marlinmon07

do our stock vehicles have detonation?

Sonic Boom NH

Not unless you have a tank of real bad gas. Otherwise no they don't and they have knock sensor to retard the timing should the motor begin to knock the computer will retard the timing to the cylinder that is producing the knock. In other words the computer will NOT retard timing across the board due to knock ONLY the cylinder or cylinders that are responisble for the knock or detonation.

Andys06GT

well, technicaly speaking, all vehicles have detonation. you cant start a vehicle without one. how else does gas and air combust? it detonates.... but yeah, thats probably not really your true question. +1 to sonic boom in his explanation. you will get knockin if you use an octane level that you're not tuned for. just use 87. be happy its the cheapest too. and if/when you tune, make sure you get rid of as much gas as you can before you put 93 or what have you in it and retune at the gas station. you can throw a code pretty quick otherwise.

Rider

Good question, I was about to ask the same thing.

I was out crusing last night and found a good road to stab it and I swore I heard knocking at about 5000 rpm. I can't be sure though because I also thought it sounded like something rattling like a heat shield. It sounded like valve chatter. I have a 93 octane tune and good gas and shouldn't the knock sensors keep that from happening. What would this sound like on the 3v mod motor?

Am I correct that I can datalog through my SCT to my laptop and log the knock sensors to see if this is knock I hear?
I dont want to torture my cylinders or ring seats with detonation.

Andys06GT

where's the tune from? always important. you can call whoever and ask if they've had similiar inquiries, could just be them. could also have some bad gas, even BP gets a bad batch once in a blue moon. as to the datalogging, yes. you can go to SCTs website and download the software, but you'll need to purchase their USB cord for the SCT. another theory, could be something in the exhaust knocking around down there. had that problem when i purchased it. WOT produced a knock, but it wasnt as quick as i thought exhaust should have been. took it in, under warranty, and recreated it for them. hasnt done it again since they replaced an exhaust isolater thingy-ma-bob. sorry i dont know the full technical term. couple things to look at for ya...

Rider

the tune was made by SCT for a intake maker. I'll call the intake guy and see if he has any others like me.

i already have the software and usb cable so I'll try that too. Good/bad about the exhaust rattle you had, I hope I have something like that and like you it just happens at WOT.

thanks

howyhowy

My manual from my 2002 GT said its normal to get some if you get on it at very low RPM. If you hear knocking at 5000 RPM get off the gas cuz you might have a serious tune/octane problem. Remember you cant really trust el-cheapo gas stations to give you 93 octane every time, so you might have been running 89 instead.
-howy

Sonic Boom NH

Technically you can still get detonation even with the knock sensors if you have an aggressive tune. The knock sensors and computer will only take out so much timing and if you’re running real lean it very well may not take out enough timing to prevent detonation.

Andys06GT:

I believe you’re correct in a way about detonation occurring or needing to occur to even start your car. The way I was taught was there is combustion and then detonation. Combustion is controlled whereas detonation is not.

In other words a proper tune, spark plugs, spark plug heat range, and fuel octane will control the flame front of the combustion so you have a smooth deliver of power in the cylinder, or think of it as an explosion that is methodically controlled to flow smoothly throughout the cylinder and not just a big bang or explosion you would get from a stick of TNT.

Properly controlled combustion happens as the piston reaches TDC (top dead center) or a little after TDC of the compression stroke where the rod is strongest or best advantage.

Detonation on the other hand is like sticking a stick of TNT in the cylinder and it just explodes erratically causing major pressure points in some areas and little to no pressure points in other areas.

Detonation usually, or more often then not, happens before the piston reaches TDC of the compression stroke which is the worse case scenario for the rod. The knock sound (usually described as sounding like marbles in a can) is the piston being slammed into the side of the cylinder or just the extreme amount of force placed on the top of the piston.

If I remember correctly, and could very well be wrong, but detonation can cause 2 to 5 times the forces to be placed on the piston and rod then normally happens with controlled combustion and since the rod is the weakest link is usually why you see people ventilate their blocks (rod going through the side of the block) when they have aggressive lean tunes that cause detonation.

Rider

My knock was sure enough bad fuel. I drove that tank down to half a gallon with some normal driving and filled her up with a fresh tank. Put another 20 miles on it to fill the lines with new fuel and went out to that good road and stabbed it WOT through the gears up to the redline and it was screaming just like it should.

That pisses me off that I got some bad fuel. I always use BP or Amoco from busy stations just so I'll get good fuel. Makes me want to wrap some barb wire around a 2x4 and ......

00 425 SALEEN

Hey decided to bump this.

I have a 2000 Saleen SC that gets some knocking at WOT or just before WOT. I live in Cali so all we have is 91 octane at
gas sations. Im hoping its bad gas. Im gonna run the tank down and try again unless you guys have another suggestions?

Thanks.