Since I rebuilt my engine ive been running premium fuel in my 460. Its a stock 1973 460 bored .040 over. No performance mods other than an edelbrock intake and carburetor. Is premium fuel necessary??

 

The usual magazine advice is..."drive with the lowest grade that dfoesn't ping a lot" "if it pings very gently under a heavy load, you are about at optimum". I think Car and Driver mag once said that the gentle ping under load is a sign of economy and that the engine is getting the most bang for the buck and is not damaging itself. The heavy rattle and constant liud ping is what destroys engines.

I have taken this advice since the 80s. Start with regular and move up in grade if the engine pings more than just that tiny little ping you might get on a hill on a hot day. You can also change grade depending on temperature and altitude and load. My experience is that heat, towing, will require higher octane. At high altitude it seems the engines can use lower octane.

My 94 F250 is used a lot for towing an 8,000# trailer. I tow it the same route several times a year but during different weather. During hot weather I need 89 for flat, and 92 for hills. During cool weather, say below 75, I can get away with regular for flat and 89 for hills. Many times I will put low test in one tank and higher test in the other and switch when I get to hills.

With the price of gas, it makes a big difference if I can load up 38 gallons of 87 instead of 92.

Good Luck,

Jim Henderson

 

Exactly what I used to do before I had my distributor recurved Jim! Works great! I used the mid-grade tank as "hill-climber" and a reserve, usually refilling shortly after the "regular" tank ran out. The engine always let me know what grade it needed, the ping just disappeared shortly after the tank switch ... how quickly gives you an idea of how much fuel is going through!! My wife commented that it was just one more thing for me to play with.

After the recurve I run the lowest octane available ... both tanks ... with no problem. This last trip was the first time I had heard a very subtle ping in a long time ... cruddier gas than normal I guess.

Roger




65,000 original miles (and counting)

 

I partially disagree. Pinging is directly related to detonation. Detonation is actually firing of the gas in the cylinder before the piston reaches top. This can be catostrophic in towing situations as it generates large amounts of heat and is generaly just NOT good for your motor. I DO agree with running the lowest octane possible without pinging. If you ping while towing, run a higher octane. This is all assuming that the timing is optimal and the motor is in good tune. i.e. good plugs, cap, rotor, etc etc. Being a STOCK 1973 460, you should be able to run the lowest octane at the pumps. As long as your compression is below 9.75, you should be fine with the cheap stuff unless racing/towing.

 

The materials I have checked list the compression ratio of a stock 1973 @ 7.5:1. That should, as 53wa2fl posted, allow you to run the lowest octance gasoline available.

Generally speaking, detonation--or the lack of it--is related to: (1) timing, (2) distributor advance curve, (3) ambient air temperature and humidity, (4) fuel octane, and (5) cylinder pressures, as well as (6) engine temperature.

Your fuel requirement will be dependent upon the lay of the land, the load imposed on the truck, and your timing and distributor advance curve.

I may be wrong in this part of my post, but, even so, I must say I disagree with what was quoted from Car and Driver magazine. Detonation is not good for an engine. Any pinging is signalling an improper timing of the firing of the air-fuel mixture. It is a "slamming" of the piston, trying to get it to go back down in its stroke before it is ready to do so. In essence, it is rather like a gasoline engine attempting to fire off of compression as a diesel does. It does put an additional load upon the piston head, the compression ring, the wrist pin, and the rod bearings. Even titanium will crack if an ill-timed load is imposed upon it continually. Further, pinging, depending upon its severity and the ambient temperature, will heat up an engine to some degree (no pun intended). All in all, pinging puts a load on an engine that can prove detrimental to it.

 

Hi, guys--

Don't confuse "Detonation" with "pre-ignition"

Detonation occurs when two (or more) flame fronts collide within the combustion chamber; the second or additional flame fronts occur at different areas within the cylinder, and begin burning the fuel at or before the point at which the spark ignites the fuel (i.e.: pre-ignition).

The fuel is usually ignited by "hot spots" within the cylinder from one or more locations, creating "flame fronts" that are heading toward each other.

When the "flame fronts" meet, they "collide", and the resulting collision will have the same effect as a hammer on the top of the piston.

Therefore, pre-ignition is NOT detonation, but rather, it many times is a component of detonation (pre-ignition also includes igniting the fuel and completely burning it prior to the spark occurring--which is NOT detonation, but rather, an opposite force against the compression stroke).

 

you forgot the most important one fuel mixture lean conditions cause the pinging you are refering to all of the ideas you mentioned create a lean condition, if yo have too much timing then it burns some of the fuel prior to it compressing, and reduces the fuel (it also causes the fuel to detonate with a harder explosion instead of burning internal combustion engines do not explode the gas they burn it, and the expansion created pushes the piston not an explosion), higher humidy, and air temp can make the air denser causing a lean condition once again, and higher engine temps will cause the fuel to evaperate before it gets into the combustion chamber causing lean condition, and also contrary to popular belief lower octane fuel actually burns, and evaporates faster than high octane fuel, causing lean conditions once again, so if you have an after market carb make sure it's set correctly, other than that I pretty much agree about running the lowest octane possible without pinging.

 

Monsterbaby's post raises a valid point which, obviously, I totally failed to put in my post. A/F ratio and mixture are crucial to avoiding pinging! Theoretically, that is an advantage computerized fuel injection is to always have over carburetion, namely, it is to keep the A/F ratio correct at all times, irregardless of atmospheric conditions, engine speed, or elevation. Good point he made!!

 

I'm sorry, but I'm going to have to disagree with you on this one. The only way any of the fuel burns before the rest of it is if there is a cause for it--i.e.: a hotspot that ignites the fuel before the spark plug fires. Too much timing is simply that--and ALL the fuel burns unless something ignites it before the spark plug fires, which would then be "pre-ignition".

I'm sorry, but that is something I'm also going to have to partially disagree with you on; while it's true that internal combustion engines burn fuel, they don't "explode" it (at least, we HOPE they don't!), it is NOT true that too much timing will cause the fuel to "detonate wtih a harder explosion".

If you have too much timing, and it burns all the fuel in the cylinder before the piston reaches TDC, then what is happening is that you are basically forcing the engine to work against itself.

The full force of the combustion process occurred before it could act on pushing the piston DOWN in the cylinder, and partially pushed on it when it was traveling UPWARD. Therefore, the work that would have resulted from burning the fuel was lost, and even worked against the engine by slowing down and pushing against the piston while it was still on it's compression stroke.

Well, I think you have that BACKWARDS--higher humidity and higher air temperature mean that you have FEWER air molecules per cubic foot of air (because higher temperature means the air is LESS DENSE, and because the higher humidity takes up some of the room that air molecules would have if the humidity was lower), which means that the mixture is RICHER.

The actual ideal is that the fuel *IS* turned to a vapor by the time it reaches the combustion chamber, because liquid gasoline will not burn, it's the vapor that burns. It also doesn't "evaporate" away from the cylinder--it has nowhere else to go--especially considering that the air forces have already pushed it through the carburetor and into the intake manifold. If it evaporates BEFORE it gets to the carburetor, it will in NO WAY affect the fuel\air mixture or ratio--it can't, because the air has to go through the carburetor, atomize the fuel, and carry it with it to the cylinder.

The definitiion of "Octane Rating" is "The resistance to detonation"; octane rating has nothing to do with the rate at which fuel evaporates. As a matter of fact, Alcohol has an octane rating of about 114, but it will DEFINITELY evaporate LONG before an equivalent portion of gasoline will!

As I said before--once air has "captured" fuel by flowing through the carburetor, it no longer has anyplace else that it can travel than to the cylinder with the air that captured it. It cannot suddenly "lean out", unless it puddles in the intake manifold, and that doesn't happen under the high-heat conditions to which you refer.

 

first off there is a BIG difference between turn to vapor and evaporate, one turns it into a state that it can burn one disipates into the atmosphere, and this can, and does happen in the carb. and please not on the humidity, temp I didn't mention higher temp just higher humidity, and humid air is denser, and colder air is denser which pushes through the carb with a higher velocity relationship causing the carb to pull more fuel through the venturis, less are doesn't pull as much fuel. and comparing alchahol to gas is like apples, and oranges why not add that the octane rating of deisel is around 250 but you aren't going to run that in a 460 (and before you start on that one yes I know deseil is rated with a cetane rating, but the octane rating is so high it won't ignite with a spark), and too much timing has the exact same affect as hot spots, and carbon deposits are almost always in high mileage engines, not new ones, and one of the things that was found out on engines with alot of carbon build up was you begin to raise the compression and not the hot spot issues as much as everyone likes to claim (if that was not the case then any engine with a single spot of carbon would begin to detonate all the time, and guess what that doesn't happen because almost all engines have some carbon on the pistons.)
But interesting as this all is, it's still not the problem, in this engine, heat, and carb tuning are, you suggested decking the block, and spending lots of time, and money with a set of heads that it will not make any difference on, he needs to get the heat, and carb right, and probably can get away with 89 octane fuel decking the block will just agrivate the situation by raising his compression without any quench benifits, now if he had quench heads than making sure the total quench distance including head gasket is less than .050 would help, but it won't help here.

 

Sorry, but with all due respect, they're exactly the same thing; here is the dictionary definition:

http://www.hyperdictionary.com/dictionary/evaporate

I got the quote directly from your post, and it is this: That would seem, to me at least, that you are saying that BOTH components make the air more dense, when in fact both make the air LESS dense, as I'll elaborate on next.

I'm sorry, but that is incorrect. Here is why it's incorrect:

A cubic foot of air at a given temperature with NO WATER VAPOR has a given number of molecules. When you add water vapor into that cubic foot of air, it does not "compress" the existing air molecules, therefore, they can only be displaced--meaning there are FEWER air molecule, which means it is LESS DENSE.

These are principles of physics--you don't have to take MY word for it, if you don't believe me, talk to a mechanical engineer or a physics professor.

This is correct, and I agree with you on this completely! That's why the more cold air you can get into the cylinder, the more power you will make.

This isn't correct, and here's why:

The air pressure at a given altitude remains relatively the same at all times, regardless of temperature. While it's true that air temperature causes the molecules to expand and contract, thereby increasing or decreasing it's overall weight, it nonetheless remains at around the same pressure.

The FORCE that pushes air through the venturis in a carburetor is air pressure, and it is pushing because there is a pressure differential, that was caused by the downward stroke of the piston. The air pressure is rushing to try to "equalize" that differential. It DOES NOT INCREASE or DECREASE because of air density enough to even be measured accurately, and if there are any differences at all, they would definitely NOT be measurable in a carbureted engine.

ALSO--if that were true, we wouldn't need a "choke" on carbureted engines.

These are also principles of physics.

They are far more alike than you think; we use gasoline mixed with alcohol every day all across this great country. That's what "MTBE" is, if you've ever heard of it, and it's added to gasoline in a LOT of places, in an attempt to make the engines that run it burn "cleaner" (alcohol burns clean). If gasoline has alcohol in it, it will raise the octane rating of the fuel--but at the same time, it will also increase the "evaporation" of that fuel.

THAT is why I compared Alcohol and Gasoline. I'll re-iterate: octane rating has no bearing on the rate at which fuel evaporates.

The evaporation rate of a fluid is directly related to volitility of the fluid evaporating.

There may be a volitile fuel that has a lower octane rating and is more volitile than another (and probably is somewhere), but when you're comparing different grades of gasoline, there isn't a difference other than when there is alcohol mixed into the gasoline, and the alcohol gives the gasoline both a higher octane rating AND a higher volitility, because alcohol is more volitile than gasoline.

Well, not quite--let's take a look at this:

1.) TIMING refers to the point at which a spark plug is fired, so as to ignite the fuel in a cylinder.
2.) If we fire a spark plug TOO EARLY, we then ignite the fuel BEFORE the compression phase has completed; thus causing the combuston process to complete before the piston reaches TDC, which will, in effect, work against the piston.
3.) If we fire the plug early enough that one of the valves is still open, it's likely that the engine won't run at all--most valves are fully closed by around 80- or 90-degrees BTDC, so as to compress the fuel-air mixture in preparation for the combustion process.
4.) At times, the heat of compression could ignite the fuel BEFORE the spark plug fires, which would then cause an opposing "flame front" to occur, which would then cause detonation when the two flame fronts collide. This usually occurs when the static compression is too high, the fuel octane level is too low, or several other different components.

If there is a "hot spot" in the engine other than carbon build up, it would have to be a sharp area--one that would easily heat up, due to smal relative surface area.
If that's the case, then that would mean it would have to be the closed valves (their edges) or spark plug itself. If it's the spark plug, changing to a colder range might indeed resolve that issue.

Regarding the statement about the engine having no ability to create "quench"--that is from a different post, but I'll respond to that here:

Now, I've taken a look at the combustion chamber on the heads he's using, and while it is indeed a very large "circle", I have a hard time believing that it is completely circular, and takes up the entire 4.36" of that engine's bore size, but it does look like it might.

(here is a link that shows the combustion chambers of several different heads, including the ones he's using: http://www.reincarnation-automotive....ge-linked.html)

Be that as it may--if it is indeed without any "quench" surface on the head, I would venture to guess that his ENTIRE "pinging" issue is because of these heads, rather than it being a factor of gasoline quality, ignition timing, "hot spots", or any of a multitude of other things that might affect the issue.

At that point, I would recommend that he follow your advise and replace the heads witht he ones you recommended--I think it was the D3VE heads, if I remember correctly. Those seem to have pretty large, open combustion chambers, but they do provide a "quench" area.

 

LOL This is beginning to look like a school yard brawl. Who knows the most about how an engine works?! LOL
Lets not over-engineer here. I mean, this REALLY is not that hard of a problem to solve. I'm not a certified mechanic, my brother is. I dont need to be. I dont even WANT to be. From what the original post stated, this motor is fairly fresh. i.e. rebuilt within the last year. So that being said, all I need to know is what do the plugs look like when you pull em out? If their black, you probably have carbon deposites on the pictons which would indicate a rich condition in the carb which would cause the motor to run too hot which will also contribute to the pinging. SO, replace the plugs, adjust the carb, pour a little water down the carb at about 2000 RPM, and replace the thermostat. Call me in the morning!
I mean, come on guys, this is a simple thing to troubleshoot. If and I did say IF it still pings after that prescription, then look deeper. But man....I'll tell ya, engineers always try to re-invent the wheel......It just doesnt need to be. I try to use the K.I.S.S. method....maybe you've heard of it? Keep It Simple Stupid. No body in the regular world cares about the molecules of air and water in relationship to how an engine runs. It either runs right or it doesnt. If it doesnt, then change something until it does. There are do-ers and think-ers out there. I'm a do-er....I do something..if it works, great, if not, then I DO something else. I used to be a think-er, but I never got anything done.
Dont get me wrong guys, you posses a HUGE amount of useful information....But it isnt necissary yet to try to show it. So....put your taliwackers away, this ****ing contest is over.
I would be interested to know if stepside64 ever tried any of our ideas and if so, which ones....and did they work?

 

If you don't know how it works and don't care to know, how do you think it's gonna ever get fixed? Luck? Divine intervention? Have somebody ELSE fix it that DOES know how it works?

You need to know the basic fundamentals of how something works in order to even diagnose what could be causing the problem.

My posts in this and the other thread are (and were) intended to correct the information that was given, and show why it was incorrect in the first place.

You can't just say, "no, that's wrong" without showing the correct information, and the how and why it was incorrect to begin with. You have to show exactly what was incorrect, and provide supporting documentation.

YOU might think that it's simple, but it certainly isn't when you start talking about ignition timing, fuel mixture, vaporization, etc., and their influence on pinging.

The original poster wanted to know whether using premium fuel was necessary or not. The answer is it really depends. The subsequent posts answered that question, as far as I can tell, with the best answer to the question, and that includes the response you posted--I thought it was a very good answer to the question asked.

 

stonecoldtx, I have to disagree to very large extent, most people do not, nor can they understand the engineering principles in an engine for the real world, (and that is not intended to be an insult to anyone but we aren't all engineers )this was something I could never get through to my exwife she worked in a university setting, and they could prove all day long how this or that worked x% better, but thats fine in a controlled situation, but doesn't work in the real world, Now yours and my posts both have alot of true, and good info in them but is beyond the problems listed. in other words most people do not need to know why there spark plugs are worn out only that they are, and need replaced.

 

Even with divergent viewpoints and emphases, I still thought it was an enlightening and entertaining and educating set of posts.

The real world and the world of laboratory physics are sometimes galaxies apart, granted, still, there are times when extra information can and will help alleviate a problem and make an engine run better and with more power.

Engineers and engineering can help make a product or a vehicle better (or worse) and many of their lessons were indeed learned the hard way...trial and error.

At its simplest, an engine is a fuel-driven air pump. But the complexities of all the things that were mentioned in this thread come into play. Sometimes, the engine doesn't do too well and these thoughts must be considered in order to solve the problem. Some are simple: retard the timing or burn premium fuel or keep your foot out of it some. Some are more complex. It does, at times, require fine-tuning the ignition, rejetting the carburetor, or the like, to really SOLVE the problem.

It seems to me, for what--if anything--it may be worth, that everybody contributed something(s) helpful to try to solve his pinging problem. If not, at least several folks tried. That surely has to count for something!