Another Newbie with a Question...

[mustangnutbcuz]

I have heard several people refer to something called engine knock. I was wondering what that was and what it sounded like. I'm assuming its a loud knocking noise, but I wanted to be sure. What causes it? Any info would be greatly appreciated. You guys are great.

[DDMTK421DS]

eNGINE KNOCK HAS SEVERAL FACTORS to it, but mostly it is caused by your Timing ......If your cam & crank are not timed correctly or it gets a bit off, your Rods and valves will "clank" or rattle, and if left too long they will fail and destroy your engine....
Also, bad gas or impropper gas will cause this also.......When my 98gt was stock I made the mistake of putting 92octane in it and it knocked bad and would stall a lot......if you put 87 octane in a car that needs 92, it will knock also...

[HiFlow5 0]

Also, bad gas or impropper gas will cause this also.......When my 98gt was stock I made the mistake of putting 92octane in it and it knocked bad and would stall a lot......if you put 87 octane in a car that needs 92, it will knock also...

That's not knocking, that's pre-ignition (aka: detonation, pinging)

[Hypsi87]

pinging on a NA car sucks. but on a forcefed car pinging can tear the block apart bigtime. The key to keeping a forcedfed car alive for a long time is to keep the pre-deationation out of the engine. Pre-deationation on a forcefed car sounds like an automatic rifle going off. It happend once on my car. The alcohol pump quit working and I took it up to 24 PSI with pump gas. I got luckeeey. Spark knock is in lameins terms a gasoline engine trying to act like a diesel engine.

[HiFlow5 0]

Yes, when the deposits become too unstable and ignite themselfs from the heat. Just one effect of running too much octane on a stock motor, and of course there's other reasons too.

[mustangnutbcuz]

well i have a 99 V6. I usually put mid grade gas in her and every once in a while i put super. I was told not to put regular in her all the time because it doesnt burn as clean and would make my car run rough. Is that true? Now that your describing engine knock, I don't think my car is doing that, thank god. Thanks again for all the replys. I really appreciate your knowledge.

[Hypsi87]

Originally Posted by mustangnutbcuz

well i have a 99 V6. I usually put mid grade gas in her and every once in a while i put super. I was told not to put regular in her all the time because it doesnt burn as clean and would make my car run rough. Is that true? Now that your describing engine knock, I don't think my car is doing that, thank god. Thanks again for all the replys. I really appreciate your knowledge.

93 does not burn cleaner that is just a myth

[HiFlow5 0]

I wish I could take credit for this, but I have to give to Chris over at RHC.

Unfortunately, many people assume that higher octane fuel is better for all engines, no matter what. This, as I'm sure you know, is absolutely false. Ultimately, the best octane for any vehicle is the lowest one you can run without detonation (pinging) occuring.

Running too high of an octane will ultimately make it necessary to continue using that octane.

Just to clarify, it's not the fuel that increases the performance, it's the fact that the timing has been advanced. The higher octane permits this to happen. Basically, the way it works is something like this:

Octane represents a fuel's stability. When you compress an air fuel mixture, it becomes quite unstable, and explosive. In fact, this is why diesel engines don't require spark plugs. They commonly have compression ratios of 22:1 (as opposed to a stock Mustang with 9:1), which makes the air/fuel mixture so explosively unstable that it ignites itself when the piston reaches TDC.

Octane, for all intents and purposes, is used to slow down, or control the burn rate. Modifications that increase performance, such as increased compression, or advanced ignition timing, will cause the mixture to become too unstable, and pre-ignition (aka: detonation, pinging) will occur. This is when the mixture fires on it's own, at the wrong time. Severe damage will occur if left untreated. Anyway, the only way to perform the mods that increase the power is to further slow down and control the burn rate of the air/fuel mixture, and the method used to do this is increased octane.

People often think of high octane fuel as being more flammable, and easier to explode, whereas that is actually the opposite of the truth. 110 octane race gas is much tougher to light than low grade 87 octane. BUT, because of that fact, it is the use of 110 octane fuel that permits the compression to be increased to 12:1 without melting the pistons.

On a side note, nitrous oxide works on a very similar principal. With nitrous, the power comes from the added oxygen. The problem has always been trying to find a way to add oxygen safely. As I'm sure you know, oxygen is EXTREMELY flammable, and if you were to try and add it straight to your engine, you would likely die, and not even be able to explain to people why it was you died. It was discovered that the nitrogen in the nitrous oxide was just enough to keep the oxygen from burning uncontrollably, thus permitting it to be used in a gasoline engine. In other words, the nitrogen is to nitrous oxide what the octane is to gasoline, except for the fact that octane is a calculation, and nitrogen is an actual element, but you get the idea.

Okay, back to the story...

Use of a fuel that has a higher octane than is required by the engine and the way it has been tuned will result in unburned deposits being created and left behind in the combustion chamber, and on top of the piston. Often referred to as carbon deposits, these cause the combustion chamber to become very unstable, for several reasons, all of which will ultimately require you to use a higher octane fuel to restore stability. Among the reasons, are increased compression (the deposits take up space, and actually increase the compression enough to make it unstable), retained heat (deposits retain heat at times when those surfaces shouldn't, increasing the likelyhood of pre-ignition), and the development of sharp edges (like sand under the waves, carbon deposits can be "shaped" by their environment, and can develop sharp edges, which act to the compressing mixture like a hat pin would to a balloon.

[Zwrangler]

I personally only use 98 octane premium fuel on my Z28 and it hauls ass compared to the 95 octane normal fuel. By the way, all the replies have completely drifted off the original question and only 1 replied yet as to what is engine knock ;p

[mustangnutbcuz]

Ok, well I'm assuming that I should stop using 93 octane? my car is only a V6, should I use regular or mid grade, or alternate? If I stop using the super, will I eventually burn off the deposits left in my engine that haven't burned off?? Again, all the help is really appreciated. Thanks again.

[speedfreak]

No, the carbon will probably be there until the engine is torn apart. If you can run 87 and not have pinging, then dont worry. In fact, the V6 stang is the economical version and shouldnt need anything more than regular. The GT doesnt even need premium.

[351wStang]

higher octane = slower burn which in turn allows for advanced timing like previously said. but back to the original question 1 type of engine knock that hasent been mentioned yet is piston slap. gives a hollow slapping sound. this happens when you have a skirt break.

[speedfreak]

Dont forget a rod knock.

[nstodghill]

2000 S-10 4.3L .I thought I had a bad EGR valve so i cleaned it with carb/throttle body cleaner and also sprayed a little in the passage ways that go to the EGR valve .Now It is knocking lick crazy and runs very bad . I replaced the EGR with a new one but still runs the same. Any Idea why. Is this the spark knock you speak of.

[TheStang00]

dude, just make a new thread, this is 3 years old.