Birty Dastards Jeep Club

Tech Forum => Workshop => Topic started by: Jeepthang on June 08, 2009, 09:03:30 PM

Title: XJ 4.0 - Does the second airbox serve a purpose?
Post by: Jeepthang on June 08, 2009, 09:03:30 PM
I6 4.0 XJ

Something that i've been wondering for a while. Apart from being a convienient place to put your mug of tea and /or your tools on when working on the engine, does the second airbox that sits on top of the engine (and is fed from the air filter box) actually fulfill a purpose.

I've noticed that the I6 engines in XJ's featured on US forums don't have this box whilst the UK vehicles do.

Any reason for this  :?:
Title: Re: XJ 4.0 - Does the second airbox serve a purpose?
Post by: dxmedia on June 08, 2009, 09:35:25 PM
My ZG doesn't have one, but are you talking about the plenum chamber?
Title: Re: XJ 4.0 - Does the second airbox serve a purpose?
Post by: dxmedia on June 08, 2009, 09:42:12 PM
heh, yeah it's there for a reason if your talking about the plenum.

If the air in went to a pipe which then fed 1 2 3 4 5 6 cylinders in that order, cylinder 1 would have the highest air pressure, decreasing down to 6. A plenum chamber is designed so that there is equal air pressure across all outlets.

Well at least that's my understanding.
Title: Re: XJ 4.0 - Does the second airbox serve a purpose?
Post by: donk498 on June 08, 2009, 11:14:33 PM
The second box on top of the throttle body is there to cut down on intake noise. It a resonance (spelling?) chamber. You can remove it and fit the hose off a mk1 xj without causing a problem.

Dave.
Title: Re: XJ 4.0 - Does the second airbox serve a purpose?
Post by: Bubba on June 09, 2009, 05:33:28 AM
it is deffo to put ya mug of tea coffee on
Title: Re: XJ 4.0 - Does the second airbox serve a purpose?
Post by: JamesH on June 09, 2009, 08:55:42 AM
As Donk said, it's to reduce noise. I removed mine and fitted the earlier model intake tube.
Title: Re: XJ 4.0 - Does the second airbox serve a purpose?
Post by: Jeepthang on June 09, 2009, 11:35:33 AM
Thanks James and Donk for letting me know what it is. I knew it wasn't the plenum.

So what's the benefit of removing it? I wouldn't have though an increase in intake noise was a benefit and it is handy for your mug of tea!!  :mrgreen:
Title: Re: XJ 4.0 - Does the second airbox serve a purpose?
Post by: JamesH on June 09, 2009, 12:10:37 PM
I needed the extra space when fitting my lpg conversion.
Title: Re: XJ 4.0 - Does the second airbox serve a purpose?
Post by: Jeepthang on June 09, 2009, 12:33:41 PM
Excellent, I was hoping that extra space was the prime reason for removal.

Mine's coming out!