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now question to ezone, typacally cars are aligned with no weight inside.
does the passengers weigth change the geometry of a car ?

u could be just a driver, could be 4 passengers...

 
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usually, on the miata world, you ballast accordingly to the weight of driver/passenger to get the most of alignment.

if usually you drive alone, ballast for the driver alone.

but then, the miatas are double wishbone, so they suffer the effects more than a macpherson strut type like the 7th gen + civics

 
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for normal vehicles that just drive on the road typically they're aligned unloaded.
unless the driver is really fat to the point where it throws off the alignment

"race" and "track' vehicles will get aligned with driver ballast, and usually corner balanced as well.

 
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Depends. Yes most cars suspension is designed to change alignment slightly as the wheels move throughout the range of travel: As weight is added and suspension is compressed, toe in typically increases slightly.......but some engineers will compensate for this in the specs (laden vs. unladen)

SOME manufacturers specify procedures that others do not. It's all in what the engineers decided was best for their design.
(side note: some engineers are far smarter than others)

Some manufacturers want specific amounts of weight added in specific places in the car

At least one manufacturer I worked with required a spring loaded toe spreader bar to be set at a specific tension and placed at the front of the front tires and the trigger pulled.....before setting up toe.

 
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u think engineers know it all.).I am an engineer, I sure dont

 
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I always wondered what effect the o2 sensor oscillating between rich and lean has on performance and gas mileage. I know that the ECU aims for the air/fuel ratio to oscillate between rich and lean to reduce emissions, but what effect does this have on performance and gas mileage compared to a constant A/F ratio? I would think that gas mileage and performance would suffer from the A/F ratio changing between rich and lean slightly, but I'm not sure. Can someone please clarify this? Thank you very much.

 
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It doesn't aim to oscillate, per se, AFR just does because nothing in this world is 100% efficient. What the ECU does is aim to keep various parameters within a specified range to keep the engine healthy. There's no way in hell you're going to tune an engine that will operate at an AFR of 14.7 at all times. Best you'll get is an AFR that maintains 14.7 +/- some amount. Only way you'll get an engine to maintain 14.7 at all times is if you were in a perfect world with perfect stoichiometric conditions (2 C8H18 + 25 O2 ---> 16 CO2 +18 H2O) no matter what. If you could design a system that can guarantee a perfect ratio of fuel (denoted as octane -- a hydrocarbon with 8 carbon molecules) and oxygen (by my quick googling skills, 2 molecules of octane and 25 molecules of diatomic oxygen) and make it burn perfectly every single time to produce nothing but 16 molecules of CO2 and 18 molecules of water (vapor) (or some equivalent ratio with respect to the amount of starting substances), then holy crap, let me get in on it.

 
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So the ECU is not designed to oscillate between rich and lean to help the catalytic converter operate more effectively?

 
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Not exactly. Think of the cat as a filter. No moving parts, just something there to appease the hippies and make mother nature hate us a bit less. ECU controlling AFR has little to do with cat efficiency, at least directly. It has everything to do with making sure the engine is happy and operating properly.

So, bear with me for this response, because I'm kinda talking out of my ***, but basing it upon my engineering background.

Also, if it seems like my language is in a demeaning tone or over simplifying manner, I apologize. I explain things as if the reader knows nothing to make sure I explain everything fully. That, and if someone that knows a whole lot less than you reads this, they'll be able to understand the information sufficiently.

If it were up to me to design something like an engine, I'd design it to maintain a homeostatic environment within the engine to keep it happy. Starts to get too hot? Cool it down. Running rich? Lean it out a little bit. There are sensors and functions built in to make sure of that (e.g. engine coolant gets to a certain operating temperature, thermostat opens up to cool down the system. Coolant pressure builds up, that's why the radiator cap has a relief valve function built in). I know the examples I just listed have to do with the coolant system, but it was the easiest go-to example I could think of for maintenance of a homeostatic environment I could think of. If you don't know what homeostasis is, in my pre-med classes, best laymen's terms description given was "dynamic steady state." Same goes for the ecu maintaining AFR. The sensors the ECU reads are usually MAF (not on 7thgen due to lack of MAF sensor), MAP, IAT, and upstream O2 sensor. I'm not 100% sure there's more that gets read, but those are the big ones. IAT and MAP/MAF sensors dictates air input, telling the ECU how much fuel to put in to maintain the air fuel combustion ratio. Upstream O2 sensor is a report back to the ECU, basically telling the ECU if it's doing a good job or not. Upstream reports lean? ECU fixes it, and vice-versa. Now, these sensors are talking constantly, sending signals within milliseconds, and the ECU will do it's best to correct any variation in the output. These small corrections is what really causes these variations, since, as I mentioned in my previous post, nothing is going to be 100% efficient. Ever. Unless you live in a theoretical world.

 
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I wish I could quickly and easily make a gif or something of what I'm seeing in my head if you designed a system that was supposed to oscillate AFR, coupled with the imperfect naturally occurring oscillations the engine would do. I can only see AFR wobbling out of control like an unbalanced trailer load.

 
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I think I understand. So the ECU aims for a steady A/F ratio, but imperfections cause constant oscillation, even though that's not the intention?

 
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When I replaced my ECU (B20/LS engine) a few months ago I ordered an OBD1 chipped basemap with o2 sensor delete. The engine no longer relies on o2 sensor input and runs directly off ECU fuel maps. Idle stays steady at 750 rpms (no load). MPG's seem to be a bit better but I can't confirm that and there's many variables to consider. The disadvantage is losing the o2 sensor's ability to detect a lean condition.

 
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Not me, man..



Like a teenager who already knows everything:
You don't know what you don't know

One of my beefs is with all the hotshot engineer kids fresh outta engineer school who get hired by (any) corporation and every last one of them thinks they gotta reinvent the damn wheel in order to prove their worth.....then it somehow gets approved and makes it into production, it goes a couple years and we have all kinds of problems in the field with the new and improved wheel (maybe even a massive recall)......so the original wheel is then reissued as the replacement.

Repeat every few years.
Your statement says you are already far more aware than most, you know what you don't know

 
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Lol, ezone, don't spill it out (from another engineer )

 
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Huh...

Kid, your thinking is considering only and engine at constant (high) RPM and load.

Meaning you are living in a non-real world.

Go get an CVT car, should get closer to that.
No power mods to it, tho.

An engine is doing controlled explosions. What is constant in explosions?

 
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An O2 sensor, by design, has to act the way it does. An O2 sensor can only detect when the oxygen content is above or below its designed threshold, and its voltage switching point (typically 0.450v) reflects that.

The PCM constantly tweaks AFR to keep the O2 sensor switching (as long as the PCM wants the mix at stoich), because that's the only way it can control the AFR in CL.

 
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Let me start ranting about the idiots who decided paper manuals and wiring diagrams weren't good enough.....

 
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hahaha! true - instead of finding the right page by feel, you need to go to search function, then search for it, etc, while using working gloves - sucks compared to paper ones

 
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Thanks. Does the same thing apply to A/F ratio sensors too?

 
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....yes

 
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Um... AFR sensors are O2 sensors..

 
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Not reallysomuch.

Because an AFR sensor can more accurately report the true AFR in real time under many more operating conditions, the PCM doesn't always have to constantly vary the mix high/low to obtain a desired average.

On a scanner with a very quick update rate you can watch the STFT fluctuate rapidly on a system that uses an O2 sensor, but on a system using an AF sensor the STFT moves very slowly by comparison.

Mixture has to be swung high/low to run the self test on the cat as well.

 
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So the ECU intentionally causes a rich mixture to test the cat? Wouldn't that waste fuel?

 
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It's a minute amount, the equivalent of a few fuel trim points higher and lower. We care about testing the cat efficiency and making sure the cat stays alive.


The engine is kinda regarded as a life support system for the catalytic converter.

 
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Would testing the cat and keeping it alive hurt performance or gas mileage though? Doesn't testing the cat meann causing the engine to run rich, therefore wasting fuel?

 
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....

 
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Thanks. Do aftermarket ECUs, like the AEM EMS do cat tests too?

 
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Depends on you and your tuners choices (I guess).



My main focus is stock, not aftermarket.

Catalyst monitoring is one of several requirements of OBD2 standards.

 
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I have been debating the pros and cons of a K20 vs. K24 swap for my Civic. I know that a K24 is easier to find, has more torque and parts are easier to find in junkyards, but a K20 revs higher and probably gets better gas mileage. Here is a list of my questions:

1. Is a K24 physically a lot bigger than a K20? I like having enough room in the engine bay to easily work on things, so this is very important to me.

2. Is a K20 more fuel efficient than a K24 with both engines being stock?

3. What differences would I notice driving the car between a K20 and K24?

 
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k24 is too big to fit in the EM2 engine bay. Well, height-wise, at least.

What people have done is do the k-series version of the frankenstein swap: K20 block with a k24 head. However, that swap isn't quite as easy as a K20 swap, either. The k24 head is something like 4cm taller than that of the k20, so you'd have to find a way to safely drop the motor to accommodate the extra height. There was a member here that did that swap, untuned and stock, putting 218whp down. Got it tuned and it was putting 232 to the wheels.

However, to answer your questions
1) yes.
2) inherently, yes
3) You kinda already answered your own question