A DETAILED overview of KNOCK and PRE-IGNITION - BOOST SCHOOL #7

AEM ECU: bit.ly/D4Ainfinity5​
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Today we're talking about the number 1 killer of boosted engines. Knock. We are going to understand what it is, how ti differs from pre-ignition, how it correlates with other things in your engine and of course how to avoid it and how to control it.
So what is knock? The simplest explanation of knock is that it's abnormal combustion, but to truly understand it we must dive deeper than that and to understand what is knock we must have a good understanding of what's actually happening inside the engine.
So let's imagine our cylinder is on the compression stroke. Both the intake and exhaust valves are closed and the piston is traveling upward and compressing the air fuel mixture inside the cylinder. Now the spark plug will actually fire before the cylinder reaches it's top most position of travel or top dead center. The spark plug must fire before the piston reaches TOP DEAD CENTER because the goal is to ensure that maximum combustion pressure builds up by the time the piston starts traveling downward. So how do we ensure that maximum pressure builds up when the piston is right past TDC? By firing the spark plug before the piston reaches top dead center. This is called ignition advance. Firing the spark plug earlier accounts for the piston speed and gives enough time to the combustion to build maximum pressure right on time.
So in the beggining of the video we said that knock is abnormal combustion. Now normal combustion inside a gasoline or petrol engine occurs like this: air and fuel is compressed inside the cylinder. The spark plug fires and initiates the combustion. Combustion spreads out evenly from the spark plug until all or most of the air and fuel is burned off.
Knock occurs like this: Air and fuel is compressed inside the cylinder. Spark plug fires and initiates the combustion. Now as the combustion spreads it exerts pressure onto the still uncombusted air and fuel. At this point one or more pockets of uncombusted air and fuel spontaneously ignites before it's reached by the flame front traveling from the spark plug.
Now knocking is also called detonation. Detonation is a combustion process characterized by a super-sonic flame front. Meaning that it travels faster than the speed of sound which is 343 meters per second. Detonation creates destructive shock-waves that have the potential to damage everything around them. When a pocket of air and fuel self-ignites it actually detonates and it's these shock waves the cause a brief but intense spike in cylinder pressures and create the characteristic knocking sound. If knocking is strong enough or persists long enough it will damage or destroy engine components.
In contrast to this normal combustion is not detonation. Normal combustion is something called deflagration. Deflagration is characterized by a sub-sonic flame front meaning that it travels below the speed of sound. Deflagration increases pressures inside the cylinder in a gradual and controllable manner without unpredictable pressure spikes.
Ok so that's knock. What's pre-ignition? Knock and pre-ignition differ from each other in their timing. As we have seen knock occurs AFTER the spark plug fires, but pre-ignition occurs BEFORE the spark plugs fires. Pre-ignition happens while the piston is still moving upward on the compression stroke. The air fuel-mixture ignites spontaneously before the spark plug fires. In most cases pre-ignition can be more destructive because it happens on the compression stroke.
So why do knock and preignition occur? The simplest and most common answer is because temperatures inside the cylinder get too high. Why is that a problem? It's problem inside a gasoline engine because a gasoline engine compresses both air and fuel. If temperatures gets high enough it can lead to spontaneous ignition of the air fuel mix and we get detonation. The actual ignition source for pre-ignition is in many cases some sort of a hot spot which can form at a carbon deposit, spark plug tip or a sharp and protruding edge in the combustion chamber. The overly high temperatures can heat the hot spot until it glows red hot and this can lead to pre-ignition or knock.
Back in the day the safeguard against knock was to run a low compression ratio and leave a big safety margin. The reason behind this is that there wasn't any active knock control. If knock occurred the engine had no way of responding to it. But today things are very different.
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#d4a #boostschool #knock

[@d4a]

AEM ECU: bit.ly/D4Ainfinity5​ AEM water-meth: bit.ly/2zrOkSp?D4A...​ AEM boost controllers: bit.ly/D4AtruboostX​ AEM wideband AFR gauge: bit.ly/D4Axserieswb​ Support d4a: driving-4-answers-shop.fourthwall.com/

[@alienpoker]

Have you looked at LiquidPiston development rotary engines. In essence an inversion of the Wankel engine. It could be used in a hybrid go charge batteries and extend range, among other uses.

[@valentinuiliqnow6198]

you can use and cool EGR like mazda sky-actyve engine

[@athalfridhu]

Talk about SAAB ION SENSING PLEASE.

[@samsungultra6094]

15:30 kHz or MHz? U said kilo and wrote megs

[@lestergillis8171]

Did you say "deflagration" ? Or... "defecation" ?💩

[@BOB24502]

One of the most underrated KZbin channels… the presentations are so well done, and so clear! Thank you for the free knowledge!

[@Pablo-Esco509]

5

[@foxman105]

*Knock knock* "I'm not playing this game." *piston has left the engine.*

[@moisesezequielgutierrez]

Piston Ring: *"Adios"*

[@WhiteTrashMotorsports]

Uncle rodney noooo!

[@bigcazza5260]

@@WhiteTrashMotorsports cant believe they left the factory rods in the 4g"k24" miVTEC swap

[@bluebird8004]

I think your confusing it with big end bearing knock, which is more what pre ignition can cause.

[@valentinuiliqnow6198]

you can use and cool EGR like mazda sky-actyve engine

[@electric7487]

Preignition, basically a situation where your piston is trying to compress an explosion.

[@sillysad3198]

he is trying to become a diesel! it is TRANS diesel motor. you need to let him be.

[@frontspring1]

@@sillysad3198 I think your cylinders are suffering from abnormal combustion. Clean them

[@Alex-di8ti]

You have an F=ma from the piston and con-rod and a F=pa coming from the pre-ignition. Something in the middle has to give, the piston and/or the con-rod.

[@bakters]

@@Alex-di8ti "F=ma" When approaching TDC the piston slows down, so the acceleration is negative. The forces you mentioned do not oppose each other.

[@Alex-di8ti]

@@bakters My question is, how can pre ignition cause such damage as bent/snapped con rods. There must be substantial forces to achieve this. If pre ignition can occur anytime in compression stroke, I am thinking is it more the pressure from the shockwave that does the damage. If piston is decellerating it still has an F=ma but yes negative, If the force is far greater from the pre ignition, than your suddenly applying greater loads to the components. My thinking is probably wrong in my previous comment, it would be easier to understand with some force recordings.

[@ahnafzahid9450]

i thought boost school was dead!...how ever, today's topic IS CRUTIAL...Thanks again brother, for bringing out another informative episode

[@generaldart6567]

Yes thats right 👌

[@KOTSR]

Pardon me for saying so a year on but it's CRUCIAL And yes I agree this guy is good

[@davidgrisez]

Another way of controlling engine knock many years ago in the days of carburetors was for the driver of the car to back off the gas pedal when the driver heard engine pinging and knocking. Less air and fuel would stop the pinging and knocking. Also engine pinging and knocking tended to occur with a wide open throttle and low engine rpm. In those cases shifting to a lower gear to increase engine rpm reduced pinging and knocking.

[@user-si5fm8ql3c]

Less fuel/air means a pressure drop across the throttle body, lowering intake air temps. Higher RPM means the fuel/air mix is not as long in contact with the hot cylinder walls, making it cooler when the spark fires. Its even more interesting on even older glow chamber/tube engines, early 20th century, big, slow running, single cyclinder engines. I remember my old neighbour showing of his skills with a 1930s tractor, got the glow bulb way hot (this advances timing) after hauling firewood up a mountain, then, to reverse he slowed down the engine, got it to stop mid compression stroke, pre-ignition occured from the overheated bulb and reversed the engines rotation. I got to drive one once, its a odd experience, you need to keep the bulb in the right temp range using a small burner below the bulb at low load and idle and water injection on the intake while its doing heavy work.

[@Herpitor]

This guy's videos are uniformly well-researched, well-presented, accurate and extremely useful. Kudos.

[@williamstewart3469]

Knock knock, "Who's there?" Not Rodney, he was here, but couldn't handle the pressure. "So Who's there?" Toe "Toe who?" Toe truck.

[@SoulTouchMusic93]

Good one!

[@ilham7345]

lmao that's the best one

[@AlphaFarouk]

😂😂😂😂😂👌

[@valentinuiliqnow6198]

you can use and cool EGR like mazda sky-actyve engine

[@mmerc1349]

Dafuq hahahhaa love it

[@MultiMightyQuinn]

As a non-gear head (term used with love, I have many friends who are) I have to say I love your videos. You obviously have a very good understanding of the science and mechanics and you are able to translate that well a larger audience without dumbing things down too much. Great content, thank you for sharing with us!

[@lilmike2710]

It's safe to consider him an Automotive Engineer. I'm not sure if I'd consider him a "gear head". Engine nerd maybe (term lovingly used). 💜 ⚙️ 🚗

[@lilmike2710]

I have definitely learned things I didn't really know or fully understand before. He certainly explains things in a way that people like myself (dummies) can understand.

[@dappxx]

😅😅

[@terjejohnsen3651]

I have allways wanted to know what knock is and now I know thanks to my teacher at D4A .i recomend this sunday school it makes the day perfect.

[@TheFakeFatLegitimate]

I’d like to say, you’re explaining things that I’m interested in super well. I would personally rank you above Engineering Explained. You’ve answered a few of my own theories in this video! 😀

[@justayoutuber1906]

I was thinking the same thing!

[@carsonho9338]

I gradually got into it myself in 1 year, and you explained it in 16 mins.

[@jakebatty530]

As a training mechanic, this video is invaluable, absolutely fantastic explanation really appreciate it

[@idontstunt2613]

Thank god ive been trying to explain knock to my brother for like the past 2 weeks

[@jamesyoung5610]

Hello McFly

[@negativeindustrial]

@@jamesyoung5610 “Make like a rod, and get out of here”

[@luftstolle]

I love your videos. I have seen several other videos of people trying to explain what knock is, why it's bad, and how the ECU manages it, but never quite understood them. This explanation is really, really good and finally made me understand! Thank you so much!

[@teshane8784]

This video deserves an award. Incredible explanation, well though out, well put together. Everything is just perfect. Bless up from Jamaica 🇯🇲 💯

[@timothybracken1728]

most underrated car channel on youtube hands down, best explanations keep up the great work!!

[@Francisco-sx7th]

Thanks for this very clear explanation. I had an idea about knock but now I understand it much better thanks to your course. You really have talent to simply explain complex things.

[@anastasisparastatidis5479]

The fact that he always answers my question just before I make it is almost frightening😂😂😂

[@almostbutnotentirelyunreas166]

One of your BEST, most accurate videos to date!. Excellent contrast between knock and pre-ignition.

[@BYENZER]

DAGNABIT! STOP! No, no, NO! It's NOT called KNOCK. YOU are describing PINGING as KNOCK. KNOCK is from worn out con-rod piston pin bushings. GeezusHKrist! Foreigners. Why can't they keep WORDS STRAIGHT. What is wrong with you people? IT IS CALLED PINGING PINGING PINGING PING PING PING PING PING! NOT KNOCK!

[@giraoshaw]

Never tell a knock knock joke to someone with a boosted car

[@pouyeux55]

Specially a subaru owner

[@billybuchanan385]

@@pouyeux55 in my supercharged saturn i never get to hear knock knock jokes. Hsrd when the STI is so far behind and blowing a head gasket

[@RianoTjo]

Knock knock

[@jozsefizsak]

Very informative. I knew the basics but the details are fascinating.

[@amirfmaster2515]

I don't know how many university courses i should've taken just to understand this subject as good as you explained. well done, you are a legend.

[@barry-cq4xg]

Great stuff. It is not easy to describe such a complex subject to non-engineers; but you do a really good job.

[@justayoutuber1906]

Great info! I never knew there was a difference knock and pre-ignition. Also the way you promote AEM is perfect as it is directly relevant to what you are talking about - well done. Promotions like this are not seen as ads, but helpful suggestions!

[@scotthodges5214]

I've been wanting to know this type of info for years. Thanks for the simplified and educational presentation. Super helpful series.

[@mickwolf1077]

I love watching your videos, you explain things so clearly then further explain incase people don't get it. I've learned so much and sometimes your videos have reinforced what I know, also you have a great accent. 👍

[@25kmgb]

This was excellent. I appreciate how you manage to explain complex technical information in a way I can understand and retain. By the way, we just had a horrible 3 month battle with AEM trying to get their ECU working on a 4AG race motor. Tech and product support was terrible and our shop is only a hour from the main office. Finally gave up an had a Haltech installed and operated on the dyno in 5 days. Hope you're able to cash their check!

[@djisydneyaustralia]

You're the best on KZbin, giving thorough, factual explanations of engine dynamics.

[@massimopusceddu6008]

Great video as always: clear, focused..Spot on!!!

[@valentinuiliqnow6198]

you can use and cool EGR like mazda sky-actyve engine

[@melwillseptember752]

That was an amazing video, always wanted to know what nock and pre ignition was. The video about ignition timing and knock, plus the visuals of internal combustion is amazing.

[@gbudning]

This is one of your best videos. I will be showing it to my grade 8 Power Technology class. Thank you!

[@valiktoma2542]

Very informative, high quality background material, and very clear explanation. Good work.

[@gort8203]

What a great video. This channel really shines in comparison to all the slipshod drivel on KZbin. Subscribed!

[@jasonkeech7513]

Absolutely the best video and most informative I've ever seen on KZbin

[@MrSupernova111]

Beautiful explanation! Thanks!!

[@JerZeyFiveOh]

Thank you for this video! I am an engine head never really understood timing, knock, and preignition. I’m going to watch this video over again. I have V8 and turbo I-4 cars.

[@johnlocatelli9633]

Congratulations on producing and presenting this topic. Excellent technical knowledge and brilliant communication skills. Thank you.

[@tinymotogarage]

Absolutely excellent from start to finish. I am more into motorcycles (older ones at that) but for someone self-learning about engines in general, this was a masterclass. Thanks!

[@peterjohn3180]

You'll be used to pistons with lumps missing then!

[@luistrejo7249]

I'm really amazed about the explanation in this video. Great work. Good balance between causes of knock, how to avoid it and how the knock sensor works. Greetings from Venezuela, thanks for this valuable information.

[@questfor10s]

Thanks for the good overview of knock for beginners. Looking forward to the next video where you discuss the details.

[@G1itzik]

one of the best explanations on KZbin good-work!!!!

[@tahoon2009]

Knock beautifully explained like no other video here , all the best

[@masoudahmadi9118]

that was informative content, tnx. My question is that is there any methods to find out which one is happening pre-ignition or knocking especially with the parameters of the engine scaner?

[@johnkufeldt3564]

I fracking love your channel, you have made this Canadian gearhead happy as I always learn something from you. Ell researched, well presented, and your love of subject is contagious as COVID. KEEP IT UP, i MAY SOMEDAY AFFORD TO SPNSOR. Cheers ffrom Calgary, Alberta.

[@dennisduval9474]

I work as an engine technician and test on fuels to find out the octane number of said fuels. you sir did a very good job on this video

[@joshuadoliveiro]

superb video. glad to know there's loads of steps to mitigate knock.

[@petertimowreef9085]

Really nice how AEM decided to spend a part of their marketing budget on this content instead of traditional commercials and advertisements. WIn-win-win situation. We get to enjoy excellent content. Driving 4 answers gets to do what they love. And AEM gets to advertise amongst exactly the sort of customers they're looking for, probably for a fraction of the cost of traditional advertising too.

[@driftorcircuit]

Amazing video. I thought I knew most of this but still managed to learn a thing or three. Thank you.

[@RakeshGuptak]

Wow, this video is operating at the TDC of the information and knowledge on engine combustion and at the edge of the knock not to create information overload! Amazing!

[@AMGTOM]

Very important and I bet lot of mechanic don't know exactly what's knock including me. Thanks a lot bro 😊

[@stuckinmygarage6220]

One of the best explanations, ever. Thank you.

[@johnlovett8341]

Watching D4A ... plus a beer or two ... awesome way to spend an evening.

[@waylander2]

Thanks for making great videos! I really enjoy your content. I learn something every time I watch.

[@mohammad7500]

your explanation is very simple and beneficial, thank you!

[@cellphonelightsaber]

"I am teaching you something. Now, here is a product from my sponsor that does the thing I just lectured you on. Not only am I still on topic, I am giving you a real-life example of the thing that does the thing." Based senpai.

[@nevilledredge910]

Thanks for all your subjects that can be very educational for those that are still learning. I say this after 58 years in the trade. Thanks again

Best explanation Ever! Don’t know how you could explain it any better! Great info!

[@gregfaris6959]

Good presentation - excellent visuals! What he says at 6:00 is crucial to understand; Most light knocking does not cause engine damage. Engine developers have run test engines for hundreds of hours under light to moderate knocking conditions, and disassembly inspection usually shows no significant damage. What knock ALWAYS causes, and the main reason we wish to avoid it is that it destroys power. As soon as the engine enters a knocking condition, power dissipates rapidly, and if the operator increases inlet mean effective pressure by pressing the accelerator, it only makes the knocking worse. A further point that I feel needed to be made; Without wishing to criticize an excellent introductory video, before introducing exotic solutions like water/methanol injection, it should be noted that knocking tendency is directly correlated to engine speed, or RPM. The ratio of indicated mean effective pressure to knock-limited indicated pressure (IMEP/KLIMEP) increases with increased RPM. This effect is even more pronounced with some bio/gasoline grades. Therefore, the driver’s first line of defense against knocking is to choose the fuel grade that works best for your vehicle (without overspending on unnecessary knock grades) and, if you are fortunate enough to be driving a manual transmission, to select gear ratios that deliver higher RPM, especially when you need to add power.

[@drtweak87]

Dude love your videos. So easy to understand and you really put it out in detail and visually

[@redneckjesus1498]

"wait so why don't diesels knock then" he started explaining it before I even finished thinking the question... Earns a sub from me

[@jevynjennings1331]

Thanks for all your hard work on this video man it really helps me learn please dont ever stopp

[@alvesthegreat]

Man oh man this man is smart..... I know my thing but this man breaks it wayyyyy down.... Thank you... Do a video about knock in old diesel engines.... You earned a sub.... Very first video ice watched for you... That has never happened to me before

[@shawnodell4382]

Nice video. In the future you might mention that knock breaks down the thermal boundary layer and melts/reduces the strength of the piston. Another sign of knock is spark plug ground strap erosion. Also for comments about the oil you want to use SP oil with turbocharged engine or whatever level the manual calls out. Oil is a source of pre ignition and the newer oils have a higher auto ignition temp helping to prevent PI.

[@jojopojo9516]

Long time watcher. First time commentor. I love your channel. Keep up the good work.

[@Jimmysidecarr]

Positively brilliant simplification and explanation of knock and preignition! SUBSCRIBED! Knock and preignition are absolutely the number one killer of modified boosted engines, that are running more than stock boost. Stop blaming your engine oil and start checking the center electrode insulator porcelain for any tiny flecks of aluminum, those are the first evidence that knock has occurred or is occurring. Then either run higher octane, less timing advance or less boost. Localized over heating in cylinders is also a thing but those are the BIG things. This video is SOLID GOLD!

[@tonywilkey4369]

Well spoken and with diagrams very easy to understand , well done Tony

[@d4a]

Thank you Tony 😊

[@TurboS-gh5wc]

Subscribed. Most informative channel on KZbin. Thank you!

[@FranciscoLeotteDoRego]

Congrats for your videos! Very informative and really well done!

[@YMJCMJC]

Great presentation and explanatory technique. Thank you.

[@MaxAviles]

What a great video! Thank you for the in depth explanation.

[@galetyler7770]

Great explanation. Best I've heard yet. The only detail that wasn't explained was that compressing of the end gases creates radicals that are not regular old gasoline anymore when knock occurs. It's not a normal air fuel mixture that autoignites. It has been changed by heat and pressure into something that detonates at the local speed of sound.

[@rv6ejguy]

Hey, that's my piston at 7:05. Stuck wastegate caused the boost to go through the roof and I attempted to modulate boost with the throttle. I was leading the race at the time (road racing). Clearly it didn't work out for me. Great vid.

[@joshbrennan8545]

Best explanation of knock I've seen to date..

[@muhammadhaq7773]

Simply fantastic....I'm learning so much...thanks a lot brother...respect from Bangladesh

[@KingdomAuto]

Fantastic explanation, animations and content. Thanks for taking the time to make such informative videos :)

[@MrFordy90]

ECU can also cut boost or reduce boost to manage knock. Hopefully you can cover the logic regarding that safe guard in a future video :D Great work as always!

[@gibronjamaludin3683]

I just enjoy watching your videos it's easy for me to understand what Is going on in a combustion chamber . So if I'm right editing a aem injection kit will help keep the cylinder temperature down but will Interfere with the AFR su you will need to tune your ECU to edit more feul .I'm no export just watching and learning .thanks in advance

[@LeZturbo]

I’m so in a hurry to see the next episode ! Greatest explanation !

[@duartecabral9983]

Thank you for the clear explanation and visual aids.

[@AbuDujana692]

Simply awesome explanation

[@PaulR387]

Absolutely brilliant video, thank you for sharing this

[@haroldloreno6277]

thank you for your sharing the knowledge to us.... and I have learned a lot because of you...

[@VinnyXL420]

Yep, i had a nice introduction to the destructive powers of knock after it blew apart one of my pistons, im currently in the proccess of rebuilding it with forged internals

[@mcdonald2037]

I been watching other user videos and yours by far IS THE BEST. Well explain...

[@jeremywhittler8591]

All this is true , well done video. Higher lift Cams and big single turbos and direct injection are today's keys to keeping engines alive and why we are achieving so much hp today. Cams act differently linear than thier static numbers suggest reducing compression at higher rpm . Coming in with boost after 3500 just like nitrous is the key to keeping everything from breaking, that's why we ditch twins. Staying in compressor map efficiency areas that are making more airflow and less heat to begin with. Then with the computers and meth or timing e85 strategies last. Gearing and the weight of the car are also players as a strategic white paper end game plan. Preventing any detonation from happening in the first place. Big single set ups are faster and live longer. Come in later and tune for boost the way you would nitrous. Move the area under the curve higher in the rpm range , especially in an open deck block . Rods especially hate big torque low , probably too often misinterpreted as a detonation side effect. This is how thier running streetbikes with such high compression ratios. The aggressive Cams and linear not static specs of the camshaft.

[@ivokiller2000intel]

great video as always, very informative. Keep it up.

[@RFVisionary]

Technically hot topic - cool video! Well explained and easy to understand even for the layman. 👍🏻

[@jolabug6163]

Excellent explanation, Subscribed!

[@sunnylucinoneovvl8985]

Extremely educational and entertaining.. love your videos!! Keep it up!!

[@darylreed7771]

I just want to say, I fuckin love your channel! This is seriously the most thorough and best explained engine internals I’ve ever heard. I’ve always wondered about knock when it came to old BMW boxer engines and this totally makes sense to me now. Way to go my dude. You really nailed it and the visuals are perfect. You the man!

[@rahandali5078]

Excellent explanation great job

[@krish-cu2rp]

beautiful lecture brother !

[@onlyeyeno]

Thanks for another 1:st rate video, informative and clear, and as always even when I believe I "know the subject" I learn something new from Your video. Best regards.

[@nadeemchaudhry6585]

Another great video!! Very well explained. Thanks

[@chesterwong9477]

Awesome presentation!!! Subbed!

[@olspanner]

Excellent presentation

[@youmikey55]

really good lesson....love your channel bro...good job

[@halsnyder296]

Excellent explanation!

[@shawnalbarghouthi4113]

This is one more video perfection ❤🙌 Really thank you 🙏🏼