Stupid question, air/fuel ratio

Yea but,...
where and when,
will the time continium take place within the flux capacitator.






.

 

OK Wizbang!! Did you get all that??
So i guess your answer is.............aaaahhhh...Let's ask Spud or Mike!!!
(Man my brains aching after readin' that shit)

Now, back to the Spud and Mike show...........
Jason.

 

Bigger Ignition

Spud/Mike,

I've seen this happen and wonder if it can be put down to the ignition system's ability to light a richer mixture, or how the initial ignition of the AF mixture affects the burn rate? The better system produces a healthier spark and better ignition. The flame front advances across the combustion chamber earlier, compressing the unburnt AF more and creating the need or ability for a higher AFR?

Your thoughts?
Paul.

 

Yes, but it would appear that you need a lean AFR if you have a lower capacity ignition system, so that it will ignite. Some people think that if it sparks you'll get combustion, but that's not true. I've seen how the ability of the ignition system (or lack of) can affect the AFR.

 

Uh oh, it looks like we're not in agreement after all

That's 3.2 - 5.0 for supercharged stuff. And that's just in my experience so far. Maybe 100 pounds of boost would make enough cylinder pressure to burn an even denser mixture (richer AFR). I can only speculate on that.

When cylinder pressure is high, more voltage can mean the ability to throw even more fuel at things. Voltage requirements increase as cylinder pressure increases. In situations where cylinder pressure is not extremely high, more mag makes no difference. I threw the example above out to illustrate that the PRACTICAL air/fuel ratio does vary. Same motor, same air, but more fuel with a mag change. Real factors that people change - that don't effect air - change the amount of fuel it will need.

It's ok that no one is measuring their AFR. They're finding the right one indirectly for their equipment by monitoring plugs and EGTs. That's how most people know if they're too rich or too lean, right? If you're going down the track and your tuneup is where you want to be, it's real easy to back into the numbers and know what your practical AFR is for that pass. And if you then go race in horrible air, you know how much fuel to take away or how much to speed the blower up to achieve that same favorite practical AFR you had that worked well before. So, it's a useful thing to know and be able to do.

If you are going to calculate (or even flow) a starting tuneup for specific vehicle/engine combination - and you don't want to be 1 step too lean or 6 steps too rich - then you MUST have some idea of how much air the motor will ingest and how much fuel will actually burn. My whole point for jumping in here was that for greater accuracy, you also need to look at factors contributing to overall cylinder pressure and go richer or leaner accordingly. For example, if you used a 4:1 AFR for everything supercharged, you'll be way too rich for many of the setups, close on a few and too lean for the rest. One size does not fit all.

Spud
www.fuelinjectionent.com

 

Ok Mike, I give up.

I've given several clear examples of how things completely unrelated to air cause the fuel requirements of the motor to change. I just keep hearing that I'm measuring it wrong. Regardless of how I or anyone else measures it, or whether you call it AFR or XYZ, the motor needs more or less fuel because of these factors. That is my point. And since air hasn't changed and fuel has, if you intend to calculate things (as the person who started this thread sounded like he was going to do), then the AFR effectively changes because of these variables. You need numbers in order to do the math

I'm hearing that I'm not taking all the variables into account, but at the beginning of this thread it was stated that one could just use so much fuel per pound of boost and they'd be ok. I was merely pointing out that there are more factors involved that must be considered besides just boost. Specifically, those many variables that contribute to cylinder pressure and not necessarily more air.

When I talk about a calculator, I'm not referring to the web calculator, I'm talking about a guy picking up a hand held calculator to figure out how much fuel he's going to need. Some sort of ratio must be established that you will use when doing such calculations (or tune-up weather calculations). If a person uses some magic multiplier instead, then there's a specific air/fuel ratio built into it.

Continuing this exercise appears pointless...I think you should keep doing it your way, Jason can use his method and I'll keep doing it like I am. As long as we continue to be successful, who will care?

Spud
www.fuelinjectionent.com

 

I think what's getting mis-understood is one guy is measuring AFR's after the fact (through the exhaust), and the other is measuring AFR before the motor (calculated off da, boost, etc, etc) Bump the static compression, needs more fuel, changes the "calculated" AFR. OR Bump the static compression, needs more fuel according to the plugs and/or O2 sensor, so you add more fuel to get the right AFR judging by a sensor or plug. Both situations being the same need obviously more fuel, but each of you is using info from different sides of the explosion, however achieving the same outcome.

Josh