SkinnyG - Loving the videos. They are a good bit of entertainment, with knowledge added in for good measure. Letting them run in corner of my screen while I work has produced less output as I catch myself listening more the videos than actually doing work.
In reply to stafford1500 :
I also tried that, but there's way too much in there to try to passively listen! I actually am waiting until later on to watch that one because I have actual work to do and can't give it all my focus!
One correction about the spark- the concept of best spark is quite good- describing it so that the max pressure is 10deg ATDC (7 is a normal target, BTW, but 10 deg ATDC is close enough). MBT spark.
But that spark value for idle is not 10 deg. At idle, MBT spark is closer to 30-40 deg BTDC for most engines. 10 deg is a good area where a small change in spark causes a predictable torque change, so the spark can be used to control engine speed quite easily. And steady engine speed is pretty important for making customers happy.
Couple of other things- when finding the best spark- you mention power or fuel economy- but the physics behind the best spark is exactly the same- most efficient combustion. The key part is that the spacing of the molecules changes the rate of combustion- as you point out. But the best spark for any condition is found the same way- the one that normally results in 50% brun at ~7deg ATDC.
And the knock- early in the video, you point out that that this is trying to be combustion (with a real flame front) as opposed to an explosion, which is very much correct. In the knock conditions that you describe- what is actually happening is that the temp, pressure, and time all conspire to auto explode- not combust, but explode. And what you hear is the shock wave bouncing around the chamber. The damage occurs when those small waves hit surfaces so hard that they erode- just like in a real explosion. It was very interesting physics to learn about- where the conditions actually result in combustion traveling at the speed of sound in the media - which is what an explosion is.
As for slower burn for higher octane, I have never seen it. Especially when the point of higher octane fuel is to change the point where the time, pressure, and temp results in an explosion. If you are seeing less power, it's probably because whoever is blending your higher octane fuel is using crappy components. Virtually all engines have been rated on indolene clear, which is at least 100 octane test fuel (and used to be the spec fuel for all emissions testing and certification).
I'm always a little nervous about posting my videos here - you all are a very knowledgeable and talented bunch, and I know I gloss over some details. My videos will likely not check all the boxes of Engineering Level Content, but it sets a good foundation for my highschool non-academic level of clientele.
I did not clarify idle timing as per MBT, but intended to mean just base timing as you would do with a timing light. My 4age does not like idling much beyond 12°. My 11:1 cammed HEI 350 really likes 32° (I could probably do more, but I have not yet increased base timing, and limited both mechancial and vacuum advance, to make it all work happy; it's working fine enough). I did try to impress that it "depends on the vehicle." I do briefly mention using spark to control engine speed at the end of the video - good point.
Theory can be pretty berkelying boring to highschool students who hide their phones in their crotch so they can instagram their buddies all class. I shoot for being reasonably factual, but in as an entertaining and captivating way as I can, to retain my audience and hopefully make things stick in their heads. That may mean I simplify a lot of concepts so that even the dumbest kid in the class can follow along. I lose a LOT of kids on what seems to be even the simplest of theory.
As an elective teacher - if I don't make the theory captivating and interesting, kids take Foods or PE or Leadership, and I end up teaching more Math. It's gotta be fun, and entertaining. And you can kill a course with theory.
And the kids still can't put the wheel nuts on in the right direction (grin).
I appreciate the feedback!
In reply to SkinnyG (Forum Supporter) :
I hope I understand that you have a pretty specific audience- so I'm trying to point out some of the concepts so that you can interpret what I am pointing out in an entertaining manner. The MBT spark thing for light load up to WOT seems to be a simplified way of pointing out that the goal of the spark is exactly the same thing regardless of a light idle or at 5 lb of boost. For sure, there's a significant difference in fuelling goals- best fuel for power isn't needed for cruise, nor is it wanted. But best spark is always wanted except for idle.
The only limitiation is when there's knock.
And the knock thing- I always foundi it interesting that knock is an uncontrolled explosion of the a/f mixture. Which isn't pre-igntion (which commonly results in really bad knock). Especially since you very correctly pointed out that the desired burn isn't an explosion, but a nice flame propegation.... Even more fun is that the explosion is what's causing all of the major damage in the engine.
In terms of the base spark- that concept came with the distributor, since that's mechanicall how they are limited in operation. How that ended up also being the nominal idle spark timing is pretty funny, IMHO. It just did.
Not being a teacher, I have no idea how to convey that- but I do want to prevent some concepts that seem to get out in the wrong direction.
Are you planning on doing a video on emissions?
In reply to SkinnyG (Forum Supporter) :
Oh, wait, I totally missed the part where these were YOUR videos - I thought you were just sharing something you found with us! These have been fantastic, thank you!
I thought idling at MBT was bad juju because it made the idle less stable/repeatable, and when we started to get electronically controlled timing, they could correct idle speed more quickly with timing adjustment than air adjustment.
Yes, these are MY videos. That's ME in them.
Because I have to provide a shop course to my shop kids without a shop - I've been pounding out my "classroom lessons."
This is exactly HOW I teach in my classroom, to my students. Ain't I handsome? (grin)
Alphadriver - yes, I will be doing emission controls in a later video. I really just focus on what the main pollutants are, and what the main emission controls do. I do not usually talk about the different spark timing philosophies that pertain to idle, and I only touch on engine design to combat pollutants. Truthfully: the relationship between HC, CO, and NOx is the biggest challenge to them; they cannot figure it out on their own.
In Steering Systems, the kids cannot get their head around Camber, Caster, and Toe. That was my focus on that video.
In Automatic Transmissions, the kids don't get any of it. I tried to keep that video pretty basic. I knew I was glossing over a lot of specifics. The kids don't get it otherwise.
In Fuel Systems, the kids can grasp what is going on as I describe (and build) a carb on the board. Making the jump to EFI is mind-blowing, and few can do it. It's too many things all going on at once for them to embrace it.
In Ignition Systems, they cannot wrap their head around the mere possibility advance, much less engineering behind it, which is why I focus more on the old school how's and why's of timing.
Cooling Systems they seem to do ok in understanding how it works, but cannot troubleshoot to save their life.
Manual Transmissions, I have them play with cut-apart gearboxes, I demonstrate it, I have video, I have pictures, I show coloured lines of paths through each gear, and then on the shop floor they cannot show me how power goes through any gear. They don't seem to grasp any of it.
Basic engine operation seems to work ok for the kids.
Suspension seems to work ok for the kids. Without guiding them, they cannot grasp how leaf springs also hold the axle AND provide suspension.
Basic Brakes seems to work ok for the kids, but they CANNOT grasp brake pedal ratio increasing force or using hydraulics to increase force.
Before spring break I'd already taught the Level 1's Engine Operation and Cylinder Heads, the Level 2's Brakes and Drivetrain, and the Level 3's Engine Performance and Balancing & Blueprinting, so I likely won't be producing videos for those any time soon.
I teach Level 1, 2, and 3 all in one class, all at the same time. I also have one Level 4 student, but I merely direct him to "Google it, then convince me that you understand how ____ works."
Pete. (l33t FS) said:I thought idling at MBT was bad juju because it made the idle less stable/repeatable, and when we started to get electronically controlled timing, they could correct idle speed more quickly with timing adjustment than air adjustment.
There are a lot of different takes on this. Some say running a lot of timing at idle is a good thing to do - it makes sense, since the throttle is closed and the chamber is "lightly" filled. Some say you should never run lots of timing at idle for reasons that escape me at the moment. Some say engines -used- to run full manifod vacuum advance at idle back in the day as it gave a more stable idle, also allows a lower spark timing during cranking to make cranking easier. This is why all the manuals said to disconnect the vacuum advance when checking base timing. Some say advance went to ported vacuum for emission reasons.
I've run my '77 both ported and manifold vacuum. I notice an ever-so-slight improvement in driveablility with manifold vacuum over ported vacuum. I do get slightly better power brakes, too, at 8inHg idle vacuum.
Some cars will increase timing if the engine is running too hot. I forgot to mention in the video that retarded timing can cause an engine to run hot as the flame is now heating the cylinder walls as it chases the piston.
30 minutes is a long LONG video/lesson for kids to chug through.
Did he make a Steve Miller song reference... to high schoolers? 
I make a lot of references that few get. But the ones that do, they love it!
Nobody get the South Park reference at the start of the Automatic Transmission video?
In reply to SkinnyG (Forum Supporter) :
The more cam timing overlap an engine has, the more it likes less timing at idle. Low manifold vacuum means less exhaust gas pulled into the intake, means a more stable idle and you can idle leaner, which is better for emissions and cylinder wall/piston ring life.
Jeez doesn't that problem sound so ancient right now? "Couldn't you just retard the intake cam to reduce overlap?" 
In the gen 1 emissions control days, Ford had a vacuum retard at idle on the Boss 302, maybe others. Because base timing wasn't retarded enough.
In reply to SkinnyG (Forum Supporter) :
WRT emissions, how about sources, too?
Like the worst emissions are actually via the blowby- which is why PCV systems are closed loop systems to burn all of the unburnt fuel that is in the sump. It's alos why in terms of the very first emissions devices, they were it.
Next would be the exahust- which is deallt with using the catalysts. (edit- I guess, since the catalysts end up being the last thing for both the PCV and the vapor system, cover that last??)
And then somewhere in between is fuel system leaks- which is why there are cannisters that then pipe all of that into the intake, just like the PCV system.
And with all of that, the current state of the art, a car's total emissions is less than 1% of what it was just over 50 years ago. Which is pretty amazing. I remember how bad it smelled when we went on vacation in the 70s... ugh.
I do cover sources, and I cover those devices, as well as A.I.R. and EGR.
I also poke fun at those who remove them for power. Almost all emission controls do not cost you in power, and some can be argued they improve fuel economy.
In reply to SkinnyG (Forum Supporter) :
EGR definitely can improve fuel economy on a modern feedback-controlled fuel injected machine. I monitor fuel economy and when my Nissan (1600cc, 12 valve, TBI setup) went from 42mpg to 35 on an all highway drive, I looked for problems right then and there at the gas station. Found the hose off the EGR valve. "No, that can't be it." Next tank, and every one thereafter, was over 40 again.
Usually, since EGR is inert, you run more timing when it's on. Without EGR "on" and adding inert material to the mix, you may be getting too much spark timing, which can reduce power.
Could also be without the EGR adding some "fill", you're clearly drawing in more fuel and air....
Hmmm. Anyone have deeper thoughts?
In reply to SkinnyG (Forum Supporter) :
When I started my work at Ford in the early 90's, EGR was a clear emissions tool. WIthin 10 years, it was not. So it went from incredibly key part of emissions control to nothing in about 30 years. Now it's just used for fuel economy, like you point out. I just remembered when I worked at Chevron in the late 80's for a summer, and had a dyno engine that suddenly made a ton more power and fuel- the EGR vacuum line melted and it stopped working. Progress is amazing.
Air injection is funny, too- was a major part of the original catalyst operation, then not. Then it came back in the early 2000's with PZEV, then went away. Now I'm hearing a lot of tones that it will come back, again.
It's always been interesting to look back on vehicle techology.
Anyway, your series is really cool, and I VERY much hope it resonates with your and many other students. Good stuff!!!
SkinnyG (Forum Supporter) said:Could also be without the EGR adding some "fill", you're clearly drawing in more fuel and air....
Hmmm. Anyone have deeper thoughts?
If you draw in more fuel and air, you make more power, so you close the throttle in compensation.
Deeper thought is that engines are generally more fuel efficient the closer they are to WOT, so adding inert gases allows the throttle to be open more without necessarily making more power. Sort of the opposite of nitrous oxide injection, in retrospect, since you're adding gases that reduce the oxygen content of the air.
It's sort of the same pumping-loss theory as a Miller or Atkinson cycle engine (or the old Crane "Economizer" camshafts in the 70s!) where the intake valve is closed so late that a lot of the compression stroke is lost.
SkinnyG (Forum Supporter) said:Could also be without the EGR adding some "fill", you're clearly drawing in more fuel and air....
Hmmm. Anyone have deeper thoughts?
Intert gas displaces air charge, allowing for more throttle, so less throttle losses.
If the engine is knock limited, the intert gas allows for spark to be closer to MBT spark.
Both of those outweigh the combustion efficiency loss due to the inert gas.
alfadriver (Forum Supporter) said:Both of those outweigh the combustion efficiency loss due to the inert gas.
Hmm... I wonder how much chamber efficiency plays a role. Like, EGR seems to have died off around the same time that 4 valve combustion chambers became standard practice. The only 4-valve I can think of that had EGR was the Mazda DISI engine, which, being both turbocharged and direct injected, really should have had no excuse. (Unless they were using the EGR for knock reduction under boost, like a limitless supply of water injection, which is something that apparently Volvo was experimenting with for a while.)
In reply to Pete. (l33t FS) :
It's starting to make another comeback. It does allow for even higher compression ratios, and there are experiments running EGR at WOT.
But the combustion chamber does have a significant impact, as to the port runners and their shape. I'm sure you know that high EGR is really tough to get lit off and even combustion- so turbulence does change both getting the mixture starting to burn and keeping it burn evenly.
In about 5 yeards, even going WOT will be stoich- so running with EGR will be very important.
Heywaitaminute... I just noticed something that has absolutely nothing to do with anything: Your scantool is set to metric units. But you've got TunerStudio set for Fahrenheit on the ECT gauge as opposed to Celsius and when you talked about the engine temp you weren't talking metric, either. What gives? If this was your truck, then it would make sense that all the parts and literature and internetting would be in imperial units, but I just always assumed that a Toyota engine would have thermostats, for example, sold in Celcius units in places that aren't the US.
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