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Old 09-09-2004   #1
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Exclamation Hot air intake to air filter

Just a thought with summer on the way (sorry, winter for most of you lot!)

Check the air filter housing flap (1116cc/1301cc models) that selects hot air from around the exhaust manifold or cold air from the front. The flap is supposed to start off with the cold air sealed off. A wax capsule expands and pushes the flap open when the temperature increases.

My tests show that the wax capsules (tested two of 'em) simply don't work when needed. Flap stays in the hot-air position even when engine bay baking hot. Testing with hot-air gun showed that capsule started to open more or less as the plastic of the air filter housing melted.

My suggestion - until we come up with a better solution, pop the casing apart and remove the flap. Block off the hot air intake. Unless you live in the northern hemisphere - in which case, now would be a good time to check your hot air pipe (to manifold) is in place.

I'm thinking of a microcontroller-controlled motor to close and open the flap when needed (properly).

Cheers,
-Alex
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Old 09-09-2004   #2
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Re: Hot air intake to air filter

Another slightly easier but more compromising solution would be to remove the flap, but instead of completely blocking off the hot air intake, use a partial block ie leave a smal cut out approx 1/4-1/3 the size of the entire opening. This will allow for when the weather is cold but wont pump through so much hot air that it has a hugely negative effect on the performance. In fact the engine could do with a small volume of warm/hot air at all times for it to work best, just not as much as a completely unrestricted pipe would let through.

Leon.
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Old 09-09-2004   #3
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Re: Hot air intake to air filter

Does this feature on the 1108cc engine?
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Old 09-09-2004   #4
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Re: Hot air intake to air filter

Yep It does indeed....It is a feature found on most cars....and removing it completely isn't the best answer for most SPI or carbed engines especially in winter, as they do rely on some warm air to run best even when the weather is hot. If the weather is hot you can get away with removing the pipe and the warm air is provided by the engine heating up the engine bay....but the best bet is to leave the pipe connected ... but control the flow rate/ volume of warm air.....of course where people go wrong is by overdoing the shift in ratios warm to cold.....by design the cold air is somewhat force inducted into the airbox by the forward speed of the car, which also has the effect of cooling the air down through wind chill.....the warm air simply is sucked up by the vacuum produced from carb/SPI and a little by the cold airflow dragging across the opening to the warm air duct hence you will never get greater volume of warm air than cold as long as you draw the cold air from the front of engine bay(ie right behind grill area). The best thing to do is to ensure a fairly large 'scoop' to collect the cold air....followed by some heat shielded piping to the airbox, and if possible heat shield the airbox itself too. Then restrict but maintain a constant warm air supply via the original pipe from the manifold.


Easiest way to set it up is get the cold air going in how you're happy. Then make some restrictors for the warm air with different diameter holes getting progressively larger. And basically test your car running with the different diameters until you find the one that allows the engine to run the best. Then stick with that one and enjoy.
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Old 10-09-2004   #5
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Re: Hot air intake to air filter

I have to say. Throw the whole air-box. Insert a conefilter from K&N straight onto the SPi. Route a 50 mm flexible hose from front and appx. 50 mm away from the filter. During winter, just route the hose somewhere else. Ive done this to my 1993 Uno 1.1 i.e.S.

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Old 10-09-2004   #6
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Re: Hot air intake to air filter

Fair enough, Mort! I'd have thought you had problems in cold weather but then again you don't have one of those poxy 2-barrel carbs. :-) I know, I know, they ought to be great but I find that Unos are very patchy to drive, plus of course the starting difficulties as mentioned in the other thread.

I guess what I was fishing for with this thread was - does anyone's thermostatic flap seem to operate correctly? Has anyone replaced the wax-capsule thingie?

-Alex
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