my question is regarding intake air temperature and the miles per gallon. if IAT is cool, below 80 degrees does miles per gallon improve if IAT is high, above 80 does it decrease MPG
The engine seems to actually like fairly warm weather -- 75F or more, IAT of maybe up toward 100F. There's a bit of an MPG bellcurve there that falls off to either side. . _H*
thanks for the reply, does the amount of air make a difference, i moved that plastic intake hose that connects to the air duct thing, and air cleaner, between the front passenger side headlamp, theres a sizeable hole by the grille where air would flow through, i am getting 51 mpg, consistently, and im not driving conservative. Im also in south florida, so i should be getting roughly 75-101 degree IAT, ill have to check it with my scanner. With my current modification it feels as if the prius has more lower end torque, not sure though, it could be psychological.
Colder air is denser air and better for the power stoke, more compression. I think that is why the air intake has a hose goes to the front of the car. If you remove the hose, presumably you would be taking in warmer and less dense air for use in the ICE. that's why turbo and super chargers have inter coolers. yes the hose does add more resistance, but is that off set by the warmer air... Cold weather lower battery performance = less MPG Warmer weather improved battery performance = More MPG
Have you ever seen the HV battery temperature? The battery temperature becomes very warm even in cold weather. In the cold weather, everything need a certain amount of energy to become their best, especially, the engine coolant... The intake air temperature is best at 100F as hobbit stated. Ken@Japan
my 2001 prius ( salvaged, and charged by a custom charger ) Hv battery temp is constantly high, this is indicated with the HV battery fan running constantly during at least a 10 minute drive. ( i really dont care about the temperature, i can always get a battery ) When the HV battery fan comes on, my 01 prius rivals that of the honda insight and gets upwards of 70-80 mpg. This is without a intake modification. my new prius, i find it harder to achieve great mileage, i tried taking out that hose from the airbox and pretty much resulted in a louder exhaust note, it seemed to keep similar gas mileage, maybe a bit lower. On the old prius i took the hose out, and horrible gas mileage, and a much LOUDER exhaust note. I keep thinking if i restrict air going to the engine i would get better gas mileage, this is based on my observations that more air = less gas mileage. Exhaust note is a real big difference when the hose comes off, its more apparent on the 2001 prius than the 2005. Once i installed the throttle position sensor on my 01 prius without hooking it up to that tensioning spring thingy, and my exhaust note was extremely loud, almost like a aftermarket exhaust. Im just thinking theres some way to improve intake air for better gas mileage ( other than hooking up a hose to the cabin )
Mr Hobbitt, Wasn't it your page I saw of the detailed test bed where the throttle body intake plumbing was re-routed to scavenge hot air off the exhaust manifold thereby piping in pre-heated air. It showed the hotter the intake air was the worse the car performed? If not you who was I thinking of please? Thanks, Ray
I'll see your re-route of the intake hose and raise you a cooler throttle body! Here's what I did with excellent results: On our cars like most cars made since 1985 the engine coolant is routed through the throttle body to keep the tb from freezing in sub zero temps during the winter. Us lucky people in Fla don't ever see that kind of temp so pre-heating of the TB is an unnecessary waste of performance. I just removed the coolant lines and connected them together bypassing the TB and the car runs really good. The intake now runs so cool I can put my hand on it after a good highway run. It has some real nice snap to it at passing speeds at around 70. Try it its easy. Home Depot sells a bronze 5/16 barrel to connect 2 PEX lines together in the metal plumbing section of Home D. It fits the two 5/16's hoses perfect. Just buy that & 2 small clamps. ICE's love cold air. Colder the better. It won't improve mileage but will def. improve performance. If I drive like I just don't care I never get lower than 44 but last 2 days I've been pokey and watch the mfd and tonight hit 53 on my 18 mile commute home with the air on & in the fast lane. Good luck!
It was indeed my "heatgames" page that set forth a bunch of endorsement of bringing pre-warmed air into the intake in the interest of heat conservation and increased MPG. And this winter I haven't bothered installing any of that, and am still holding around 55.x in mixed driving with the air-box inlet just open to underhood ambience. Without a controlled A/B test we won't really know for sure, but it's looking like the whole warm-air- intake theory just doesn't make any difference on a Prius. . Grille blocking is still valid, on the other hand, since it helps prevent engine block heat loss in general and falling back into stage 3b and other inefficiencies peculiar to cold weather. . _H*
Thank you. It was an excellent article. I agree without a controlled study and a dyno test its hard to state matter of fact that there is a performance improvement but all I have right now is a butt dyno and I swear my car runs really good with a cooler throttle body. If you don't mind if you get a chance maybe you could post a linky to that article as I forgot to bookmark it last time. Thanks alot, Ray
The only benefit of warmer inlet air is that it more-quickly gets the engine to optimal operating temperature. The energy loss caused by reduced air density reduces efficiency, all else held constant. That is why the cold climate fanatics who block their radiators get MPG improvement; the combustion air entering their engines is just as cold either way. If it were cheap to do it, it would be better to cool inlet air during the summer and not bother warming it during the winter.
Hmm, Might be good to pull intake air off the exhause through a heat sink pasted onto the engine. The cooling of the air back would make for the same cold air intake, (better mass volumetric efficiency) but the engine would get warm allot faster. That way the engine pumping, and waste heat is being used for a secondary purpose. Once the engine compartment is up to 65 F, a valve could open that just lets the air come from the compartment.
Take a look at some cars from the 70s and 80s. They had something exactly like you are talking about. There was a little pipe that ducted hot air from the exhaust manifold to the intake air filter. There was a little valve that modulated the operation of that duct.
Hi Winston, Yep, I am familiar with those cars. It was my high school chore to retune the family Pinto every 6 months. Plugs, points, rotor and sometimes distributor cap. Gap, dwell and time. But that is not exactly what I am talking about. What you are talking about was an intake air stove. What I want to do is keep the air into the engine near the outdoor temp, but dump the heat out of the exhaust stove into the engine block via a heat sink, like you would have on the back of a piece of electronic equipment.
Hmm... donee's idea might be realized without moving parts by using a heat pipe. With the right choice of working fluid and pressure it could be arranged to stop transfering heat from the exhaust stream when the engine block reaches optimal temp.
Please direct me to an artical or publication that states that. Yes I know that the battery and ICE warm up even in cold weather. durning that time MPG is lowered we all know that. The more O2 (air) or the more dense the air is in the intake the more HP and better MPG. The warmer the air, the less dense this air is the lower the HP and the lower the MPG for a give amount of gas. Google super chargers and turbo's, they raise pressure and inter-coolers and N2O that lower temps in the intake temp by 75 deg. But you go ahead and warm you intake air, even after the ICE is up to running temp, and think that that will get you better MPG.
Sorry, but there is no article. Believe or not, it's up to you. My personal opinion is... "The more O2 (air) or the more dense the air is in the intake the more HP"=true Prius always adjusts the air/fuel ratio to the stoichiometric 14.7:1, therefore more air means more fuel and more power. "better MPG"=not true The more fuel does not mean better MPG. Same opinion here. The warmer the air does not mean lower the MPG. Again, believe or not, it's up to you. A good Pulse&Glide driving = don't use the battery power... Pulse = no battery assist Glide = just coast with no battery assist Therfore, the battery performance does not relate to the high MPG Pulse&Glide driving. That's my opinion. Ken@Japan
