Newbie questions

[ChillyBear]

Ok,
CAI=worse mileage
Headers=debatable
I may try the belly pan, but I wanna do some before and after tests because I don't want it to cause lift (my old car would lift after about 100mph-VERY SCARY).

[Christ]

The only way a belly pan should cause lift is ground effect compression, where the quantity of air that goes under the vehicle can't accelerate quickly enough and "piles up" under the car.

Other than that, it should actually create a lower pressure zone under the car that will induce negative lift, albeit a small amount, due to the acceleration of flow that isn't obstructed.

[MetroMPG]

Re: Pulse plugs... this is anecdotal, but Tim (Daox) had them and mentioned to me just this week he was starting to get a misfire after a relatively low number of miles on 'em. (Maybe he posted about this, I haven't been around as much as usual this week.)

Anyway, he yanked them and installed some Bosch plugs. Problem solved.

[ChillyBear]

yeah, I read a thread about that. Sounds like more headache than the gain is worth.

[El Duende]

Originally Posted by Bicycle Bob

"The air pump can't tell the difference between manifold restrictions and throttle butterfly. At part throttle, their relative percentages are irrelevant. Real ecomodding is a lot cheaper than performance work in some areas. What's the length of a tuned exhaust at maximum mileage? Can pulses get through the close-coupled cat, anyway?

If warm air can carry enough oxygen in for the power required, it will flow easier, and vaporize the gasoline better. Presumably, except in open-loop, near wide open throttle, the injectors will keep the mix lean, just enough for good ignition. See the "warm air intake" threads. (WAI)

What "air pump?" You mean the intake system? My Sentra's intake has two sensors: a Mass Airflow (MAF) and an Intake Air Temperature (IAT) Sensor. Both have very relevant significance as to how the car will run. If the MAF craps out, my car will go into "limp mode" as a precaution and won't go past 2K- 3K RPM and the IAT regulates idle at start-up. And if you mean to tell me that reducing pumping losses yields "relatively irrelevant percentages" then the same could be said about keeping a restrictive airbox, so as to keep the air-to-fuel ratios leaner. Guess my $45 cone filter replacement isn't a bargain. You asked what the perfect length would be for a fuel-economy oriented. Please note that a stock cat won't contribute enough backpressure (Barely +/- 0.5 PSI) to warrant a replacement, unless you want a high-flow type, (To make way for a monster turbo setup) but those aren't as effecient at controlling emissions than the former. The ideal setup would be as I just said: a larger diameter pipe, not too big, to allow for more exhaust scavenging, reducing pumping loses and maintaining a constant stream in both the open and close cycles of the exhaust valves. Personally, I don't want to attract too much attention, so when I put one on mine, you better believe I'm investing in a resonator. (If it's not included)

There seems to be a rebellious spirit against the establishment of aftermarket performance parts amongst some of the members here. While those companies may jack up their claims to get a stronger base, their products are results of research and development, as well as actual customer usage in various places, (Street, track, top MPG tourneys, etc.) for the most part. (EFI throttle body spacers not included in my ex.) Maybe it's not even them that rubs dudes like you the wrong way. Could be the stereotypical rice-doucher image that plagues your head. (Thanks, makers of "Fast & the Furious.") Either way, the same proven aftermarket replacements of intakes, exhausts, headers, etc. could definitely be used to achieve more MPG's, aside from HP. Most tuners I know love boasting their highest miles-per-tank. It's very common in Sentra, Fit and Civic forums, which I frequent. It's not all about power.

I'm gonna see this WAI thread that you speak of. You can't seriously be putting in one of those for a leaner A/F ratio. I wouldn't feel too comfortable with my car running leaner than it already does from the factory. (14.7 or so) In the event that you do need to run in open-loop, acceleration will surley suffer. How hot do you want your engine to operate, anyhow?

[Christ]

Originally Posted by El Duende

I'm gonna see this WAI thread that you speak of. You can't seriously be putting in one of those for a leaner A/F ratio. I wouldn't feel too comfortable with my car running leaner than it already does from the factory. (14.7 or so) In the event that you do need to run in open-loop, acceleration will surley suffer. How hot do you want your engine to operate, anyhow?

Internal combustion engines, being of the adiabatic sort of beast family, are inherently more efficient when they're "soaked" closer to combustion temp. The hotter intake air is proven to be more efficient per volume of intake because there is less tendency of the combustion heat to soak into the engine (the engine has already reached equilibrium with the intake air, so less heat is pushed into the metal on combustion because of the already higher cylinder wall temp), and less energy from heat necessary to increase the temperature of the intake volume.

There have been published studies which show these, and other examples, as benefits of increased engine temperature and intake air temperature, where efficiency is concerned.

To clarify the term - Efficiency, in this case, is the amount of energy derived from an amount of fuel during combustion, compared to the actual energy content of the consumed amount of fuel.

The WAI in general doesn't lean the A/F ratio - it reduces the dynamic displacement of the engine, and reduces pumping losses. A less viscous fluid is ALWAYS easier to move. (Air is a fluid.) And since less mass will fit in a given volume when the temperature is increased, the engine sucks in less on the intake stroke, further reducing pumping losses.

[El Duende]

Originally Posted by ChillyBear

Ok,
CAI=worse mileage
Headers=debatable
I may try the belly pan, but I wanna do some before and after tests because I don't want it to cause lift (my old car would lift after about 100mph-VERY SCARY).

Originally Posted by Christ

I'm pretty sure that's exactly what he was referring to.

This discussion is basically endless, no matter where you go. There's always a bunch of people who heard from someone else who was told by some other guy that this way or that way was better, and very few of them have any background or math/science to back any of it up.While it's refreshing to see that someone else understands the difference between "bigger" and "too big", it's also a burden to see, yet again, the term "back pressure" come into play.

You mean like the quote I just highlighted in red? Come on o.p., I just listed my reasons stating the opposite. Guess my explanation has no value to ya. There are pleny of things that could worsen your gas mileage more than a CAI.

Hope you're not questioning me, cuz if you are, we're gonna need to take this outside, (This thread, I mean) Bub. lol!

The burden isn't seeing the term... It's looking at your tail-pipe. Don't know what you meant by saying that. Your response also has that tone of nerd-rage against tuners and one who also lacks a math/science background. I'm starting to get the feeling that open-mindedness is a virtue.

[Christ]

Back pressure does not exist in logical terms. That's exactly what I meant by it.

Literally, back pressure would describe a force which was pushing exhaust back up the exhaust channel, which does not occur. In reality, what most people refer to as "back pressure" is the slowing of the flow of exhaust gasses due to over cooling/over expansion.

It's a burden on my mind to see that yet another person who appears to have some grasp on the engine as a whole is using the term back pressure as though it actually means something that applies to engines, when in reality it does not. A more accurate term would be flow restriction, and that doesn't fully encompass the circumstances either.

[El Duende]

Originally Posted by Christ

Internal combustion engines, being of the adiabatic sort of beast family, are inherently more efficient when they're "soaked" closer to combustion temp. The hotter intake air is proven to be more efficient per volume of intake because there is less tendency of the combustion heat to soak into the engine (the engine has already reached equilibrium with the intake air, so less heat is pushed into the metal on combustion because of the already higher cylinder wall temp), and less energy from heat necessary to increase the temperature of the intake volume.

There have been published studies which show these, and other examples, as benefits of increased engine temperature and intake air temperature, where efficiency is concerned.

To clarify the term - Efficiency, in this case, is the amount of energy derived from an amount of fuel during combustion, compared to the actual energy content of the consumed amount of fuel.

The WAI in general doesn't lean the A/F ratio - it reduces the dynamic displacement of the engine, and reduces pumping losses. A less viscous fluid is ALWAYS easier to move. (Air is a fluid.)

I had to look up "adiabatic" in the dictionary. No match found. I see what you mean by "soaking" the metal by way of the intake charge. Don't worry about losing precious heat with cooler air because the combustion chamber will inevitably heat up. Pressure in the engine bay will keep hot air around the motor, too. You're telling me that an already warm engine will be a more ideal environment for combustion than a cooler one. Sucks for my MPGs, it's cold outside! That explains why this demographic has such a high demand for engine block heaters. I thought it was compression or spark plug location that affected thermal-effeciency. (The term you clarified, but didn't specify.) Swapping in a CAI/SRI also reduces mechanical effort along with more HP. There's no use in keeping the intake system hot. The coolant is in charge of keeping the head at the temperature it needs to be, not the outside air.

Not trying to be a smart-ass, but I'd like to see a link to one of those studies.

[El Duende]

Originally Posted by Christ

Back pressure does not exist in logical terms. That's exactly what I meant by it.

Literally, back pressure would describe a force which was pushing exhaust back up the exhaust channel, which does not occur. In reality, what most people refer to as "back pressure" is the slowing of the flow of exhaust gasses due to over cooling/over expansion.

It's a burden on my mind to see that yet another person who appears to have some grasp on the engine as a whole is using the term back pressure as though it actually means something that applies to engines, when in reality it does not. A more accurate term would be flow restriction, and that doesn't fully encompass the circumstances either.

Oh it doesn't happen? Well, I'm not referring to the slowing of exhaust flow, I'm talking about recirculation of spent gasses. Wait... So that means that backpressure does exist!

Hope I'm not truly burdening your mind, because you're not burdening mine.