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.

[@InfiniteCheeseCrates]

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

[@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

[@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.

[@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

[@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.

[@filibertodelacruz727]

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

[@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 :)

[@user-sd1ry6jw3u]

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

[@captianknuckles]

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

[@soggysweatsocks]

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

[@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

[@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 :)

[@mtbiata]

Finally the diffuser vid!

[@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.

[@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.

[@revlimiternet]

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

[@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.

[@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.

[@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.

[@afhostie]

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

[@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.

[@ThatoneFRC]

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

[@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.

[@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???

[@TheEverWickedWonder]

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

[@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

[@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.

[@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 ;)

[@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👌

[@ClownPoot]

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

[@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....;-(

[@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.

[@supercarmio]

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

[@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.

[@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.

[@killer_bro_empireitsme3613]

Been waiting for this video for a while now thanks Greg

[@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

[@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!!!)

[@thebrowntown1337]

Saving dis for summer time

[@coreygrace4856]

Why not plastic weld? Great job it does look rad

[@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

[@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.

[@chancealger4740]

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

[@mrmidnight32]

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

[@llmexicanlm7885]

are the bolts more better and more secure than something like plastic welding? I was thinking that potential money could be saved using a plastic welder.

[@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

[@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.

[@abcsteve]

Super rad, good job man!

[@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

[@38tech]

That is so tight!!!! Love it.

[@iamadmin240]

Greg.. you the man ❤️

[@drpiv]

Looks so good. Awesome.

[@rac3kar]

Just what we miata people needed! Thanks dad

[@chadobrien3352]

Just curious why you didn't rivet the vanes to the support brackets? Why nutless bolts?

[@frekensuselesschannel1297]

What do you think about making full aero flat bottom and front splitter? Also DIY off course. I think it would be awesome! I plan to make one for my zzw30 mr2 spyder sometime.

[@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

[@slicktop2jz855]

So sick man well done

[@kevinroberts9096]

Looks AWESOME 😎

[@scmiata99]

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

[@Zoomafou]

Do you think you could use some sort of epoxy to connect the fins to the baseplate instead of a bunch of L brackets?

[@jasonc2948]

Looks amazing man! Nice work.

[@CoryBan777]

So what are your thoughts on skipping the heat deflecting sheets or mounted embossed aluminum heat deflecting sheets in lieu of simply covering everything axle back with ceramic fiber wrap? I understand that wrapping is rarely a good option for a street vehicle, but if the fab'd diffuser shields the muffler so much that it requires heat deflection to avoid damage, should it not also shield the muffler from the water and road grime coming from the other side of the diffuser as well, thus making the main caveat of the wrap (fluid retention and consequent rust) no longer a caveat?

[@claudiowarrens]

why dont you add some of that autozone trim to the edge of your hardtop, will hide the chips, ive been meaning to do that to mine aswell.

[@pablocrvzz2985]

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

[@elliotcurry2284]

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

[@jeanboy9108]

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

[@juniorcruz960]

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

[@ajsaracina8380]

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

[@markstorer7204]

Great job Greg ✌

[@jake10386]

Definitely trying this on my 95M!

[@brokeboycustom]

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

[@jimd1617]

Great job, dad!!!

[@johnnycashh7148]

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

[@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.

[@Humco_ND2]

Thank you guys so much for this, this will be my next mod for sure. Hopefully we can see a front splitter mod too. Quality KZbin channel, highly underated.

[@lander917]

Awesome!You are the best.

[@mmarkzx]

that is neat! thanks for the video!

[@lucca9540]

Hi CarPassion. Just want to start off by saying thank you all the informative videos you put out for us. I have a question about upgrading my miata. In regards to the transmission for boosting, do I need to make any changes? I have a 6 speed from a 03 miata. Should I swap it in with a new clutch? I dont plan on making more than 5-8psi boost.

[@TheCarPassionChannel]

What's up man The 6-speed is plenty safe for more power than the stock engine will ever handle, so no worries there. You will need an upgraded clutch somewhere in the 150-180wtq range. You might be able to get away with 5-8psi on a stock clutch depending on your specific turbo setup.

[@lucca9540]

@@TheCarPassionChannel I still have the 5 speed in my 1990 miata. I have to swap on the 6 speed. I plan on buying the Flying Miata 1.6 turbo kit for maximum reliability. I like to play it safe with low boost so I'd like to go 5-8psi. I'm just wondering if the 6 speed swap/and or clutch swap is necessary :) Hopefully since I want low boost, paired with the Flyin miata turbo being a ball bearing turbo, I can have stututu noises with no BOV haha

[@TheCarPassionChannel]

@@lucca9540 Your 5-speed will also handle about the same amount of power as the stock engine (they usually break around 240-260wtq). At 5-8psi on an FM turbo kit with a GT2560R and pump gas you should expect around 140-175whp and about the same torque. at 8psi you'll probably be at the limit of the stock clutch.

[@DOM-cc]

this is awesome, definedly will build one for my civic

[@kylehasfun3114]

Project turned out really good man! Was there any science behind the size/shape/position/mounting at all? Or just make it cool looking and secure?

[@yevier7898]

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

[@ttinnovations3310]

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

[@reborngarage1]

Yeahhh fresh content 😍😍😍

[@ninokri]

Cool!! How much does it weight?

[@Austin_s4]

Ima have to try this seems pretty simple

[@cooljoe226]

Awesome video! Do you think your exhaust would melt part of the splitter cause its made of ABS?

[@TurbineResearch]

how many miles do you have on your AR1 tires ?

[@timocallaghan4408]

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

[@danjones5655]

So sick when you gonna do the front splitter also

[@UnluckyxiiiNV]

Great video!!! I looks amazing

[@ghostpunkkilla]

Yiiiiisssssssssss! Been waiting for this :0

[@ir4kk]

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

[@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?

[@NippyMoto]

Damn those AR1s turned into full slicks real quick haha