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Car Forum / Ford / Ford Mustang / August 2005Ping Ping Ping Knock
Guys, I've bumped the timing on my 93 5.0 I set it by ear to the max I could run on 87 octane gas. Normally, the temps up here in Alberta don't get too hot, and 87 octane works nice at about 70F or 20C. Lately, it got up to the high 20s low 30s (mid to high 80s) and it was knocking under WOT at about 3 grand. So I put 89 octane in it and it now pings under WOT at about 4 grand. Apparently, temp makes a lot of difference, I assume cause the air is thinner, but what does the higher octane have to do with that? I guess when it gets this hot, I have to run 91 octane, but I'm not sure why. Anyone? Thanks all. BRad > I've bumped the timing on my 93 5.0 I set it by ear to the max I could > run on 87 octane gas. [quoted text clipped - 9 lines] > guess when it gets this hot, I have to run 91 octane, but I'm not sure > why. Anyone? Normally, thin air can run higher timing. My guess is that your computer is messing with the timing. You should look for evidence of overheating which can cause preignition. <snip> >I've bumped the timing on my 93 5.0 I set it by ear to the max I could = >run on 87 octane gas. [quoted text clipped - 12 lines] > >BRad The reason that you need higher octane fuels when you advance the timing to the max is.... The lower octane fuel burns faster than the higher octane fuels thus when a lower octane fuel is ignited at an earlier time, the fuel being lower octane burns too quick causing an explosion before the piston can even get to the top of the stroke. The explosion you hear is that darned ping and if it continues to do this, eventually you will wear into the wrist pin or the rod bearing or it can just as well put a hole in through the top of the piston. ...Ron -- 68' Camaro RS 88' Firebird Formula 00' Mustang GT Vert > <snip> >>I've bumped the timing on my 93 5.0 I set it by ear to the max I could = [quoted text clipped - 30 lines] > 88' Firebird Formula > 00' Mustang GT Vert That would royally suck. Royally. And how does air temperature affect this? When it's cold, it never pings, when it's hot, it does. Thanks. Brad >That would royally suck. Royally. And how does air temperature affect this? >When it's cold, it never pings, when it's hot, it does. > >Thanks. > >Brad Sorry on the late reply, my ISP is quite suckola. Density, the colder the air is the more dense it is, the warmer it is the less dense it is. The colder the air, the less area it needs to fill a given amount. Molecules close together means that you can put more in a given space, or more air/fuel in, the less pinging out. If you really want to learn about how temperatures work in conjunction with air density you can probably find more information by researching Nitrous oxide detonation an your favorite search engine. I'm in no way an expert on the subject, there are people here that know the physics much better than I do. ...Ron -- 68' Camaro RS 88' Firebird Formula 00' Mustang GT Vert >> <snip> >>>I've bumped the timing on my 93 5.0 I set it by ear to the max I could = [quoted text clipped - 18 lines] >> >> The lower octane fuel burns faster than the higher octane fuels thus It does not burn faster, it ignites earlier. The compression stroke compresses the air/fuel mixture in the cobustion chamber. Lower octane fuel combusts at lower pressure. The trick is to get the compression up as high as possible (power) but not too high before the mixture ignites by itself before the spark plugs ignites it. Higher octane basically delays the ignition longer (by itself). >> when a lower octane fuel is ignited at an earlier time, the fuel being >> lower octane burns too quick causing an explosion before the piston [quoted text clipped - 15 lines] > >Brad >It does not burn faster, it ignites earlier. The compression stroke >compresses the air/fuel mixture in the cobustion chamber. Lower octane >fuel combusts at lower pressure. The trick is to get the compression >up as high as possible (power) but not too high before the mixture >ignites by itself before the spark plugs ignites it. Higher octane >basically delays the ignition longer (by itself). >>Brad Higher octane slows down the combustion process giving you a slower, more controlled burn. The advantage is that it helps to prevent pre-ignition, preventing detonation from hot spots in the combustion chamber. (taken from the link below) http://www.imagestation.com/picture/sraid69/pd754fc3092cc94beb04a7f1d3b5bf00e/fb b758d6.jpg Here's one that describes the combustion process even better. A long read though. http://www.sdsefi.com/techcomb.htm ...Ron -- 68' Camaro RS 88' Firebird Formula 00' Mustang GT Vert Jezus. Buy a cheap timing light, disconnect the spout connector, and then set the timing correctly (and then replace the spout connector). And since you have a 5.0 go-fast car, why put regular in it? Does it not make sense that mid-grade would be better anyways? If you insist on being cheap, I would strongly suggest setting the timing via a timing light to get an accurate measurement. If you adjusted the timing with your calibrated 'ear', you still needed to remove the spount connector first. If you do not know what the spout connector is, I would suggest a Haynes or Chiltons manual. Crappy Tire sells the manuals and the timing light for decent prices. HTH, Chris in Calgary. > Guys, > [quoted text clipped - 15 lines] > BRad > Chris, I know how to set timing. What I want to know is why temperature affects timing. Obviously, it must be the thinner air.... thanks. Brad > Jezus. Buy a cheap timing light, disconnect the spout connector, and then > set the timing correctly (and then replace the spout connector). And since [quoted text clipped - 25 lines] >> Thanks all. >> BRad Well if you know how to set timing, why is your car pinging? And WHY THE f.ck WOULD YOU SET YOUR TIMING 'BY EAR'. What sort of accuracy are you hoping to get from that? Are you retarded? > Chris, I know how to set timing. What I want to know is why temperature > affects timing. Obviously, it must be the thinner air.... thanks. [quoted text clipped - 30 lines] >>> Thanks all. >>> BRad |
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