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Intake Air Temp and Pressure vs Economy 


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 Post subject: Re: Intake Air Temp and Pressure vs Economy
Posted: Wed Oct 05, 2005 8:57 pm 
Getting Side Ways

Posts: 6449

Joined: 11th Nov 2004

unclewoja wrote:
tickford_6 wrote:
it's a very well thought out theory.

Though i have problem with it.

i agree that with denser air there is more oxygen and hence a small throttle opening, But using less throttle in the instance will not increase pumping losses. WHY? because with the colder air you have MORE oxygen. and hence for a smaller throttle opening the SAME amount of oxygen is going in. so the engine needs a smaller amount of air to make the same power. Not the same amount. if it was trying to suck the same amout of air through the smaller opening then yes more pumping losses.
the instance that this would happen is if a larger cam was fitted. and we all know what happens to economy then.

if you want to reduce pumping losses focus on getting gas out not in.

What about if I talk in CFM? Endothermic reactions and differences in temperature aside, if you need to make 20kW, you neex X amoutn of fuel and y amount of oxygen molecules.

Now, let's say @ 10C, the amount of oxygen required perminute is 20 CFM (cubic feet/min for those of you who don't know) If you decrease the density, the amount of oxygen needed remains the same as you're using the same amount of fuel, but it's taking up more volume. So, now you might need 30CFM if the air temp goes up to 30C.

It takes power to create a vacuum. The more vacuum you need, the more power you need. This can be seen if you switch your engine off going down a hill. If you hold the throttle wide open, you accelerate down the hill due to gravity. If you close the throttle off, you slow down.... depending on how steep the hillis of course. Why? You're needing energy to create the vacuum with the throttle closed and the car is getting this energy from the kinetic energy of the car itself.

So, if you have to suck in a greater volume of air to create the same power, just like if you lean out the engine, you are creating less vacuum and hence need less power.

then all would be evened out by have to compress a larger amount of air on the compression stroke. wil use your 20CF and 30CF again.

your now trying to compress %50 more air. that will also suck up power.

if you want to reduce pumping losses do what HDT did with the VL group A race cars get a pressure senser (a spare MAP senser will work) and find the hight pressure zones behind your front bar and in your engine bay.
and feed the engine air from those places. In the case of the VL there is a high pressure zone just behind the headlight, if you ever see engine bay photos of them you'll a huge fibreglass intake that runs over to it.

I also invite you to to actualy give proof your theory works. and not some half a*** testing driving to work every day.
put your car on a dyno where you can controll every thing.
an easy way would be to get the wheel speed up to 60 put the cruise on and check TPS voltage. the feed it some hot air and recheck the TPS voltage. also put vacuum gauge on the car. if you can reduce cavuum by 3 or so inches you might be getting some where
if you can change the TPS by 2 or 3 degrees you might be getting somewhere

prove we can save a worthwhile amount in fuel, save me 10 to 15L a week I'll bet youd be lucky to save 2 or 3




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