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Old 07-01-2008, 09:32 AM   #121
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Originally Posted by severach View Post
Not only that but when the charge is compressed into a very small space it no longer matters whether the heat came from the air or the fuel.


The degree to which it is heated depends on how effective the heat exchanger is. I used a 10 plate which had no problem producing 200*F fuel "at any delivery or pressure". While fuel may transfer heat slowly it also doesn't take much heat to get it warm.

There's too much flow for the fuel to absorb much heat without a heater. I've felt the bottom of the injector in the winter and it is stone cold. The first serious heat the fuel sees is the hot valve which I think provides as much heat as any heater I could install.



No need to bet. I verify it continually. As winter turned to spring I watched my mileage increase with IAT. As the spring temps varied from hot to cold I constructed my WAI to see if I could artificially combat the mileage reduction. I found the mileage was determined entirely by the artificially raised IAT and not the actual outside air temp which determines fuel temp and air resistance.

Even more interesting, the mileage improves by 10's of degrees Fahrenheit. 60-69 produces almost exactly the same mileage but 69-71 produces a noticeable bump. That means the fuel maps are programmed in 10 degree increments for computer memory convenience and the warmer fuel maps are more efficient than the colder ones. That tells me that the computer knows that cold fuel vaporizes less and wastes more fuel to keep the engine running well.

So far as I can tell the reasons commonly provided for mileage reduction in the winter are all invalid. The least lame reason they give is that cold air is more dense leading to more air resistance. Definitely wrong since my mileage always increases when I drop altitude from a cool 950 feet to a warm sea level and the power increase from the increased air density from altitude reduction is much more than the increased air density in the winter. Heat and vaporization seems to explain it all. I'll soon have a Scangauge down by the sea to verify it more accurately.

The strangest thing is that some vehicles already implement some form of WAI and they don't see a winter summer mileage difference. I know about the few non American cars that do it but there seems an entire class of American vehicles that have WAI, or at least I have two for two in my yard: trucks.

A 10 plate heat exchanger is $40 from eBay. The necessary fittings are at Menards or Parker and cost about $20 more. $25 for soft copper doesn't seem very cost effective to me.
I can tell you that my 1981 Buick and my 1986 Chevy truck have WAI from the factory. My 1980 Pontiac wagon did, and I'm quite sure my 74 Chevy p/u did as well, but I had defeated it on the 74 by flipping the bonnet on the air cleaner upside down. The engine breathed a lot better, and with a light foot on the accelerator got far better mileage.

-Jay
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Old 07-01-2008, 10:23 AM   #122
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Anyone who only gets 30% increase after spending 6 figures doesn't earn much of my confidence.
They are not changing anything else- no change in driving style, no aero changes, the system is emmisions compliant. 30% FE improvement would be significant for any reasonable consumer.
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Old 07-01-2008, 11:20 AM   #123
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They are not changing anything else- no change in driving style, no aero changes, the system is emmisions compliant. 30% FE improvement would be significant for any reasonable consumer.
So now that they got the R&D costs out of the way, if they could make it $500 or less we got something then...
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Old 07-01-2008, 02:41 PM   #124
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After scanning over the recent posts I would guess it was detrimental to my car because it couldn't adjust for the higher temp fuel and that messed with the engine efficiency. I say this because my EFI is fairly early (91) so it's not as "smart" as the new vehicles on the road. (at least that's my un-educated shot in the dark)
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Old 07-02-2008, 12:10 AM   #125
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How does your engine measure mass flow?
All of the engines I've driven to sea level were IAT+MAP based 4 cylinders too old for a SG. One was a turbo. The mileage improvements were verified by knowing the typical summer city/highway mileage and the 10 gallon point on the gas gauge. The 10 gallon point is where you can read the mileage right off the odometer.

Now that my MAF based V6 no longer gets ridiculously low mileage I might take it to the sea with a Scangauge so I can get better measurements.

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A broader question is this: how are fuel maps created? Wouldn't the setup of the map depend on the sensing system?
You'd want computers to dynamically adjust for every possible variable but unfortunately such computers would be impossible to build. The way to simplify is to test the engine under the specific conditions like IAT and come up with the simplest method for handling it. For IAT all you need to do is cut it into 10 degree Fahrenheit increments and come up with a simple formula or table for the rich factor below 60*F and above 120*F. There are 22 such increments from -60*F to 160*F which allows the entire temperature map to be held in 22 bytes plus a bit of simple code. A bit more simple code will richen more for low ECT. FWIW I am a FI computer pundit and not a designer.

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Lastly, how does the lambda sensor play into all of this?
Between 60*F and 120*F IAT the rich factor appears to be zero so the efficiency goes up as the fuel vaporization goes up. By 100*F IAT knock starts to rise so I lose mileage if I am not careful with the pedal. The computer will provide the mixture that shows the best oxygen sensor reading unless it has other reasons to richen. Unfortunately I don't have a scope to verify that and LTFT isn't dependable enough. Sure would be nice if those new cars with the TV in dash would include an oxygen sensor scope.

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I can tell you that my 1981 Buick and my 1986 Chevy truck have WAI from the factory. My 1980 Pontiac wagon did, and I'm quite sure my 74 Chevy p/u did as well, but I had defeated it on the 74 by flipping the bonnet on the air cleaner upside down. The engine breathed a lot better,
Carb cars had them to prevent carburetor icing and improve cold weather emissions. The two trucks in the yard are FI so don't need WAI but have it anyways. Why were WAI removed for most cars but left in for many trucks particularly when...

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They are not changing anything else- no change in driving style, no aero changes, the system is emmisions compliant. 30% FE improvement would be significant for any reasonable consumer.
a car company could implement this in less than $100 in extra parts. Most of it would be cast into existing parts.

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and with a light foot on the accelerator got far better mileage.
Too hot is worse than too cold. After 140*F the computer pours fuel in as a disposable coolant to save the engine and knock retards timing to gas guzzler levels.

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at least that's my un-educated shot in the dark
Without a Scangauge that's exactly what it is. I have two nearly identical Delta 88's. Over time I have done the same mods to both cars including swapping sensors and parts back and forth to find problems and eliminate suboptimal parts. Several other similar cars are available should I suspect that parts are bad in both cars. One works so well that anyone could drive it and get averages that ridicule the EPA spec. The other gets the same good mileage when warm but knock kills the mileage when hot making the averages turn out exactly where the EPA spec says they should be. Without a SG I wouldn't even know that the mods were doing anything at all nor would I know what I need to do to get the averages up.

OP recommends that everyone with the same car needs to do the mod. If only it was that easy.
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Old 07-02-2008, 12:07 PM   #126
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You'd want computers to dynamically adjust for every possible variable but unfortunately such computers would be impossible to build.
There is a DIY system called Mega Squirt, it's a stand alone ECU that has sensors for almost everything I think, Fuel pump, fuel injectors, Air flow, 02 sensor, intake temperature and pressure sensor and throttle position and engine temp, spark and retard as well, you basically program the fuel table yourself, it can turn your engine into a pussy cat and lean it out safely or dump loads of fuel and get peak performance from it.

I don't have the time or money to buy this system but as an electrically inclined person I can see the benefits of this system.


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a car company could implement this in less than $100 in extra parts. Most of it would be cast into existing parts.
Probably even less than that because lets face it, they make $20K cars for a about $3000


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Too hot is worse than too cold. After 140*F the computer pours fuel in as a disposable coolant to save the engine and knock retards timing to gas guzzler levels..
I think some cars use EGR to try and lower temperature and reduce knock, what would you say is to hot on a typical car engine?
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Old 07-02-2008, 12:13 PM   #127
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Probably even less than that because lets face it, they make $20K cars for a about $3000
Your info is way off on that one. small cars are often money losers for auto makers.

http://www.bloggingstocks.com/2006/1...in-comparison/
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Old 07-02-2008, 12:17 PM   #128
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Your info is way off on that one. small cars are often money losers for auto makers.]
American Auto makers, lets face it they have been losing to the Japanese and Eastern imports for decades, small wonder they can't make a small car profitable.

India has a $3000 dollar car, these Corporations don't make anything unless there is a healthy profit in it for them.
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Old 07-02-2008, 12:56 PM   #129
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All of the engines I've driven to sea level were IAT+MAP based 4 cylinders too old for a SG.
OK. So your car is using temperature and pressure to somehow determine the mass of the air entering the engine.

Next question...how is mass determined? Is there a standard atmosphere table in the computer, including a way to calculate density using temperature offsets? Or is there one base density number from which the mass is calculated?

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You'd want computers to dynamically adjust for every possible variable but unfortunately such computers would be impossible to build.
That wasn't what I was getting at. If your car has a sensor that can directly measure air density and temperature, in combination with the lambda sensor it should be able to very precisely control the fuel-air ratio.

It doesn't make sense to me that the intake air temperature would be the primary variable controlling the fuel metering. However you have made an interesting observation, and your vaporization hypothesis could be correct.

I'm not sure I fully understand what's happening here, though, so let's continue the Q&A discussion.
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Old 07-02-2008, 05:46 PM   #130
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Best way to understand it.

The computer reads

Mass
Atmospheric pressure
Temperature
Humidity
Velocity

Most mass AF sensors use a heated wire, which changes its resistance depending on the conditions described above.

The MAP sensor measures the atmospheric pressure available after the throttle butterfly. It works out to the true atmospheric pressure, minus the engine vacuum reading. If your outside pressure is 30 inches and your vacuum reading is 16 inches, the atmosphere available to the cylinders is 14 inches.

Throttle postion determines desired load applied.

The computer calculates the injector duration based on these readings. Then the oxygen sensor sends the computer a report, consisting of a voltage signal which tells the computer if it needs to refine the signal ot the injector to keep the mixture at the ideal amount.

Any change that would affect the mixture can not stop the O2 sensor from doing its job, since it is determining the oxygen content of the exhaust after combustion. The system sweeps above and below the ideal amount many times a second and is continuously adjusting the mixture within a very narrow range.

Exceptions are cold starts and wide open throttle in most engines.

regards
gary
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