Were any of the old Ford engines that came stock in Cougars designed to be run on leaded gas? This is a subject I’ve almost never heard mentioned but recently saw an episode of Wheeler Dealers where they had the valve seats rebuild because the car they were working on had originally been designed to run on leaded fuel. So I got to wondering, is this an issue with any of the old Ford engines from the Cougar era? And if it is, then is using lead additive a solution, need to get the heads reworked, or something else?
I don’t believe there was unleaded gas in 1968. I don’t think it became readily available until the late '70’s. The solution that I’ve heard is to get hardened valve seats installed.
In a funny twist, the TR6 episode of Wheeler Dealers is on again right now, I just watched the valve seat replacement part. 
So Al have you ever had hardened valve seats installed? Or are you just running unleaded without changing anything?
You’re asking the wrong guy there, I’m not running anything at the moment. It’s on the to do list though.
As long as I can remember Amoco had Hi test white gas, unleaded. I helped out in a paint and body shop back in 59 and they used white gas to wipe down the cars before paint, they only had enamel or lacquer at the time.
I talked with my machinist about harden seats, and he said if you are only going to use for show or weekend driving, that is not necessary, but for daily use he would recommend it. I use unleaded fuel in all my cars and add a product called CD-2 lead substitute 1/2 oz to 5 gals. It comes in a 32oz bottle and is cheap.
Bottom line, your Cougar was designed to use leaded gas. Do you need hardened seats? Depends on how much driving you do, and what kind of gas you use. You can buy 100 octane unleaded street legal gas, which would solve the problem. Or use 3 gallons of leaded 110 octane race gas mixed with 9 gallons of 92 octane unleaded.
None of the octane boost additives do anything worthy of note except waste your money.
Installing hard valve seats allows you to operate the engine with less ignition timing for long periods. That way the engine does not “ping” with the crappy 92 octane fuel. Often it is also best to use stainless steel valves, because hard seats can cause rapid wear on OE style steel valves.
Plus the exhaust fumes from race fuel smells like candy and turns your exhaust tips white.
The common wisdom is what Royce said, if you don’t drive a lot of miles, you should not have a problem. On my build, I put in hardened seats (exhaust only are needed - don’t think this point was touched upon) and I run SS valves, mostly because I had facilities available to me in order to do this work.
I’ve often wondered about this myself and the dealer has hand written to use “premium fuel” on the original window card.
So to play it safe I try and only use 98 octane and from time to time 95, but then I would struggle to travel 1000miles pa.
I’ve run my 68 daily for over 8 years now almost exclusively using unleaded (non-ethanol, 91 octane or better) and while I am sure there’s been some wear on the valves, so far she still runs good. Of course, I generally drive like an old man so that may have something to do with it.
Yeah, what Royce said.
As a side note, the stock valves in the canted valve engines of classic Cougars and anything 351m/400 powered need to be changed because they used a 2 piece valve. I’d put new valves in and valve seats and run whatever gas I felt like running, especially in your Bronco, if you haven’t already.
My buddy Keith had issues from an aggressive aftermarket cam (Comp Cams 292 Magnum) causing issues to the 351C-4V in his ‘winter beater’ '72 Gran Torino Sport… It ended up pounding the valves hard enough against the seats in the heads that the seats ‘regressed’ (the valves pounded the heads) to the point where the valve ‘seats’ were so far sunk into the heads that the car barely ran. So he parked it. Then the car’s frame broke (Cleveland rust). Engine yanked and is still to this day on engine stand. Car becomes tube-chassis race car with a 514 stroker motor… It has been happy for 15 years since!
I was using the CD-2 additive until I thought about it for a while.
My car averages around 1,500 miles/yr, so I’m saving the $10-12 a bottle and buying better stuff in bottles!
Note to self Do NOT drink scotch at catman’s house.
As a fellow scotch drinker, I wholeheartedly agree. 