So I bought a K&N filter in September of '03. It was a 6 inch long cone with a 3 inch outlet. Your typical K&N cone filter. Since the MAF (air flow meter) of the Nissan Sentra SE-R has a hole in a flat plate, the flange of the K&N had no pipe to attach to. So I went to Home Depot to look for some plumbing supplies to ghetto rig something up. But I was unsuccessful there. Then I realized my favorite plastic store, Tap Plastics probably had some 3 inch acrylic tube. I could buy a short section of the tube, attach it to a flat sheet of acrylic with an appropriately sized hole in it, and BAM! instant MAF adapter. So that's what I did.
Acrylic is pretty brittle, but it has held up in my car for all these months. No, it hasn't melted. So I had that attached to my car with the K&N up until last week. A few weeks ago, I met up with a fellow forum member. He saw my MAF adapter and wanted one for himself, and he asked me to make one for him for trade for an old cold air intake he wasn't using. I agreed, and headed down to the Tap Plastics website and saw that they now had polycarbonate tubes! (Lexan is GE's trademark for their polycarbonate products) What this means is that the MAF adapter will be even stronger than the acrylic one. Polycarbonate is easier to drill into for the bolt holes too. Acrylic tends to melt very easy when drilling. So I bought the polycarb tube and made a couple of new MAF adapters.
So this is what's in my car as of last week. Worked just as good as the acrylic one. But that wasn't good enough. Ever since I installed my SSAutochrome header, I've been hearing air being sucked into the intake. It's a pretty loud whooshing noise and I can hear it whenever I get on the gas. The engine roar takes over at about 4500RPM, but I'm betting that the noise is due to turbulence in the intake system. The K&N filter has a base diameter of about 6 inches, and that abruptly reduces to the 3 inch outlet. JWT has a POP Charger that does a great job at funneling air into the MAF. The trouble is that it costs about 100 bucks at the cheapest place I could find. Me being the typical cheapskate decided to make my own funnel.
It's still a work in progress. It's 6inches OD (outer diameter) and 3inches ID. I bought a 1.25inch long section of 6inch OD acrylic tube and formed the tube inside that. It's hand sculpted with this stuff I found at Tap Plastics called Magic sculp
It's a two part epoxy putty that's great for sculpting all kinds of stuff. People are using it to make models, action figures, and of course, sculptures of all shapes. At PacBell Park (SBC Park now), there's a humongous baseball glove in the stands that's made of Magic sculp. It remains workable for about 3 hours. And dries rock hard over night. It's an epoxy, so it's chemical curing, so that means it can even cure under water! Pretty neat stuff.
So I didn't really know what the shape of the darn thing should be for optimal performance. It was hard to see what shape the JWT Pop Charger was based on pictures on the Web, and I've never seen one in real life, so I decided to do some Googling. I found this site and it said a "full radius" was best. After a lot of googling, I didn't find much else for air horn/venturi tube/velocity stack design. So I said what the hell and I sketched my own profile.
From pictures I could find of the JWT POP, it looks a littledifferent from my horn. The JWT seems to be more of a funnel shape, and mine seems more horn-like, if that makes any sense. So I still have to do some final sanding, and I have to drill the holes in the back. And then I have to find someway of putting threads in the holes. I don't know how well a tap would work in the hardened Magic Sculpt. I think I'll have to find some kind of threaded insert to shove into the hole so bolts can grab. If anyone knows if such a thing is commonly available at homedepot or someplace, feel free to let me know.
I ordered a new K&N filter with a 6inch oulet to fit over my horn. I made a simple support for my current filter setup out of L-section aluminum. But the horn weighs a little over a pound versus the next-to-nothing weight of the lexan/acrylic adapters. So I think I'm gonna have to beef up the support. When I'm done I'm gonna do some Gtech comparison runs. I'm too cheap to dyno it.
That's the final sanding of the donut. Behind the donut, you can see a 3inch OD acrylic tube. That's just to show how close the inner diameter of the donut is to 3inches. After sanding it down with 100 grit, then 220, then finally 400 grit sandpaper, it's silky smooth, almost satin-like. The grain texture of the Magic Sculpt is super fine, so it allows for a really nice finish. Now all I have to do is drill holes, and thread them somehow.
Monday March 15, 2004
So I thought that would try using some threaded inserts I found at the local Home Depot.
But those inserts have a flange on them, and on 2 of the holes in the velocity stack, the flange would intersect the O-ring that's on the MAF. So I decided to do it the old fashioned way. Drill and tap. So I used the el-cheapo Tap and Die set I got from Harbor Freight.
The bolts I was using are 1/4-20. The tap for this threading requires drilling a hole smaller than 1/4inch, but to find out exactly what size hole I had to do some googling. According to this page I needed a #7 drill bit which is .201 inches. I didn't have one, but I did have a 13/64 which is .203 inches. Close enough. So I use my el-cheapo drill press, and drill out holes on the air horn (measured carefully off the MAF). And then I tap the holes. And here's the result:
Now I gotta get the air filter in. And then fit it on, then maybe make a new mounting bracket. Stay tuned...
Update: March 25, 2004
So I finally have the thing installed.
1.25inches of 6inch OD acrylic tube: $3.90
Magic Sculp: $26.25 for 5 POUNDS! I used about a fifth of this=$5.25
New 6inch outlet K&N: $38.57
Bolts and washers: $0.76
I'm sure many of you are saying, "Dude, just buy a used JWT Pop charger and be done with it!" Yeah... well... I didn't! So there. If you were a cheapass like me, you'd understand...