Fitting a Huge PVC Ram Air Intake--Bad Idea?

[Soul Shinobi]

I've realized that I can fit two massive four inch (inner diameter) 90 degree bend PVC tubes from the back of where the OEM fog lights would have gone right to the front facing side of the stock airbox. I'd show you pictures but my damned digital camera is broken.

To fit the tube to that wall of the airbox would require cutting a hole that would take up about 60-70% of that wall. Big. The 90 degree bend of this piece will turn straight down into a hole that I'll cut right where the ABS controller would sit if I had ABS, which I don't.

From there that tube will connect to the other 90 degree bend through the huge hole I'll have to put in the steal. The other end of that tube will be right at the back of the OEM fog lamp hole. The entire intake end of the tube may not be completely exposed, but I'm sure I can get it mostly exposed, and I'll put a wire mesh over it.

Now, my question is will this be too much for my 1992 Legacy L with 252,4XX miles to handle? In principle I'd be making the car half way (I exaggerate grossly) to being a turbo, so forcing this much air in might cause premature detonation (engine knocking), in which case I'd have to buy higher grade gasoline as well.

I just can't make up my mind as to whether or not this would be a good idea for an old N/A engine. I might just leave out the lower tube so that I'm not forcing air in but still letting the engine breathe more freely.

[americanyouth]

I strongly doubt this would have any perceptible affect on your motor, much less cause det.

[rallysam]

I'm not saying it wouldn't be a cool project, and I'm not saying you shouldn't do it, but you should at least be aware that the performance gain is going to be very small. The stagnation pressure (your boost) generated by any scoop will be well under 1 psi (at least, until you get well above typical highway speeds). Doesn't matter how big the scoop is.

[Soul Shinobi]

I was hardly expecting to create positive pressure at most speeds, but rather eliminate the negative boost that all stock cars have. I was spurred on by this massive five part article: http://autospeed.com/cms/A_0629/article.html

In that article the author managed to create positive pressure before the turbo in his Audi, canceling the pressure drops from the shape of the airbox and even the airfilter itself using the same sized tubing as I have selected. Now of course I don't have a turbo so I think I can get slightly better gains as the massive air volume will also force its way past the restrictions of the MAF and any non perfect tubes to create at least a full atmospheric pressure at the intake manifold.

EDIT: If I do get gains less than that it will still be the equivalent of a drop-in K&N filter but with $16 of PVC and some work instead of $50.

[Bheinen74]

If you think a K&N is 50, then you need to spend some of this research time searching. I just picked up one on Ebay, with 3000 miles on it, and got it for 13: bucks, including the shipping.
http://cgi.ebay.com/ebaymotors/ws/eBayI ... AMEWN%3AIT
Over on the other Site, Nabisco, they go for 20 shipped all the time. You can get a brand new one at www.ajusa.com for 35 shipped.


You will not see any worth while increase with your tubing plan. You would be better off spending your 16 buks on new plugs and go to the junkyard for newer plug wire. Course, if you are a ricer, then never mind.

[evolutionmovement]

I have an intake similar to this and it makes a negligable difference, but it sounds a little better.

[rallysam]

I was hardly expecting to create positive pressure at most speeds, but rather eliminate the negative boost that all stock cars have. I was spurred on by this massive five part article: http://autospeed.com/cms/A_0629/article.html

In that article the author managed to create positive pressure before the turbo in his Audi, canceling the pressure drops from the shape of the airbox and even the airfilter itself using the same sized tubing as I have selected. Now of course I don't have a turbo so I think I can get slightly better gains as the massive air volume will also force its way past the restrictions of the MAF and any non perfect tubes to create at least a full atmospheric pressure at the intake manifold.

EDIT: If I do get gains less than that it will still be the equivalent of a drop-in K&N filter but with $16 of PVC and some work instead of $50.

Well, generally what you're saying is true. But, note that in the article they only got an improvement of about 1psi or so, pretty close to what I said. It doesn't matter if your adding 1psi, or removing negative 1psi. But, like I said, that's not nothing, it's just small... and, it's still a fun project.

Here's some good news... you don't have to worry about their cockammamy theory that the extra 1psi caused detonation. I think they're smoking it. It's much more likely that they created a leak during all this tinkering, or by damaging their airflow sensor by removing the protective screens.

[free5ty1e]

I just opened up the airbox hole to the fender and put a 3" PVC 90 degree bend there in place of the snorkus, aimed generally at the open foglight hole. I didn't feel like going through any more than that for the negligable gains it would result in over just removing the snorkus, replacing the resonator with a coffee mug, and dropping in a K&N.

Instead, I spent my time on FMIC piping.... much more noticable gains

[Soul Shinobi]

Here's some good news... you don't have to worry about their cockammamy theory that the extra 1psi caused detonation. I think they're smoking it. It's much more likely that they created a leak during all this tinkering, or by damaging their airflow sensor by removing the protective screens.

That had to do with the article car being a turbo, which I had forgotten about. I was actually just being pessimistic on my own.

I was at Home Depot today to find a big enough hole saw and I found it, but it was $47! I'll have to ask friends if they have the tools I need... Or I'll find another way of making a perfect hole.

[Bane]

Just thought i'd share...

on my 96 wagon i screwed around with this concept, i installed a "ram air" hood scoop that went directly to the cone intake, which i had isolated from the engine bay heat with a DIY heat shield wall.

unless you tune your car to recognize that there is more air, you won't see any huge difference, other then getting colder air, which offers slightly better mileage.





However if you replace the stock exhaust, in combination with the intake, you might see some more power. intake and Borla headers + borla catback = the car was quicker then stock, and sounded mean as hell. However it's nothing compared to a stock leg turbo on boost.

if you do go through with it... make sure you have some way to divert water in heavy downpour, otherwise you may have issues with the MAF (err, did first gen leg's have mafs?) i had piece of plastic i could swivel into the way of the air flow if it REALLY was raining hard outside.

hope that helps.

[kimokalihi]

If you go to Harbor Freight tools, I bought a hole saw bit kit that came with like 8 sizes ranging from something like 2" - 5" I can't remember exactly what sizes there were but it was only like 4 bucks?

Hell of a deal! I too went to my local hardware store and the hole saws were outrageously priced.

1st Gen legacys have MAFs right on the airbox.

[Bheinen74]

Bane<
how well does your car in the above picture run: no Alernator/Power Steering belts

[Bane]

lol, smartass.

that 2nd pic was after i spun a bearing, and was parting the car out.