sweet that book basically just explained to me what the hell you guys are talking about. Is it sad that this shit really excites me?
sweet that book basically just explained to me what the hell you guys are talking about. Is it sad that this shit really excites me?
Page 322 uses the chainsaw analogy!
ICHIBAN!
"Now, even more better!"
whats funny about that is anyone who understands anything about fuel injection can see the chainsaw analogy and realize that it doesnt quite work that way.Originally Posted by guyhatesmycar
MAF, speed density, carbed? Obviously, with a honda, speed density, the idle is controlled by vacuum leak, aka the idle air control valve. The map sensor reads this, and picks the idle up even more by maintaining 14.7 at the new higher manifold press. MAF, you're now getting more air for the the same pulsewidth, which the concept that I started this entire thread on. Carbed, basically the same.
I don't agree with the explanation above, but I do agree that high load low rpm operation can be damaging to a motor. The a/f might burn more quicky as the piston is rising more quickly, but the whole reason for ign timing being different at different engine speeds is trying to optimize the cyl press vs crankshaft angle by compensating for a the non changing or minimally changing burn speed.
So how is it going to be more harmful to a motor to have fewer firing impulses of the same power (torque output) for a given amount of time? Shit, if anything, I'd argue the opposite, within a certain rpm range. For a given torque output, the motor uses less ign timing at lower rpm. Since torque is a function of cyl press vs crankshaft angle, and the motor isn't fighting itself with higher overall press to compensate for the increased press before tdc at higher rpm, the motor actually has lower avg/peak cylinder press for the same torque at a lower rpm.
However, I would say that this is no longer the case at really low rpm. I don't have a number here really, but maybe somewhere below 2000rpm? There, I suspect the piston can't get out of the way quickly enough, and the motor knocks. Ever heard of "pulse detonation"? Light an a/f mixture in a given space that can't expand, restrict the flow out of the space, and light the mixture. The pressure increases to the point where it reaches it's autoignition point, and it detonates. If you design the setup properly, the detonation chamber can actually scavenge itself, by the velocity through the exhaust tube pulling in the new mixture through a valve. Weird form of aircraft propulsion, only problem is it's unimagineably loud. Supposedly it's actually more efficient, because the extremely fast flame propagation of detonation reduces the amount of energy conducted into the chamber by reducing exposure time, transferring more energy into increasing the temp/expansion, and therefore propulsion.
You bring a lot of interesting information for us to sort out and make work in our head. That part I can appreciate. But as smart as you may be, trying to make out everyone else is an idiot seems kind of going in the wrong direction of educating us and leans (love that play on words? ) towards insulting. Not so lean man, I am enjoying it otherwise. I do tend to agree with what you said about H-T tuners, lol, but not so much about mase. Just like you say in the quote, it is hard to write this stuff and not have someone tear it apart for sentence structure, less than perfect terminology, or a misunderstood point.
I recently aquired a drive by wire vehicle, so I have made it a point to fully understand the theory of operation. I have already written some on another forum, but when I get time and lose this headache I will write some up on this thread I suppose.
I think you just answered your own question there. At low RPM/high load/high throttle conditions the piston can't move out of the way quickly enough to compensate for the VOC of the mixture. Thus, cylinder pressure rises to above autoignition point and detonation of the remaining unburnt mixture occurs. A characteristic of early Toyota 22R engines is that they rattle LOTS when under high load and low RPM. Listen next time you pull up to a beater Toy truck, chances it'll rattle when it pulls away from the stop light. If your window is open, you'll hear it.
Also, in regards to "pulse detonation", ever light gunpowder with a match? It sits there and burns. Confine it inside a rifle cartridge with a big heavy bullet in the way and we all know what happens.
Last edited by Ichiban; 12-24-2007 at 09:51 AM.
ICHIBAN!
"Now, even more better!"
Roodoo2, I'm not trying to make anyone out to look like an idiot, at all, and i don't think anyone on here is an idiot. I brought up the thing about mase on h-t because he is one of the most respected tuners on there, has actually started threads specifically about tuning, and when He doesn't want to get into something, that means it is Really hard to figure out/find info on it. I'll admit it does frustrate me when people either don't read what I've written, try to oversimplify it, (oversimplifying is not giving the subject the respect it deserves, and usually gives the wrong explanation) and then try to contest something about it that's already basically universally accepted and taught, like that a lean of stoich mixture burns slower. Yet I still attempted to illustrate that and explain that for how many posts? You want to criticize me, well, where is my credit for doing that? I could have just said fuck off, but I didn't, I kept going at it, trying my best to figure shit out and put it down in words. I don't have any problem with people contesting shit that isn't acepted when they actually Can contest it, esp when I straight up say, as I've said numerous times in my threads, that I am theorizing to my best efforts. I constantly see people coming up with explanations for things that aren't accurate/complete, not necessarily in this thread, but in the whole world, and when I see that, I'll try my best to figure out if that's what's really going on. The low speed operation thing is a perfect example of this, I knew the exposure time thing was wrong, but I knew that low speed engine operation under load can cause knock, even with the lower VE at that speed, but didn't know why. I didn't even think of the detonation vs piston speed thing until I had already written the 2 previous paragraphs, and had actually never even thought of it before or read about it anywhere in my life. But it makes sense though, doesn't it? It seems like that's the kind of shit you're criticizing me for though. Me criticizing someone for sentence structure, no, misunderstood point, maybe if they're trying to contest without understanding, pefect terminology, fuck no. I straight up said I had never heard of the term afterfiring and explained what I meant. The only time I gave anyone shit on this board about something sentence/grammar/whatever related was when I said I was going to clown 89turbo'ed for his apostrpohe use, and I was totally joking around, and he didn't get upset.
I know damn well I don't know everything, and I'm not trying to make myself look smart, or anyone else look dumb. I'm just busting my fucking ass trying to figure shit out for this thread, if you can't see that, then what more can I say? If anyone else thinks I'm trying to be insulting, speak up. Shit, if I were to take a guess on who'd be pissed at me on this thread, I'd say it'd be guyhatesmycar, for how I totally dismissed his chainsaw analogy.
Come on, guyhatesmycar, I know you have something to say about this...
...decaf?
Im lurking from this point, good thread guys.
It is clear that the RPM of the chainsaw is limited normally by the richness of the mixture. Reducing the richness of the mixture makes it rev higher. For all I know, the saws are tuned rich and blow up if you run at stoich. After all, that's where the highest energy release is, mixture wise.
Wait, I finally got what you're saying. The over-reving saw is creating enough vacuum to pull enough fuel to run. Once the RPM drops due to load, vacuum drops and so does fuel delivery, so saw dies. Reasonable so far.
But why does the saw (or my car) increace speed at idle momentairly as it runs out of fuel? Less fuel=more energy? I doubt it. Any increase in RPM means an increase in energy output, you can't get something for nothing. Also, inducing a vacuum leak on a carbed vehicle will not only add air, but raise manifold pressure and further reduce fuel delivery. Yet idle still goes up. Why?
Last edited by Ichiban; 12-24-2007 at 11:13 AM.
ICHIBAN!
"Now, even more better!"
Well, I said before that I didn't think the chainsaw runs at 14.7 at idle, just like the aircraft engines I learned about in a class I took, so that's why it would pick up, as it crosses 14.7. The aircraft motors I learned about idled really rich, around 10 something to 1. Basically just spitting black smoke to stay cool, with the very limited airflow available for cooling. Are you saying that with a carbureted car idling at 14.7, the idle will momentarily increase before it stalls if you cut the fuel? How would creating a vacuum leak on a carb setup reduce the amount of fuel going into the motor? The manifold press would go up for that rpm, reducing the vacuum and therefore airflow across the carb momentarily, but then the rpm would pick up, provided it didn't stall, and then you'd end up with around the same fuel but more air, no?
I'm going to have to buy an eighth before posting again, you guys might have to wait for anything else out of me..
Last edited by Accordtheory; 12-24-2007 at 07:53 PM.
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