[07-3.7-4wd street jeep]

I have this in the WK section too.
I am putting together a new intake tube and I was wondering how I should terminate it inside the air box. The tube will be able to go into the air box and end above the air filter. If both ends are cut at 90 degrees, due to the bends in the tube, the short side length is 27 1/2 inches and the long side length is 32 inches. Should I leave the ends at 90 degrees or cut the end off at an angle to make both the short and long sides 27 1/2 inches, so the traveled length be the same across the tube? I looked through the hemholz resonator info online and never saw a good answer. I figure the acoustic pulse will occur around 4500 rpm during WOT., so it should be a nice boost when the power is starting to fall off.

 

[Seakir]

Interesting project. I was looking at air turbulence and its effects inside an air intake system and came across this a short while ago:

Design improvements of an automotive air intake system

This project was conducted in conjunction with Proton R&D department to study and improve the air intake system (AIS) for the current Proton Iriz vehicle. The AIS comprises of few parts: snorkel, a...

aip.scitation.org

It says they made 3 designs to the air box of the model in question used for the analysis, to see which gave better performance and 4% was the best they achieved for design 1, but doesn't show the design- grrr!

However, they state air delivery is weakest at the point where the air turns from laminar to turbulent, which is inside the air box/filter housing itself. With this in mind, are you plugging your new pipe into the standard entry hole for the box, or are you redesigning the box itself?
If using the plastic standard entry, I would say the cut wouldn't matter as long as you can get enough grip with the jubilee clip/band on the pipe that will be used to seal them airtight.
If a redesign, then maybe the angle cut might be good to consider, as long as the travelling air isn't given a lip to get trapped by to create turbulence.

 

[07-3.7-4wd street jeep]

My current plan is to run the tube into the box just like it is laid out in the pictures. I would like to add a horn to the end of the tube ( IIRC I've seen this layout on ultra-performance autos) to help the entry into the tube to have nice smooth flow, but first I have to get to the tube into the box. I want to keep the tube as long as possible as this will keep the resonant frequency in a lower RPM range ( around 4500 RPM) to provide some boost....getting above 100% Volumetric efficiency. It looks like I'll need to cut about 1 1/2 inches off the current air box outlet to slide the tube in and then I'll use a 3 1/2 x 3 silicone coupling to seal the tube to the box. I don't think air flow volume will be an issue. My calcs show that 3 inch is just right for a 3.7L running up to about 5500 RPM. Also the air filter should be able to support about 400HP,so that's not a bottleneck. I need to take a closer look at the inlet to the airbox and see if that needs opening up. My main question is how the uneven lengths of the two sides of the tube will effect the resonance. I may call the pipe organ builder I know to see what they say.

 

[Seakir]

I got no idea on how the uneven lengths of tube affects resonance, except what logic might guide- if the pipe is smooth the acoustics and pressure should be equal, but at bends the dynamics are going to change and yhe sound -depending on the material containing it- will react in different pitch where air is compressed at these bends. Your bends look clean though, so I would guess that with a little experimentation, you will find that resonance you're after.

The reason for asking about an air box mod is that I've tried a k and n filter in
my wj variant using the standard box and tbh, I noticed no acoustic difference, even when the turbo kicks in. I think that a closed air box might muffle a lot of the air being sucked in and the acoustic sound/grunt from a k and n/sports style air filter, which is why I took mine out and put a mopar filter back in as there seems to be no difference with mine regarding performance either.
Now, when I did a cold air intake mod with a cone filter on a Gasoline Ford cougar v6 a few years ago, that really opened up the acoustics and you could hear the air being sucked in ten times louder.
Not sure what others would recommend, but maybe a cone with no air box might be worth looking into? (Thinking about it, I've still got that cone filter from the cougar set up. I might have an experiment with it and take out the air box, to see what an open set up in my diesel lump sounds like. Kudos for the idea 👍.)

 

[07-3.7-4wd street jeep]

Thanks for the input! I don't want any more noise and I want the air as cool as possible, so that is why I am keeping the stock air box which pulls air from in front of the radiator. I never got around to talking to my organ people today.

 

[Seakir]

Oh I see. Keep the standard box for sure. Now I see that you're looking for performance and air pressure ratio being as equal as possible down the pipes, therefore making it as less restricted as possible?
I would go with your instincts regarding your mod therefore, as it seems you've done the math and know your stuff- maybe experiment with both cuts you're considering? One thing you could try, in order to do this, is to buy a 3 inch exhaust sleeve and another air box from ebay. That way, you have the means to correct pipe work by using the sleeve to connect end sections of your pipe should you find your end cuts wrong- the extra layer of metal, considering its an exhaust system part, might also help keep the air cooled somewhat by adding another layer of insulation, but it might be worth remembering it could also trap heat if idling. Heat wrap for exhausts could also be another option, but I would go for heat resistant paint and coat it over the air pipe. Go for a nice colour 👍(I painted my cougar exhaust and manifolds in a nice flame red.)
Also, it won't matter too much if you're hacking into a box brought off ebay and you'll also have spares to fall back on should you need them or want to keep your mod if you come to sell the vehicle.

The horn cap sounds a good idea to create less turbulence- the easiest way to visualise air movements is to imagine it as water flowing -they follow the same rules of motion, just different textures but same force/pressure relationship.
In this context, maybe treat the pipe connection into the air box like a sinkhole, so air is funneled in like when a plug is pulled in a sink?

 

[07-3.7-4wd street jeep]

Yes, I am looking for quiet and powerful ( or at least more powerful). The stock intake tube with its accordian probably creates all sorts of turbulence, so I am trying to smooth the air flow and hopefully hit an acoustic resonance to help force feed the engine at a usable RPM. I also plan to do some front more front end aero mods to increase pressure above the bumper to use it as a splitter to create downforce and bring the air dam down lower to cover all the low hanging hardware. That air dam will tie into a front bellypan to again increase downforce and create a low pressure zone in the engine compartment which should improve air flow over a now more restricted radiator. The little 3.7 v-6 has room for increased mpg if the aero drag is reduced on the highway. I've done some drafting with semis and saw a nice increase in MPG holding steady speeds. Strongjeff in the 3.7l Performance love thread said he gets between 26 and 34 MPG on the highway with his heavily modded 2 wd 3.7 ( all bolt-on, including chip). That's my target, though I have 4WD. We plan on buying a southern CA WK in a few years that I want to transfer all the upgrades I work out to it so the time invested won't be a waste. Rust is strarting to take a toll on our current WK, though it runs great at 208,000 miles with no oil burning.

 

[moparado]

This all remimds my of some XJ owners who tap into their HVAC fresh air intake at the firewall then run the tubing right into either the air filter box or directly into throttle body through some jury rigged air filter.
Cold ram air at moderate to high speed?
Supposed to work great with the downside of noise.

Yeah anyhow the coldest air possible is typically gonna be at the OEM air filter box intake.
The reason i think these aftermarket CAI kits are baloney.
On my XJ i run a high flow air filter in the OEM filter box and call it a day.
Installation is as quick as replacing an OEM filter.

 

[07-3.7-4wd street jeep]

Yeah, and for the little v-6 the air box filter is plenty big. I forgot to say I will also be insulating the air tube and the air box to keep engine bay heat out of the air stream... like this Iceman intakeon my Zetec equipped 98 Escort wagon. That's foam duct and pipe insulation that I also used for sound deadening and insulating the load floor of the wagon. If you want to go fast cheap, the Ford ZX2 with ZETEC and Manual trans stock goes 0-60 in about 7.8 seconds. A few built ons and now you have a hemi beater.... or at least older hemis.... and get around 25 city and around 33 highway MPG. The magic of older, lighter weight compact cars.

 

[moparado]

Too bad the TB intake is vertical and not horizontal which would eliminate that hard 90 deg. angle. haha
Let us know if there's any noticeable improvement.

 

[07-3.7-4wd street jeep]

Yeah, I've thought that too. I had to trim the silicone connector as short as possible to keep the intake from rubbing up against the hood. I believe the SVT version has the TB a bit lower and angled slightly up the driver's side of the engine. However, that Intake setup seems to be good to around 160 to 170HP out of the little 2.0l engine. It funnels down from about 3 inches to about 2 1/4 over its length and really bumped the mid and upper power on the stock engine with only a shorty header. Interestingly enough, dyno tests with shorty headers on this motor saw low rpm power increases while flattening out at High rpms..... weird.