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500, 472, 425, 368 Discussion, running unleaded in a classic caddy in Cadillac Engine Technical Discussion; Oh yeah, we are well know here for our 'fruits and nuts'. There are a lot of goofy ideas that ...
  1. #16
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    Re: running unleaded in a classic caddy

    Oh yeah, we are well know here for our 'fruits and nuts'. There are a lot of goofy ideas that govern this state. Never forget though, the old saying; "As California goes, so goes the nation." Enjoy the good stuff while you can boys and girls, it may not be long before you are treated to the same regs as we.

    We are the Nation's guinea pigs........

  2. #17
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    Re: running unleaded in a classic caddy

    Definately run premium. If the car still has its owners manual, it will probably say that. I know my 1970 owners manual (10:1 compression) says to run premium.

    Don't trust the previous owners to know what the car should need. The guy I bought my car from was running 87. Also complained about loss of power under heavy load. Probably because it was pinging. Trust me, this 472 has no trouble hauling 5500# of steel up some really steep hills with the cruise on!

    It is not the valves that need to be switched for unleaded, it is the exhaust valve seats in the head. Some have said that Cadillad heads (at least on the 472/500's) are tough enough and do not need lead additive. I still run lead additive in my '70 anyways. It is cheap and will ease my mind untill I get hardened valve seats put in sometime.

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    Re: running unleaded in a classic caddy

    Quote Originally Posted by BluEyes
    Definately run premium. If the car still has its owners manual, it will probably say that. I know my 1970 owners manual (10:1 compression) says to run premium.

    Don't trust the previous owners to know what the car should need. The guy I bought my car from was running 87. Also complained about loss of power under heavy load. Probably because it was pinging. Trust me, this 472 has no trouble hauling 5500# of steel up some really steep hills with the cruise on!

    It is not the valves that need to be switched for unleaded, it is the exhaust valve seats in the head. Some have said that Cadillad heads (at least on the 472/500's) are tough enough and do not need lead additive. I still run lead additive in my '70 anyways. It is cheap and will ease my mind untill I get hardened valve seats put in sometime.
    actually i did get with the car the owner's manual and the service manual for the car and neither say what octane of fuel to use so i'm gonna buy 93 unleaded and just throw some lead additive in there.

  4. #19
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    Re: running unleaded in a classic caddy

    I would recommend running premium. It may cost more, but you will be able to run the timing at or near spec and ut will be easier on the engine.

    Retarded timing leads to lack of power and higher running temperatures. Along with poorer fuel economy.

    If you drive the car in a normal fashion, not hard or pulling a lot of heavy loads, it will be fine without the additive. In Canada we have been without leaded gas since 1990 and I have been running my '70 on premium unleaded (Sunoco 94) since I bought it in '93. I have not had any issues with the engine whatsoever.

    , Mike

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    Re: running unleaded in a classic caddy

    I ran my 70 Eldorado in the US on Premium. But it has the one and only 500 with that high CR. The later Eldo's 500's came with lower CR.

    Here in Holland we have 95/98 and even 98 with lead substitute on the tab. In Germany there is also 91. Though I think in Europe the Octane number is calculated differently than in the states, so I don't think the actual difference is that big.

    My 500 has been totally overhauled with harder valve seats, so I don't have to worry about unleaded...

    Congrats with your classic Framingham!

  6. #21
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    Re: running unleaded in a classic caddy

    Actually, all Caddies up to '70 had high compression, not just the Eldos. '71 and later GM had mandated a max 9:1 compression.
    I'm pretty sure you Europeans actually have higher octane. Our EPA prevents alot of octane-enhancing chemicals from being used and I believe Europes standards are less strict (kinda like why Hi-Po European cars lose 10-20HP due to the US emissions regs). In the US we use the (R+M)/2 method for octane. They ought to post what method is used to calculate octane somewhere on the pump.

    My owners manual doesn't list a specific octane number though, it just says premium. I suppose that would have been 100 octane back in 1970, but 92 works fine, even with advanced timing and full time vacuum advance.

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    Re: running unleaded in a classic caddy

    Wow, I thought it was a calculation difference. That solves a lot for me. Indeed the manual says premium and no actual octane number. I'm going to save some money on both driving my 70 Eldo as my CTS!

    Oh, I knew about the other models up to 70 had the high CR. I just meant from the 500's the 70 Eldo had the highest CR...

  8. #23
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    Re: running unleaded in a classic caddy

    Quote Originally Posted by 70eldo
    Here in Holland we have 95/98 and even 98 with lead substitute on the tab. In Germany there is also 91. Though I think in Europe the Octane number is calculated differently than in the states, so I don't think the actual difference is that big.
    You use the Research method. We use the Research + Motor average method... (R+M)/2. Research has a tendency to be higher than motor. However there's no real way to exactly convert (R+M)/2 to R or vice versa since the M component is missing... So you're correct, the actual difference isn't that big.

  9. #24
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    Re: running unleaded in a classic caddy

    I wouldn't worry about the lack of lead in the fuel. Unless you are running the engine for extended periods of time at heavy or full throttle the exhaust valve seats will be fine. Usually engines that are run at heavy throttle openings (such as in boats and airplanes) are the ones that need the lead in the fuel to help lubricate the valve seats to prevent wear and recession of the seats. Boats engines were basically converted over to unleaded fuel via engine replacement over the years. Aircraft fuel (for light plane, piston engines) still has lead in the fuel due to the number of engines out there that are not set up for unleaded operation....but unleaded Av gas will come along soon I bet.


    In any case, light throttle operation with unleaded fuel is fine and the engine will run forever on it.

    Interesting that lead was added to the fuel along about the mid-40's for octane improvement and people discovered that the valve seats lasted longer with lead due to the lubricating properties. When lead was removed, everyone was concerned about the valve seat wear.... Lead wasn't put in for that, it was put in for octane improvement.

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    Re: running unleaded in a classic caddy

    Also, on the subject of exhaust valve seats......the high heat of the exhaust gases will, to a certain extent, "heat treat" the valve seat area making the outter most surface hard lessening the need for hardened seats.

  11. #26
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    Re: running unleaded in a classic caddy

    Quote Originally Posted by chevelle
    I wouldn't worry about the lack of lead in the fuel. Unless you are running the engine for extended periods of time at heavy or full throttle the exhaust valve seats will be fine. Usually engines that are run at heavy throttle openings (such as in boats and airplanes) are the ones that need the lead in the fuel to help lubricate the valve seats to prevent wear and recession of the seats. Boats engines were basically converted over to unleaded fuel via engine replacement over the years. Aircraft fuel (for light plane, piston engines) still has lead in the fuel due to the number of engines out there that are not set up for unleaded operation....but unleaded Av gas will come along soon I bet.


    In any case, light throttle operation with unleaded fuel is fine and the engine will run forever on it.

    Interesting that lead was added to the fuel along about the mid-40's for octane improvement and people discovered that the valve seats lasted longer with lead due to the lubricating properties. When lead was removed, everyone was concerned about the valve seat wear.... Lead wasn't put in for that, it was put in for octane improvement.
    Thats incorrect.

    Lead is used to lubricate the valve stems. Before unleaded fuel, valve stems did not have a chrome plating on them. The lead was there to lubricate the stems to keep them from wearing down. The lead also caused the fuel to burn much cooler which worked well with un-hardened valve seats.
    Unleaded fuel came around and they had to put chrome on the valve stems to keep them from wearing down due to the lack of the lead lubricant (chrome is tough stuff!) And they now had to use hardened seats because the fuel was burning much hotter without the lead in it. And so it continues.


    Quote Originally Posted by lux hauler
    Also, on the subject of exhaust valve seats......the high heat of the exhaust gases will, to a certain extent, "heat treat" the valve seat area making the outter most surface hard lessening the need for hardened seats.
    Perhaps that is true but they get damaged in the process. Plain and simple you need updated valve seats for today's fuel to prevent any damage. Thats fact.

  12. #27
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    Re: running unleaded in a classic caddy

    Quote Originally Posted by lux hauler
    Also, on the subject of exhaust valve seats......the high heat of the exhaust gases will, to a certain extent, "heat treat" the valve seat area making the outter most surface hard lessening the need for hardened seats.
    I would have to disagree on this idea. There are two basic ways to heat treat steel (there are many other more complicated methods but for this converstation let's keep it simple).

    1. Heat the metal evenly until it is cherry red and then dowse it in cold water. This causes the steel molecules to condense quickly creating a more dense and brittle structure.

    2. Heat the metal evenly until it is cherry red and then dowse is in oil (30W). This causes the molecules to condense more slowly than the first, the effect being a hardened exterior with a softer core. The metal is less brittle, more durable in the long run.


    Now, with either of these methods, if the steel is heated again it will loose it's temper, either become softer again or become fatigued and subject to damage. Here is the problem with the idea that the seats are hardened with the heat of the engine. They are heated and cooled over and over, but not enough to truly temper them, though the expansion and contraction resulting from the heating and cooling that they experience will have the effect of fatiguing them in time.

  13. #28
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    Re: running unleaded in a classic caddy

    Also, by the time you get steel hot enough to heat treat it, doesn't it also start getting soft? So, if we were getting the exhaust valve seat soft enough to heat treat it while the motor was running, wouldn't that end up with significant deformation due to the pressure of the valve against the seat? I mean, I recently bent a wrench to fit in a tight space using a propane torch. The wrench handle never even got red, but I was able to bend it 45* without that much trouble.

    I have never heads anything about the lead being to lubricate the valve stems. Is so, how come the fix for unleaded gas is the hardened seats, and no mention of the valves themselves?
    Also, if lead causes the mixture to burn that much cooler, you would be making less power on leaded gas

    Sorry, but the '70 Eldorado doesn't have the highest compression. All Caddy models up to 1968-69 had 10.5:1 compression. 1970 they all had 10:1, 1971 and later got 8.5:1 . But, in any given year the compression ratio was the same across the board for Eldorados, Devilles, Fleetwoods, and the Calais...
    You are right that 1970 Eldorados are the only car that got a high compression 500ci motor.

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    Arrow Re: running unleaded in a classic caddy

    Quote Originally Posted by BluEyes
    Sorry, but the '70 Eldorado doesn't have the highest compression. All Caddy models up to 1968-69 had 10.5:1 compression. 1970 they all had 10:1, 1971 and later got 8.5:1 . But, in any given year the compression ratio was the same across the board for Eldorados, Devilles, Fleetwoods, and the Calais...
    You are right that 1970 Eldorados are the only car that got a high compression 500ci motor.
    Well, I did not say the 70 Eldo had the highest CR of all Cadillacs. I did say, as you mention in your last line, that it was the highest CR rated 500

  15. #30
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    Re: running unleaded in a classic caddy

    Quote Originally Posted by JTraik
    Plain and simple you need updated valve seats for today's fuel to prevent any damage. Thats fact.
    How do you explain the tens of millions of miles people have put on these motors without adding lead? You paid for the valvestems and hardened seats so now you're defending your purchase.

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