Air intake mod question

[Carve]

One thing I did on my TJ back when I drove 30 miles 5 dais a week to work was remove the 90degree horn looking thing attached to the airbox.
I did notice a slight change in fuel savings after I removed it. These days my job is only 1.5 miles away so the TJ does not get many miles on a weekly basis anymore.


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I don't believe any intake mod will save you fuel. The biggest restriction in your intake is the throttle. If you have higher pressure air in front of the throttle, you'll have to close the throttle more to get your appropriate pressure in the intake runners for your desired power setting.

 

[Carve]

He said he specifically ordered it designed with no restriction.

There's really no such thing as "no restriction" when moving a fluid through a tube, butterfly valves and through filters. It's just a matter of how much there will be. There's probably some threshold they were shooting for at WOT at redline...perhaps 4" of water pressure difference. I'm sure there's a little room for improvement with a non-corrugated tube and a tiny bit more with a bigger air filter. That said, the stock intake seems pretty good. I just wish it had a source of cooler air.

 

[SkylinesSuck]

Stupid question maybe. But where does the Windstar intake come into play here? Is it just as good as stock but gives you room for other things?

Protection from water, colder air from the cowl, fitment if you want to put something where the factory box was, and in some cases, performance.

 

[antighboatye]

I put an AEM intake on my Jeep way back in 08 because (if I remember correctly) I needed it for the TNT full tube fenders that I mounted. For those that are running tube or flat fenders that replace the stock inner fender, especially high clearance models, are you still able to use the stock intake somehow?

 

[pc1p]

I put an AEM intake on my Jeep way back in 08 because (if I remember correctly) I needed it for the TNT full tube fenders that I mounted. For those that are running tube or flat fenders that replace the stock inner fender, especially high clearance models, are you still able to use the stock intake somehow?

Most tube/aftermarket fenders allow the OEM airbox to be retained (not all however).

Highline fenders on the other hand require modifications to the intake (the Aerostar intake mod is a common one).

 

[Jerry Bransford]

There's really no such thing as "no restriction" when moving a fluid through a tube, butterfly valves and through filters. It's just a matter of how much there will be.

Of course there will always be restrictions somewhere, you missed the point. The point being was that the TJ's air intake was designed to have no additional restrictions added on purpose as some air intakes contain. Jim Repp explained very carefully that it is fully capable of easily flowing more air than the engine can consume. He, as Jeep's senior-most engineer at the time (and father/developer of the Rubicon) described the TJ's air intake as "non-restrictive". So when an air intake can easily flow more air than the engine can consume at WOT and redline rpms, most people would consider that to be non-restrictive.

And while colder air is indeed denser and thus allows more fuel to be contained at the right ratio, that benefit is lost on a Wrangler unless perhaps you're racing it at the dragstrip. Theoretical benefits are one thing, truly useful benefits are quite another. When cold air become beneficial is at a point not often reached by most Jeep owners.

 

[WallyWest]

I ran cold air intakes on various sports cars, they may have done some good but we're talking about a few HP. If you were making those things and could demonstrate a 10+ HP gain you would make a shitload of money.

To add to Jerry's last post, I don't think anyone designs their intake to be restrictive. Unless we're talking about those variable systems that only open up fully under WOT. But you can certainly buy some aftermarket intake and LOSE performance because it restricts more than stock. Saw a lot of that in my day.

For anything other than a sports car I would not mess with the stock intake unless there was a known issue to solve.

 

[Jerry Bransford]

To add to Jerry's last post, I don't think anyone designs their intake to be restrictive. Unless we're talking about those variable systems that only open up fully under WOT.

Actually there are some with purposely factory designed restrictive air intakes, often on very high performance engines. For just one semi-famous example... Chevys Z/28 was tested on the GM proving grounds and it proved to be faster than the Corvette. Corvette's brass had a fit that the Z/28 was faster. True. Chevy was forced to install a restrictive air intake to reduce its performance to slightly below that of the Corvette. Mustang's 5.0 is another that comes with a factory designed restrictive air intake.

 

[Woodrow]

The Mustang 5.0 and Camaro Z-28 being two examples of engines that will pick up significant performance gains with nothing more than an intake air system replacement. The TJ's air intake system, on the other hand, was well designed and it is absolutely non-restrictive.

Jerry,

First, what you've said about the TJ stock airbox makes complete sense to me. Even if it were restrictive, it wouldn't make much sense to mod or replace it since these motors aren't high RPM engines; low end torque is more the goal (which I think is often negatively effected by decreasing intake and exhaust restriction?). Power aside, my TJ had a conical filter stuck on the end of the intake tube crossing the valve cover when I bought it. It was really dirty. I put a stock box and filter on it to keep dirt and water out of the engine and noticed no loss of power vs the HOT air intake the PO had set up.

Second, I have a 5.0 Mustang (2012). That IS a high RPM loving motor (easily spins to 7K). Do you have a specific reference for dyno proven intake mod power gains?

 

[SkylinesSuck]

Even if it were restrictive, it wouldn't make much sense to mod or replace it since these motors aren't high RPM engines; low end torque is more the goal

Yes

(which I think is often negatively effected by decreasing intake and exhaust restriction?).

No

 

[pc1p]

Actually there are some with purposely factory designed restrictive air intakes, often on very high performance engines. For just one semi-famous example... Chevys Z/28 was tested on the GM proving grounds and it proved to be faster than the Corvette. Corvette's brass had a fit that the Z/28 was faster. True. Chevy was forced to install a restrictive air intake to reduce its performance to slightly below that of the Corvette. Mustang's 5.0 is another that comes with a factory designed restrictive air intake.

And to add to this - the more common "restrictions" are the addition of Helmoltz devices which are intended to reduce (or enhance) intake noise. My older G35 was a perfect example of this. Same engine and front-end layout as a 350Z. Swapping the OEM Infiniti intake and tube with a 350Z version added more air (as measured by Stillen) and a good bit of sweet, sweet intake noise.

 

[Carve]

low end torque is more the goal (which I think is often negatively effected by decreasing intake and exhaust restriction?).

It's not the restriction that increases torque, but the velocity of the gas. At lower RPM's, a smaller intake or exhaust doesn't add an very much restriction, but it does increase the speed of the gas. If you get the resonance right, it'll actually cram a little more in as the intake valve is closing, or scavenge a little more exhaust out as that valve is closing, which more than makes up for the tiny amount of extra restriction. An intake and exhaust optimized to do this well at low RPM will do it less well at high rpm, and vice versa.

 

[SkylinesSuck]

It's not the restriction that increases torque, but the velocity of the gas. At lower RPM's, a smaller intake or exhaust doesn't add an very much restriction, but it does increase the speed of the gas. If you get the resonance right, it'll actually cram a little more in as the intake valve is closing, or scavenge a little more exhaust out as that valve is closing, which more than makes up for the tiny amount of extra restriction. An intake and exhaust optimized to do this well at low RPM will do it less well at high rpm, and vice versa.

EXACTLY! So many people out there don't get this but think they do based on some bullshit wive's tale about motors "liking a little back pressure."

 

[Woodrow]

It's not the restriction that increases torque, but the velocity of the gas. At lower RPM's, a smaller intake or exhaust doesn't add an very much restriction, but it does increase the speed of the gas. If you get the resonance right, it'll actually cram a little more in as the intake valve is closing, or scavenge a little more exhaust out as that valve is closing, which more than makes up for the tiny amount of extra restriction. An intake and exhaust optimized to do this well at low RPM will do it less well at high rpm, and vice versa.

Well said. That much more clearly describes it. Thank you.