My Prius dead again, with techstream this time.

Here's a simple solution for clearing up space for the OCC. Just remove the pre-filter air horn and use the M6x1.0 tapped hole that it used to mount it near the engine upper passenger side engine mount.



It serves only as a noise attenuator. To see how removing it affects noise, just temporarily remove it to see how much sound attenuation it does provide.

 

It would be hard for the resonator to serve "only" as a noise attenuator. The noise that it "attenuates" represents a certain amount of pressure-wave energy in the inflowing air. The resonator doesn't destroy that energy. Instead, it uses that energy to more effectively charge air into the cylinders when the valves open. Having the flow at the inlet be steadier with less pulse noise as a result is one of the ways you can tell it is doing its job.

 

The flow straightening occurs in the filter box. The attenuator horn and it's expansion chamber apparently only breaks up sympathetic reinforcing vibrations. Given it's shape, it doesn't provide any enhancing venturi effect to enhance the air stream.

 

If you are able to demonstrate that more formally, please do.

Until then, there's simple conservation to think about. Those are Helmholtz resonators without energy-dissipating elements, so, analogous to capacitors in electronics. The mechanical energy of the flowing air isn't being reduced by the resonators (at least, not by any more than the unavoidable friction in the tube), only delayed and returned to the air stream.

"Flow straightening" isn't what they are about. "Venturi effect" isn't what they are about. They are about resonating with a pressure wave in the intake, so that when the airbox pressure would normally decrease (valve opens during intake) the resonator pressure is adding to it, and when the airbox pressure would normally increase (valve closing) the resonator absorbs a portion of the increase.

The reduced amplitude of the pressure wave escaping at the inlet is an outward sign of that happening.

 

In the early days before computer modeling, Toyota would have built a clear acrylic model of this part, installed multiple pitot static tubes throughout different positions in the model and used a special smoke generator and multiple sound capturing microphones to study all the parameters of this intake piece.

Attenuators disperse sound to avoid reinforcing sympathetic vibrations. Resonators smooth out a rough sound wave to emit a more ear pleasing sound. They do not perform the same function.

 

These are completely recognizable Helmholtz resonators, relatively large empty cavities connected by narrow necks to the side of the inlet passage, where the flowing air blows over them as in playing a flute.

Here's a relatively informal description of the function of those resonators in the intake airflow.

Here is one a bit more technical. It is on a motorcycle site and the worked example is for a V-twin, but they include adjustments to the formula for single-cylinder or four-cylinder engines too.

 

It's partly the reason ppl who install short RAM/"cold air" intakes like them, because they make the engine sound sportier. /s

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It also frees up space for the OCC. Here are photos of mine and my friend's installs.



Going on five years with no issues. Works perfectly.

 

The HPS intake has a K&N filter and is not that expensive.

https://hpsperformanceproducts.com/pages/search-results-page?type=products&q=air+intake&page=1&rb_snize_facet1=Lexus+CT200h

 

@gromittoo , you're not bridging between engine and chassis? Hard to tell from the pics. You wouldn't want to do that, the engine is "sprung", shifts positions relative to the chassis.

Just for a laugh, there's two (Moroso 85474) in mine :

 

There are cheaper, for sure. Yeah just trying to illustrate a "stealth" install. I put the 2 cans in series, and empty them spring and fall. In fall the 2nd can has next to nothing, but in spring it has almost twice as much. Mostly water, some oil though. The second can just kinda fell into my lap: another family member wanted one, then got cold feet, so I thought hey...

 

Yeah not sure how much the engine moves around; I'd think a half inch clear would be safe. Mounting something extra can often have surprising ramifications.

I mounted mine on a slotted angle bracket bolted atop the lower cross beam, below the air intake. Then the next time I jacked up the front of the car, using the front/central jacking point, I heard all these creaks and groans. That jacking point is on the underside of that beam, and it flexes when used with a jack.

I added rubber washers between the slotted angle bracket and top of beam. Also used two nuts on the hold-down bolts for the slotted angle: did the first one finger-tight, then the second torqued against the first, to lock it.

 

Raise the chassis mount by 1/2” ?

 

I had similar issues, just barely enough clear from the AC compressor IIRC. There's always a way.

Maybe snip:

 

@gromittoo, you can lop off the overhang on your bracket, the corner that extends past the riveted joint. It's unnecessary material that doest lend any strength to the bracket or joint.

That should give you the clearance you'll need between the bracket and the engine mount. Even more clearance can be found if you further remove material after the initial cut from the bottom corner of the joint area, worse case is you're left with 3 rivets in the joint, which should still be plenty rigid.

Edit: Just saw your last post, where you did what I just posted. Also, check the clearance between your refrigerant line and your bracket, you can remove material from the bracket if the clearance is tight, you don't want the bracket to damage the soft aluminum refrigerant line.

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