Ideal Intake Air Temp?? - Fuelly Forums

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Old 11-27-2007, 05:53 AM   #1
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Ideal Intake Air Temp??

I recall a thread discussing controlling the intake air temp with temp sensors and servomotors. Where?

Most importantly, what's the ideal intake air temp?? Somehow I recall reading that it's 60-80 deg. F but I have no idea if that's correct.

Reason I'm interested - my Volvo 240 came oem with an intake air temp regulator in the air box. Mine and most of these by now have the regulator disabled for various reasons. I can restore it to oem or set it up any way I want. I have a digital thermometer that I'll set up to read IAT so I'll know the temp of air going into the engine.

Thanks, guys!
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Old 11-27-2007, 10:11 AM   #2
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The 87 Honda civic engineers decided it should be 100 degrees F and set up the system to regulate itself to achieve this temp. But this car has a carb, it might be different for EFI.
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Old 11-27-2007, 11:57 AM   #3
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Quote:
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The 87 Honda civic engineers decided it should be 100 degrees F and set up the system to regulate itself to achieve this temp. But this car has a carb, it might be different for EFI.
Thanks.

My guess is, fuel + air ignites optimally at some particular air temperature. Maybe slightly different depending on compression. I think what does change with fuel injection is, an AMM sensor it is not fooled by air temp changes. So it can be designed to accept incoming air of a wider range of temperatures.

Anybody else have input on ideal intake air temperature?
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Old 11-27-2007, 06:22 PM   #4
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bruce, I'm by no means knowledgeable on this topic...but I was under the impression that colder air is denser air and dense air is more condusive to maximizing ignition efficiency.

Maybe someone can set me strait on this?
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Old 11-27-2007, 06:40 PM   #5
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bruce, I'm by no means knowledgeable on this topic...but I was under the impression that colder air is denser air and dense air is more condusive to maximizing ignition efficiency.

Maybe someone can set me strait on this?

colder, denser air is typically what people want for more power, not efficiency. More oxygen molecules in colder air requires more fuel and produces more power.

Warmer air, conversely is not as dense and needs less fuel to maintain stoich.
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Old 11-27-2007, 07:11 PM   #6
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Originally Posted by brucepick View Post
Thanks.

My guess is, fuel + air ignites optimally at some particular air temperature.
Given the range of potential air temps possible for a car... Nope - given air and fuel (in proper mixture), it will ignite It's the sensors in the car that change that, which seems to vary from mfr. to mfr. Go as hot as possible - just before engine management doesn't like it
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Old 11-27-2007, 07:27 PM   #7
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175 to 180 degrees will give optimal economy that I've seen. Over that I seem to lose too much power, possibly due to spark retard from ping. If you can get 175 degrees, you can calculate the difference in fuel consumed by taking the percentage of weight reduction of using the hotter air. Of course, this assumes your car injects fuel to match oxygen at 14.7 to 1 by weight like mine does.
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Old 11-27-2007, 08:53 PM   #8
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before you guys get all hot air=efficient gung ho and stick a blow torch in your engine bay, the reason it's more efficient to bring hot air in (to a point) is that yes, the air is less dense and less fuel to match the oxygen BUT you still need to produce the same amount of power to travel down the road at a constant speed. the reason for the increase in efficiency is that to counter the power LOSS from warm air, you open the throttle wider. what is the throttle? the biggest restriction to your car breathing freely. warm air does NOT=efficiency, warmer air results in less throttle restriction which results in efficiency
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Old 11-27-2007, 09:00 PM   #9
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Quote:
Originally Posted by kamesama980 View Post
before you guys get all hot air=efficient gung ho and stick a blow torch in your engine bay, the reason it's more efficient to bring hot air in (to a point) is that yes, the air is less dense and less fuel to match the oxygen BUT you still need to produce the same amount of power to travel down the road at a constant speed. the reason for the increase in efficiency is that to counter the power LOSS from warm air, you open the throttle wider. what is the throttle? the biggest restriction to your car breathing freely. warm air does NOT=efficiency, warmer air results in less throttle restriction which results in efficiency
However you have to slice it... Hot Air --> less fuel

It's not so much the lack of restriction - it is restricting, but less air is physically in the cylinder. It's less pumping losses -- higher load
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Old 11-27-2007, 09:22 PM   #10
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at a given speed, you have a given drag, which you need to expend a given amount of energy to counteract. the energy in gas is fixed and to maintain a stoich mixture, so is the air. therefore you have the same air in the cylinder but yes, less pumping loss due to sucking it through a bigger hole (more open throttle)
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