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 Place for switches or gauges 
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Firing on two.
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Joined: March 21st, 2013, 12:04 am
Posts: 1005
Location: Exeter, Devon
Post Re: Place for switches or gauges
Thinking about again, im wrong, because it going to depend on thecbias resistor.

More to follow :)

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May 11th, 2020, 7:08 pm
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2CV Fan

Joined: October 12th, 2019, 6:40 pm
Posts: 59
Location: Limburg Belgium
Post Re: Place for switches or gauges
Our 2 cylinder boxermotor is air cooled. A CLT seems to be superfluous, and where to put an AIT ?


May 12th, 2020, 10:32 pm
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Firing on two.
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Joined: March 21st, 2013, 12:04 am
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Location: Exeter, Devon
Post Re: Place for switches or gauges
The iat can go in the air filter box I think.

Regarding coolant, you need to be able to enrich the mixture to start the engine. Warm up enrichment (WUE). Could do it with a knob on the dash :)

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If you can't fix it with a hammer, it's probably electrical (or, an electric fuel pump!) ....


May 12th, 2020, 10:56 pm
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2CV Fan

Joined: October 12th, 2019, 6:40 pm
Posts: 59
Location: Limburg Belgium
Post Re: Place for switches or gauges
@Roger V: OK, so both CLT and AIT are in fact needed. For AIT I would then place it somewhere in the box around the cooling fan, the CLT would go on the heated airbox around one of the exhaust pipes. Can these solutions be supported ?


May 13th, 2020, 8:52 am
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Firing on two.
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Joined: March 21st, 2013, 12:04 am
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Location: Exeter, Devon
Post Re: Place for switches or gauges
To know where to place them, you need to understand why they are needed. :)

Engine temperature (Coolant!).

Contrary to what what people think, petrol does not burn, petrol vapour burns. And its only the surface area of the petrol droplets that give off the vapour. Warming up the petrol also helps the liquid petrol turn into vapour faster.

So when an engine is cold, the petrol going into the engine is cold, and the surface area of the petrol droplets cannot so easily turn into vapour.

The simple answer is to increase the surface area of the petrol to achieve the required amount of vapour for the engine to run. This is done by adding more droplets. Or simply put, by increasing the amount of fuel entering the cylinder.

Not sure the air temperature in a heat exchanger is going to be sufficiently accurate of have enough range to work.

IAT (Inlet Air Temperature)

The iat measures the temperature of the air coming into the engine to determine its density. the density is important because a denser material (gas in this case), has more molecules in a given volume than a less dense one. With a gas the difference can be considerable over the range of temperatures that air enters the engine.

Obviously, it's oxygen in the molecules that we are interested in, as this is combined with the petrol to burn, As the amount of oxygen varies with temperature, we need to vary the amount of petrol.

Then, if we want to be as accurate as possible, then we mount it as near the place where it combines with the fuel as possible.

However, it not practicable to mount it at the injector, because the heat from the engine will affect the sensor as much as the air temperature.

General consensus appears to be to mount it in the air inlet to the throttle body. However, this can cause an issue (same issue as at injector) with engine heat. The issue is known as Heat Soak. The sensor heats up from heat from the engine and this can cause starting problems. The issue wil also vary from vehicle to vehicle. Big V8 with lots of heat trapped under the bonnet, to small 2CV with lots of air circulating via fan.

For simplicity and ease of wiring, I've drilled a hole in the side of the air filter. Its not tested yet as its only running on ignition at the moment.

I'll write a bit about these sensor operate later to help understand why I previously said a knob on the dash. :)

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If you can't fix it with a hammer, it's probably electrical (or, an electric fuel pump!) ....


May 13th, 2020, 12:02 pm
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Joined: March 5th, 2009, 6:23 pm
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Location: Near Monmouth
Post Re: Place for switches or gauges
V good description.


May 13th, 2020, 12:49 pm
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Joined: October 12th, 2019, 6:40 pm
Posts: 59
Location: Limburg Belgium
Post Re: Place for switches or gauges
@Roger V : The process of getting a good mixture of air and petrol (14,4 to 1) is more or less known, but thanks for the details of it.
The AIT is indeed also dependent of the radiant heat coming from the engine. So just taking the outside air is not accurate enough. Maybe the best place for the sensor is on the backside of the manifold underneath the carb. It’s easier to fix it in the spider on either side of the carb fixation point. I would place it on or in a bung so that the air in the manifold is not restricted.
About the CLT. There may be a problem indeed. The heater box is heated by the exhaust maybe too rapidly, whereas the air intake for the combustion is still not stabilized. So a slower heating up of the CLT should be found. Like with the AIT, this CLT sensor could also be placed on the heater box such that a “certain distance” is created between the sensor and the air going through. Could a longer bung help here too ?


May 13th, 2020, 6:14 pm
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2CV Fan

Joined: October 12th, 2019, 6:40 pm
Posts: 59
Location: Limburg Belgium
Post Re: Place for switches or gauges
@jasu : You have indicated to have built experience with EFI over some years.
Maybe you can add extra info over the above subject ?


May 13th, 2020, 6:22 pm
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Joined: October 12th, 2019, 6:40 pm
Posts: 59
Location: Limburg Belgium
Post Re: Place for switches or gauges
@Roger V : sorry I forgot to say that I am not using the standard intake air box with filter, but a small sports filter. I cannot add the AIT in that.
On the other hand, when I can drive again (covid 19 measures don't permit me to drive around for fun, only for essential things) I can do some measurements with a pro thermometer and thermo couple (calibrated). I can read the slope of the rise on various spots. But that's for later.


May 13th, 2020, 8:42 pm
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Firing on two.
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Joined: March 5th, 2009, 6:23 pm
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Location: Near Monmouth
Post Re: Place for switches or gauges
See also @lpgo for Igntion & Injection


May 14th, 2020, 9:00 am
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