lead additive

[John D.]

Re: lead additive

Only if it's in a boat or if you're towing a trailer at 100 mph all day long (constant high power settings); valve seat recession in our classics in normal driving is a myth, although the marketers of all the "miracle elixirs" would have you believe your engine will surely disintegrate in a ball of flame and a hail of shrapnel unless you use their product religiously.

Now that's funny Hinckley.
You guys made me read all these posts on lead. Whew!!!
Can tell it's a boring Sunday nite. JD

[Joe C.]

Re: lead additive

Most in this thread seem to lost track of the fact than detonation and preignition are NOT the same thing, but one can lead to the other.

"Octane number" is a measure of a fuel's resistance to DETONATION.

Duke

That's right. Detonation can lead to pre-ignition, but not vice-versa.

Pre-ignition is much more damaging than detonation, due to the fact that p-i can sometimes occur while the piston is near the bottom of its stroke, and on its way up during compression. The tremendous heat absorbed by the piston during this event, combined with the downward force applied to the upward moving piston is normally enough to melt and/or blow a hole in the piston crown. This is known as "detonation induced pre-ignition". It generally occurs after repeated incidence of detonation causes the spark plug to glow, since it cannot shed heat fast enough. The "glow plug" causes the intake charge to ignite at the beginning of the compression stroke, since it is here that the mixture first reaches its LEL (lower explosive limit). It can also occur due to other hot spots, such as carbon deposits, sharp edges in the chamber, gasket overhang, or overheated exhaust valves due to narrow seats, or insufficient margin width.

[Clark K.]

Re: lead additive

If Duke writes that you don't need more than 93 octane pump gas or lead additive, that is enough for me. If your engine is not used for racing and the ignition has been set to factory specs, non of the snake-oil "remedies" is necessary. When I bought my '65 L76 coupe a year ago, I was told to buy avgas/racing fuel and/or pump premium with octane booster and add lead substitute. I wasted some money until Duke set me free.
-Clark

[Kenneth H.]

Re: lead additive

OK guys, I'm really thick. I have a '70 LT1 with a completely original engine. I've been adding Maxlead 2000 to every tank of Sunoco 93 octane gas since I purchased the car 1 1/2 years ago. Is everyone saying that I should just stop using it and go with pump 93 octane unleaded with no additives? And what about my brother's '67 435hp vette. Same for him?

Thanks.

[Joe L.]

Re: lead additive

OK guys, I'm really thick. I have a '70 LT1 with a completely original engine. I've been adding Maxlead 2000 to every tank of Sunoco 93 octane gas since I purchased the car 1 1/2 years ago. Is everyone saying that I should just stop using it and go with pump 93 octane unleaded with no additives? And what about my brother's '67 435hp vette. Same for him?

Thanks.

Ken-----


This is very simple. Try using pump premium. If you get no significant "pinging" (I'll use that term in the vernacular rather than other terms which might get us further involved in "semantics"), then you don't need any higher octane fuel, including avgas. Period. The same goes for any other engine.

As far as lead, you don't need it and you're better off without it. If you want to make yourself feel better, use the product I described in a previous post.

[Bill C.]

Re: lead additive

In FL we have 10% (and lots higher at times I would guess) ethanol in our gas.

I have - as well as others - serious purculation issues. My car runs like crap in the summer.

However - if I add the TEL (maxlead or lead Supreme) my car will run much nicer in the hot summer days using the crappy ethonal based fuel we have. I can say though, that when I can get get non ethanol fuel I don't have issues running just 93 pump gas alone.
Also - I can't explain why, but I will get a 5-10 degree lower running temperature with the TEL added.

That is why I just decided to always add it.

Only issue I can report on is shorter plug life.

[Joe C.]

Re: lead additive

Ken-----


This is very simple. Try using pump premium. If you get no significant "pinging" (I'll use that term in the vernacular rather than other terms which might get us further involved in "semantics"), then you don't need any higher octane fuel, including avgas. Period. The same goes for any other engine.

As far as lead, you don't need it and you're better off without it. If you want to make yourself feel better, use the product I described in a previous post.

Joe,

Some of these engines have been so emasculated by substituting flat top pistons, and/or extra thick head gaskets by gun-shy engine builders, that I wouldn't be surprised if they run detonation free on regular fuel. This is particularly true of 327 engines equipped with the 30-30 cam. Somewhat less true of those with LT1 cams, and probably inapplicable to engines with 093 cams.

[Valeria H.]

Re: lead additive

It is up to you Ken, but my 60 which I've owned for 30 years has really and truly never run better on the avgas 100LL. It may be a an anomaly but I really do not think so. Even my husband has noted an extreme difference in performance Take it for what it is. I can buy this gas for 2$/gallon more than regular and it is dam near stupid not to put it in my 50 year old car for as much as I drive it.
Valeria

[Duke W.]

Re: lead additive

Detonation can lead to pre-ignition, but not vice-versa.

Nope! You failed the test.

Duke

[Joe C.]

Re: lead additive

"Detonation can lead to pre-ignition, but not vice-versa."

Nope! You failed the test.

Duke

Explain. I can't find it in the archives.

[Kenneth H.]

Re: lead additive

Thanks, everyone, for the responses. I'll try going without additives, as Joe and others have suggested, and see what happens. Since having the original LT1 engine in my vette makes it a rather valuable commodity, I really don't tax the engine all that much anyway. I do have a "lead" foot, but I guess that doesn't translate into needing "lead" in my gas. If I have issues as described previously, it sounds like there are steps I can take to resolve them without going back to a lead additive.

Last question, how about that '67 L71 that belongs to my brother? Is he in the same boat, that is, he doesn't need to add lead to his gas?

Thanks.

[Michael W.]

Re: lead additive

he doesn't need to add lead to his gas?

Thanks.

That's correct.

[Kenneth H.]

Re: lead additive

Thanks Michael.

[Duke W.]

Re: lead additive

"Detonation can lead to pre-ignition, but not vice-versa."



Explain. I can't find it in the archives.

First a couple of definitions:

Detonation: The sudden, nearly instantaneous combustion (like an explosion) of unburned fuel air mixture prior to being consumed by normal flame front propagation across the combustion chamber.

Preignition: Initiation of normal combustion by a source other than the timed spark.


Case 1: Detonation initiated by Preignition.

Preignition can be caused by a "hot spot" in the combustion chamber, which initiates normal combustion before the spark plug fires, or initiates additional flame fronts after the spark plug starts the primary normal flame front. It is the equivalent of advancing the spark or having mulitple spark plugs. If the preignition is significantly ahead of the normal spark, detonation can ensue, just as it can if the spark is advanced too far.

Case 2: Detonation not initiated by preignition, but leading to preignition

Detonation can occur if fuel octane level is not sufficient for a given load and spark advance. Detonation causes shock waves in the combustion chamber, which is the "knock" or "ping" we can usually hear if detonation is present. These shock waves increase heat tranfer to the combustion chamber boundaries by about an order of magnitude, which rapidly increases the temperatures of these boundaries, which can then cause preignition, which rapidly makes the detontion more severe. If load is not reduce or spark retarded to stop this positive feedback loop, damage can occur such as burned pistons or valves.

Some additional notes:

The fuel-air mixture does not "explode" inside the cylinder as you may often read. Rather, combustion progresses in a relatively predictable manner - much slower than typical explosives, like TNT. This is called "normal combustion".

Detonation IS the sudden explosion of the unburned mixture - reaction rate similar to a true explosive. This is called "abnormal combustion".

There is a myth that "high octane gasoline burns slower". In the absense of detonation most gasoline blends, regardless of octane, burn at the same rate as long as combustion is normal. If detonation is present - abnormal combustion - higher octane fuel will usually eliminate it. This is where the myth comes from. Yes, the total mixture is consumed faster if detonation is present, but this is abnormal combustion, which is a very different phenomenon that normal combustion. The myth stems from those who fail to understand this difference.

Now you can explain it the next time it comes up, which is sure to happen.

Duke.

[Stuart F.]

Re: lead additive

Bill;

The only issue you noted about using the lead additive (for those of us who can afford it) is possible shortened plug life. That has not been an issue for me since I went to electronic ignition many years ago. I now only change plugs as a matter of long term maintenance, not due to fouling from stop and go trafffic, etc. from back in the good old days. That is also why I use Champion plugs which are less prone to rusting into the heads like AC's.

Mere mention of electronic ignition conversions ought to keep this thread going for another year or so. Nothing lead additives and electronic ignitions to stir up some controversy.

Hope to see you again at the winter meet here this January.

Stu Fox