"Trimming air box"

[spokanesoob]

so i cut the bottom of my air box out today and i noticed a major diffrence in time it takes to get up to speed and shift points ect. no ill effects noticed yet much louder but a cool sound though i think i might get a K&N air filter if one could be found has any body else done this? if you have i would like to know how much faster you could go

thanks

spokane soob zzz

[azsubaru]

Good luck to you on this one... Do a search and you'll see how the engineers on this board have pretty much beaten up anyone who even suggested that drilling holes or cutting out the bottom of the box can do more than change the sound. They have all the math, to prove it, too.

[calebz]

so i cut the bottom of my air box out today and i noticed a major diffrence in time it takes to get up to speed and shift points ect. no ill effects noticed yet much louder but a cool sound though i think i might get a K&N air filter if one could be found has any body else done this? if you have i would like to know how much faster you could go

thanks

spokane soob zzz

 

 

You can't go any faster. You can have slightly better throttle response though.

[carfreak85]

They have all the math, to prove it, too.

 

Show me one example where someone used math...

[baccaruda]

it improves performance for turbos quite noticeably. for all other engines the increase is negligible but the noise isn't

[monstaru]

you sound offended.

 

Show me one example where someone used math...

[carfreak85]

I agree with Baccaruda, I noticed a huge difference in power when my cat was plugged up. All the power my little motor had to BARELY make it up hills was because of that cut up air box. I also haven't run across too many folks (Myself included) on this board who have the means to actually back up any mods they do with hard data (i.e. dyno tuning, measuring flow on a calibrated flow bench, etc). If I sounded a bit offended, that would be why. Its been a long weekend fighting :Flame:The Man.

[azsubaru]

Show me one example where someone used math...

I'm not too good with the search engine, but it had something to do with the fact that the intake is only 1" or so in diameter, so opening up the box isn't going to change that - unless you use a Turbo or something of the sort to jam more air through it. Probably was posted by NorthWet or GeneralDisorder, but I don't remember.

 

I tired it myself by the way, and thought at first that there was more power. But after running it that way awhile, I changed it back. No power gain that I could prove, and I was wasting gas by punching it so I could hear the WAAH sound.

[baccaruda]

My "data" is one run up the east (steep) face of the pass at Vantage, WA with my turbowagon, pre-chopped, wherein I maxed the car out in 4th gear at like 55mph.... then I had occasion to take the same route later that year, similar weather conditions, post-chop, wherein I was pulling 90 in 5th and could have pushed the car harder.

That, and 45 felt like 30 for a short bit whilst bombing around town. Whoops.

[Tom63050]

so i cut the bottom of my air box out today and i noticed a major diffrence in time it takes to get up to speed and shift points ect. no ill effects noticed yet much louder but a cool sound though i think i might get a K&N air filter if one could be found has any body else done this? if you have i would like to know how much faster you could go

thanks

spokane soob zzz

I drilled 25 holes in bottom of Loyale airbox about three years ago, which I calculate doubled the airbox's capability to admit air, and noticed a big improvement in upper-RPM breathing...I don't care what anyone says. Below 4000, the same; above 4K, much better.

 

I also bought a K&N filter recently. No improvement. The stock filter seems to let in all the air that the intake can handle, even with the airbox opened up.

 

Since this mod only affects upper-RPM breathing, if you continue to drive conservatively there is no change in gas mileage.

[psylosyfer]

I drilled 25 holes in bottom of Loyale airbox about three years ago, which I calculate doubled the airbox's capability to admit air, and noticed a big improvement in upper-RPM breathing...I don't care what anyone says. Below 4000, the same; above 4K, much better.

 

I also bought a K&N filter recently. No improvement. The stock filter seems to let in all the air that the intake can handle, even with the airbox opened up.

 

Since this mod only affects upper-RPM breathing, if you continue to drive conservatively there is no change in gas mileage.

Doesn't K&N guaranty 10-15% improvement in mileage/performance?

[Tom63050]

Doesn't K&N guaranty 10-15% improvement in mileage/performance?

 

Maybe with a stock airbox. But I drilled out the bottom first. Unless you really want to spend the money on a K&N and never replace a filter again, I'd say just do the free fix and open up the airbox. You can also get 25-50% more use out of a paper filter by just vacuuming it!

[daeron]

if memory serves, our soob uses the same air filter as a first generation 300ZX.

 

If it flows enough for 3.0 liters to make over 150HP stock, then it flows enough for an EA82 to do ANYTHING it can.

 

The filter is NOT a restriction, the THROTTLE BODY and the heads are.

[baccaruda]

Daeron, you're 100% right on that.

 

I'm suspect of the K&Ns anyway. I don't accept that they are as clean as paper filters. I know they flow better but something's gotta give somewhere.

More air = more airborne particulate matter.

If you give the stock filter a larger inlet through which to breathe, and make sure it gets the coolest air possible, then you've given the EA81 or EA82 as much air as it can use. There are very few people on this board who have even flirted with optimizing an EA82T's performance (I am not one of them, for the record) and they would all tell you that it's not any particular type of air filter that is the ultimate hindrance, it's the engine's self-handicapped design.

 

Anyone who wants better performance out of their old Subaru would be better off spending the time and money not on the air filter, but on catching up on 20+ years of neglected maintenance and then moving on to port & polishing and exhaust improvements, etc.

If you have motor and transmission mounts with 150k+ miles on them, spend your money on new mounts instead of a deluxe air filter/intake system. Same with strut rod and sway bar bushings and wheel bearings. And the radiator.

 

Bob (Bobistheoilguy.com) also says the fancy filters don't filter as well.

He also points out that using an oil-soaked filter could be very bad for your car's MAF sensor (especially a hotwire sensor such as from an 87 or later Subaru).

[baccaruda]

Aaaaaaaaaaaaaaand I just hacked out the bottom of my EA81T coupe's air filter box.

 

The turbo light comes on sooner and with less input from the gas pedal - and the acceleration curve is a little steeper now. I just bombed around the neighborhood and back and the car is much more responsive. Sounds better too.

[Syonyk]

I may give this a shot this summer - I'm going to get a set of Delta cams (260 degree) for my EA82, if this helps upper RPM power, that should combine well with the cams.

 

How much louder is it?

 

-=Russ=-

[baccaruda]

maybe 10-15% louder at higher RPMs.. not really noticeable while @30mph+

 

I have a 2" exhaust after the stock downpipe so it's maybe less loud for me than for a totally stock car.

[Tom63050]

The filter is NOT a restriction, the THROTTLE BODY and the heads are.

 

I understand Daeron's argument that the throttle body and heads are a main restriction. But I have to square this with my and Baccaruda's seat-of-the-pants experience, and probably other folks as well.

 

I look at it this way: if you try to breathe while sucking thru a straw, you can't get much air. If you're sucking thru two straws (i.e. doubling the air intake by opening up the airbox), you can obviously breathe better.

 

You can flow test the heads and throttle body off the car, but that won't take into account how much suction the pistons are capable of on the intake stroke. Since people are noticing more power at higher revs, this leads me to believe that the pistons can pull in more air, thru the TB and heads, than the stock airbox will allow. Once that's taken care of, then we can look at improvements to head and TB flow. Air intakes are restricted on purpose for noise reduction, and maybe gas mileage; there's no other good reason to do so. You'll notice that all those cold-air intake kits come with huge air filters. Because it's not just about air temp, it's also about volume.

[baccaruda]

The throttle body is restrictive

The heads / valves / injectors' capacity are restrictive.

The crossover pipe is restrictive.

The downpipe, cats, backpipe, and muffler are restrictive.

The air filter and airbox are restrictive.

 

The airbox just happens to be the easiest / cheapest restriction to remedy.

[baccaruda]

(wrong thread)

[daeron]

I understand Daeron's argument that the throttle body and heads are a main restriction. But I have to square this with my and Baccaruda's seat-of-the-pants experience, and probably other folks as well.

 

I talk too much; many of my posts are longer than needed.

 

I didn't waste any time (mine in typing, or anyone else's in reading) by saying any more.. I have been experimenting with brevity. My only point was the filter itself. I was knocking the K&N for our car, not the filter box modification; I am all FOR that. The stock filter is MORE than adequate for anything a 4 banger under 2 liters can make; its adequate for a 150-170 hp 3 liter V6. (300ZX uses same filter, look it up next time your in the parts store)

 

Thanks, Tom, for making my statement clearer.. I should have put more emphasis on the fact that I only meant my comment to apply to the filter element itself, not the airbox/filter assembly as a whole.

[baccaruda]

exactly.

It's also worth mentioning that the "cold air intake" idea is sort of addressed in chopping the airbox, because the part you chop is on the bottom, and gets cool air from right under the car. The air does have to go up past the exhaust, either the Y-pipe or the crossover pipe, but I don't feel it's significant.

[Tom63050]

exactly.

It's also worth mentioning that the "cold air intake" idea is sort of addressed in chopping the airbox, because the part you chop is on the bottom, and gets cool air from right under the car. The air does have to go up past the exhaust, either the Y-pipe or the crossover pipe, but I don't feel it's significant.

 

Right. If the car is moving, airflow will keep exhaust-pipe air down under the car; so the air under the airbox shuld be relatively cool.

 

Here's a thought I just now had--for cars with A/C, how about some creative way of ducting to the airbox for really cool air? Hole in passenger-side firewall, for instance, running ducting thru it to airbox.

[daeron]

Right. If the car is moving, airflow will keep exhaust-pipe air down under the car; so the air under the airbox shuld be relatively cool.

 

Here's a thought I just now had--for cars with A/C, how about some creative way of ducting to the airbox for really cool air? Hole in passenger-side firewall, for instance, running ducting thru it to airbox.

 

You would lose more power through running the A/C than you would gain from the colder intake air charge.

[Tom63050]

You would lose more power through running the A/C than you would gain from the colder intake air charge.

 

True; but if you were using A/C anyway, it would be no extra energy loss. And when you need the A/C is also when the engine needs cooler air more.