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Old 04-28-2008, 11:47 AM   #1 (permalink)
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AutoSpeed article: spoofing the intake air temp for slightly improved MPG

Everybody's favourite Australian ecomodding site has posted another good one:

The 5 cent modification

The subject this time is a mod of the intake air temp sensor, spoofing the engine computer into thinking the ambient temps are lower than actual. The result is more advanced dynamic ignition timing, which if used wisely (ie. earlier light load upshifts, driving with load in a higher gear, or lower speed than usual) can result in improved fuel economy.



The mod was performed on the owner's Honda Insight, and changes in timing were recorded via an OBD scanner.

The usual caveats are mentioned: beware of detonation!

Conclusions?

Quote:
This is not a groundbreaking modification. There’s not 30 more horsepower or 20 per cent better economy. ... There’s clearly improved driveability and potentially a little better urban fuel economy. And at a cost of less than five cents (the cost of the resistor), that’s one helluva bang for your buck.
For the full details, the article is worth a read: http://autospeed.com/cms/A_110350/article.html

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Old 04-28-2008, 11:53 AM   #2 (permalink)
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A better mod would be altering resistance of the coolant temp sensor. That only effects ignition timing AFIK. Air intake temp alters ignition timing and injector duty cycle.

As usual, this mod is a trade off. It will likely increase fuel economy, but result in worse emissions. Then again, who is using WOT all the time? Not many, and especially not us.
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Old 04-29-2008, 12:33 AM   #3 (permalink)
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This puts a damper on the warm air intake theory.
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Old 04-29-2008, 07:45 AM   #4 (permalink)
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Quote:
Originally Posted by tjts1 View Post
This puts a damper on the warm air intake theory.
Not at all, this could add leverage to the WAI if you don't ping. We already knew that the warmer the air, the more retarded the timing is. It all depended if the advantages from the air temps were enough to offset the retarded timing losses. For some it was, for others it wasn't. With an IAT mod, you can get a little bit of that timing back, thus making the WAI even more effective.
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Old 04-29-2008, 10:50 AM   #5 (permalink)
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No I don't think so. Its pretty obvious that the warm air intake doesn't work.
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Old 04-29-2008, 10:54 AM   #6 (permalink)
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Based on??? Nothing in the Autospeed article suggests that it's obvious.

I'm in agreement with tasdrouille. The sensor mod PLUS actually increasing the intake temps may result in potentially greater fuel savings than just the sensor mod (assuming detonation is avoided, as usual).

Actual results will depend on the particular vehicle's ECU programming & detonation tendency.
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Old 04-29-2008, 12:22 PM   #7 (permalink)
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Quote:
Originally Posted by MetroMPG View Post
The sensor mod PLUS actually increasing the intake temps may result in potentially greater fuel savings than just the sensor mod (assuming detonation is avoided, as usual).
Thats assuming a lot. Intake temperature is just as critical to knock control as octane. If you pay close attention to the autospeed article, they were using 98 ron fuel in a car that requires 95 ron in order to avoid knock. The Insight they were using is already equipped with a forward facing cold air intake which was also shown to both increase power and improve fuel economy.
http://autospeed.com/cms/A_109217/article.html
Its pretty obvious that what they are trying to keep the intake air as cold as possible. This whole warm intake theory flies in the face of reason and all my experience with 4 different cars.

The only rigorous comparison test between cold and warm air intake I can find didn't show an advantage for warm air intake.
http://www.metrompg.com/posts/wai-test.htm

I think autospeed is on to something with this IAT resistor and I'll give it a try on my BMW. From my service manual:
http://farm4.static.flickr.com/3104/...8bf16fe5_o.jpg
A 3-5k ohm pot should do the trick. The problem is this engine is not equipped with a knock sensor and the spark timing map is very conservative. BMW recommends using only 91 octane in this engine. I'll use the IAT to advance timing, forward facing cold air intake and a water mist spray to make up the octane difference.
A resistor in the engine coolant temp sensor circuit could also be useful to trick the engine into closed loop sooner after a cold start.

Last edited by tjts1; 04-29-2008 at 01:06 PM..
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Old 04-29-2008, 12:53 PM   #8 (permalink)
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The FE impact of the forward facing CAI does not come from lower IAT, but from the added intake pressure vs stock, or reduction of the pressure drop in the intake if you prefer.

BTW there is sound proven facts behind the WAI

Here's what I found out when I was doing my homeworks before going ahead with the WAI.

WAI arguments

- Pre-heated intake mixture at low rotational speed improves combustion. (Chiu and Horng, 1992)
- Specific fuel consumption varies inversely proportional to the square root of the suction air temperature (Nakajima et al. 1969).
- Higher ambient temperature is found to increase the flame speed, the combustion reaction rate, the uniformity of the fuel-air mixture and reduce the heat transfer rate though the cylinder walls (Pulkrabek, 1997).
- For lower temperatures, only a small part of the injected fuel is vaporized, causing nonhomogeneity. As a result, lower flame speeds, higher unburned mixture, higher hydrocarbons and carbon monoxide emissions, and loss of power are observed (Pulkrabek, 1997; Heywood, 1988).

References:
Chiu, C.P., and Horng, R.F., 1992, “Effects of Intake Air Temperature and
Residual Gas Concentration on Cycle-to-Cycle Combustion Variation in a
Two-Stroke Cycle S.I. Engine Equipped with an Air – Assisted Fuel Injection
System”, JSME International Journal, Vol. 37, N.4, pp. 957-965.

Nakajima, K., Shinoda, K., and Onoda, K., 1969, “Experiments on Effects
of Atmospheric Conditions on the Performance of an Automotive Gasoline
Engine”, SAE Transactions, SAE 690166, pp. 745-766.

Pulkrabek, W.W., 1997, “Engineering Fundamentals of the Internal
Combustion Engine”, Prentice Hall, Inc.
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Last edited by tasdrouille; 04-29-2008 at 01:06 PM..
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Old 04-29-2008, 02:23 PM   #9 (permalink)
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Just stumbled on an article on the 67 Olds Turnpike Cruiser

FTA:
Quote:
THE TURNPIKE engine includes another feature that contributes a great deal to fuel economy. This is the new "Climatic Combusion Control" air intake system, which is option No. K-50, available at $33.70 on all Olds V-8 engines. The system employs vacuum-operated valves in the air cleaner housing to mix warm underhood air with hot air from a muff around the exhaust pipe to maintain a constant inlet air temperature of approximately 100 F. Warm air arrives at the carburetor within seconds after a cold start. This, for all practical purposes, carburetor air temperature remains constant. The system offers several advantages, including close control of exhaust emissions to meet antismog laws. What helps overall fuel economy most, however, is that the carburetor can be calibrated for the constant 100 intake temperature. Normally, the carburetor must be jetted for the lowest underhood temperature in normal operation, which can be as low as 20 or 30 F in northern states. Tests who the difference in overall fuel economy is 0.75-1 mpg. Olds decided to include the air temperature control system in the Turnpike Cruiser Package to derive that last ounce of fuel economy.
That was a 20 mpg car.
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Old 04-29-2008, 06:45 PM   #10 (permalink)
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I've read about cars during the 1950-60's national fuel economy runs using a warm air intake for increased mileage. Some of them seemed to be modified intake warmers used for carburetor de-icing. They also had a much more limited (and thus more controlled) ignition system.

There are engine modifications that can be done to lower the tendency of an engine to ping. One is to radius all the corners within the cylinder/piston cavity...something only practical during a rebuild, but useful nonetheless.

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