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Discussion Starter · #1 ·
I thought by going to the bigger jetted Edelbrock 1405 and bringing my timing in a little slower, I had my pinging taken care of. Today while sitting in traffic, I decided to move over to the next lane wich was empty instead of the stopped lane that I was in, and had to nail it to do it (no, I wasn't in Citrus Heights where Barney Fife patrols). I accidentally lit the tires up, and there's that insesant pinging again!

I don't get it. I'm running rich, only running 10* initial timing, total timing of 38* isn't all the way in until 3000 RPMs, and running 91 octane, and STILL get this pinging. This only happens if I put the pedal on the floor from a dead stop. I can go up a hill in Overdrive at 30mph and the car will pull fine without a hint of a ping. What gives? What am I doing wrong? I'm about ready to buy a Demon carb and see if that makes any difference.

Any thoughts? My setup is:
289 bored .030. KB flat top pistons, 351w heads (not ported), Edelbrock RPM intake, Lunati 214/224 cam, Harland Sharpe roller rockers, Edelbrock 1405 carb, MSD billit distributor with MSD6A-L, MSD 8mm wires, Autolite 45 plugs gapped at .051, March underdrive pullies.

I know I should have ported the heads, but didn't have the time when I put the engine together. Could a smaller plug gap help me out?
 

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I went to a Demon carb. It didnt help.

I had the same symptoms... put the engine under sever load from a dead stop and it would ping. If the tires broke loose it wouldnt ping as much, but when the tires caught, it pinged a lot.

I went to a higher stall convertor (via the AOD swap), and I have yet to hear it ping. I attribute this to LESS load on the engine at lower RPM's

Just a theory. I would hate for you to swap TC's only to find later that it didnt work.
 

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weeeeird stuff.. what is your CR in that 289 ?
 

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Discussion Starter · #6 ·
Yes, I have 28* of advance in my MSD distributor. 10* initial and all in at about 3200. I used to have it in by about 2700. No vacuum advance (before I went to the MSD distributor I did have a vacuum advance with the same problem). I have verified that the mechanical advance works fine in the MSD dizzy with a timing light.
 

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Discussion Starter · #9 ·
I always run 91 octane, but we all know that California gasoline is pure garbage. Come to think of it, today is the first time I've heard it in a while and it was not long after filling up at Shell, where I never go because their prices are outrageous (today I was in a hurry, though, so paid the $2.15/gallon).
 

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Mixture or timing or both - what else could it be? Investigate less advance first to see if it has an effect, if minimal, richen it up with the timing of the secondaries (earlier). I'd like to know what you find out. I assume your distributor is steady?
 

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I AGREE !! CA gas is real sh*tty . i always run premium in mine JUST BC . it seems to last a bit longer but, dont you hate it when ppl in other parts of the country have acess to a premium with an octane rating of 93 ? * G * .. just for ****s n giggles why dont u just throw in octane boost into your tank to raise the octane level, and then go punch it a bunch of times and see if you notice any differences?
 

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What rod/jet combo are in the primary? Secondary jet size?

Do you know your quench spec? (How far the piston is in the hole + compressed thickness of the hg)

When exactly did it all start?

Sorry if I missed this info earlier.
 

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Have you thought about reducing the amount of mechanical advance -- going from 28° to 25° advance? What springs are you using in the dizzy, and have you played around with them?

Well...don't feel too bad John. I'm going to be yanking the 351W soon. I started it up on Saturday to just warm it up and maybe harrass the neighborhood a little *G*. I took a look under the car, too see how bad the rear main seal was leaking and I noticed a little bit of coolant on my tranny coolant lines. Upon further investigation, it looks like it's coming from back near #4, between the head and block. Hopefully I just blew a head gasket, and didn't wipe out my $$$ heads. :(
 

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Temperature. Its all about the temperature. You mentioned you had been sitting in traffic. My Mustang will ping like none other if it is hot outside and I have been sitting in traffic. But on a less than 80 degree day and with some air moving through the engine bay, it runs strong.

I know it was hot in Sac today too, L20068 was complaining to me earlier about it. I am not saying this is your problem, but it is something I have experienced with my Mustang so I figured I'd share the info.

I have my poor 10.7:1 351w at about 8° intitial with about 25° total advance to curb pinging problems. Power is noticably low, but atleast it doesn't ping on a regular basis. I had pinging described to me by one of my old mechanic instructors like this: "Think of hitting the piston with a huge sledge hammer as it comes up in its stroke, that is what pinging or preignition is doing."
 

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Sorry to hear this... check the wires ::

I'm thinkin' it's a temperature thing, but you've got that aluminum setup and everything going. Is 91 octane tops out there? What coil?

Try something stupid you'd never consider... will probably be it... that's what I found.
 

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Hot spots in the head (carbon) or any amount of oil blowby could also cause pre-ignition. Burning any oil? Plugs look clean? Crap buildup will also raise your compression a tad which doesn't help. (I just finished a complete de-crapifying of my 351 - and am hoping for less blowby with mo betta rings and cool teflon valve seals)
 

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OK, so what you're saying is that you've done everything you can, the setup should work, but it's still giving you grief. Time for a little "Out of the Box" thinking. I ran across THIS site that perhaps offers another perspective. If you go to the section labeled "Nucleate Cooling Phase", you will find the following:
As coolant flows through the system it absorbs heat from the parts it contacts. As it does this some of the coolant will boil and form tiny steam bubbles (absorbing a lot of heat) on the internal engine surfaces. When these bubbles get larger they become a flow restriction and the flowing fluid pushes them away from the surface and that process starts over again. This process is called the Nucleate Cooling Phase. When the coolant boiling point is too low or the flow rate is too slow, these bubbles can become too large and form steam pockets that insulate that part from being cooled. This usually happens around the combustion chambers. Once the steam pocket forms the surface can rise in temperature (even though the coolant is not overheating) and cause that part to overheat, which can cause detonation or other problems.
Just thought I would throw this out as something a little different to think about, since all of the more obvious causes have already been exhausted. You may just have a few spots where it's getting a little hot around those 0.030" cylinders and not flowing properly to cool it down. Wouldn't it be a hoot if all you had to do was put in a little different mix of coolant, a higher flow water pump, or up the psi on the cap 1-2 psi? The pressure and flow rate is low at the RPM you are experiencing the problem, so it plausible that there is an answer in the above info.

Of course, you may have a sharp edge inside one of the combustion chambers where a little carbon has built up and gets hot. That could cause it too.
 

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That was a great link on coolant and cooling! Definitely learned something from it. Made a believer out of me and I'm a natural born skeptic. Thanks!
K
 

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JP, unshaven 69 351w heads and a compressed gasket thickness of .041" should be ok....but temperature is the key here....

My hypothesis is hot spots in the combustion chambers caused by cast flashing or carbon build up. Pistons with sharp leading edges can also be the culprit.

Detonation occurs when the charge (mixture) is ignited by compression and rapid chemical reaction. The results are pressure-waves which vibrate the cylinder walls causing the rattling sound we all dread.

An engine suffering from detonation experiences a non-uniform flame front. Inside the combustion chamber, this causes components in the power stroke to experience anomolies which are not present in normal combustion. This combines with a higher internal temperature and can cause inevitable component failure.

Detonation is not the same as pre-ignition though it can be a cause of it. Pre-ignition is caused by "hot spots" in the combustion chamber which ignite the charge prior to the spark. These are usually caused by carbon deposits from rich combustion processes, but can be caused by failing components due to material melting. This is the result of severe detonation over some period of time.

There are several factors which can contribute to the engines susceptibility to detonation. Some common ones are:

The Combustion Chamber; Hemispherical heads are one of the least susceptible designs. In general designs with squelch areas are more likely and flat head the worst.

Spark Plugs; the hotter the plug the more prone to detonation. It is also worth noting that multi-spark plugged heads are marginally better.

 Spark Timing; the more advanced the timing the greater susceptibility to detonation. By retarding the spark it is possible to stop detonation, but at the cost of efficiency.

Octane; this reaction is directly proportional to the compression ratio of the engine. Ideally, one could increase the octane until detonation ceased, though this can not be accomplished easily in California. Many club members suggest either octane booster (some are much better than others) and/or mixing premium unleaded with leaded regular.

 Inlet Temperature; Cooling the gas entering the combustion chamber reduces the tendency to detonate. This has a similar effect as a lean charge mixture thus increasing the reaction time.

 Atmospheric Humidity; increasing the humidity can have advantageous effects against the engines susceptibility to detonate. First, increased humidity raises the charge density giving a less volatile mixture thus increasing the reaction time (aka octane rating). Secondly, the increased humidity tends to cool the combustion chamber during the intake stroke lowering the internal temperatures.

I hope this helps a bit...

R
 

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Discussion Starter · #20 ·
Yeah, 91 is all we can get out here. Coil is a MSD Blaster II. The thing that irks me is that the oldest part under my hood has 19k miles on it. I think this engine has always done this, but very rarely do I actually get a chance to put the pedal to the floor from a dead stop (I have enough problems with the cops as it is *LOL*). I really first noticed it at the drag strip, and once before that when I had to bring a ricer back down to earth.
 
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