Metalmaker's build thread begins

[metalmaker12]

I am looking over my options for the aero material. Alumiite looks pretty neat and is prob what myself and others will choose as a easy working, lite and very strong/durable material.

[Santiago]

Scargo, that was 2001...they've really upped the ante these days with diffuser technology. Last I heard they were getting upwards of 40% of the total downforce from their diffusers.

I think what's important to note is that the diffuser isn't actually "creating" downforce in the same way a wing does. They act more as ways to get something out of other elements (primarily the underbody ahead of it, but they are also interacting with the rear wing on something shaped like an F1 body). So I think it's better to say, "we'd lose 25% of the downforce we can make when we take the diffuser off the car and test." You can tailor where the downforce is felt on the car by adjusting where the lowest pressure region will be ahead of it (i.e. just forward of where the diffuser begins).

I'll be the first to say I don't fully know much about how a diffuser works - or better, what I do know raises many questions I've yet found answers to in studying them. These days I think of them as analogous to the bottom part of a carburetor venturi (just think of it in side view with the body sliced in half). Most of us know that system pretty well, and we get the basic gist of it. The diffuser is where the air that had previously been drawn into a narrow choke (and thus created so much vacuum/low pressure) is allowed to expand. In the expansion itself you don't get tons of negative pressure, what you get is actually a gradual increase in overall pressure. So you would think it would be doing a disservice to the task of producing downforce, until you realize that what you're really doing is allowing the air to expand into a larger area. The more expansion you get in the actual diffuser area, the more low pressure you'll have at the throat of the diffuser as you're able to draw more and more air through it. Back to our carb venturi, the parallel would be something like having a bigger cubic inch engine, with bigger pistons displacing more area to draw in more air through that same venturi (which would require faster & ever lower pressure air). The diffuser is kind of like your piston retreating into the bore, and like them bigger isn't always better (bigger is better only when you can get away with it).

Here's the rub, you only get this if you get more expansion you can make use of. In an engine, you have a moving physical part tasked with the job of creating that expansion in virtue of its movement while sealed to the wall. With a diffuser, you have a fixed part moving through air. But just as with your piston, if the seal on the bore is shot, you're not going to get that expansion (I find it helpful to think of an extreme case: what would happen to your carb signal if you had a 302 slug being drawn into a BBF bore? - you get diddly at the carb). Because there's no moving part w/in a part with a diffuser, we need to address how to get a seal that will effectively move air through it as it expands the area for the air to go. To get "a seal" on our diffuser, we need to maintain laminar flow through it (most of the "draw" of our "inverted/fixed piston" is through the low pressure area along the walls of the diffuser -that, I think, is where you find the analogy of the piston seal/tolerance, etc.). You can't just throw on the largest most-monster opening out back and expect to get much action; the air flow will delaminate and you get turbulent junk mucking up the scenery. So you have to control the angle, size, element area, and a host of other factors I know little of to get the best flow through there. There are some rules of thumb to go by, so folks like us can make a stab at it, but we should just contend with the fact that we're either making an aesthetic piece or committing to iterative testing.

And with that, I both horrify true aerodynamicists and expose the depths of my ignorance. Still, that "piston analogy" is what is making sense to me these days. If others can chime in to clarify or correct me, please help.

Best,
-john

[shinn497]

I was under the impression that diffusers are so effective that they have to be regulated in motorsport. as I understand, they create a low pressure zone through adiabatic expansion, which can be a very powerful effect.

Then again I'm a physicst not an aerodynamicist...which is a highly specialized physicst.

[FFR-ADV]

Center exit on its way!

I only did a 30 minute fit up, gotta tweak it more tomorrow for clearances, tack in place and tig it up. I am glad i stuck to my guns. If I do go down the road to creating this product I will have the pipes bent and use a stainless flange.
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That sure would be a great product! Nice work!

Looking forward to seeing the center exhaust with the CF Rear Diffuser and 818R style cutouts!

[Blitzkrieg]

What is the 0-60 looking like?

[metalmaker12]

From my go-pro from start to finish (0-60) it is under 4 seconds. I would say the car wih my setup ( wrx gearing, 8,600 redline and cusco 1.5 lsd, and decent grip) I should be able to get a low to mid 3 sec 0-60. My power to the wheels will be around 300-315 once tuned.

[Frank818]

Finally some performance numbers on the 818. lolll

That's perfect, cuz I target low 3, now I know I can probably reach it. Assuming I have enough traction, that will be THE biggest wall to jump over.

The thing is with this car is the top speed limitation, due to the gearing (even me with the VW 02A gearing). But anyway, that won't be a problem for me as I don't drive that fast on the roads and probably won't go on a track often.

[Scargo]

Was that with 255x35x18 rears you had talked about? What tires specifically? How much wheelspin during the 0-60?
Is that box one that has 3.90 gears?

[metalmaker12]

Yokohama s drives,good grip with 20psi 255/35/r18 rears,low- moderate wheel spin, temperature dependent. 60 degrees plus recommended.
The box is a 02 wrx:
Manual transmission gear ratios:
1st - 3.454
2nd - 1.947
3rd - 1.366
4th - 0.972
5th - 0.738
reverse - 3.333
final drive ratio - 3.90

[bompus]

Random question.. The Cusco 1.5 LSD.. can you install it yourself? Does it require any special tools, precision measurements, expertise? I'm planning the same LSD for my build and was curious if it was something I am capable of doing or if I need to have a shop do it.

[metalmaker12]

Fair question, have you ever rebuilt any transmission? If so what kind, if I remember right there might be a few subie specific tranny tools but, other tools can take the place of them. They are not super easy to get just right, so if your not experienced get a tranny guy to install it. The whole tranny needs to be taken apart for this upgrade.

[bompus]

I have not rebuilt any transmission. Thinking more about it.. and with your advice, I'll find a reputable local shop that has experience working on these and hopefully have some peace of mind. Thanks for the info!

[STiPWRD]

I recently rebuilt my 02 wrx trans using this link as a guide:

http://www.ultimatesubaru.org/forum/...l-replacement/

I took this chance to replace all the bearings on the input shaft as well as the input shaft seal, two trans axel seals and the selector seal. Once you crack the two case halves open, the input shaft, lower main shaft, and open diff (which you'd replace with an LSD) lift right out. I brought my iput shaft to a local subaru performance shop (Andrewtech) to replace my bearings - this cost $200. 8 years ago, this same shop installed my PPG gears. Then I put everything back together. My trans had 150k miles on it.

[RM1SepEx]

My local Subaru shop installed my Quaife and checked everything, replace output bearings and seals for low$ only 2 hrs or so labor with the transaxle out of the car

[Scargo]

It's been years, but I've rebuilt trannys and diffs in my garage. Mostly, you need a dial indicator to set preload. I would not recommend tackling it if say, you have never successfully been into an engine or aren't comfortable working on something with a lot of pieces. A plus is if you like doing mechanical puzzles. Technically, it's more challenging, but it's not much worse than a lawnmower engine overhaul.

[metros]

Love your exhaust work. I'm thinking of doing a center exit exhaust in the mesh above the trans. That would mean there would be very little bends to the exhaust system as a whole. The 'downpipe' would be more of a straight pipe with possibly a very slight downward slope.

These are just thoughts as I don't have a kit in front of me to look at for spacing. But that would help keep heat off the transmission/fluid as well because the heat would be above it.

[metalmaker12]

Anything is possable. Your idea is another idea I am plaining. I am putting a v band in so I can make more ideas that myself and others might want. I will post some more when I get to cutting and welding the v band in. Come to find out the ri dmv wants me to at least add an exhaust to lesson the sound a tad, so I am going to just make a section v band on that dumps to the ground for now, and than put the center exit back on later.

[metalmaker12]

Trying to get plates in say a month

[metalmaker12]

Flap wheel 60 grit sand/grind aluminum, epoxy primed and rolled on herculiner bedlinerphoto 2-2.JPGphoto 4-2.JPGphoto 5-1.JPG photo 1-1.JPG

new 330mm momo wheel and hub. I modded hub to work with clock spring and return blinkers. its a lot smaller than the oem momo
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The two different 818 exhaust hot off the bench
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Some final carpet work on firewall
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[Erik W. Treves]

looking good! I painted my radiator for silver and I regret it because it allows the front triangle bracing (black) to contrast against the silver...Black will make it disappear! I WILL be spraying mine black!

[wallace18]

Looking good.

[Frank818]

I guess I missed something, what are those fins doing exactly on the floor panel in front of the rad? Getting water out in the rain?

[AZPete]

Nice work. It's helpful to see the future since you are ahead of me. I've slowed down on the 818 build because my business is hoppin' now.
No sway bar? Coolant reservoir in the front?

[metalmaker12]

No sway bar just yet, want to see which mm I will use if need be.I put in two coolant overflow tanks, one in front an rear.

[metalmaker12]

I guess I missed something, what are those fins doing exactly on the floor panel in front of the rad? Getting water out in the rain?

Lol, yeah most likely, FFR cut them out on my aluminum so I went with it.

[RM1SepEx]

the manual says that they cut them in in case you needed to open them up to bring in more cooling air

I also put an overflow front and rear...

[Frank818]

Oh, so it comes pre-cut but not bent, ok, nice. They should do that on the rear belly panel too.

But are those fins really effective? I mean wouldn't they be more efficient if the bent would be upwards instead of downwards? The air would move upwards following the fins and into the rad. At least that's what I think, maybe I'm wrong. Just small details that may not do any difference on the road anyway.

[metalmaker12]

Oh, so it comes pre-cut but not bent, ok, nice. They should do that on the rear belly panel too.

But are those fins really effective? I mean wouldn't they be more efficient if the bent would be upwards instead of downwards? The air would move upwards following the fins and into the rad. At least that's what I think, maybe I'm wrong. Just small details that may not do any difference on the road anyway.

I am assuming it is to create airflow through the front cover to the ground to reduce turbulance in front of radiator

[Frank818]

Not a bad explanation, that might be true. Anyway I guess if FFR says to bend them downwards it's cuz there is a valid reason for that.

[Scargo]

It's going to suck... (air out). Seems it takes the air that feeds the radiator and deposits it under the car to disturb the flow and ruin any downforce under the car. I'd say it's wrong-headed.

[metalmaker12]

I just installed it the way I felt it was intended, and actually the front splitter is below this piece of aluminum so it does serve the purpose I mentioned. The splitter would create down force below itself and the aluminum duct would suck turbinate air in front of the radiator out above the splitter. Theirs a gap if you look at completed cars

[RM1SepEx]

I bought the front splitter fro FFR, when you use it, you don't use the aluminum panel...

[metalmaker12]

You don't need to, but the way it mounts would seem you could use both. When or if I get one I will see the setup, but to me at this point it is not important enough to keep talking about, since it is very easy to change out if need be etc.

[metalmaker12]

It sounds great, more too come low on memory, gotta delete a bunch of stuff, busy with getting my second child's room ready.

http://m.youtube.com/watch?v=SmA73sz...ture=c4-feed-u

[flynntuna]

Always leave them begging for more. More please!

[metalmaker12]

Lol, let the damn snow melt

[metalmaker12]

I have been snow/new baby bound this month, but there is some progress on my windshield surround (which i added about 1/4 inch to the edge that sits over the mirrors), center console re-fit (cut to fit better and epoxied) and door panels ( had to trim aluminum slightly and than carbon wrapped and put some finish stainless screws in. my door grab handle and door sill will be powered black if your wondering.

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I vented the section under the humps with FFR style mesh, will be powered blackphoto 4.JPG

[wallace18]

looking good. I like the scooby do mats. LOL.

[Greg G]

Love it, especially the door panels!

[metalmaker12]

Lol, yea they add a touch of class. I am priming some parts over the next couple days to get things going. My windshield surround is going satin black along with my mirrors. Body is prob going white, charcoal or pearl white, decisions decisions. I still gotta do some more body work, but the consistent snow lately is making moving the car around to my buddies shop a bit difficult.

The door panels are coming out nicely, I think I am one of the only guys to have plastic ones though. They look good as they come so it is much easier to use them compaired to the fiberglass ones. I guess I lucked out here. I am powdering the grab handles black and I will counter sink the holes an 1/8 like FFR did on the green car.

I also have some other goodies coming in to button up the engine area