DIY Warm-Air Intake

[H-Man]

50/50 split.

[Davinator61]

My reasoning behind a WAI is that warm air would help the engine warm up faster and stay above 195 degrees Fahrenheit, in order to stay in closed loop operation more often, and to bring about a more complete atomization of the fuel droplets from the individual injectors as each one of them sprays a pre-determined amount of fuel (based on RPMs, load on engine, current engine temperature, etc., etc.) into each intake port of each cylinder in turn.

I've found that my 1991 Jeep Cherokee Laredo 4.0L engine runs best at between 210 and 225 degrees Fahrenheit, ESPECIALLY when it comes to fuel efficiency. As the cooling system is pressurized to around 13 PSI above atmospheric pressure, I'm not too concerned about overheating, as long as ALL links in the engine cooling system are free-flowing when they need to be, and properly maintained on a regular basis (back-flushing, thermostat operation checks in boiling water with a thermometer, replacing hoses when they begin to swell up at their clamped ends, etc., etc.).

Cold air slows down the proper atomization of fuel, even from the injectors on a multi-port system, requiring more fuel to compensate for the slower evaporative rate at colder air temperatures. Why do you think the cold-start fuel consumption, before closed-loop operation temperatures are reached, is much higher than when the engine is fully warmed up? This is due to open loop enrichment in order to compensate for the fuel droplets' tendency to clump together during colder engine operations during warm-up, especially right after cold start-up. Also, cold air would cause an engine to take longer to warm up to closed-loop operation temperatures, adding to the higher-fuel-consumption-after-cold-start-up issue.

No, cold air intakes are NOT the best for fuel economy, even though they are SUPPOSEDLY great for boosting high-end Horsepower and Torque. However, fuel efficiency appears to be the MOST optimal in about the 1/3-2/3 RPM range, or between 1650-3300 RPMs in the case of my 4.0L Jeep Cherokee Laredo, at an air intake stream temperature of around 90-120 degrees Fahrenheit. However, cooling the fuel to prevent vapor lock, which has occured on my vehicle already at least once, on a really hot day in which the fuel got really heated up to the temperatures inside the engine compartment, might be a good idea, if it doesn't interfere with improving fuel mileage to any appreciable level. Does this reasoning make any sense to you at all?

[13B_88FC]

Originally Posted by Davinator61

My reasoning behind a WAI is that warm air would help the engine warm up faster and stay above 195 degrees Fahrenheit, in order to stay in closed loop operation more often, and to bring about a more complete atomization of the fuel droplets from the individual injectors as each one of them sprays a pre-determined amount of fuel (based on RPMs, load on engine, current engine temperature, etc., etc.) into each intake port of each cylinder in turn.

I've found that my 1991 Jeep Cherokee Laredo 4.0L engine runs best at between 210 and 225 degrees Fahrenheit, ESPECIALLY when it comes to fuel efficiency. As the cooling system is pressurized to around 13 PSI above atmospheric pressure, I'm not too concerned about overheating, as long as ALL links in the engine cooling system are free-flowing when they need to be, and properly maintained on a regular basis (back-flushing, thermostat operation checks in boiling water with a thermometer, replacing hoses when they begin to swell up at their clamped ends, etc., etc.).

Cold air slows down the proper atomization of fuel, even from the injectors on a multi-port system, requiring more fuel to compensate for the slower evaporative rate at colder air temperatures. Why do you think the cold-start fuel consumption, before closed-loop operation temperatures are reached, is much higher than when the engine is fully warmed up? This is due to open loop enrichment in order to compensate for the fuel droplets' tendency to clump together during colder engine operations during warm-up, especially right after cold start-up. Also, cold air would cause an engine to take longer to warm up to closed-loop operation temperatures, adding to the higher-fuel-consumption-after-cold-start-up issue.

No, cold air intakes are NOT the best for fuel economy, even though they are SUPPOSEDLY great for boosting high-end Horsepower and Torque. However, fuel efficiency appears to be the MOST optimal in about the 1/3-2/3 RPM range, or between 1650-3300 RPMs in the case of my 4.0L Jeep Cherokee Laredo, at an air intake stream temperature of around 90-120 degrees Fahrenheit. However, cooling the fuel to prevent vapor lock, which has occured on my vehicle already at least once, on a really hot day in which the fuel got really heated up to the temperatures inside the engine compartment, might be a good idea, if it doesn't interfere with improving fuel mileage to any appreciable level. Does this reasoning make any sense to you at all?

Yes the reasoning makes sense. I can easily see how it would warm up the engine quicker, but, at least for my driving habits, that wouldn't be very beneficial.

Comparing cold start efficiency isn't a good comparison because the engine is cold. A warm engine, even on a day with cold temperatures will not necessarily have a problem evaporating fuel due to the heat from the warm engine right underneath that throttle body.

Also, if you want to increase operating temperature, why not just change your thermostat?

This is my understanding: there is some point at which the intake air is "warm enough" to not have efficiency losses, and I never would have imagined that you would need to modify your intake to achieve that. I suppose it would make sense, if you do alot of cold starts, to do the modification to improve warm up time, but it would still cost you power when the engine is warm.

Even on relatively cool days (40 degrees), if I open my hood, it is plenty warm and I can't imagine the intake air being much colder.

You might consider editing this page http://en.wikipedia.org/wiki/Warm_air_intake

Because whoever wrote it clearly doesn't get it

[13B_88FC]

"My reasoning behind a WAI is that warm air would help the engine warm up faster and stay above 195 degrees Fahrenheit"

Every car's cooling system makes sure that the car stays at operating temp after it's warmed up by using a thermostat. If you're dropping below what your t stat is rated at, then you have a bad t stat or you've been coasting down a hill too long.

[Davinator61]

Originally Posted by 13B_88FC

Yes the reasoning makes sense. I can easily see how it would warm up the engine quicker, but, at least for my driving habits, that wouldn't be very beneficial.

Comparing cold start efficiency isn't a good comparison because the engine is cold. A warm engine, even on a day with cold temperatures will not necessarily have a problem evaporating fuel due to the heat from the warm engine right underneath that throttle body.

Also, if you want to increase operating temperature, why not just change your thermostat?

This is my understanding: there is some point at which the intake air is "warm enough" to not have efficiency losses, and I never would have imagined that you would need to modify your intake to achieve that. I suppose it would make sense, if you do alot of cold starts, to do the modification to improve warm up time, but it would still cost you power when the engine is warm.

Even on relatively cool days (40 degrees), if I open my hood, it is plenty warm and I can't imagine the intake air being much colder.

The issue I have is NOT with my t-stat, as it is already the maximum available opening temperature, and is working as it should, as of my last drive. What IS the issue is the temperature of the AIR going into the engine cylinders through the intake manifold, from outside the engine compartment's exhaust manifold side, where a lot of the heat-flow seems to be concentrated.

Also, I'm basing my idea on a "heat riser" on the intakes of older, carburated vehicles to not only warm my vehicle up to operating temperatures faster, but to also keep the intake air temperatures warmer than outside-the-vehicle temps, or even ambient engine compartment temperatures, as well, using heat off the Exhaust Manifold to do so.

Plus I'm not looking to increase Horsepower and Torque in the upper RPM band (3300-5000), but to improve fuel efficiency in the mid-range power band (1650-3300 RPMs). In fact, I DON'T give a Rat's Fat Ugly Tuchus about upper RPM band gains, as I've already done a number of mods on my engine block for better air flow (Ported and Polished Head, Roller-Tipped Rocker Arms, Anti-Pump-Up Valve Lifters, Oversized Intake & Exhaust Valves).

All I REALLY care about is squeezing as much fuel efficiency out of my I-6 as I can, based on what I've observed over the years as to what works v.s. what doesn't, even if my Upper Power Band suffers. Cold Air Intakes have NOT worked for me in my current vehicle's application, so I'm going the opposite direction to see what that will do, that's all. Do you now understand my reasoning a little better?

Plus your having mentioned your own driving habits as you did, would suggest you're a Jack-Rabbit-Style Skinny-Pedal-Stomper from all stopped positions, at least to my way of thinking, not someone who eases their foot onto the gas pedal in a common-sense manner, like I always try to do. I also have to wonder if you've got one of those Coffee-Can-Mufflers on your car, like one of those Rice-Rocket-Honda-Boiz. If so, then I'll just have to start calling you "Fart-Knocker-Ricer-Boi" whenever interacting with you on this forum, from now on, just to get my lols, heh, heh, heh.

[t vago]

Originally Posted by 13B_88FC

I suppose it would make sense, if you do alot of cold starts, to do the modification to improve warm up time, but it would still cost you power when the engine is warm.

Maximum rated power would go down, but who cruises down the highway at wide-open throttle?

I've seen about a 5% improvement in FE from raising my truck's intake temperature 50 F above ambient.

Originally Posted by 13B_88FC

Because whoever wrote it clearly doesn't get it

How so?

[13B_88FC]

Originally Posted by Davinator61

The issue I have is NOT with my t-stat, as it is already the maximum available opening temperature, and is working as it should, as of my last drive. What IS the issue is the temperature of the AIR going into the engine cylinders through the intake manifold, from outside the engine compartment's exhaust manifold side, where a lot of the heat-flow seems to be concentrated.

Also, I'm basing my idea on a "heat riser" on the intakes of older, carburated vehicles to not only warm my vehicle up to operating temperatures faster, but to also keep the intake air temperatures warmer than outside-the-vehicle temps, or even ambient engine compartment temperatures, as well, using heat off the Exhaust Manifold to do so.

Plus I'm not looking to increase Horsepower and Torque in the upper RPM band (3300-5000), but to improve fuel efficiency in the mid-range power band (1650-3300 RPMs). In fact, I DON'T give a Rat's Fat Ugly Tuchus about upper RPM band gains, as I've already done a number of mods on my engine block for better air flow (Ported and Polished Head, Roller-Tipped Rocker Arms, Anti-Pump-Up Valve Lifters, Oversized Intake & Exhaust Valves).

All I REALLY care about is squeezing as much fuel efficiency out of my I-6 as I can, based on what I've observed over the years as to what works v.s. what doesn't, even if my Upper Power Band suffers. Cold Air Intakes have NOT worked for me in my current vehicle's application, so I'm going the opposite direction to see what that will do, that's all. Do you now understand my reasoning a little better?

Is your jeep throttle body injected?

Carb'd engine did get their intake air from a hot source when warming up, but once the car was warm, it had a mechanism to switch to colder source. Also, Fuel injectors make it much less important since they evaporate the fuel better.


If you say it gives you better mileage, I'll buy that.

[13B_88FC]

Originally Posted by t vago

Maximum rated power would go down, but who cruises down the highway at wide-open throttle?

I've seen about a 5% improvement in FE from raising my truck's intake temperature 50 F above ambient.



How so?

More power means you can get up to speed faster with the same shift points.

5% is a good improvement, and worthwhile. I'm curious how much this mod helps with an already warm engine going down the highway - in other words, if you took the cold start out of the equation.

[razor02097]

I don't know that much about warm air intakes but I have read a lot about them...


from all the things I have read the 2 major benefits are introducing heat into the engine for a faster warm up to get to closed loop faster which saves fuel.

Then the other benefit is to potentially reduce pumping losses. Cooler air is more dense and contains more oxygen. More fuel can be added for the given volume which produces more horsepower. This is useful if you want to get every bit of power from an engine while running down a drag strip. However idling at a light or cruising around town you don't need power. Yes you may use less throttle but your pumping losses will increase. It takes fuel to turn the engine, with cooler air it takes more fuel to reach stoichiometric combustion....since you aren't using the power the engine is making most of the power is being used to turn the engine.... ergo pumping losses... you are paying money to move cold air through the engine.

In theory warmer air = less fuel for given volume = throttle open a little more = less pumping losses = more efficient engine = ???more mpg???....

[Davinator61]

Originally Posted by razor02097

I don't know that much about warm air intakes but I have read a lot about them...


from all the things I have read the 2 major benefits are introducing heat into the engine for a faster warm up to get to closed loop faster which saves fuel.

Then the other benefit is to potentially reduce pumping losses. Cooler air is more dense and contains more oxygen. More fuel can be added for the given volume which produces more horsepower. This is useful if you want to get every bit of power from an engine while running down a drag strip. However idling at a light or cruising around town you don't need power. Yes you may use less throttle but your pumping losses will increase. It takes fuel to turn the engine, with cooler air it takes more fuel to reach stoichiometric combustion....since you aren't using the power the engine is making most of the power is being used to turn the engine.... ergo pumping losses... you are paying money to move cold air through the engine.

In theory warmer air = less fuel for given volume = throttle open a little more = less pumping losses = more efficient engine = ???more mpg???....

This is what I'm trying to make the point on to you, 13B_88FC, a.k.a. Fart-Knocker-Ricer-Boi, about Warm Air Intakes v.s. Cold Air Intakes. Plus I'm not looking to build a racing machine. Instead I am looking to improve what I currently have for my daily commute. Since I don't go driving around at near-WOT-to-WOT like SOME people seem to think they should for MAX-Performance, I'm hoping to maximize fuel efficiency by driving conservatively, while using the Warm Air Intake idea I have to ensure a more complete mixing of air and fuel droplets from EACH of the SIX injectors on my 4.0L I-6's Intake Manifold.

My thinking is, if the Intake Air Stream is 30-50 degrees above Engine Compartment Ambient, the fuel droplets from each injector's pulse would be more likely to evaporate quickly enough to compensate for the lowered oxygen density of the warmer/hotter air, than if I were to drop the intake air charge temperature to BELOW Engine Compartment Ambient Temperature, which is what CAIs are supposed to do.

The use of a CAI would be more likely to cause the droplets to clump together more as they entered the Cold Air Stream into each of the intake ports on the head(s), requiring more fuel overall to be used per cylinder, whether on post-cold-start-warm-up, or once at operational temperature. By heating up the intake air charge to well above Ambient Engine Compartment Air Temperature, I'm hoping to avoid this, or at least reduce its likelihood, especially if it improves overall MPG, like I think it will.

Btw, the 4.0L Jeep engine NEVER had Throttle Body Injection since Day One. Even during the Renix years, it was a Multi-Port FI system. The earlier 4.2L Jeep I-6 WAS carb'd with a Carter "Chug-and-Glug", which was not as fuel efficient, or powerful as its younger 4.0L sibling, but not the 4.0L itself.