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Guest Message by DevFuse

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air filter / box question

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15 replies to this topic

#1 86subaru


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Posted 30 August 2003 - 10:05 AM

hello all , i have a question , buy putting a hole in the bottom of the air filter box , will this increase hp ? i have 86 spfi a/t sedan , with ngk plugs, k-n filter 8mm wires , how about during the winter would it suck to much cold air into the motor ? thanks :banana: :brow:

#2 86subaru


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Posted 30 August 2003 - 10:10 AM

also would a accell super coil really help ? since there 33 bucks ? :banana: :brow:

#3 JonOfScio



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Posted 30 August 2003 - 10:40 AM

If you're trying to get more power out of your car, put in a manual transmission. Automatics can steal up to 40% of the engine's power. Whereas manuals are only 10%.

An Accel coil with good wires, new cap, and rotor (I paid $45 for a super stock, $20 for new wires, and about $12 for a new cap and rotor) will help alot. so all you really need is a good cap, rotor, and a good coil.

As for the air box, cut out the bottom to get a more beefy sound. Take off the warm air duct if you want to suck in cold air more. Depending on how cold a climate you live in (I'm in oregon, so it's no big deal) but if you're in alaska, I'd really not touch it at all.

Here's a good picture of something to do to a carburated car.

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#4 thealleyboy


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Posted 30 August 2003 - 10:44 AM


Very nicely done...

How about some more details on your carb setup.


#5 86subaru


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Posted 30 August 2003 - 10:45 AM

well i live in ohio , which it can get to 0 , i will try a super coil thanks, i already had the lower cat cut off not the y pipe one , thanks :banana: :banana:

#6 oobnuker


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Posted 30 August 2003 - 11:08 AM

Check this out: http://www.arventerprises.com/subaru

Here's a basic rundown of what I have done to hop up my SPFI:

  • Removed Power Steering
  • Removed A/C
  • Accel SuperStock Coil
  • NGK OEM Plugs
  • 8mm Accel Wires
  • Timing Advanced 24 Degrees
  • Run highest Octane Gas (otherwise it pings now with the advance)
  • 2" exhaust after second catalytic convertor, right angle out to rocker panel, side exit in front of rear tire - no muffler
  • Oil/Air Separator modification to PCV system
  • Relocated Air filter to spare tire shelf - replaced airbox with 3" cone filter - custom fabricated MAF adapter plate
  • Dual Core Turbo Radiator
  • Cut large hole in hood for heat to escape and air for the intake
  • 4 Wheel Disc Swap

I think that's it. I can't remember off the top of my head. But I tell you what, this little SPFI with 172K miles on it screams like a MOFO. I drive it 100 miles a day and don't have any major issues with the car. Taking off all of the parasitic accessories, the engine revs to redline with easy - will chirp the tires - will smoke them if I do a 3500 RPM clutch drop (bad!) Easily pulls to 100+ MPH and pulls in every gear now.

I never really had another Subaru to baseline against, but based on where this car was when I got it - it's a HUGE improvement.

#7 JonOfScio



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Posted 30 August 2003 - 11:19 AM

I basically did this.

bought a 4" deep dish chrome cleaner kit. modified the bottom piece by taking the top lip off. Used the 2 5/8 to 2 5/16 spacer. bought a 9" chrome air filter assembly, with the 2 5/8" adapter. Used the bottom part of the 9" chrome cleaner upside down. Put the spacer/adapter under it. Now the problem, the difference between the spacer/adapter and the neck of the carb is 5/16. So, use the adapter and the bottom part of the modified 4" cleaner to hold it in place. So it's all snug. It's an interesting thing, so you really need to see it in person.

The valve covers have breathers on them, the air pump to the second cat has an identical breather, and my crankcase breather needs one like it... but I haven't had the money for a $22 cleaner for it. (specially made for the smaller tubing)

When the secondary valve opens, you can hear it sucking air. It's sweet. Now the engine breathes alot better. That with the electrical things I've done (coil, wires, cap, rotor) and the performance muffler (see picture) have all helped to put my'88 EA81 N/A carbed engine a little bit faster.

With the tires I've put on the car (the cheapest 175/70/R13 tires I could buy) I can chirp the tires in every gear, really peel out in first and a little bit in second if I let off the clutch just right. FWD.

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#8 Caboobaroo


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Posted 30 August 2003 - 01:42 PM

if you do plan on cutting the bottom of the airbox out and putting in a K&N air filter, you'll probably increase by about 10 hp or so. 2 of the easiest ways to make any car preform better is open the intake (less restrictive) and open the exhaust up. When the air can pass into a car smoother that it did, you'll increase hp like gutting the airbox out. Same with the exhaust; put a better flowing exhaust on it and you'll notice more power. If you decide to only mod either the intake or the exhaust, thats fine but you won't get the full effect of it until you mod the other. It works hand in hand.

#9 calebz


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Posted 30 August 2003 - 02:47 PM

There is absolutely NO WAY you will get 10hp out of modifying your airbox.. 2-3 maybe.. but it sure sounds a lot cooler than stock

#10 baccaruda



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Posted 30 August 2003 - 03:04 PM

i'd say more like 5, but it is noticeable. first thing i did to this car; i remembered how much it had helped the last one i had.

#11 Tom63050


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Posted 30 August 2003 - 07:44 PM

I did the airbox mod, and then installed a free-flowing Turbo muffler. Definitely cutting out the bottol of the airbox is the single best mod you can make--it's free and easy, and gives noticeable improvement over 4000 RPM. Maybe 10 horses. The muffler made no difference, but that may be because I did the airbox first. Possibly doing the muffler first would have made a noticeable difference, but I believe the big restriction is in the intake.

And pulling off the PS and AC sounds good, too. My Loyale wagon has a non-functioning AC switch, so I've been thinking of pitching the AC. Might as well do the PS too...

#12 86subaru


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Posted 30 August 2003 - 08:16 PM

ok if i cut out the air box on my spfi a/t sedan , will this affect the car during the winter time ?? here in ohio it can get below 0

#13 incognito



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Posted 30 August 2003 - 08:19 PM

Whatever dude, you can get 10 HP easy out of Air Mods.


#14 Caboobaroo


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Posted 30 August 2003 - 10:23 PM

its fine if you take it out even for the winter time. What do you think we do when winter comes and we have cut our airboxes apart? Glue them back in and cut them out in the spring? No we go out to the snow and play!!!:headbang:

#15 SubaRube


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Posted 30 August 2003 - 10:45 PM

Hey, if people would start contributing to the USRM, then us new guys wouldn't have to ask all these questions. Give us a break.:D

#16 86subaru


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Posted 31 August 2003 - 11:01 AM

ok, thanks out west what 30 degrees during the winter , here in ohio it can get below 0 and snow alot

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