detonation

['01WSsick]

I am hearing what sounds like detonation at around 5000rpms and up. i always run 93, so i am thinking it might be a fuel pump issue and was wondering if anyone else might have experienced a similar problem?

[Kevin - Blown 95 TA]

Your car should be pulling timing before you ever get audible detonation or knock. You need to get a scanner on there to see what's really going on, but you can also read the plugs to see if you had detonation. Also, if you get detonation, the RPM will often vary on the graph as the car hesitates. You may need to get a fuel pressure gauge on there to see if your regulator & pump is working or not if that's what you suspect. Do you have the stock plugs in there?

[raroZ28]

my car would do something like that. When I pulled the plugs they had no electrode left on them. New plugs and wires took care of it. It would pop after 5000 and not want to climb any higher, jerked the car a little.

[fastTa]

Detonation or "spark knock" is essentially a result of end gas spontaneously igniting after the spark event due to excessive heat and/or pressure within the bore and combustion chamber. This is normally caused by hot spots in the CC (excessive carbon buildup) and too low an octane of gas. The end gas that is failed to ignite at the normal time of spark event is instantly deteriorated and thus lacks sufficient octane to withstand this combination of increased heat and pressure. This essentially creates a flame front additional and separate from the normally ignited flame front at spark. You will hear lots of "car guys" tell you that the pinging sound you hear is the result of these two flame fronts colliding, but this is not the case. Detonation causes a very short but significantly sharp pressure spike in the CC. This sharp spike in pressure creates an extremely strong force in the CC which in turn resonates the rotating assembly and block. This is the audible pinging or spark knock that you can hear and hopefully that which the knock sensor "hears" as well. It is said that this resonation occurs at about 6400 Hertz and thus what knock sensor "listen" for.

It is not uncommon for higher compression motors to experience consistent and non-damaging detonation on a regular basis, but when you can actually hear the detoantion occuring, that is not good.

Like Kevin said, you need to get it on a scanner and look for timing being pulled due to knock retard. It's highly doubful that a lack of fuel would cause detoantion.

[Kevin - Blown 95 TA]

Detonation is a lot more violent than pre-ignition or pinging. A lot of cars might ping a little going up a hill like in the early unleaded days, but if you detonate for very long, something is going to break, unless, of course, it's a deisel. Detonation is a more violent banging sound & it might jerk the car a little bit as the rpm jumps around and the car loses power whereas pinging or pre-ignition sounds more like rice being dropped on tin foil. The pinging is a warning sign that you might get detonation next if you push it. I had detonation once in an old 383 Roadrunner, and I finally got rid of it with colder spark plugs. Since I had forged crank & pistons, the car didn't have any damage, but cast and HE pistons might crack a lot sooner. Now my old 78 Grand Prix, which was a smog monster, always pinged, but it never detonated. Pinging can also be a sign of bad gas. Modern cars have to protect themselves with knock sensors cause they are all high compression.

[fastTa]

Actually just the opposite. Pre-ignition is far more destructive than detonation by far. Remember, with pre-ignition, the ignition event of the a/f can and normally happens very far ahead of the spark plug firing, anywhere from 180 to 160 degrees BTDC (more likely at 180). So as you can see, pre-ignition can occur literally as soon as the compression stroke begins. There is no very rapid pressure spike like with detonation. So unlike detonation, with pre-ignition, there is no sharp pressure spike to resonate the block and the head to cause any noise. There is instead, a large amount of pressure which is present for a very long dwell time during the continuation of the entire compression stroke. So pre ignition is inaudible. That is why it called the "silent killer" amongst pro engine builders.

If pre-ignition occurs in a motor, you can be assured something will break instantly. Like I said, Detontion is actually fairly common in higher compression late model motors. It can go un-noticed for long periods of tiime without causing any damage whatsoever. But, when you can hear the spark knock, that is when it is time to figure out what's wrong before you put a hole in your piston, skuff the skirts, or lose electrodes.

[Kevin - Blown 95 TA]

I'm going to look it up. We both know what we are talking about, but the nomenclature is where we are disagreeing. I'll try to see what's what and post it here...

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I looked it up - You're right Kevin - I've been wrong for all these years probably from a wrong book I read. Anyway, it is as you said above - I had it backwards. Pinging is detonation & pre-ignition is breaking pistons. Now that's going to drive me nuts til the day I die why I learned it that way.

[fastTa]

I'm going to look it up. We both know what we are talking about, but the nomenclature is where we are disagreeing. I'll try to see what's what and post it here...

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I looked it up - You're right Kevin - I've been wrong for all these years probably from a wrong book I read. Anyway, it is as you said above - I had it backwards. Pinging is detonation & pre-ignition is breaking pistons. Now that's going to drive me nuts til the day I die why I learned it that way.

You still aren't gettin' my Bud Light!

[Kevin - Blown 95 TA]

I think "detonation" sounds a lot worse than "pre-ignition" don't you. "Pre-ignition just sounds so politically correct. Anyway, that's what I get for reading Car Craft in Sunday School as a youth (removing foot from mouth).

Ooops - Hold the phone! - I just got home and am taking a long draw off the crack pipe and looking at How to build High Performance Ignition Systems by Todd Ryden - and he says "Pre-ignition is sometimes referred to as detonation." with no other qualifying explanations.

I usually call the pinging "knock" and the worse stuff "detonation", but what I reported earlier, I had looked up on the internet where the guy said detonation is pinging. Either way I was wrong about pre-ignition being the pinging or knock. So who the hell really knows. And, Kev, I never heard of a Texan who drank light beer! Oh well, as long as your John B. Stetson doesn't have a bunch of rhinestones on it...

[fastTa]

Ooops - Hold the phone! - I just got home and am taking a long draw off the crack pipe and looking at How to build High Performance Ignition Systems by Todd Ryden - and he says "Pre-ignition is sometimes referred to as detonation." with no other qualifying explanations.

There is another phenomenon called detonation induced pre-ignition. The entire detonation process can occur for a long period of time relative to crankshaft rotation. As a spark plug fires, the voltage ionizes the air between the "gap". This establishes an electrical path across this gap that in turn lowers the voltage requirement to fire the plug adequetly and current is alowed to properly jump (flow) across the gap. Then of course the normal combustion process begins.

This can cause the plug to heat up because the pressure spikes and resulting temperature spikes break down this protective boundary of ionized gas surrounding the electrode. This rapid and significant increase in plug temp then in turn can induce pre-ignition. There would be both evidence of detonation and pre-ignition in this case. This is exactly why ALOT of car guys and engine builders confuse detonation and pre-ignition.

So detonation and pre-ignition as you can see can be somewhat related, but they are very different indeed.

And, Kev, I never heard of a Texan who drank light beer! Oh well, as long as your John B. Stetson doesn't have a bunch of rhinestones on it...

Just referring to the commercial. Actually, you would be surprised how many sissy's down here drink that piss. It's the biggest seller down here.

[Kevin - Blown 95 TA]

Just referring to the commercial. Actually, you would be surprised how many sissy's down here drink that piss. It's the biggest seller down here.

LOL! That's too funny. I drank a Billy beer once , but when I was low on funds, I drank Piels beer at $1.19 a six pack. Light beer almost never.

BTW, Thanks for the lecture professor. You're getting bad as me...

[Jay 02 TA ws6]

blah blah blah blah blah

[Kevin - Blown 95 TA]

blah blah blah blah blah

Tough words from a man with no car, chump. Oh, and that Cavalier doesn't count.

[fastTa]

Maybe we have thoroughly confused '01WSsick. Let us know what you find.

[Kevin - Blown 95 TA]

Maybe we have thoroughly confused '01WSsick. Let us know what you find.

I'm confused myself. The internet source and you say one thing, My Ignition/MSD book & my Smokey Yunick book say another. Smokey ought to know what he's talking about, but like I said, it's a terminology problem where we are getting conflicting answers.

The best way to describe it is if you get knock & pinging (the rice & tin foil sound which usually triggers the knock sensor to pull timing) in a high compression engine, thats a potentially harmful warning sign, and if you ignore the knock, you might get bang, bang, bang, - maybe busted piston lands, holes in pistons or smashed & battered crank & rod bearings. Need to avoid the abrupt violent pressure spike when the piston is on the upstroke. Everyone agree?