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View Full Version : Reducing the size of air intake



UKJeepThang
07-10-2009, 02:38 AM
Just want to get some thoughts on this.

I've got a Safari snorkel that uses a factory adapter to connect to the airbox. The internal diameter of this adapter is 2.5".

I want to reroute the piping from the snorkel into the airbox (to remove some of the bends) and I'm having to make up a new adapter from plumbing parts. The issue is that the new adapter will have an internal diameter of 1 3/4".

My question is will this have a major impact on the performance output of the engine as effectively I'm reducing the size of the air intake pipe into the airbox by 3/4"

Thoughts?

Mudderoy
07-10-2009, 03:40 AM
Wow that's a great question. My gut tells me it would be a bad idea, but I really don't know. If you are going from 2.5 to 1.75 then back to a larger size you are effectively creating a venturi that would cause the air pressure to drop and speed up.

This should be an interesting thread.

UKJeepThang
07-10-2009, 05:18 AM
Yes I can't decide on this one either!

The hose through the snorkel to the airbox will be 2.5 (internal diameter) and the hose out of the airbox to the manifold will be the standard XJ hose which I beleive is also 2.5. It's just where the snorkel to airbox hose actually enters the airbox and the fitting that I plan to use only has a 1.75 internal diameter.

I just can't find a fitting that I can use that has a 2.5 internal diameter, 1.75 is the largest I can find at the moment. :headshake:

muddeprived
07-10-2009, 05:28 AM
That smaller fitting will slow down the flow of air, not ALOT, but some. You may or may not notice anything. Have you tried going to your home improvement store and looking at pvc pipes and stuff? i made a custom snorkel out of pvc on my wrangler and they have all kinds of sizes from 1"-6" and I'm sure you you can find something that'll work. Got any pictures of what you are fiddling with so we can get an idea of what to look for? I can find you ANYTHING on the internet ;)

UKJeepThang
07-10-2009, 05:47 AM
I'll go out and take some pics and come back in a mo!!

muddeprived
07-10-2009, 06:20 AM
I'll go out and take some pics and come back in a mo!!

I hope "mo" doesn't mean a month. lol

UKJeepThang
07-10-2009, 07:06 AM
Ha Ha!! Moment!!

OK here's some pics:

Here's the snorkel hose

http://i150.photobucket.com/albums/s91/UKJeepThang/Jeep/hose.jpg

And here's how I'm connecting it to the airbox using a "connector" that I got from a swimming pool company. Obviously I'll be sealing up the original opening.

http://i150.photobucket.com/albums/s91/UKJeepThang/Jeep/jeep003.jpg

Here's the connector side on and you can see the difference in diameters at each end

http://i150.photobucket.com/albums/s91/UKJeepThang/Jeep/coupling.jpg

The connector is a snug fit for the hose and I can screw the narrow end into the airbox using a plastic nut on the inside of the box. Once it's all siliconed up it will be nice and watertight.

I've tried home improvement stores over here in the UK but they only supply "standard" sized PVC fittings for things like guttering and downpipes etc. This snorkel hose is not a "standard" diameter.

What do you reckon??

BlueXJ
07-10-2009, 07:24 AM
Check with an elecriical contractor for a 2.5" conduit connector. They are the size you need unless Europe has way different stuff.

UKJeepThang
07-10-2009, 07:57 AM
Ahhhhh! hadn't thought about an electrical contractor. I'll check some out locally!

UKJeepThang
07-10-2009, 09:52 AM
I got the following response on another forum:-

At 2.5 inches, the cross sectional area is 4.9 cu in.
At 1.75 inches, the cross sectional area is 2.4 inches.

Thats less than half, so you'd be choking your engine. It would tick over fine, but when you need some air, there's no
room to get enough down the pipe, which is less than half the cross sectional area it should be.

This actually makes sense to me. So my search goes on for an appropriately sized adapter!

muddeprived
07-10-2009, 10:15 AM
Modify that adapter. Cut the threaded portion off. You should still have a smaller diameter hole. Enlarge that hole so it's the same as the other end, whatever size it is you wanted. Flip the adapter around and place the smooth end from the inside of the intake box to outside and connect the hose to the end of the adapter that's sticking out. Use Silicone before you push the adapter in. It'll fit and stay put.

muddeprived
07-10-2009, 10:27 AM
Here ya go:

Part 1

http://i37.photobucket.com/albums/e73/muddeprived/cherokee/SNORKEL/coupling1copy.jpg


Part 2

http://i37.photobucket.com/albums/e73/muddeprived/cherokee/SNORKEL/couplingcopy.jpg

UKJeepThang
07-10-2009, 10:59 AM
Yahoooo!!! :thumbsup:Muddeprived!! :thumbsup:You are a genius! :thumbsup:
Having looked at the adaptor just now, I think that will work!! OK, that's my job for tomorrow! If I could send you a beer from the UK I would! I'll post pics up here when finished!!

muddeprived
07-10-2009, 11:42 AM
Yahoooo!!! :thumbsup:Muddeprived!! :thumbsup:You are a genius! :thumbsup:
Having looked at the adaptor just now, I think that will work!! OK, that's my job for tomorrow! If I could send you a beer from the UK I would! I'll post pics up here when finished!!

Glad I could help. Hope it works out good. :)

One more thing, make sure the hole on the air box is just the right size. A little too big and the whole adapter will slide through it.

UKJeepThang
07-10-2009, 11:59 AM
Glad I could help. Hope it works out good. :)

One more thing, make sure the hole on the air box is just the right size. A little too big and the whole adapter will slide through it.

Yes I thought that. There is not much tolerance between the smooth end of the adapter and the "nut" part so it's got to fit exactly. I'll post pics when done!

UKJeepThang
07-12-2009, 11:55 AM
OK, it all worked out like a dream. :thumbsup:

Here is the airbox with the original intake hole sealed off (and siliconed from the inside) and the new connector modifyed and installed as per Muddeprived excellent suggestion.

http://i150.photobucket.com/albums/s91/UKJeepThang/Jeep/airbox/236.jpg

I'm going to install the air box back in the XJ this week and I'll do a complete write up in the technical section regarding why and how I did this little project complete with pics.

Another big thanks to Muddeprived for helping me out. :thumbsup::thumbsup:

muddeprived
07-14-2009, 01:29 AM
Looks good. :thumbsup: What kind of sealant did you use on that? I'm looking for the same. I got this window/door silicone sealant II from home depot but the texture of it doesn't look like yours. It's more "chunky" than jelly like yours is.

UKJeepThang
07-14-2009, 04:11 AM
Looks good. :thumbsup: What kind of sealant did you use on that? I'm looking for the same. I got this window/door silicone sealant II from home depot but the texture of it doesn't look like yours. It's more "chunky" than jelly like yours is.


I used the same sort of stuff, just general window/door sealant from my local home improvement store. I only put this sealant on about 5 minutes before I took the picture. That's probably why it looks "soft". After a few hours, it cures up to a nice think rubbery jelly.

muddeprived
07-14-2009, 05:29 AM
I used the same sort of stuff, just general window/door sealant from my local home improvement store. I only put this sealant on about 5 minutes before I took the picture. That's probably why it looks "soft". After a few hours, it cures up to a nice think rubbery jelly.

Hmm mine must be different cuz it spreads out like....cottage cheese. I ended up using black silicone rtv instead. I got this neat can applicator that you sqeeze the handle and it dispenses the rtv. I guess it's working :)