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Old 05-23-2004, 07:10 PM   #1 (permalink)
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Default Warm Air Intake VS. Warm Engine Temp

I have seen a few different attempts at making the Insight get better MPG by increasing the temp. My question is: The temp of what? Some people block radiators, some people put a hair dryer down the air intake. Is it the fact that the intake air is warm which aids mileage? Or, is it just a warm engine in general? Is it both? If you do run the engine at an "artificially" warm temp, is that bad for the engine? I would really like to make some type of simple temp altering mod. Please let me know if you have anwers to any of my questions. Also, any links to sites with examples of mods would be great. Thanks.
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Old 05-23-2004, 07:55 PM   #2 (permalink)
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Hi Brpeterson:

___You want to increase both the temperature of the coolant (radiator block) and the temperature of the air into the air intake manifold (warm air intake mod). Both have there purpose in an Insight.

___The Coolant temperature is the one that rises and falls as you run through Autostop, Fuel Cut, or simply stays low when traveling highway speeds in colder temperatures. This turns your lubricating oil into syrup Ö That was an extreme exaggeration of course but viscosity increases with lowering temperatures thus causing anything lubricated to run with a bit more friction thus reducing fuel economy. That is just one theory Ö

___The Air intake is the one that will keep you from lean burn in real cold weather or shrink the lean burn window to the point you donít see much of it below 40 degrees F. It is not just lean burn window that shrinks but the ability for the fuel/air mixture to mix properly up to the point of ignition in the cylinder. I have read that some of the fuel in the fuel/air mixture can actually pool (condense?) when cold or when injected into colder surfaces and this pooling against a cylinder wall leads to unburned or at best uncontrolled flame fronts leading to a further reduction in fuel economy and performance. This second effect hurts the CVTíers as well so it is recommended that they use this mod in colder temperatures also.

___Once you are above lets say 75 degrees F, the warm air intake isnít really needed as you usually have a 95 - 100 degree F AIT which gives close to maximum fuel economy IIRC. The coolant temperature however is dependant on the thermostat and the Insightís ability to create and maintain the heat in the block. If you are a hyper miler, you are only burning lets say 1.5 to 2 oz. of fuel a minute. At that rate, I am sure you can understand that the fuels energy not only warms all the rotating parts involved but also propels the Insight down the road at 50 - 55 mph. Take a thimble of gas and light it off. Now consider how small the amount of heat generated is when burning it efficiently across a minute of time. This tells you how little energy the Insight actually uses to do all the things it does and why coolant temperatures can vary so much when the ICE stops or Fuel cuts for any length of time. A 70 # chunk of aluminum heated by < 2 oz. of fuel a minute (remember that 30 - 35% of that 1.5 - 2.0 oz. goes to propel the Insight through the air) can cool off pretty darn fast with any amount of air flow moving across it.

___If anyone has a better or more straightforward explanation, I would certainly be glad to include it in any future posts on the Warm Air Intake/Radiator block mod subjectís myself.

___The real solution is to warm the incoming fuel and air intake to ~ 90 degrees as well as sealing off the entire block assembly from any external temperatures effects. I have looked under the Insight and it would take a hell of a specialized plate to cover all the exposed openings as well as a specialized contraption to warm the fuel before it hits the injectors as well. Someone will eventually do it if they havenít already but I havenít seen it done by anyone for our little beauties just yet. Another benefit of a full cover plate is our Insightís Cd would probably fall another 1 or 2/100 of a point given the front underside of our Insightís is relatively rough with the openings even with the aero shields/plates already installed from the factory.

___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
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Old 05-23-2004, 08:48 PM   #3 (permalink)
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I have some mods at:


I will be posting more on the warm air intake mod I have done.

It is funny that you can be driving with the cabin too hot (because of sun) and the poor little engine with the air running over it isn't hot enough at all because it doesn't burn enough gas to make it hot!

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Old 05-24-2004, 12:22 AM   #4 (permalink)
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Great explanation xcel! :)

Maybe the simplest explanation of why warmer intake air (up to a limit) improves MPG is better fuel vaporization and the more complete combustion that is enabled by the Insight's lean burn design.

But then I'd be leaving out all the other good aspects you included! <g>

Brpeterson, if you want to see one type of hot intake air system see the link in my signature. :)

HTH! :)
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Old 05-24-2004, 03:42 PM   #5 (permalink)
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I have done some mods on my Insight, I started with placing six thermocouples in several places in engine, the first one is for outside air temp, second is for air intake temp, third is for coolant return to the engine, the fourth is for coolant coming out of engine, the fifth is for oil temp, the sixth is for exaust temp.

This is what I found so far, DO NOT block the radiator directly with cardboard, as temperature will rise to about 235 F with the outside temperature being around 60 F, the coolant return was about 217 F
air intake temp was about 75, the fan turned on but the temp will take a long time to go down. I immediately stopped the car, removed the cardboard and took off, in less than 1/4 of a mile the temp was back down to normal, Even at 235 F , I didn't see the stock temp gauge climb significantly, it only moved about 2 bars.

What I found it works best to leave some space between the radiator and the cardboard, so here is what I did. I bought a bra for my car, I decided to modify it as well as make it more aerodynamic, I covered the lower air intake, and the results are as follows:

Outside temp 60 F. Incoming air temp 75 F, Coolant returning to the engine 140 F, Coolant from the engine to radiator, 190 F.
I have not done the Hot air intake mod yet, I will keep you posted what the temperature reading is, but I noticed that when you run the AC the intake temp. goes up about 20 - 25 F.
I took some pictures with the bra cover, I will try to post them soon.
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Old 05-24-2004, 04:48 PM   #6 (permalink)
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So did you find that these mods had a significant impact on mpg down there in "frosty" Northridge?
Sean Ware
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Old 05-24-2004, 06:55 PM   #7 (permalink)
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Hi Calpod:

___You can watch the Coolant temperature via the OBD-II. If you are traveling in the city w/ stop and go, at 32 degrees, you will see in the low 200 - 210 degree F range. On the highway even up to 70 degrees F ambient, you will see ~ 200 degrees F so no; you do not have to pull the radiator block if you are a highway driver almost exclusively. If you see 8 bars on the temp gauge, it is time to pull, otherwise, leave it fully covered for maximum fuel economy until 70 - 75 + degrees F. The AIT is also available via OBD-II as well.

___SeanW, it depends in what temperatures you are driving in. I havenít had a tank < EPA highway estimates w/ the warm air mods installed since I owned her and that includes one cold SOB tank with an average of ~ 10 degrees F! I have pulled the radiator block ~ 10 X so far this year for afternoon commutes home when it is > 75 but other then that, everything stays as is and I reinstall the radiator block for my commute to work in the morning (usually 45 - 55 degrees F) when I am on days.

___Good Luck

___Wayne R. Gerdes
___Hunt Club Farms Landscaping Ltd.
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Old 05-24-2004, 06:58 PM   #8 (permalink)
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Very funny.
I lived in Georgia and the it would be below freezing sometimes, and I noticed my mileage would drop like a rock, I started taping the air dam about 3 years ago. but I noticed even here in California it helps getting the engine warmed-up, I get auto-stop about 2 blocks from my house in the morning, and I have had the front covered in temperatures as high as 80 F and the coolant going to the radiator does not change much, it only gets to temp much quicker, I am setting up some pictures in Cardomain.com, so you'll be able to see the pics, and also the data, I may drive the car back to Georgia when the weather starts getting cold, so I can see the temp in cold weather, as I did not install the thermocouples until I was here in California.
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Old 05-25-2004, 07:13 AM   #9 (permalink)
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How about warming the fuel line, thus incresing the fuel temp for better vaporization.
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Old 05-25-2004, 09:40 PM   #10 (permalink)
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You could warm the fuel lines - that's the opposite of what many drag racers do. Cooler fuel means you get a denser air/fuel charge inside the cylinder - which is good for power. Warmer fuel would result in a less dense air/fuel charge, which would likely improve mileage, but reduce power. It would be similar to having a slightly smaller displacement engine.
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