Cold air VS Warm Air Intakes - what's the difference?

[deadman1474]

Originally Posted by RH77

I have a brief response -- incomplete answer.

From the shop manual on my vehicle, the engine is intended to run richer at intake temperatures below a certain figure (I forget the exact number, let's say 60F). Warm air is needed to satisfy this requirement, especially in Winter.

Beyond that, I've determined with repeated testing that my engine operates most efficiently with IATs at 90-100F. Beyond 120-130F, it starts to dump-in more fuel to compensate for pre-ignition, and fools with the timing. So that temp above the maximum requirement of ambient up to at least ~90F yielded around a 15% increase when I first tested it 2 years ago (the abstract is floating around somewhere -- I think there was a cold-air intake on the car before). FE drops when colder air is introduced, even at ~70F, which is well within the requirements of the sensor/ECU closed-loop management. You may find terms of HAI and WAI (hot and warm air intakes).

How it works -- not exactly certain. A couple years ago I did quite a bit of testing with different temps and found the "sweet spot" for my car. There's still quite a bit of discussion on the topic and the term "pumping losses" can best be explained by someone with more Physics knowledge than I have.

My advice? Experiment yourself with different temps -- and stay as Scientific and consistent as possible. See if you can obtain info on IATs and the vehicle ECU's compensation from a shop manual or enthusiast website. BTW, what kind of vehicle do you have?

Let us know if you test and come to some conclusions.

RH77

I own a 2008 dodge ram 4*4 with the 5.7 hemi with mds. I was offered a brand new free cold air intake with ram air and I took it. It makes a decent amount more mpgs and way more power so Im pretty happy. Driving normaly in the city I get around 15mpg and highway around 23 mpg

[tasdrouille]

I just got the SGII in today and went for a run to test my WAI. It hoovers around 100 at highway speeds. It went up to 132 when I took the exit as there was less air coming in the engine compartment from the 20 square inches I got left open in my grills. FTW went up to 220 after 15 mins as a result from the block. I wonder at what temp the fan's kicking in.

Since my WAI takes less than a minute to take off and put back on, I'll do a test in the following days to see it's impact on mpg.

[tjts1]

Every car I've had thus far got better fuel economy with cold air intake of my own design. Warm air might help fuel vaporize better in extreme cold but it also takes more energy (pumping losses) to breath in that air. If your car has a knock sensor, hot air will cause the computer to retard timing and reduce power hence efficiency.

[tasdrouille]

Originally Posted by tjts1

Every car I've had thus far got better fuel economy with cold air intake of my own design. Warm air might help fuel vaporize better in extreme cold but it also takes more energy (pumping losses) to breath in that air. If your car has a knock sensor, hot air will cause the computer to retard timing and reduce power hence efficiency.

I won't debate the fact that you can get better FE than stock with a CAI, but have you ever tried a WAI?

[Daox]

Originally Posted by tjts1

Every car I've had thus far got better fuel economy with cold air intake of my own design. Warm air might help fuel vaporize better in extreme cold but it also takes more energy (pumping losses) to breath in that air. If your car has a knock sensor, hot air will cause the computer to retard timing and reduce power hence efficiency.

The idea of the WAI is to reduce pumping losses (and increase fuel vaporization in some cases). Since the air is less dense the throttle must be opened further to maintain the same amount of power. This will reduce pumping losses, not increase them.

Yes, warm air will tend to retard timing on some engines. However, on others it won't. It depends on their design and how the engine is tuned. I believe its fairly well known that Saturns react very well to WAIs. Other cars won't. You really just have to try and see if it works.

[trebuchet03]

Originally Posted by tjts1

Every car I've had thus far got better fuel economy with cold air intake of my own design. Warm air might help fuel vaporize better in extreme cold but it also takes more energy (pumping losses) to breath in that air. If your car has a knock sensor, hot air will cause the computer to retard timing and reduce power hence efficiency.

depends how warm - some cars, the temps need to be pretty hot for this to happen.

And explain just why pumping losses increase?

Finally, on the subject of vaporization.... Not on a fuel injected car - that's what injectors do - regardless of temperature Given that the amount of unburnt fuel that leaves the car is less than 1% - this isn't a big issue

[tjts1]

Originally Posted by tasdrouille

I won't debate the fact that you can get better FE than stock with a CAI, but have you ever tried a WAI?

Yes. I've had 4 warm air intakes from the factory thus far.

Every Volvo up to the late 90s had a thermostatic intake designed to take in air from either in front of the grill or near the exhaust or a combination of the two in order to maintain a minimum 70f intake temp. When the thermostat fails (every single one does after 10 years) it gets stuck in the hot air position and absolutely decimates both fuel economy and power. All 4 of these cars had compression ratios of 9.8-10.7 and a knock sensor. They all got FE numbers between 17-23mpg with the hot air intake, and 21-30mpg with cold air intake. I kept track of every one very meticulously. So have you ever tried a cold air intake?

Originally Posted by Daox

The idea of the WAI is to reduce pumping losses (and increase fuel vaporization in some cases). Since the air is less dense the throttle must be opened further to maintain the same amount of power. This will reduce pumping losses, not increase them.

Yes, warm air will tend to retard timing on some engines. However, on others it won't. It depends on their design and how the engine is tuned. I believe its fairly well known that Saturns react very well to WAIs. Other cars won't. You really just have to try and see if it works.

The pumping losses you describe exist when there is a difference in air pressure between the intake manifold and the and the bottom side of the piston (AKA crankcase). The simple solution if you want to eliminate pumping loss isn't to heat up the intake air but to apply a vacuum to the crank case. A lot or racers do this. I tried it years ago and it work but its too much of a hassle to maintain.
There are very few cars on the road built in the last 20 years without a knock sensor. I don't know if the 1.9 motor in your Saturn has a knock sensor but I would like to see the FE number increase with your warm air intake.

Originally Posted by trebuchet03

depends how warm - some cars, the temps need to be pretty hot for this to happen.

And explain just why pumping losses increase?

Finally, on the subject of vaporization.... Not on a fuel injected car - that's what injectors do - regardless of temperature Given that the amount of unburnt fuel that leaves the car is less than 1% - this isn't a big issue

I'll give you that, but I haven't seen one warm air intake that doesn't lose more power and efficiency because timing is being retarder than it gains from any pumping loss decrease.

Another point. When Volvos have the thermostat stuck in on the hot air side, they tend to fail smog because of extremely high NOx numbers. Most mechanics don't know how to diagnose this so they end up in the junkyard.

cheers
Justin

[trebuchet03]

Originally Posted by tjts1

The pumping losses you describe exist when there is a difference in air pressure between the intake manifold and the and the bottom side of the piston (AKA crankcase). The simple solution if you want to eliminate pumping loss isn't to heat up the intake air but to apply a vacuum to the crank case. A lot or racers do this. I tried it years ago and it work but its too much of a hassle to maintain.

Pumping losses also occur during the actual intake down stroke - as there's a pressure gradient between the cylinder and intake manifold. It doesn't help that it's pulling against a vacuum (which in turn was created by that same action - making a vacuum isn't free, unfortunately). This is one benefit diesels have fundamentally - no throttle.

But even if you apply vacuum to the crank case - now you've got pumping losses while traveling up as opposed to traveling down. But that said, the reason as far as I know, for racing applications applying vacuum is to remove blow by. First because that pressure can build up quickly in their application and second because it's not a good thing to have such gases in there. I've seen setups with limit switches/valves to pull full vacuum during peak power and then limit the vacuum when not under heavy load - to reduce parasitic losses from their vac pump....

----

Originally Posted by tjts1

I'll give you that, but I haven't seen one warm air intake that doesn't lose more power and efficiency because timing is being retarder than it gains from any pumping loss decrease.

Where do you live? I can show you mine - and you can peek at the SG to see the timing... My timing hasn't changed and my intake temps are around 120 once fully warmed up (which, just so happens to be close to the temp of my intake while driving through the sierra Nevada last summer - without the WAI ). I got the best economy on that stretch - except during the long downhill periods




But yes, this is a case where one must go with what works... There's no rule of thumb - there's a theory (as defined as well substantiated explanation) - but it's largely dependent on engine management - which of course varies from make to make and even model to model. Oh feedback control

[AXMonster]

How about utilising a WAI and putting a resistance in series with the intake air temp sensor to fool it into thinking the intake air isn't hot, but mildly warm. This should combat the retard function that some cars see??

[tasdrouille]

Originally Posted by tjts1

[...]So have you ever tried a cold air intake?[...]

My car came with a factory cold air intake, taking it's air between the leading edge of he hood and the upper grill.

I'm using the WAI to get decent intake temps I would otherwise be unable to get in the winter.