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Old 04-07-2009, 09:16 PM   #21 (permalink)
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I still feel that the puming losses are significant. In many cases, a car with WAI will see an improvement--likely due to the reduced pumping losses due to less-dense air.

If you're going to use the maximum power, or near maximum, that your engine can generate, you're already throwing fuel economy out the window. (Or out the tailpipe.)

Then again, some cars don't seem to respond that well to a WAI. The only way to know is to test one yourself--or to find someone with a nearly-identical car who has tested it on theirs.


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Old 04-07-2009, 09:20 PM   #22 (permalink)
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Originally Posted by rkcarguy View Post
My opinion, the WAI is a limiter that slows your acceleration and reduces your WOT power output by inducing a hotter and therefore less dense air/fuel charge to the engine. Measured side by side I'd bet the CAI equipped car would be near identical mpg as a WAI equipped one, but obviously will walk away under acceleration.
Just put a wedge under your gas pedal so it only goes to 75% WOT and enjoy the same gains instead...
And that's all it is. The science actually does back up the use of controlled temperature intake systems. If you read a few posts up, you'll see references that I haven't read thoroughly, which denote this very concept.

Common physics also makes it quite obvious that yes, you're losing power, but you're not making anything close to "power" in eco-ranges to begin with.

If your engine makes 310 HP at 4400 RPM, it's doing that at WOT, not at 10% throttle, where you're sitting.

The primary function of a WAI is NOT to reduce pumping losses by heating the intake air and making it less dense, it is to increase the speed at which the flame kernel turns into a front and increase the amount of the (more) homogenous mixture which has been burned by the combustion event.

As a result of pre-heated intake air, the engine stays warmer, which means that more power from each combustion event (relative to the available power from the combustion event at the given temp) will go into moving the piston, rather than be leached into the cylinder walls as heat.

IOW - the WAI just makes it easier for the engine to turn, not b/c of pumping losses, but because of more complete combustion causing more power relative to the fuel/air mix's concentration and capability.

Obviously, if there is less air due to warmer temps in the cylinder, it will reduce pumping losses and compression losses, since there is less density to compress and pull in/push out. That's just relative though. It's not a primary function.
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Old 04-07-2009, 09:30 PM   #23 (permalink)
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Well Tas has a point that its not all about density.

It is important but its not the only thing that matters. If they air is initially at a higher temperature when the fuel ignites the heat soak in the charge will be slightly greater. In the summer or after having run the vehicle for stop and go traffic in the nether regions if you have a knock sensor you are going to defeat yourself. The higher initial temperature can cause knock which means for that cycle your engine is going to avoid that and create alot less power(but the fuel won't be used effectively). On the other really dangerous thing if the mixture ever pre-ignites because it gets a few degrees above where your coolant can handle its game over for your engine.

Also he is right the spark will advance more quickly because the molecules are vibrating faster. There is a point of lost returns here though. As long as all the fuel burns before the exhaust valves pop you're really not losing out on anything. Also if the spark advances too quickly the power comes in pulses, which you won't notice but its going to be harder on your engine than a "smoother" burn over the expansion cycle.<Edit> sorry I forgot to mention that if you look at guns and bullets the optimal load of powder will burn not all at once, but for about half the time the bullet is still in the barrell. If it burns immediately the bullet only accelerates as long as the pressure creates more force on the butt of the bullet than the drag and the friction. If the kernel goes too quickly it washes through the block(heat capacity is exceeded) and the pressure is not greater than the friction and drag of fluids. If it is just right it maintains force greater than the parisitic forces and allows the air to absorb more heat(the air can absorb more BTUs at greater specific volumes).</edit>

As someone else said. . .it depends entirely on what your car was designed to do.

Last edited by theunchosen; 04-07-2009 at 09:40 PM..
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Old 05-26-2019, 05:41 AM   #24 (permalink)
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