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Anyone know why there is an air restrictor leaveing the air box to the engine. This is the case for all 6 cyc YJs as far as I know. It is a little plastic tube insert that is just before the hose as it leaves the air filter box.I was told that if you remove it, it will add 5 to 10 HP of power. It stands to reason that with more air you get move power and better gas milelage.

I have taken mine out now for about a month and haven't really noticed any difference. However....does anyone know why it is there in the first place?:confused:
 

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A lot of vehicles have air restrictors on them.

I think they are meant to slow down the air which reduces the sound. Auto makers when manufacturing a vehilce try and make them for the masses and most people don't want to hear rushing air when they stomp on it.


I didn't find that much of a difference. But when you combine that with a free flow air filter and a high flow exhaust, it all starts to work together.

You can also bore out your throttle body behind the butterfly. Now that with the other mods, I noticed the difference.
Rob
 

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Drevs said:
Anyone know why there is an air restrictor leaveing the air box to the engine. This is the case for all 6 cyc YJs as far as I know. It is a little plastic tube insert that is just before the hose as it leaves the air filter box.I was told that if you remove it, it will add 5 to 10 HP of power. It stands to reason that with more air you get move power and better gas milelage.

I have taken mine out now for about a month and haven't really noticed any difference. However....does anyone know why it is there in the first place?:confused:
I got the same results as you.

...lars



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I think it's a venturi. If I recall correctly, there's a small rubber hose plugged into the intake tube right at the point where the "restrictor" is, right? My guess is that the venturi is used to create vacuum, to draw fumes through that small hose, which is probably connected to the charcoal canister or somewhere else in the emissions system (PCV?)

...or I could be entirely mistaken :p

Chris
 

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Discussion Starter · #6 ·
So then would this be a bad thing to remove then???
 

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Drevs said:
So then would this be a bad thing to remove then???
I noticed no difference. That begs the question: why bother removing it? Perhaps if you modified other stuff like your exhaust etc, then it might be worthwhile, but I don't know if it would adversely affect that vacuum line that is going to it.

OTOH, I don't think it would hurt. In fact, you probably wouldn't notice any diff unless you dyno'd it before/after and also did emissions tests before/after.

...lars



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When I removed mine from my XJ I noticed a slight difference in the throttle response... I've got a cat-back and K&N also...and I drive it a lot during the week, so I noticed it. It wasn't anything to run though the streets crazily about, but I noticed a little. I got a lot better results out of boring my throttle body though. ;) There's no lag anymore when I stomp it. Improved my gas mileage too (as long as I am conservative tih the pedal!).
 

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I've heard some people complain of a raw gas smell when the truck's off, after doing this "mod". Lars, did you notice that?

Anyway, it's not like you're going to see a huge benefit or anything. Maybe give the engineers who designed the thing the benefit of the doubt until a better idea comes along...?

Chris
 

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The reason for the restrictor, which increases air velocity, is to tune the air entering or passing through the tube. The main purpose is to reduce noise. Kind of an intake muffler. Much like flipping the lid on the old circular air filter boxes but without as much effect. I didn't notice anything either but any restriction can't be good.
 
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