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Old 06-16-2011, 10:30 AM   #1 (permalink)
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Ideal HAI question

I was daydreaming, as im sure alot of people here do, and I was thinking of the benefits of ram air intakes. Then I thought of hot air intakes Then I thought of hot ram air intake. Like some how trapping air that has passed through the radiator and route it to the intake. But then I thought that there must be an ideal hot temperature for engine efficiency before it looses too much power or causes problems.

What kinds of HAI temps are beneficial?


By the way im not following through on some odd hot ram air intake. Its just the thought that led me to the question.

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Old 06-16-2011, 01:10 PM   #2 (permalink)
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Hot air intake, sounds like watching C-SPAN when Congress is in session.

I'm aware of the following:
  • Ebay resistor scam - from time to time, you'll see someone advertise a $0.05 resistor that for $20 or more improves fuel economy "xxx%". These typically shunt the manifold temperature sensor so the car thinks the air is warmer than it really is and 'fool' the control computers. This is a fuelish decision and has been widely debunked . . . still, a resistor customer is born every minute.
  • Honda Insight Lean-Burn - my understanding is some of the original, lean-burn Honda Insights achieved mileage improvements by having a duct bring heated air from around the exhaust manifold and pipes. I suspect it was from getting the engine to run in 'lean burn' more frequently but am not sure.
  • Good Prius Friend Hobbit experiment - tried it but his reports were that any effect was beyond his ability to detect.
  • Some Prius idle effect, maybe - in my oil additive testing, I noticed the initial fuel consumption was quite low at idle after running at highway speeds and parking but after a few minutes, I could see the spark retard and fuel consumption increase. This MAY be due to the intake manifold cooling off and thus cooler air. However, I have not yet studied this effect. Given the Prius normally turns the engine off rather than idle with the engine running, it may be moot.
Do you have any engine instrumentation that includes: spark advance, coolant temperature, MAF and intake air temperature?

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Old 06-16-2011, 01:55 PM   #3 (permalink)
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Quote:
Originally Posted by bwilson4web View Post
I noticed the initial fuel consumption was quite low at idle after running at highway speeds and parking but after a few minutes, I could see the spark retard and fuel consumption increase. This MAY be due to the intake manifold cooling off and thus cooler air. However, I have not yet studied this effect. Given the Prius normally turns the engine off rather than idle with the engine running, it may be moot.
I think you have part of that backwards after getting off the HW the engine (when running) should be at the lowest fully warmed up temp. Once the car stops the intake manifold now has less air moving around it and the engine holding more heat in the engine bay causing it to heat soak. From this heat soak the IAT (intake air temp) will read higher and the coolant will get warmer. On all the PCMs I have looked at as IAT rises it subtracts timing when it is lower it adds timing usually there is a flat spot that 0 is added to the timing. The same goes for coolant temp but also scales it with RPM or AirMass instead of just temp.

So with that said I believe that the resistor is used to A. Set a single cold value to increase timing or B. Placed parallel with the sensor to give a reduced IAT value to add timing.
Some people tuning cars will place a variable resistor in place of the sensor and use that to add or subtract timing on the fly.
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Old 06-16-2011, 02:04 PM   #4 (permalink)
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So what IAT is too high, recently blocked grille on stratus, IAT peaked once at 185, but normally in 120-40, probably up 30f from pre grille block. Water temp in town in reaching 222 before fans come on, pre never over 205 didn't even know if fans worked, and still 205 on hwy.

I can't tell yet if grille block increase MPG any, but since IAT temp went up as well I will never know.
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Old 06-16-2011, 02:30 PM   #5 (permalink)
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Quote:
Originally Posted by Floordford View Post
...But then I thought that there must be an ideal hot temperature for engine efficiency before it looses too much power or causes problems.

What kinds of HAI temps are beneficial?
Hi Floordford,
I like the question, I hope someone with actual experience can help.
My understanding is that the point of HAI is to improve vaporization of the fuel. Mostly gasoline boils at about 180 F maybe that is a good target. Gasoline ignites at about 500 F, so it shouldn't be that hot until the spark plug fires. At WOT and assuming 10:1 CR the temperature increase in the cylinder (due to the pressure rise on compression) will be about 1.8 times, so 500 F (960 R) where preignition would occur, only allows the intake fuel temp. to be about 75 F - so crap, I don't see how engines run even with no HAI.

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Old 06-16-2011, 02:47 PM   #6 (permalink)
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Higher intake temp = less dense air charge = lower O2 content = less fuel injected = more throttle required for same amount of power = lower pumping and throttling losses = better efficiency. My Jeep starts to knock around 140*, my girlfriend's Focus starts to knock around 150-155* (at least that's when the knock sensor says it's knocking)
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Old 06-16-2011, 02:56 PM   #7 (permalink)
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I don't think a HAI will help a vehicle with a MAF sensor, as the Focus doesn't seem to use more gas with a lower IAT, the Jeep on the other hand does benefit. Fully warmed up (35 Mile drive to my girlfriends parent's house) it uses around .45GPH at Idle with an intake temp of 65*, and around .32-.38GPH with an intake temp of 110*. I tested this on 1 trip, when I got there I let it Idle for several minutes as the intake temp increased (due to less air flow through the radiator and engine compartment), once i got back home I opened the hood to let cool air into the intake and again let it idle for several minutes. I'm not sure how much difference this will make at highway speeds but it does show a positive effect at idle.
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Old 06-16-2011, 04:17 PM   #8 (permalink)
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You know the charter of Ecomodder is experimentation and this sounds like a good project for those who have instrumentation and curiosity. So what I'll do is rig up my Prius to record more data and see if we can find what parameters appear to impact timing and fuel flow. You' all might consider doing the same for your cars.

Perhaps someone has a pot they can hack onto the air inlet and/or manifold sensor to show what happens with different values.

Seriously, let's 'do the experiment' and see what happens. Of course if the original poster isn't curious, I'll just add it to my 'to do' list.

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Old 06-16-2011, 04:33 PM   #9 (permalink)
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My Mustang does have a MAF and an intake temp sensor. The best way I think I could access it is through my UltraGauge. Unfortunately my UG froze up and im having to deal with tech support. So its down for the time being.
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Old 06-16-2011, 07:48 PM   #10 (permalink)
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You'll probably find best results in the 120-140 degree F range. In the few expirements I did, I found it difficult to nail down the benefits because of the constantly changing variables while driving on a road. I think you'd need to be on a dyno with a constant load and then vary they intake temp to be able to detect the changes in fuel consumption. Never the less, I still run one because the theory makes sence....I think

Oh yea, almost forgot about the Hot Ram Air idea. I've thought about and played around with the idea, but found it difficult to get enough heat transfer to significantly heat the air as it moves through the radiator, or an additional heater core like I tried. You gotta get really hot to get a significant heat transfer going...like off the headers.

Try the HAI and check back in!

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