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Old 03-25-2009, 08:52 PM   #1
LegacyWRX
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Default Hood scoop ram air?

I was wondering about trying this on MAP sensor Soobs. If you cut a nice hole in the top of your air box right off of the throttle body and sealed it against your scoop, & then blocked off the real intake hole if it would work as a way of getting forced induction. Faster=More power!
It seems that at highway speeds this could net you another 20-30 hp pretty easily. I've got a MAF impreza so I couldn't try this but I was wondering about trying this on a newer MAP soob. Now there's rain to worry about, but that can be solved with some simple removable panels that can be fabbed up. I don't see why it wouldn't work. What do you guys think?
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Old 03-25-2009, 09:31 PM   #2
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I know it's been tried a couple of times. I've see a few posts in the past where people hacked up their air box and hood scoop to try it. I can't say to what level of success though. Some of them looked pretty hacked up.

However, there is no way 20-30 HP could be gained. You'll get perhaps a little better breathing with a little less restriction, and even a small increase in VE due to a likely small increase in pressure. But, I would eat my hat if you could find 20-30 hp from it. I'd hesitate to even claim 2-3HP to be perfectly honest.
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Old 03-25-2009, 09:32 PM   #3
Patrick Olsen
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I think you're the first to ever think of this. There have never been any discussions of this in this forum, ever.

20-30hp?!
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Old 03-25-2009, 09:39 PM   #4
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The sound angers low flying SRT4s that drop to 1/4 impulse speed.
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Old 03-26-2009, 02:22 AM   #5
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Ram effect, no, but it is a good way to get cold air in as long as that's where the air is being pulled from and it's isolated well from the rest of the engine bay so you're not just pulling hot air.

I've been looking into doing something like this, not ram air but intake via hood scoop location. Non-MAF cars make things easy. Scooped hoods for old Foresters are hard to come by though.

20-30HP. You might see 5HP on the top end from a little better breathing. The biggest benefit will more likely be a good, cold charge and throttle response. There's a number of dyno plots floating around showing some (minor) gains via intake modifications.

The best things you can do is don't restrict, provide smooth, laminar flow, and make sure you're pulling cold outside air and not hot engine compartment air.
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Old 03-26-2009, 07:03 AM   #6
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this has been gone over numerous times, you need to search, but its called gravelsport.. they make an awesome set up, if you have MAP and its just a nice day driver then buy one, but you can also take your stock air box and stick it in there backwards somehow.. look on rs25.com and you should find it, and 20-30hp? youll never see that much, 5-10 more like
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Old 03-26-2009, 10:10 AM   #7
LegacyWRX
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I did a quick search before I posted and didn't find too much, but a more recent more thourogh search revealed some info.Sowee. This is pretty much what I found out (I'll tack some info on here so this doesn't join the heaps of useless threads);

The general consensus is that it will work, for better or worse depending on your fab skills. There was a bunch of talk about hydro locking your engine in the rain but not really a good final answer that I found. I think you'd be fine because whatever your engine is taking in at speed will probably be fine droplets/mist, when your driving in the rain you can just say you have water injection! hah. This could also be solved with a couple flaps/covers you could make pretty easily, carry a wrench with you and spend 2 min swapping out if it rains.

Yea, 20-30 was a guess based on not really anything at all. I just figured at 70mph you could gain 4-5psi positive pressure in the manifold, which again, was based on no kind of evidence of any sort, haha.

Another interesting thing I came across was useing a wrx tmic for the intake and useing a turbo scoop shroud. You would have to remove the entire center of the tmic and then seal a square plate over the back, maby evan some fiberglass or something in the corners to smooth out the harsh edges and some kind of cloth over the whole top as a filter.
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Old 03-26-2009, 05:45 PM   #8
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@ 100 mph, ram-air effect will generate 0..2 psi....
They tested it on bikes. Article below (keep in mind that 10mb = 0.145psi)
http://www.sportrider.com/tech/146_9508_ram/index.html
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Old 03-26-2009, 05:48 PM   #9
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Gravelsport.
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Old 03-26-2009, 10:09 PM   #10
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It's not a ram air that makes gains, it's the restricted intake getting opened up. That MAP sensor will hose you, though. I don't know how it deals with losses or changes in air velocity, but I found that a bad header and intake will both mess with it. That's the only reason I can think of why the AFR and power curve went wacky on some of my creative stuff. It's not just the airflow through the motor, but the signal it generates or lack thereof that matters a lot.

For the record, I've never seen any other engine like such damn long nd narrow intake and exhaust tracks. WTF? If you dumped the headers straight down, the car wouldn't touch the ground. If you had the intake's pointing straight up, they come up a little shy of the roof-line. I had to play with that measurement on my ITBs. It needs long stacks to keep its velocity up. Velocity stacks up to the roofline would be the ultimate little cartoon to drive .
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Old 03-26-2009, 10:22 PM   #11
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That's questionable.

The main things you control is velocity and pressure waves. This is done via the intake manifold and exhaust header. Prior to and after these parts should, for all scientific purposes, not matter. The only way one could mess up is to restrict or cause other problems like pulling hot air into the engine instead of cool air.

I ran two exhaust setups post my current exhaust header, both completely different in design. Power levels and curve where very near each other. I have yet to touch the intake, but I'm curious where people mess up with this. I tend to guess turbulence, intake temp, or something with restriction. The MAP is center in the plenum area of the intake manifold. The throttle body does the air flow metering. Anything prior to shouldn't be able to mess this up much.

I've come across mixed comments on the various intakes, and they run the gambit from great power gains to crappy losses low and mid to no change at all. Who's right? How were these set up? Should we blame the intake or the intake method (crappy flow, hot air, etc.) and more human implementation error?

Old, old thread over stock, Cobb, and filter on TB setups:
http://forums.nasioc.com/forums/show...=164463&page=2

Results on post 27. They just measured air flow and intake temps, no comments on driveability though. Temp numbers were nice when boxed off.

Mixed comments:
http://forums.nasioc.com/forums/showthread.php?p=710762

I'm too curious about this, so I did buy a filter + velocity stack setup from Blox to try out. I could see heat as a big issue if done wrong and a big killer of power. You might drop 5-10TQ just from that alone. This could be why short ram intakes get a lot of blame too and why the long intakes that bring the filter down to the fender work better.

Last edited by Back Road Runner; 03-26-2009 at 10:32 PM.
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Old 03-26-2009, 11:07 PM   #12
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I see some of what you're saying. I think the issue with the various intakes causing an issue actually exists in front of the MAF. You need a velocity stack of some kind going into that sensor, but behind the airfilter.

I just changed out my 8in primary headers for a stock setup to see how things compare. The first one I built from the back of the car up to the motor. This is built going from the exhaust valve outward. I'm curious to see how an unrestricted stocker performs. I hate having no top end, but it does have some more grunt from idle-5500. There really are few restrictions in the stock piece, and its diameter is correct at 1.5ID. Near the valves is where the stock piece needs the most work, and I built mine backwards getting to there last. It's better to work from the valve outward.

I really have to wonder if people are going to start porting their stock manifolds first before installing or modifying headers. I know this is an intake thread, but the stock pieces have flaws worth working on that reveal impressive gains. I saw just as much torque across the rev-range, and even more in the middle, when I cleaned up the stock primaries I was using. My tri-y has a lot more top end, but right off idle is where the stock piece shines. 4500-6k is not what is was compared to my other piece.

We'll see if I hit 35mpg on E85 with the stock header. Playing the torquey character of the motor is how I got the mileage up to 32mpg. Right now, it's great off idle when driving around town but it's only got 25 miles on it. The very first spot I'm going after is right up next to the exhaust valves.
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