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Author Topic: Hot inlet air device  (Read 10944 times)
roy4matra
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« Reply #15 on: August 14, 2007, 05:36:28 pm »

My bad english... I understood that ...true 'S' does have one of these, but Prep 142 it has not connected...
Sorry for stupid question  Roll Eyes  Wink

No.  Both the Prep 142 and 'S' have the original air filter which is connected to the cold/hot air intake device, but the air flap diaphragm is not connected to anywhere, so it stays permanently open to cool air only.  It never changes to the hot intake side.

On standard 2.2 Murena, the plastic elbow bolted to the top of the 34CIC down-draught carburettor has a small temperature sensitive device inside it, which is connected to vacuum (inlet manifold) one side and the other side is connected to the air flap.  When the intake air is very cold, the temp. device opens and directs the vacuum to the air-flap diaphragm pulling it so that the intake air is drawn from the hot side.  When the intake air is warm enough the temp valve closes and the vacuum is blocked, so the air-flap returns under spring pressure to its closed position and only cool air is drawn in.

The 'S' has a different device mounted under the manifold which the Prep 142 does not have.  I think you are confusing this device with the regulated air intake device.

Roy
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Anders Dinsen
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« Reply #16 on: August 19, 2007, 07:16:44 am »

I got the device and vacuum installed yesterday. Finding T-pieces in different sizes wasn't straight easy, but I managed to find a 10-6-10 piece that I installed in the vacuum hose to the manifold base coming off the engine breathing filter.

A photo showing the complete installation:


In case anyone wonders what the vacuum thermostat looks like, here's also a photo of that. Blowing through it before installing it showed me that it seems to switch at around 20 degrees, which makes sense as I have read somewhere that the carburettor is design for 30 degrees air.


I'll report my experiences driving with this installed over the winter.
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'82 Murena 2.2 prep 142
'01 Grand Espace 24v
'08 Smart Fortwo 0,8 cdi
Anders Dinsen
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« Reply #17 on: August 19, 2007, 10:58:49 am »

Uhoh, just realised that I have connected to the only vacuum connection on the manifold where there isn't vacuum at all: The other end is connected straight to the inlet elbow through the three way filter! I'll move it later today.
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'82 Murena 2.2 prep 142
'01 Grand Espace 24v
'08 Smart Fortwo 0,8 cdi
Anders Dinsen
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« Reply #18 on: August 24, 2007, 09:03:04 am »

I fixed the vacuum, tapping into the hose to the headlight lifters.

There is a noticable difference on the engine in practical driving with the hot air device fitted. Cold starting is easier and it runs a bit better cold. This is probably due to the reduced amount of condensation of fuel in the manifold as Roy mentioned. Warm up time is also improved - the engine is now noticable quicker to warmup. Also predicted by Roy. It wasn't bad before, but now it is even quicker. City driving in low rev's and idling is also improved with a more stable and slightly better sounding idle.

Hot air burns faster than cold, so by allowing the engine to breath warm air, a similar effect as advancing the ignition may be accomplished. As I do a lot of city, low rev, low throttle driving, I expect a slightly improved fuel economy because of this.

Some might think the hot air will reduce performance. True, cold air contains more oxygen per volume than hot, but first of all, the temperature isn't that much higher (e.g. a temperature increase of 20 degrees results in only about 7% more molecules per volume) and besides, in full load situations, the device switches over to cold air anyway. This is because at full throttle, vacuum in the manifold is reduced and even if was still breathing from the hot air inlet, the increased airspeed around the exhaust will mean less temperature increase.

Winter will tell the difference regarding carburettor ice, but so far, I can say that if you have the device, don't consider it insignificant! I have learnt something interesting by running without and now with the device Smiley
« Last Edit: August 24, 2007, 10:40:35 am by Anders Dinsen » Logged

'82 Murena 2.2 prep 142
'01 Grand Espace 24v
'08 Smart Fortwo 0,8 cdi
Anders Dinsen
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« Reply #19 on: November 19, 2007, 10:17:53 am »

Time for an update:

No carb ice so far, excellent cold running - this thing is very recommended unless you *only* use your car in the hot.

I thought I had carb ice the other day though. After 70 km on motorway, the idle settled at 2000 rpm and only slowly climbed down. This was what I had been experiencing last year post-acceleration in cold weather, but when I opened the hatch just to check, I found that the little lever operating the accelerator pump had jumped off the lifter on the throttle - I had been experiencing some dead spots lately - and with that back on the idle was back "spot-on", it was just the arm that had kept the throttle slightly open...
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'82 Murena 2.2 prep 142
'01 Grand Espace 24v
'08 Smart Fortwo 0,8 cdi
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