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Old 09-09-2005, 05:48 AM   #1
JW240
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Default Air box mod for 240's

Airbox mod for the 240

Why to remove the airbox restrictions and air preheat thermostat?
-more power, it made a noticeable difference on the butt-o-meter.
-better MPG (mine got a little jump better, but the thermostat in the airbox had failed on my 240 so it sucked hot air the whole time). I get 29 MPG now..
-If the engine gets hot air the AMM (Air Mass Meter) can be damaged and thats a very expensive part..

And on aside note, the engine has a bit more agressive sound when revving it





You start with this... completely remove the airbox. this is done by removing the battery, the battery tray and disconnecting the 45 degrees elbow that goes from the air box to the rest of the engine (amm). Removing it takes maybe 10 minutes..

Tools required: 13 mm socket for battery tray, 10 mm wrench for battery cables (watch out not the short the + to the body, so disconnect negative first!) and a 7 mm socket or flat screwdriver to remove hoseclamps.





To remove the thermostat flapper, there are 3 points where its held in place with little plastic thingies. They are visible when you look at the airbox from the air outlet side. Visible is one of the 3 mounting points. The thing releases when you press the 2 plastic tabs toward each other.

The next 2 steps can be left out if you completely remove the thermostat and valve. I didn't remove it because I didn't had a suitable way of closing the preheated air inlet and I wanted it to be reversible in case I would need it for a government emissions check. Untill now, this mod hasn't given any problems with emission checks.





This is the removed thermostat with flapper. I added maybe 10 small stainless steel washers, so that no matter what the thermostat does (mine was broken, so my engine got preheated air all the time), its always stuck in fully cold air position.





This is what it looks when fitted in the airbox again. It doesn't close all the way, so I added another washer to get it completely closed.

I still added a 50 mm cap on the hot air hose to prevent huge amounts water and dirt from getting in the airbox (the airbox has water drainage holes at the bottem so a bit water won't do much). Then, I connected the hot air hose again over the cap, so when I get a check, no one can see that it is not used..



The preheat hose fitted but if you look carefully, you can see a small red edge where the hose connects to the airbox. The cap is between the hose and the inlet. So the hose has no function, but its still there so they won't whine about it when they chack your car for emissions..





Here is a picture of the snorkel and 90 degree bend that volvo put in front of the air box. Notice the enormous decrease in diameter of the tube! the whole inlet system is at least 70-80 mm, and this is maybe 45 mm! so stupid. Only removing the snorkel gives some gain, but the bend is also very restricting.
The little piece of PVC tube next to it is what I replaced it with, but that was stupid. You have to replace the snorkle and bend with a single 90 degree PVC bend and a piece of pipe and point it upwards. a few water draining holes in the bend can be a good idea.
I want to point out that removing the snorkle and replacing it with a small pieze of tube is not smart! that way more dirt and water can be sucked into the air filter. not that that would hurt your engine immediately (well a lot of water would), but it reduces the lifetime of the air filter and it can damage it.
So a 90 degree bend should be used, but there isn't much space and when the airbox is back in place, its very very difficult to put the new bend in! I had to install the bend while the airbox was fitted and it was very difficult and it required some brute force...





This is where the 90 degree bend is fitted.. It fits barely in the small space behind the headlight and its a PITA to install with the airbox fitted.. Some zip ties can be used to calmp everything firmly against the bodywork.








The piping I used as a replacement of the snorkel. Its 75 mm outside diameter. about 3".


The next step is to remove one or bothe of the screens of the AMM. I would leave the first one in place to prevent any debry's from entering the engine and damaging the AMM if the airfilter would fail or a hose break.

What I did soon after the aibox mod was to clean the Throttle body and I checked for leaks past the AMM, and I found one in the thick hose between the AMM and the TB, just after the AMM, there the hose rubs over the battery cables that run to the starter. The car drove better after cleaning the TB and injectors.
I get almost 29 MPG with my 240, and I don't drive slow at all.. so I recon the upgrades are good

JW

BTW: during the winter, i use a extra 90 degree bend on the intake that points a bit to the rear to prevent rain and snow from entering the airbox...
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Old 09-09-2005, 05:49 AM   #2
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I would like to add for which years this mod works. I have a 1991 240, I believe all B2XX 240's from 1985 and on have it this way but i am not sure...

I did this mod in May 2005 and it hasn't given my any problems since then.

Last edited by JW240; 09-09-2005 at 05:53 AM..
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Old 09-09-2005, 03:24 PM   #3
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removed

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Old 09-10-2005, 10:51 AM   #4
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so what exactly do i need to drag out of there?
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Old 09-10-2005, 01:47 PM   #5
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just rip out the snorkle, and bend, replace that for a 9- degree elbow sewer pipe fitting, and remove or block the thermostat....
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Old 09-10-2005, 03:02 PM   #6
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I'd like to add that it's not so much improved sound when you rev it, but when you get on it under load. That's when you hear it the most, and it's yummy!

I think you could also adapt our pictures of the mod from the other post we have, where we cut out the front of the box on an '84 240.
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Old 09-11-2005, 03:40 AM   #7
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OK I'll look at it
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Old 09-11-2005, 10:32 PM   #8
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this was one of the first things i did when i got my car, about 4 years ago. Only i left the Volvo plastic snorkal, and cut a V out of the top to try and get more air flow into the box. I also used a cutting wheel to cut the hole in the air box that is shaped like a funnel so that it would be flat and that even more air would enter the box.

You can see the funnel shaped hole molded into the box that points right at the thermastat for the hot air hose assembly
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Old 09-14-2005, 05:39 PM   #9
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Don't do this in CA...My '84 240's preheat was stuck open, so I removed it and the smog inspection failed my for tampering with it.
 
Old 09-21-2005, 10:06 AM   #10
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anyone know if compleatly removing the thurmo will make you fail inspection in TX?


and couldn't you just clog the warm air hole, so that even if it opens no air would go into the box.
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Old 09-21-2005, 09:45 PM   #11
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They don't care in TX
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Old 09-22-2005, 06:30 AM   #12
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Quote:
Originally Posted by chunky
....
and couldn't you just clog the warm air hole, so that even if it opens no air would go into the box.
if it would turn to preheating, your engine won't get any air or with a very high resistance...
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Old 09-22-2005, 11:04 PM   #13
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ok, is the thurmo wired in at all? if i cut the wires and just pull the thurmo out is it going to throw codes or anything?

if i pull the thurmo out and then just put a cap over the hole will it still cause resistance?


as of now i just pulled the hose off so when the flapper opens it just pulls in air from under the car.
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Old 10-21-2005, 12:15 AM   #14
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Quote:
Originally Posted by chunky
ok, is the thurmo wired in at all? if i cut the wires and just pull the thurmo out is it going to throw codes or anything?

if i pull the thurmo out and then just put a cap over the hole will it still cause resistance?


as of now i just pulled the hose off so when the flapper opens it just pulls in air from under the car.
mechanical thermostat.
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Old 12-16-2005, 05:10 PM   #15
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bump for adding some pictures!
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Old 12-20-2005, 12:14 AM   #16
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I think i'm gonna do this to my 240. I'll probably remove the headlight for easier access though. How exactly did you ziptie the bend down? Oh yea, I removed the thermostat assembly a while ago. I'm gonna have to saw off the rest of the preheat hose or something b/c it won't come off. And then i'll just cap off the preheat hole.
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Old 12-20-2005, 12:17 AM   #17
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nice write up and great pics.
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Old 12-20-2005, 01:32 AM   #18
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Quote:
Originally Posted by growley
I think i'm gonna do this to my 240. I'll probably remove the headlight for easier access though. How exactly did you ziptie the bend down? Oh yea, I removed the thermostat assembly a while ago. I'm gonna have to saw off the rest of the preheat hose or something b/c it won't come off. And then i'll just cap off the preheat hole.
I've done something similar on 2 of my 240's now. There's no need to remove the headlight, the battery, or the battery tray. Just put the 90 degree bend in first, then the snorkel you made, then finally hook it up to your airbox. I also removed the air heater from the exhaust pipe, and the brackets for the preheat hose, to save weight and tidy things up.
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Old 12-20-2005, 02:31 AM   #19
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Quote:
Originally Posted by Dauntless
I've done something similar on 2 of my 240's now. There's no need to remove the headlight, the battery, or the battery tray. Just put the 90 degree bend in first, then the snorkel you made, then finally hook it up to your airbox. I also removed the air heater from the exhaust pipe, and the brackets for the preheat hose, to save weight and tidy things up.
I was thinking the same thing. In fact, you probably wouldnt even have to remove the airbox...
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Old 12-20-2005, 03:10 AM   #20
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My version is to cut out the front of the airbox, not all of it, but most of it, and then re route the preheat hose(after removing the T-stat) under the bumper to one of the holes down there. Leave the stock bendy elbow in place, but not have anything else in front of the support panel there, just the open elbow. Makes for a nice growl, and better performance than just putting some more restrictive stuff up front... And it's cheaper as well. FWIW.
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Old 12-20-2005, 12:43 PM   #21
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I wanted to clamp the pipe with zip ties to the frame, but I never got around to do that. The pipe hasn't come off, it's still on there very good.
I mamaged to mount the bend behind the headlight without removing the airbox, but it was very difficult... I guess that 5 mm matters a lot, the bend was just a bit too big.
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Old 12-20-2005, 01:43 PM   #22
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Nice mod!
I'm seriously considering doing this.
It should be a good follow-up to my headlight mod (working on that now) - dual 6x8" sealed beams should leave room for some ductwork.

Can you confirm?
1) Original short hose goes from air box to existing hole in headlight/radiator support bracket.
2) New 90-degree bend goes on front side of bracket, points towards front of radiator area.
3) 30 or 45-degree bend points approximately towards the horns?

Thanks!
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Old 12-20-2005, 02:08 PM   #23
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Quote:
Originally Posted by brucepick
....
1) Original short hose goes from air box to existing hole in headlight/radiator support bracket.
2) New 90-degree bend goes on front side of bracket, points towards front of radiator area.
3) 30 or 45-degree bend points approximately towards the horns?
exactly!
the 45-degree bend is not really needed, but that way it takes the air from a bit higher so in the case of deep water its a bit safer.
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Old 12-20-2005, 02:52 PM   #24
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I just bought a 3" (what is supposed to be a 3 inch but ended up being more like 3.5") 90 deg bend but it was too large for the aforementioned reason. I measured the hole that goes through the headlight support and it was about 3 inches. Removing the headlight helps alot, but it is still hard to fit it in there with the frame and the wiring harnesses. I'm going back to the hardware store to get a smaller diameter bend.
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Old 12-20-2005, 03:16 PM   #25
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Quote:
Originally Posted by growley
I just bought a 3" (what is supposed to be a 3 inch but ended up being more like 3.5") 90 deg bend but it was too large for the aforementioned reason. I measured the hole that goes through the headlight support and it was about 3 inches. Removing the headlight helps alot, but it is still hard to fit it in there with the frame and the wiring harnesses. I'm going back to the hardware store to get a smaller diameter bend.
3" is usually inside diameter I guess...
Over here in europe, the things are measured in mm and the outside diameter. 75mm fits very good, so 3" OD or maybe 2.5" ID (IIRC, that means 76 mm OD) is the best I guess..
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