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Old 04-07-2009, 01:49 PM   #111
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Not just older cars use MAP. Almost all Hondas use it still. I don't know if the Insight does or not but I know everything else does.
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Old 04-07-2009, 01:49 PM   #112
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Mass air flow sensors measure density as well. Air density decreases by 20% from 32 degrees F to 200 degrees F. Hot wire mass AF sensors also adjust mixture according to temperature.

All that being well known, as I stated previously the oxygen sensor is the final arbiter of fuel delivery. It measures oxygen content in the hot exhaust stream and decides injector cycle duration, regardless of the preliminary delivery cycle determined by different designs of air flow sensors.

The only time the O2 sensor is not the final judge in mixture decisions is on cold starts, until the sensor is heated by exhaust gas. In some cases the sensor is heated electrically to provide faster warm up and closed loop operation.

Disconnect the AF sensor and the car will still run. In the event of mulitple sensor failures the CPU will still operate the engine based on available parameters. In this case the closed loop feedback will not function and you get a check engine light.

Certainly there are situations where the basic imput will be more rich or lean, which would make a very minor difference in overall fuel usage, but in the end, any signal that controls basic mixture is subservient to the O2 sensor signal. If it was not that way you could not pass emissions.

regards
gary
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Old 04-07-2009, 02:36 PM   #113
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In modern engines, detonation probably isn't too large of a concern, with better materials and designs for heads having more even heat distribution and better dynamic spark timing combined with good knock sensors. Modern engines are more and more detonation-resistant, and run higher compression on lower octane fuels than ever. For those same reasons that you can't truly lug a modern engine, I expect that a WAI probably wouldn't cause detonation in most engines.

That's not to say if it is or isn't effective for increasing FE (I think I've already posted everything I know about that), it's just addressing the detonation concern.
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Old 04-07-2009, 04:27 PM   #114
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I don't think by a simple A to B test you can rule WAI or HAI a failure. Since the gains may not be a huge amount in some cases, environmental variables or even driver behavior could taint the results. Isn't the proper method to use averages of multiple trips? Seat-of-the-pants measurements don't seem very conclusive to me.

I do agree that WAI does reduce power, but that is kind of the point. Most times you don't need the full range of horsepower that an engine can produce. The manifold vacuum is reduced and becomes a savings in fuel. Try sucking on a vacuum gauge and see how hard it is to draw a vacuum.

I have felt significant power loss on my truck when I had a grill block creating a WAI. That was back before I knew anything about hypermiling, I was just trying to keep the heater warmer. I was pulling a trailer with an old POS bronco on it, and could hardly get up to speed to merge onto the highway. For this reason if i do create a permanent HAI on my truck, it will have a electric selector valve for near WOT conditions, to draw in cold air.
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Old 04-07-2009, 04:27 PM   #115
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In modern engines, detonation probably isn't too large of a concern, with better materials and designs for heads having more even heat distribution and better dynamic spark timing combined with good knock sensors. Modern engines are more and more detonation-resistant, and run higher compression on lower octane fuels than ever. For those same reasons that you can't truly lug a modern engine, I expect that a WAI probably wouldn't cause detonation in most engines.
Warm intake air leads to detonation. Detonation is bad in any engine, modern or not. Modern engines limit detonation by retarding timing. While that stops the detonation, retarded timing means more unburned fuel, higher emissions, lower power and lower efficency. That's the problem. While the engine is saved from detonation efficency goes down as a result. This is why a warm air intake is a bad idea.
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Old 04-07-2009, 04:33 PM   #116
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I don't think by a simple A to B test you can rule WAI or HAI a failure. Since the gains may not be a huge amount in some cases, environmental variables or even driver behavior could taint the results. Isn't the proper method to use averages of multiple trips?
That?s exactly what I did. My baseline test (stock cold inlet) was over a week and 256 miles. The second test (warm air intake) was also over a week and 263 miles. Results were slightly lower mileage (too small to be statistically significant) and loss of power. Right now I'm in my third test (stock cold inlet back in place) lasting a week and hopefully the same amount of miles. That will make for a true A-B-A test.
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Old 04-07-2009, 04:37 PM   #117
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I don't think a HAI gets all that close to the detonation point. Old non-intercooled turbocharged engines are forcing pressurized high temp air into the engine. If you start to increase the boost past the stock PSI, then its time to worry about detonation. That is when you add an intercooler.
The difference with HAI in a naturally aspirated engine is there is no added pressure, and less fuel, so less chance to spark a pre-ignition.
Did you hear your engine ping?
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Old 04-07-2009, 04:53 PM   #118
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I don't think a HAI gets all that close to the detonation point. Old non-intercooled turbocharged engines are forcing pressurized high temp air into the engine. If you start to increase the boost past the stock PSI, then its time to worry about detonation. That is when you add an intercooler.
But they also ran on more expensive premium fuel with higher octane that resists detonation.

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The difference with HAI in a naturally aspirated engine is there is no added pressure, and less fuel, so less chance to spark a pre-ignition.
Yes, a turbo does create higher cylinder pressure and that leads to the chance for detonation. However hot intake air also leads to detonation.

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Did you hear your engine ping?
Because of knock sensors, modern cars rarely ping anymore. The just lose power because the ignition timing is retarded by the computer.
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Old 04-07-2009, 05:21 PM   #119
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The wife ran regular in her Murano, which recommended premium. Not a trace of spark knock in 32 K miles. She averaged 22 MPG cpmbined on regular. Never tried Premium long enough to see if there was an improvement in mileage. EPA highway was 24, I think city was 19 (new ratings). Old ratings were 20 and 25.

Mercedes warned against using regular fuel, and had specific recommendations against using full power if you had to use regular in an emergency. That is a supercharged engine that was designed specifically for Premium.

Cast iron heads retain heat which would normally be dissipated much more rapidly with an aluminum head. Engine knock was a product of poor fuel distribution combined with cast iron induced hot spots as well as poor combustion chamber design.

When oxygen sensors were introduced by Nissan in the 1981 280Z using the early Bosch type flap resistor AF meters, they could raise compression ratios. Later with the introduction of knock sensors fuel quality did not cause engine knock with ignition timing retarded to the point of elimination of knock based on the knock sensor imput.

Bottom line is most modern engines are designed to use regular fuel. My 06 Corolla manual stated clearly that the engine was designed to run properly on regular. Premium provided no benefit as far as economy or performance.

In high performance engines with combustion chambers designed specificially around the combustion characteristics of premium fuel, where the owners manual specifically requires premium (like the Benz), then you should use only premium.
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Old 04-07-2009, 05:39 PM   #120
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I guess a quick test would be to remove the knock sensor from the block to see if the power loss disappears. After all it is basically a microphone listening through the engine block material, if it cant hear, it won't retard timing.

A non-intercooled turbo engine IS a HAI, and could run with out detonation back before knock sensors where even used.

My Turbo Coupe had a switch for regular or premium gasoline. From what I've read the premium setting caused more advanced timing and a few more PSI of boost. Premium fuel is only needed if the engine is tuned for it.

If you believe the HAI is causing ping and retarding timing, you could test the HAI detonation theory by using high octane compared to regular octane with the HAI and a comparison with out the HAI.
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