I know its an older vid, but man that shit is popping!!!! maximum street cred!!!!

[@l3lvck0ut]

greg it's called flatbar! also, use simplegreen and spray it onto your caulk bead then run your finger across it. i promise it'll look a lot better than the screwdriver method lol

[@marcjoseph8300]

The exterior fins toward the engine should be closer to the center. The one center fin should be straight. So to create a vacuum effect or sucking effect.

[@rac3kar]

Just what we miata people needed! Thanks dad

[@iamadmin240]

Greg.. you the man ❤️

[@imboredadr]

You can buy door edge guard on Amazon that looks a little better and grab on way more effectively. Not only does it fit well around the bumper cut but it also fits around the rear lip of the hardtop and cleans up the look of it a lot.

[@alexjohn5086]

Pool liner edger works better, but only comes in white....;-(

[@pablocrvzz2985]

Spray the nuts and bolts black and its perfect👍🏾🔥

[@jimd1617]

Great job, dad!!!

[@afhostie]

Are you going to have to put in a full under-tray to keep air from going between the car and the diffuser ?

[@SmukKully]

It’s defo getting done... was gonna go the omg miata way but this is much more home brew.. and not as time and money consuming 👌🏼👌🏼💪🏽 for when I fuck it up on track

[@supercarmio]

dude, that came out awesome! really nice work & super easy to follow.

[@gedas3419]

I think Flat undertray would make this diffuser way more efficient, also entire car way less aerodynam... I mean less aerodragic. Like flat under engine tray, following the contours of the lip of the bumper, following with entire trans, driveshaft, diff cover plate should increase the flow of air around(or atleast under) the car.

[@fatalgaming6068]

cant really do that since everything is air cooled. you would need a cooler for the trans, diff, engine or just make ducts under the car that funnel air to the fins on the oilpan, trans and differential

[@Gekko12482]

Like FatalGaming said, I'm not sure if that hurts the cooling too much, but additionally this diffuser is wayyyy too steep to be effective as an aerodynamic device. Diffusers are usually pretting long and pretty flat because the ariflow needs to stay attached in order for the diffuser to have the necessary expanding effect on the underbody airflow

[@b00sted_mx59]

I didnt even think about the edge trim on the bumper cut ill have to try it out. Also i love that tire setup, looks super good from the back. I cant find many places to buy the Nanking tires unfortunately.

[@NippyMoto]

Damn those AR1s turned into full slicks real quick haha

[@BeckersGarage]

I have a few of these to make now!! One for the Miata, one for the Vette, and maybe even one for the daily lol

[@filibertodelacruz727]

It ain't perfect but it looks so good! ❤

[@ttinnovations3310]

looks great, but the top sheet should be made of a sheet of aluminum to avoid melting on catching fire =P

[@castaway__7235]

ZERO DISLIKES!!!! GREG OUT HERE POSTING THAT GOOD SHIT

[@jrivera2240]

Now I got to make one out of aluminum and flush rivets

[@maccarioandrea]

You should do a test with some wool ropes and tape + GoPro to see if the flow is attached. What's the weight? Do you feel any difference? Looks sick ;)

[@Obeisance01]

will you perform a string test to see how well airflow follows under the diffuser? i mean, tape some string or yarn to the diffuser on the rear part of the strakes and plane, point a gopro at the string (keeping the camera out of the airflow) and check to see that the strings are pulled straight back in laminar flow instead of being pulled randomly in turbulence. this can show if the upward sweeping angle of the diffuser is too steep.. in that case the airflow will be stall-like and turbulent.

[@brokentougers8252]

Welp, don't own a miata yet , but sure this is in the bucket list :D

[@killer_bro_empireitsme3613]

Been waiting for this video for a while now thanks Greg

[@waynethegiant]

Maybe you could try replacing the nuts and bolts with rivets 🤔 would look more slick. Dunno if you'll find anything for 5mm+ thick material though

[@reneneron2971]

Nice work. Consider attaching the fins with rivets instead. Rivets sit flush, are cheaper, lighter, faster to install. and will not come loose over time.

[@AlexPerrucci]

Yeah this looks badass! The rear of your car is sooo mean looking with this and the meaty tires haha. Great vid! Really want to try this now for my car.

[@flipflop7577]

Yes go for it! Your NB is mint👌

[@jake10386]

Definitely trying this on my 95M!

[@38tech]

That is so tight!!!! Love it.

[@DOM-cc]

this is awesome, definedly will build one for my civic

[@philjones5728]

Looks great. Pro tip: wet your index finger and run it over the silicone bead to smooth it out. (P.s. when did you get those slicks!!!)

[@chancealger4740]

This is so cool! Not to mention an amazing idea!

[@gangstarboy702]

Bro, watching the first bit of the video sounds like Im watching a video back in like 2008 😂

[@TheCarPassionChannel]

Yeah since I planned to do pretty much full voiceover I didn't bring any mic setup with me lol. Combine that with a small room where all 6 surfaces are hard and you get meme level echos

[@KingandTitanRacing]

Awesome video guys, very helpful and informative. Diffuser will be one of our next projects on our MRS and this os exactly how we were thinking of doing it.

[@ajsaracina8380]

Looks sweet! But I probably would've used rivets for a cleaner look, and also save money on all that hardware.

[@jeanboy9108]

looks good, might have to try to do this on my NB

[@JonahAberle]

Looking forward to the next ECU vid

[@crewjones]

Go to Marshall's hardware for all you nuts and bolts, they are in Miramar. They have a crazy selection and great prices and no I don't work there.

[@kevinroberts9096]

Looks AWESOME 😎

[@abcsteve]

Super rad, good job man!

[@timocallaghan4408]

the 'unangled angle iron' is called flat bar stock. aluminium bar stock is cheap and easy to work with.

[@drpiv]

Looks so good. Awesome.

[@kingjay3301]

I need some like this for my ek coupe

[@brokeboycustom7655]

I love this so much. Can’t wait to try it out on my car

[@coreygrace4856]

Why not plastic weld? Great job it does look rad

[@dansattler882]

Holy cow! Your car has a nice caboose.

[@michaelbull6906]

You should paint the nuts and bolts all black so they blend in more

[@ir4kk]

I can't believe it took ya this long for the edge trim lol it's the best

[@jasonc2948]

Looks amazing man! Nice work.

[@markstorer7204]

Great job Greg ✌

[@slicktop2jz855]

So sick man well done

[@juniorcruz960]

Badass build guys where can I get the plastic to make ine of my own.?.

[@austinmorris8490]

Ima have to try this seems pretty simple

[@FiveFiveGarage]

Another project to add to the list! What is the butt dyno telling you about its effectiveness and do you think you will be able to see a difference via Dragy runs?

[@Kthreeyou]

Damn that guy is tall! Nice NB!

[@UnluckyxiiiNV]

Great video!!! I looks amazing

[@danjones5655]

So sick when you gonna do the front splitter also

[@elliotcurry2284]

Finding this 2 years later, how'd it hold up? Long term review?

[@muaddib2678]

Im seeing a Diffuser in my Miata's future, that is once Home Depot replenishes stock Miata Nation must have descended on my local store :D

[@lander917]

Awesome!You are the best.

[@Gnasherism]

Fully sick

[@RobWhittlestone]

Now the Miata will drive on the ceiling! Greg, show us the video!

[@CCTreason]

Greg spray da boltz! Looks sick tho, those fat tyres make it look nutty

[@PropKnucklesFPV]

Do a full flat floor now 😁😁😁