Cold air VS Warm Air Intakes - what's the difference?
What are the advantages of a warm air intake over a cold air intake? I know that I have always seen cold air intakes as being for performance/ Efficancy. Your thoughts
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Cold air has more oxygen by volume. So you can stuff more fuel into the cylinder while maintaining the proper air/fuel ratio. That's one reason why the go-fast people like it.
The idea behind using warm air for efficiency is to intentionally depower the motor. Less oxygen by volume means you must open the throttle further to generate a given amount of power. A wider throttle opening means reduced pumping losses. BTW, the O2 sensor will always strive to maintain the proper air/fuel ratio, so it's not running lean. In a way, it's similar to driving at high elevations (less O2 in the air), which can be more efficient for a number of reasons. In practice though, whether it works seems to depend on the specific vehicle and how it's programmed to respond (or not) to the increased air temps. Some ECU's may back off timing to prevent knock, so you end up with a zero gain. The Saturn drivers seem to have good luck with it though. |
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Thanks I always wondered about it. |
I understand that cold air is denser and contains more oxygen by volume than warm air, but the reason for depowering the motor I don't quite get. Maybe if you can explain what you mean by "pumping losses" I'll begin to get it. I was under the impression that under steady state circumstances the motor produced the amount of power required to maintain the steady state (say 55mph on a flat freeway with zero wind). Regardless of the amount of power the engine is capable of producing, it only actually produces the amount of power required of it at the time. I was also under the impression that the amount of power produced by an engine, all other things being equal, was proportional to the difference in the temperature of the air/fuel mixture entering the combustion chamber vs. the temperature of the combusted air/fuel mixture (exhaust) leaving the combustion chamber. The temperature difference would be greater if you start with a colder air/fuel mixture. Wouldn't this mean that with cold intake air the engine would not have to work so hard to power the car? This being the case, could you have a smaller engine or a smaller carburetor/throttle body and still get sufficient power for your needs? In the end, wouldn't this result in better economy?
I don't mean to be argumentative, but I'd like to understand. I come from a hotrodding background and it always seemed that a cold air intake was a cheap way to increase performance without suffering other ill effects, such as poor economy from a performance cam or a big carb. It seems that some of the performance tricks work okay for economy (free-flowing exhaust, aerodynamic mods, etc.) but others don't. Sometimes the differences are obvious (hot cams come to mind) but I don't get the cold air thing. Enlighten me please. Thanks! |
Incomplete Answer
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 |
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The quick and gritty explanation.... Reduce vacuum and you reduce pumping losses.... There's plenty of products out there to reduce intake restriction - but they overlook one point... The throttle plate is the biggest freaking restriction in the whole line :p Quote:
Perhaps it's nit picky - but if you're generating the same amount of power over the same amount of time.... The amount of work generated is exactly equal ;) |
Having said all that, when I tested cold (~55 F) vs. warm (~116 F) intake air @ 39 F ambient with my car, it made no significant difference. No gains or losses:
http://metrompg.com/posts/photos/wai...ts-chart-z.gif Details: http://metrompg.com/posts/wai-test.htm Not saying this will be the case for every vehicle. Also, my testing of this mod wasn't ideal (no additional set of "A" data). As with much in life, "it depends." |
Okay, it's starting to make a little more sense now... The ECU is overthinking the situation and correcting for what it sees as problems. If the computer didn't do so many "favors" for us we might be able to tweak our engines more for better economy. Maybe not. Maybe I'm just too "old school." Generally it seems like the computer does a pretty good job of keeping the mixture in a reasonably good range most of the time; a lot better than most old carburetors did. But like most car design features, it is a compromise for the average driver under average conditions.
I'm not an average driver, and I'm guessing you're not either. It looks like, as you suggested, I'll have to figure out what the computer likes best and then try to duplicate that condition. Still, I'd like to be able to adjust the computer for what I think it should do, and then verify it myself. (I plan to get one of those cool Scan Gauge II's). I think your advice is right, considering things as they are. I'll have to test to find out what intake air temperature works best for economy and try to provide that to the intake air sensor. Maybe at some point I can figure out how to trick the sensor and get colder air into the engine without the computer knowing about it, and see what that does... Thanks for the explanation, and if I try anything along those lines I'll post the results on the forums here. BTW, I will be driving a 96 Metro 2dr HB base model. No options, 3cyl 5spd. So far I have put less than 5 miles on it in the week that I've had it; I drive very little; mostly I am on foot. It runs kind of rough; I don't know if that's typical for a 3cyl or what. (any ideas?) I am mainly concerned with saving gas for geopolitical and environmental reasons, so it wouldn't make much sense for me to drive the car just for fuel economy testing purposes. That said, I won't give up my autocrossing so easily... Fo that I have a factory stock 98 Neon ACR (American Club Racer version). It actually gets decent mileage considering it has lower gears (3.94 final drive) than the standard models (3.55). It's a 2.0 liter DOHC, with few options so it is fairly light. |
Response to trebuchet03 and metrompg:
Okay, the EGT not being static, but rather increasing along with intake air temp gives me more to chew on. And the Firefly charts are most helpful; they would probably apply almost directly to my Metro. Basically what I read then, is that I can leave the air horn running out through the front bulkhead, as is the stock configuration, and it won't help or hurt my mpg, though it may give me more hp at wot. Right? It may lower my egt and combustion chamber temps however, perhaps allowing me to run slightly more timing advance or use a lower grade of gas.
I can't thank you guys enough for your thoughtful and informed input! And I like the idea of not doing anything at all; inertia is my specialty. I just love to leave well enough alone every chance I get. Cheers! |
The cold air vs warm air issue will be more of a factor in carbed engines, then in FI engines, and again more of an issue in outside temps below 50 degrees F. In carbed engines cold air may even present drivability issues in extremely cold climates. On a carbed engine , hot air allows the engine to run a leaner air/fuel mix, as the hot air tends to allow more fuel vaporization, and less of a need for the combustion chamber to use the actual burn in converting raw fuel into vapor , or useable fuel. Deterents to this process are the fact that the air and fuel mixed past the carb rarely spend more then .6 seconds in the intake before entering the combustion chamber,(hardly enough time to cause an appreciablle change of state in the fuel). Hot air on an FI engine could easily help if the fuel is also heated,particularly on a wet manifold system or TBI, and this is doable because of the increased fuel pressure before the line, that will inhibit vapor lock. When the hot fuel is introduced to the air stream, the hot air will further help to keep it in a close to vaporous state as long as the puter does nothing to dump extra fuel into the mix. Systems using hot air tend to run in a smoother fashion again because the air/ fuel mix is normally more homogenous. |
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You'd think I would have returned my car to the stock intake configuration after apparently learning it didn't improve efficiency @ cruise. But I didn't. There are other considerations - such as the fact that the heated intake air will help warm the engine more quickly, so you get away from fuel enrichment sooner after a cold start. |
Hey - welcome, oldschool. Feel free to post up a "hello" in the Introductions forum.
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Beaver: I moved the discussion about whether or not your engine is idling rough:
http://forum.ecomodder.com/showthread.php?t=548 |
Low cost air temp readout:
For anyone who like me is driving a car that can't support a ScanGauge (pre '96), you can get an "Interior/Exterior" thermometer for about $10 that will do it. I got mine from Autozone. JCWhitney.com and Advance Auto also sell them. Probably most big box auto retailers so. This past December I restored the regulated warm air intake in my daily driver, installing the thermometer was part of that project. As my new route is drastically different from anything I've driven in the last couple years I can't comment on whether it actually helps FE however I'm very happy that when it's 20 deg. or less outside, the intake air temp is generally between 75-90 deg F. Darn close to the range some suspect is ideal. And as MetroMPG pointed out, I think it has to help get the car warmed up sooner. I installed the sensor into the airbox after drilling a small access hole for the wire. The wire lead supplied with the unit was long enough for me to place the display on my dash, nicely mounted (Velcro) on a home-built bracket. I did need to cut the wire to get the sensor inside the airbox, and soldered the cut wire back together. You want maximum wire conductivity as the sensor's resistance is quite high. Low effort, good result. |
You know, I have one of those temp gauges lying around somewhere; thanks for the idea! Back in the 60's the Detroit automakers put a "manifold stove" on many of their cars; some ductwork around one of the exhaust manifolds with a pipe running from it up into the bottom of the air cleaner airhorn. There was a temperature-activated butterfly that directed the air into the air cleaner from the manifold stove until it became warm enough to open the butterfly and block the hot air, opening up the other intake on the airhorn (which usually aspired underhood air that was often quite warm). I think they used a similar arrangement well into the 80's. Of course nobody thought much about fuel economy back in the 60's...
Beaver |
To make everyone a bit more confused about the warm air, I am running a megasquirt and wideband oxygen sensor in my metro so I can compensate for practically anything on the computer since I have full control over it.
I tested warm air before running the megasquirt and with super heated air it made me drop ~10mpg. This winter with my car well tuned with the megasquirt computer I tried it again. This time I was able to redo my timing and fuel maps to match the intake air. This time at best it didn't change my mileage and at worst I got about ~10mpg drop again. I ran various configurations to regulate the intake air temp and really wasn't able to get it running right. Of course I also am running 11.5:1 compression ratio so the engine knocks easier than a stock one would. I just don't think there is enough of a gain with warm air to actually improve mileage any measurable amount. It can improve warmup times though so that is worth hooking something up but it needs a way to keep the air temperature from getting really hot though or any engine will start knocking. So feed as much hot air into the engine as you can when it is cold then turn off the hot air and let it pull ambient underhood air after it is warm is what I think an ideal setup is. |
beaver and coyote already got to what I was thinking. for years automakers were using hot air tubes to help engine warm up. carbs of the 70s and 80s did not have good emissions when cold, so they had to find some way to start warming the carbs up. you guys could use a similar concept to get warm air on start up, that eventually opens back up to fresh air. depending on how creative you are, you could even have the system be able to switch from hot air/underhood air/cold air depending on intake temperature. that way the engine could be getting "ideal" air temp as much as possible.
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LMAO, now we can completely confuse the folks here Coyote, when I was doin my vapor carb building in the 80's we had an exhaust heated exchanger mounted directly on top of the stock carb so we could use both the carb and the vapor unit. This was a 74 Chrysler Newport with a 400 cu in engine. In stock form it got 12 mpg, runing hot air(265 degree air) in the stock carb it went to 22 mpg.
It could be that high compression effects the intake air temps viability to increase mileage.My truck is running a 10.75 :1 compression ratio and like you avoiding knock has been an issue. In the winter however I run a stock air cleaner with the heat stove off the exahust manifold and disabled the temp sensor inside the aircleaner, running the snout butterfly directly off manifold vacumn so when I am cruising I have hot air and when I am accelerating cold air; while I don't drive the truck enough to get any accurate mileage figures , I do know the hotair stove helps the trucks drivceability. |
Here is a pretty good overview of preheating fuel and intake air
http://freeenergynews.com/Directory/...ell/index.html |
I'd like to test the idea of a WAI.
One concern that I have is whether or not it increases the engines emissions. I would think that since less fuel is being added to the mix, there would be less pollution. |
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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. |
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.
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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. |
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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 ;) |
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http://farm3.static.flickr.com/2105/...8372259eee.jpg 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? Quote:
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. Quote:
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 |
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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.... ---- Quote:
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 :rolleyes: |
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??
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I'm using the WAI to get decent intake temps I would otherwise be unable to get in the winter. |
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On another note about applying vacuum to the crankcase, I don't know what modern engine doesn't do this. Any modern engine is fitted with a PCV valve and anytime there is vacuum in the intake manifold theres vacuum in the crankcase. |
My '00 Civic (with knock sensor) is showing ~10% mileage improvement with a WAI pulling hot air from right next to the exhaust manifold. Aside from driving style, it has been the best single thing I've done for FE.
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The whole crankcase discussion is nice...I had never thought of that. In a multicylinder engine, isn't it kind of a moot point? When one piston descends, another rises. There shouldn't be any compression/expansion going on. The PCV valve exists solely for piston blow-by...
The retarded timing is definately to prevent knock, but I wonder how much of an effect WAI's have on chamber temperature. As far as I know, intercoolers and CAI are used mainly for increased charge density. I wonder how dependent knock is to these changes in temperature...:confused: I've tried thinking of ways to decrease air density through expansion (i.e. increase a closed volume), but it always seems to be complex/power hungry. Everything has an opposite, right? Heat engine - heat pump. Black - white. Supercharger - subcharger?...:p - LostCause |
I'm up some on increased IATs
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I did some IAT monitoring last week as it relates to fuel flow. While it has a positive impact (45-115 degrees), the FWT increase has the biggest fuel flow affect across the range. Changing timing has less overall effect than friction reductions it appears. Now with summer approaching, the WAI may be icing on the cake. http://forum.ecomodder.com/showthread.php?t=1506 |
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The best systems have learning functions that populate steady state and transient knock limit correction maps. The normal way to get these maps to re-learn is to disconnect the ECU power supply so that it is starting again from zero. Any engine modification to a vehicle that has a self learning function (even a fuel octane change) can benefit from a forced system reset. Actually reaching the knock limit and staying there IS something we want for the engines to be as efficient as possible. Quote:
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cold air=more power, and you use less of the accelerator pedal, which is basically the throttle control. less use of the pedal= (basically) closed throttle plate. closed throttle plate means a restriction of the "air pump, or intake" you have a pumping loss in that air is not getting in efficiently.
Warm air=less power, and you use more of the accelerator pedal, which is basically a throttle control. more use of the pedal= a more open throttle plate. open throttle plate means there is less of a blockage that's letting the air in, reducing the pumping loss. at wide open throttle, you have (basically) no pumping loss at the throttle plate. so warm air intakes won't do anything here. but unless 55mph makes you have to floor it to keep going 55, a warm intake will do something. that something depends on the vehicle. Diesels don't have a throttle plate, so you don't have a pumping loss problem from the T-plate. |
WAI arguments
In favor: - Pre-heated intake mixture at low rotational speed improves combustion. (Chiu and Horng, 1992) - Specific fuel consumption varies inversely proportional to the square root of the suction air temperature (Nakajima et al. 1969). - Higher ambient temperature is found to increase the flame speed, the combustion reaction rate, the uniformity of the fuel-air mixture and reduce the heat transfer rate though the cylinder walls (Pulkrabek, 1997). - For lower temperatures, only a small part of the injected fuel is vaporized, causing nonhomogeneity. As a result, lower flame speeds, higher unburned mixture, higher hydrocarbons and carbon monoxide emissions, and loss of power are observed (Pulkrabek, 1997; Heywood, 1988). Against: - Engine brake torque varies inversely proportional to the square root of the suction air temperature (Nakajima et al. 1969). - Higher intake air temperature increase the occurence of engine knock (heywood 1988). - At high engine rotational speeds, higher intake mixture temperatures decrease the volumetric efficiency of the engine (Chiu and Horng, 1992). References: Chiu, C.P., and Horng, R.F., 1992, “Effects of Intake Air Temperature and Residual Gas Concentration on Cycle-to-Cycle Combustion Variation in a Two-Stroke Cycle S.I. Engine Equipped with an Air – Assisted Fuel Injection System”, JSME International Journal, Vol. 37, N.4, pp. 957-965. Nakajima, K., Shinoda, K., and Onoda, K., 1969, “Experiments on Effects of Atmospheric Conditions on the Performance of an Automotive Gasoline Engine”, SAE Transactions, SAE 690166, pp. 745-766. Pulkrabek, W.W., 1997, “Engineering Fundamentals of the Internal Combustion Engine”, Prentice Hall, Inc. Heywood, J.B., 1989, “Internal Combustion Engine Fundamentals”, McGraw-Hill Book Co. |
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