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B 21 FT Air Box Modification For Cold Air...

7K views 5 replies 5 participants last post by  gdill2 
#1 ·
I just have one question regarding the air box modification that I've been seeing for the last few years. What is so much better about it then using the original, big snorkel that comes through the radiator support and angles over to right behind the grille, and just removing the hot air thermostat and blocking off the hot air intake side of the box while removing the hot air pipe from the manifold shield? I don't get it. I just did the above mod this afternoon, and even with temps over 100 degrees, I could really feel the "pull" in a gear that I would have downshifted from into a lower gear. The difference is really phenomenal. After I removed the thermostat, all I did was to place a little spot of epoxy on the hot / cold air flap to keep it in the cold-air mode, removed the heat tube, and capped the hot air inlet to keep any under hood air from being sucked in. Then, I painted the cap that I used black so that the smog guy wouldn't see it. What could be simpler? Volvo already put a big molded pipe angled over right behind the grille for atmospheric temp air.
Any input? George?
 
#2 ·
Re: B 21 FT Air Box Modification For Cold Air... (JBLasVegas)

Here is my easily reversed air box mod on a stock 240 B230F non-turbo...

(modify as needed for B21, etc)

Materials: New or used good exhaust manifold pre-heat flex DUCT/HOSE just like on the car.

1. Remove and save: fresh air box thermo and flap (snaps out/in), mass air meter screens (2) and stock air filter.

2. Disconnect the pre-heat duct from the heat collector at the exhaust manifold. Re-route this end under the fan shroud to a point just above and behind the front air dam near the RF corner of the car - secure.

3. Connect one end of the new/used duct to the heat collector and follow the stock route to the fresh air box but do not connect - just dummy under the fan shroud and secure.

4. Re-install stock air filter or aftermarket as desired (if re-usable aftermarket filter do not over-oil).

5. Inspect the ENTIRE intake system for leaks and repair as needed (including the flex hose between the mass air meter and throttle body).

Now the fresh air box has TWO sources of cool air - the original snorkel and the duct at the air dam.

Next would be a free-flow exhaust and a test of the cat for no flow restrictions and proper Ox readings at the tailpipe.

George Dill
 
#3 ·
I'm running similar to George's.

* Took out airbox flap/solenoid, trashed.

* Kept AMM screens in place.

* Preheater hose rerouted to air dam.

* Second preheater hose routed from exhaust header to under bumper for "emissions" reasons.
 
#5 ·
Where I live we still have real winters. All of my 240s (now three since two days ago) run with no pre-heat hose and the gubbins in the air box, and I've never had any problems firing them up in the cold. You live in a warmer climate, so remove the pre-heat hose for some other use, remove the whole pre-heat thermostat and door assembly, and seal off the pre-heat hole in the air box. And the latter is important as you don't want the air intake sucking in hot air from the engine compartment as that could eventually fry the MAF.
 
#6 · (Edited)
Rather than disconnect the pre-heat hose from the air box just re-route the other end along the bottom edge of the radiator, out the engine compartment below the side sheet metal and then tie it up just above and behind the front air dam. Be sure the hose has a downhill run somewhere away from the air box. If you run on gravel/mud a lot slap a piece of 1/4" mesh over the open end of the hose. The air box will draw fresh air from both the hose and the existing snorkel. For inspection just run a dummy hose from the pre-heat chamber on the exhaust manifold along the same route as the original hose then hide the loose end under the air box but not near the snorkel.

During extended periods of very cold weather this mod can hurt mpg and may cause engine wear.

George Dill
 
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