hey
So, through auto mech. school, working on cars for 10 years, and having many mechanic friends, I have learned that lead does not increase octane. It protects the valves.
Now, some yahoo in another forum is trying to tell me that lead raises octane,and thats why airplanes are allowed to run leaded fuel.
I dont belive it.
Who is right?

 

It does increase octane. That's why back in the day you could buy 100+ octane at any gas station. Once the feds said that the lead had to go bye bye, octane ratings took a massive nose dive.

AJ

Edit: Let me rephrase that. They didn't say bye bye to lead "persay", they introduced catalytic converters. Cats do not work with lead at all, so the lead had to go.

 

No it does not increase the octane level, it decreases the probability of detonation. Increasing the octane rating, not the octane level. Octane is a hydrocarbon with the formula C8H18

 

thats why all the muscle cars had crazy comp ratios like 11:1 on the street

 

DUDE!!!!!!!......

He didn't ask if it raised the octane level or the octane rating.

OK..... so you wanna be a picky ***..... how's this?

"It decreases the amount of detonation in an engine because it has lead in it."

There...... ya happy now?

AJ

 

Like he said, it doesn't raise the "octane", but it does increase the "octane rating", which is a measured resistance to detonation.

But it also lubricates the valve seats, which can actually make an engine last longer. Too bad it used to make a pile of real heavy sludge in the bottom of motors... that's one thing I don't miss about tearing apart old motors, that stuff was nasty beyond description (not to mention poisonous).

The "quality" of fuel is one of the most interesting studies of advertising vs. actual product. It's alot like the blind beer tests: about 95% of the population, even the ones that will swear they like this os that brand of beer or cigarettes, can't tell which one is theirs out of a group of blind samples. There's a huge amount of deliberately induced misunderstanding about how fuel works, and the oil companies do a great job of keeping it that way, mostly by ego appeals to those of us who consider our cars "special", to try to get us to pay more for the identical product out of one pump than out of another.

 

Aircraft engines run leaded gas for longer engine life. Actually a 4 banger cessna engine is about as complicated as a lawn mower engine. No timing advance, magneto ignition, carbureted. The timing is set at cruise rpm, which is why when you hear a small plane at idle, it kinda idles like crap. Less parts to malfunction, though, which is the whole point. Kinda makes you feel safer when flying from texas to michigan with your dad piloting a cessna skyhawk...

 

so if i get my hands on an old engine ('65 455 to be exact), never rebuilt, should i run race gas in it along with lead substitute or will premium be enough to keep it from knocking?

 

the "octane rating" you need to run will depend on another of things, including compression ratio, where timing is set at, and the condition of the motor. high compression, advanced timing, or a motor with a lot of carbon build up with require fuel with a higher resistance to detonation (higher octane rating). you will have to test out various grades of gas and determine which one the motor runs best on. you want to the run the lowest octane possible with the motor detonating.

 

octane rating also can depend on what cam you are running

or rather what octane rating you need


as well as intake and exhuast mods, porting to the heads, comb chamber shape, and all that stuff

 

You will need lead or additive to lubricate the valve seats. Engines from the 60s had non hardened seats.

 

very good point.....i forgot about that. yeah if the valves seats are original they will be non-hardened and will need the lead/lead substitute to lubricate them and help them survive

 

My brother was talkin about how he used regular gas in one of his cars that didn't have hardened seats, he put some kind of additive in the gas tank, forget the kind. anyone know/heard of this before.?

 

Mark, yes it is called lead substitute.

 

Yea, and the substitutes dont work worth a damn. Either plan on replacing the seats, or get different heads.

 

yep.
lead (plomo tetra-etilico, in spanish) its just to reduce detonation, so you can have higher compression, the problem with this is that is VERY CORROSIVE and get anywhere near it and you will end up with CANCER, so is is also VERY poisonous.
the most popular avgas now is 100LL (low lead), but you can also find 85 (red). when i was a rookie, there was still 115/145, that was wild, (it was created for the P&W R-4360 wasp major)
i remember setting most of the advances to 25 degrees (as per maintenance manual) and thats it. at the time a new computer controlled ignition was being developed for small aviation, but to the question...massive electrical failure, what do you do??? lose the engine and crash???, there was no answer so, it was not aproved, that was in 1995, i dont know now (i lost track of it)
have fun guys.
Fernando.

 

With leaded fuel you'll increase the smog and pollution and the catalytic will be clogged in a short time. In the next emission control your HC measurement will increase too.

 

I used lead sub in my 70 stang ran great no probs but I always ran sunoco 94 in it as well. I had a 351w in it till I put the 460 in it *** I love BB power

 

I just figured I'd add this. Most of us already know this, but since it hasn't been mentioned, I want to make sure somebody says it.

Leaded gas will wreak havoc on an oxygen sensor. If you're running an oxygen sensor, don't use leaded gas.

 

Not to mention your catalytic converter, It'll trash that too.


Now I'm no chemistry major, and while I am aware that Lead is very carcinogenic, it is not, to my knowledge, corrosive. Perhaps you are thinking of a lead-acid battery, in which the acid (sulfuric, in this case) is extremely corrosive, not the lead.

 

When boiling water, lead, carbon, and a few other chemicals found in the combustion process get together at high temperatures, it can form a slight acid, called lead acetate i believe. However i doubt it would be enough to do any damamge to an engine, as older engines last as long if not longer then most modern ones.

After speaking to my father who restores older cars as a living, he said that lead acetate can be very corrosive if left to sit for long periods. It is often a reason why older exhaust systems go bad(that "water" from the exhaust pipe in older cars contains this acid). However if your car is driven frequently it poses no corrosive problems to anything excet your exhaust, which will be minimized by not drving in cold whetehr as much as possible to prevent condesation. And the coatings it puts on internals, and increase of octane RATING much prolong engine life. Sry for the long post just though id share.

 

That had already been mentioned, which is why I omitted it.

 

Well, the chemistry-part of my brain has just kicked in. Lead Acetate is not an ACID. Not to say that it doesn't cause corrosion or damage, but that is not the defining point of an acid.

 

U are probly right, thast just what my chemisty book said, it has dissapointed me before. I think i see its not an acid because the H is not a H+ ion. Eitehr way the the EFFECTS are correct, sorry for any incorrect info.

Also, some history, lead acetate in part caused the fall of the roman empire, they boiled their wine in lead lined barrels, forming lead acetate(lead syrup, it has a sweet taste), which when injested has the causes lead poisening.

 

Engines are a strange beast, no use taking apart a perfectly good engine to have hardened seats installed in the heads, unless the valves start to recede.

No, not all pre-unleaded-days heads will have issues.

Ofcourse if you're into a rebuild on an early set of heads, spend the extra $$ and have hardened seats installed.

Interesting thing about the AV gas. Has it always had lead in it?