what year did they swich from leaded to unleaded. and what dose lead do to the gas

 

Lead is an anti-knock agent, but when the EPA mandated lower hydrocarbon emissions (HC), catalytic converters were invented to burn the extra gasoline in the exhaust. The catalyst is Platinum, which gets coated and rendered ineffective by even small amounts of Lead, so unleaded gas was developed. It uses other (cheaper) anti-knock agents. The change began around '75 and was complete around '85.

 

Lead also helped to conduct heat between the valves and the head, and lubricate the valve stems.
A low-octane fuel in the 60's was around 95, with over 110 available at the pump. I can only imagine what kind of power we'd be able to get out of engine with todays technology and yesterday's gas.

 

So if i would buy a 76, 77, 78, or 79 ford would it take leaded or unleaded

 

More than likely it would take Unleaded, considering the fact the EPA reg's had taken effect in 75. At least i know my 76 had "Unleaded Fuel Only" written above the fuel gauge.

 

thanks

 

Any vehicle after 74 should be able to run on either, unless it specifically says "Regular Fuel Only", "Leaded Fuel Only", etc. 74 was the first year for federally mandated catalytic converters.

 

To reduce HC emissions, the AIR (air injection reaction) system was developed. The Ford brand is "Thermactor", but the common term is "smog pump." This promotes further combustion by adding fresh air (additional O2) into the exhaust gas just downstream from the exhaust port, where the exhaust is still hot enough to burn. AIR was introduced in CA as early as 1967.

The catalytic converter catalyzes CO and HC into H2O and CO2. It also requires a little extra oxygen, which the AIR system supplies.

Beginning in MY1975 (i.e., autumn of 1974), the USEPA required all light-duty vehicles (under 6000 lbs GVW) sold in the US to be equipped with catalytic converters. At that time, unleaded fuel had to be available to keep from damaging the catalytic converters. Leaded fuel was completely phased out in CA by 1988, but it remained available for road use until the mid '90s in some locales.

As steve83 said, lead was used as an anti-knock agent. It effectively increased the octane rating of the fuel. A side-effect was that it helped lubricate the valve seats (not the stems).

When manufacturers started producing vehicles with catalytic converters, valve seats in cylinder heads were hardened to resist excessive wear without lead lubrication from the fuel. Any cylinder head manufactured in the 1975 model year or later should work fine with unleaded fuel. Earlier heads can have hardened valve seats retrofitted.

If you want to see what can be done with high octane and modern technology, look at the vehicles available now in the Australian market, where 100 octane road fuel is readily available. For example:

http://www.fpv.com.au/index.asp?link_id=2.162

 

Only the very newest catalytic converters have ANY effect on CO. Until ~'95, they ONLY reduced HC emissions.

 

Both two way and three way cats removed HC and CO. The three way cats also removed Oxides of Nitrogen (NOx).

 

I think you're confusing CO with NOx. All cats oxidize CO and HC. The newer generation (so-called 3-way) cats oxidize CO and HC, and reduce NOx to NO and O2.

Here's an article that has some explanation on the CA SmogCheck Web site:

http://www.smogcheck.ca.gov/stdPAge....s-Sep_1998.htm