DIY cheap intake upgrade

[TerribleTim]

I did this trick years ago to a Civic and the guy that told me about it claimed it gave him 5 more hp on the dyno.
I recently did a valve job on my Vibe and realized by looking at the throttle body diameter and comparing it to the snorkel going into the airbox that there was a major choke point. I went looking in my local boneyard for the lower half of the airbox and grabbed one from an 05 Corolla (tbw!?) for $7.
I plan on cutting out a few panels on the bottom and rear of the airbox bottom to reduce the restriction to the filter and hopefully make the engine breathe better.
The only effect on the Civic besides the desired hp gain was a neat little howl on acceleration, but that motor had a resonator on the intake tube before the airbox.

Before I do this, I was wondering if there was anyone out there that already tried this mod and how it came out?

[JohnO]

I tried a similar thing on my VW New Beetle. It has a venturi-shaped snorkel attachment inside the air filter housing on the end of the hose coming from the front of the car. It necks down to about half the area of the throttle body opening. Many people were advocating removing it to increase horsepower. I decided to run a test, though, since there must be a reason the engineers put it there. I measured the time to accelerate from 2000 to 3000 rpm in 5th gear and 3000 to 5000 rpm in 3rd gear both with and without the snorkel on the same stretch of road. What I found was that the 2000 to 3000 rpm time was unaffected, but the 3000 to 5000 rpm time was about 0.2 seconds faster with the snorkel. So I left it in place.

My '06 vibe has a similar venturi-shaped piece running into the air filter housing. (I'm often amazed at the engineering similarities between my VW and the Toyota-engineered Vibe. One must be studying the other, but I'm not sure which way it is.) I would advise you to be careful because your modification may not have the intended effect.

[TerribleTim]

Tnx for the input. Sounds like an iffy proposition, which is why I'm keeping the original lower airbox intact.

I did notice the upper airbox from the boneyard 05 Corolla looked nothing like mine. It has all kinds of screens and other stuff inside. Mine is empty above the filter except for the opening to the throttle body and downstream the MFS / IAT. FWIW

"...there must be a reason the engineers put it there."
Sometimes its a feeble attempt at CAI, on my Civic apparently it quieted the intake noise, with performance motors the dimensions of the intake can be designed to change the torque curve due to pressure pulse resonance.
On the other hand, a friend drove his stock Saturn thru a big puddle and sucked up enough water to hydrolock, crack pistons and ruin the engine. I notice there are drain holes all over the Vibe intake before the filter. The actual intake hole is right behind the driver headlite.

[TerribleTim]

I finally did this mod a few weeks ago with a flat bore drill and a small jigsaw. Cut out about a six inch wide section across the bottom and went up about two inches on the front and back sides. IOW a major opening. I was surprised that the lower airbox was still very rigid and strong after these cuts.

I've put about 1500 miles of highway and city driving on it so far and am very pleased with the results. The power increase is noticeable and significant especially on the highway at higher revs. Need more data, but the miles on a tank of gas appears to have gone up about 20%. 300 to 360. Engine appears to really like more air.

Under hard acceleration, there is a definite increase in sound level as you can hear the air being pulled in. Sort of a howl or growl. Goes away after letting up on the gas and there is no noise increase under normal driving. This was not unexpected from my Civic experience, but I would say the Vibe results are better. If you want to test it, pull the air filter element and drive it around the block a few times(not on a dusty day!!) with the airbox open.

The only hazard is rainwater getting into the filter. This is pretty marginal since the new hole in the airbox is on the bottom and is behind the battery and above the fender wheel well. Not to worried. Never rains in The Nix anyway.

[aranlar]

I ran a test for this by opening the air box and temporarily taping the filter to the top of the box so as to run the test with clean air. A definite performance increase and the same growl/howl at higher revs. I put the air box back together normally but on a trip to the junkyard I picked up a spare air box for $20. I didn't have a jigsaw so instead drilled a couple of holes with a large hole-saw bit around the bottom front right corner (close to the factory Intake hole). I've been driving with the molded box for a few days and have the original if I need/want it. I still can't decide if I like the sound or not!

[gtv237]

Any improvements would be minimal at best. I'm not sure exactly what snorkel you're talking about but if it vents out of the engine bay it's probably pulling cooler air into the engine. Cooler air is more dense so the engine adds more fuel to it to maintain a proper air fuel ratio resulting in a more powerful combustion.

Remember too that any restriction improvements made after the throttle body are only useful when the throttle is wide open. The throttle itself is nothing but an air restrictor.

[aranlar]

Understood. Would enlarging the factory Intake hose from headlamp to box make a difference, like this (in the 4th post down by "blue94")
http://matrixowners.com/index.php?/topi ... +%2Bfilter

[gtv237]

Understood. Would enlarging the factory Intake hose from headlamp to box make a difference, like this (in the 4th post down by "blue94")
http://matrixowners.com/index.php?/topi ... +%2Bfilter

Probably not. Even if there were any improvements, it would only be when the throttle is wide open.

[TerribleTim]

Glad someone else is doing this trick. It improved my highway mpg and the pep around town. That Matrix owners website is informative. Not surprised the Matrix improved with the CAI since it has a similar setup to the Vibe, wheras the Celica is more open and designed for performance. Like I said, this is the cheap version of a CAI. Only caution is not putting the holes / hoses where they can suck in gulps of water from rain or puddles.

Apparently, the air isn't warmed up much flowing under the battery. Checking the IAT with and without the mod via the OBD2 sensor only showed a 1degree F change on the highway. The factory snorkel pulls air from an open plenum behind the left headlight. The airbox is near there behind the battery.

The 1zz-fe engine has a 60mm throttle body. The duct from the airbox to the tb is about this diameter and straight and smooth, so the pressure drop should be small at any flow. The snorkel from the airbox to the headlight plenum is small and contorted, creating friction and pressure loss at even low flows. Hence, poor throttle response and lower hp.
The change in pressure and flow by removing the snorkel and opening up the airbox at a set TP is picked up by the MAP and AF sensors which adjusts the injectors for the proper mixture. The mixture is further refined by the pre and post O2 sensors. So the engine can compensate for better breathing by putting out better performance.