Just curious if my '78 was originally made to accept unleaded fuel (hardened valve seats).

Also, does a 400 engine only require regular unleaded? I'm not sure what the compression is on these engines.

Thanks!

 

IIRC hardend valve seats started around 71-72 due to the coming introduction of unleaded gas for the 75 model year with cats. Your 78 should be able to drink unleaded.

 

Were the hardened valve seats in the 73 & 74 model years on all of these trucks? I have a 74 F250 would it have them?

 

If it's the same engine used in the cars with cats...yes. A 300 six?? Not sure. My best guess, the change would have been made across the product line.

 

If the motor is original to the truck, then you can go by the size of the fuel filler opening. If the truck takes unleaded fuel, the fuel filler opening is the smaller, modern diameter. If the truck took leaded fuel, the fuel filler opening is much larger.

 

I agree but my 77 F-150 does not say "UNLEADED ONLY" on the gas gauge like my dads 79 does and it has the larger filler opening. Seems like a leaded truck in 1977?

 

My dads and my 1978 have the large fill and does not say unleaded only, but my neighbors 1979 does say unleaded only.

 

Some trucks were exempt from cats for a few years. they could run both fuels.

 

First year for mandatory catalytic convertors and unleaded fuel was 1975 iirc. However, my 73 Monte Carlo recommended the use of unleaded fuel so it was more like a phase in. The narrowed filler necks were added in '75 to keep consumers from filling up with good old leaded fuel, which would render the convertor useless after a couple of tanks. Trucks were exempt for the first few years and I believe unleaded became mandatory in '79 on trucks. If you have the narrowed filler neck, it can be reasonably assumed you can burn unleaded. If not, I'd check back into manufacturer specs b4 delubricating a couple of valves.
All of this is from memory and past vehicles so I may be off by maybe a year but not likely more.

 

My understanding on cats is that they came standard on '78 F-150's, and larger trucks got them in '79. I'm not sure if that means '78 F-250's took leaded, both or what...

 

My '78 did not come with cats. I do believe that in California, they were required, but I'm not certain on this.

 

An original engine in your '78 will have hardened seats. It may or not have been required to run unleaded fuel. 49 state F150's and up were not required to run unleaded and had no cats. F100's came in under the federally mandated 6000#'s, and had cats. Ford got by this by coming up with the new in 1975 F150 model, rated at 6050#'s.

 

1975 and newer F-100's required cats and unleaded fuel.
1978 and newer F-150's in california required cats and unleaded fuel.
1982 and newer F-150's 49 state required cats and unleaded fuel, (Why the F-100 was dropped after the '83 model year).

By 1985 leaded fuel was banned in california, except for diesel.

my 1973 F-100 did not have hardended seats, 302-v8. The 78' most definately did, no matter what fuel it burned.


GVWR still regulates pickup trucks smog systems today. Why the 2011 F-150 can haul 10,000 lbs. The standard weight rating of a 1980 F-350.

 

Are those stats the same for a '78 F-250?

And are we talking regular unleaded that a 400 would burn? Not plus or premium?

 

A F-250 didn't require cats untill after 1980.

The 1978 would have hardened seats because the F-100 and F-150 shared simular engines.

Talking regular gasoline, 87 or 88* octane. they had 88* octane regular unleaded in the begining... etc...