A&Q about 350Z
Q:
Bottom line here is we're talking about things like pumping losses, combustion efficiency, and air consumption.
At WOT, hotter air will use less fuel period, and make less power. There is less mass, fewer molecules, and therefore less fuel gets injected. That is not to say however that it will change MPG. That is a part throttle phenomenon that is tough to quantify, but the IMEP map will tell you.
However, having said that, cool air intakes can help MPG but NOT because of the cool air. If they remove a significant restriction from the intake tract they can reduce pumping losses, but cold air alone does not increase fuel efficiency. It CAN improve combustion efficiency which is a completely different animal.
Its true that if you reduce the intake air temperature it will take less throttle opening to maintain cruise. Its also true that the computer will maintain a stoich mix regardless. That is to say, the net amount of air and fuel molecules ingested will remain the same regardless of air intake temperature. Let's not forget however that a cooler intake air signals the IAT to richen the mixture. There are also modestly increased pumping losses like SaabJohan talked about.
It may be a widely held notion, but its generally wrong. Hot intake air helps MPG. It is still quite common to heat the intake manifold with exhaust gas and coolant, as well as source hot air from under the hood to help MPG. Hotter thermostats were also used for the same reason. Sorry to disagree with you on this one guys, but saying cold air intakes help MPG is simply regurgitating propaganda that the cold air intake manufacturers feed you. Its BS.
A:
to add a small bit to that....one thing you can always note is the current trend of the manufactures. They have changed designs many times over the years. As Curtis mentions, it used to be very common to channel some/all of the intake air through a heat exchanger off the exhaust....this was particularly common on carb'd engines. The reason might surprise some, it wasn't for performance, obviously, it was actually to help negate temp changes effecting jetting. The control valves that operated teh flapper in the snorkel, would attempt to maintain 100*F intake temp, or something around there.
Modern cars though, are going further and further away from those types of ideas though. Now with modern engine management systems, there is no need for hot intake temps anymore. No worries about carb freezing, or AFR issues. Most of the intake systems these days are plastic, which disapate heat very effectively. Throttle bodies may or may not have a very small coolant line going to them, but its only there to prevent throttle freeze. Air intakes are more intelligently placed, and no modern car worth mentioning draws in hot engine air anymore. Which is why I've always kinda smirked when someone mentions the "cold intake"s. They look cool and sound cool. Thats about it. Very little gain with any decently engineered engine, which is most these days.
A:
You get carried away with the hot air idea and some one will mention the Pogue(sp?) carb craze...woops guess I just did........I got the plans for it around here somewhere.........
JD
A:
I want to edit the censor on this forum to eliminate the word "pogue." Have it show up as something like p**ue. Kinda like f**k and s**t.
By the way, unclebob; good call on the hot air and jetting consistency.
A:
I may stand corrected re: the amount of fuel used per gallon with cold air.
(However when testing fuel consumption with these units no changes were noticed.), But logic seemed to indicate to me that it would have been better. I will have to go back and try some of these tests.
However there is no question that cooler air (and cold air systems provide more HP (at WOT), and these gains are significant. We have probably installed 15 or 20 K&N etc. aftermarket systems and another dozen fabricated systems for race cars. Before and after and (after and before) RWHP dyno runs show gains in the 3 to 6% area. As a matter of fact, I think our web page has some graphs of before and after runs on it. As you point out, steady state eddy current loaded may runs show no fuel consumption changes, but the HP is improved.
We do dyno testing here for the manufacture of Granitelli MAF's etc.
BTW, We do NOT sell any of the above systems and are not associated directly with GMS or K&N so we have no bias either way. We only build and maintain race vehicles with the intent of getting the most performance available from a given engine.
As I mentioned in another post we are now doing a series of tests (as a contracted independent) on "MPG-CAPS" from "Fuel Freedom International".
They make some pretty wild claims which will be of interest to verify or negate.
Jim
SR Racing
A:
its a bit off topic, but the effectiveness of a cold air intake depends greatly from the make of the system. I've seen more than a couple that actually routed the intake to consume MORE hot engine air.
IMO, it doesn't so much as drop the intake temp (in general), as reduce restrictions. This again, will vary from engine to engine. Some are more free-flowing than others. You could make the same claims with exhaust of course.
A:
Hot air vaporizes fuel more effectively. This doesn't work for high performance because heating the air reduces its mass, reducing the amount of Oxygen in a given liter of air at WOT, but when you're trying to improve fuel economy, I'd say hot air with minimal restriction is the way to go. You won't any see phenomenal gains unless you add to it one of the 200+ patents claimed to get over 100mpg spanning all the way from the 1930s to the present day.