Does the '74 Eldorado w/500cid need premium?
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500, 472, 425, 368 Discussion, Does the '74 Eldorado w/500cid need premium? in Cadillac Engine Technical Discussion; The '74 Eldorado with the 500cid, I believe its compression is 8.5:1 or so, does it need premium fuel?...
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    eldorado99's Avatar
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    Does the '74 Eldorado w/500cid need premium?

    The '74 Eldorado with the 500cid, I believe its compression is 8.5:1 or so, does it need premium fuel?

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    Re: Does the '74 Eldorado w/500cid need premium?

    I've done a search on threads mentioning the 500 and most people who posted in those threads said they use or you use should premium in that type of engine. Especially if you have or are going to make some high performance mods to it. But also I would also say with it being properly tuned and maintained you might be able to get away with 87 or midgrade.

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    terrible one's Avatar
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    Re: Does the '74 Eldorado w/500cid need premium?

    Before I got my '76 ElDorado (same compression, engine size, etc.) my grandfather used to only put premium in it. I filled her up with 87 once, she ran great, and that's all I use now. Unless there is something wrong with it, it doesn't have to have premium.

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    Re: Does the '74 Eldorado w/500cid need premium?

    It depends on tuning. You can run 87 but 89 might pay off because of a little extra timing. If you hear spark knock then there is a problem. Make sure the EGR is working.

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    Re: Does the '74 Eldorado w/500cid need premium?

    It should run fine on regular as long as the timing and EGR are within factory specs.

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    terrible one's Avatar
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    Re: Does the '74 Eldorado w/500cid need premium?

    EGR= exhaust gas recirculation, right? Is that the valve at the end of the drivers side exhaust manifold?

    Just wondering because a long time ago mine was disconnected.

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    Re: Does the '74 Eldorado w/500cid need premium?

    That's what EGR stands for, but the valve is behind the carb. The valve on the exhaust manifold is the EFE valve.

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    Re: Does the '74 Eldorado w/500cid need premium?

    what about a '69 472 with 10.5:1 comp?

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    Re: Does the '74 Eldorado w/500cid need premium?

    Quote Originally Posted by Adumb
    what about a '69 472 with 10.5:1 comp?
    Use the highest octane rating you can get.

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    terrible one's Avatar
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    Re: Does the '74 Eldorado w/500cid need premium?

    Can someone descriptivly describe to me where the EGR valve is, or show me a pic? Just curious, thanks.

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    Re: Does the '74 Eldorado w/500cid need premium?

    Mr. EGR valve is mounted right on top of the intake manifold a few inches behind the carbonator. It is held in place with a couple of 1/2" bolts and has 1 vacuum line port. Top is a round stamped steel thingy and the base is cast iron. Weight is just about right to throw at passing Fords.

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    terrible one's Avatar
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    Re: Does the '74 Eldorado w/500cid need premium?

    Alright, as I should have expected, mine has a stopper at the end of it, instead of a line. How important is it? Where is the line from it supposed to go? Or should I just leave it as it is? No emmisions testing goes on around here.

    Thanks guys.

    About 20 years ago my gradnfather had a really bad head on collision in this car and whoever fixed it didn't do a very good job at all I'm always finding things like this.

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    The Ape Man's Avatar
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    Re: Does the '74 Eldorado w/500cid need premium?

    Everybody and their brother used to disable EGR back then. It was not generally understood. You should have a vacuum schematic on the fan shroud cover. If not then it's time for the factory service manual. The EGR goes to ported (not manifold) vacuum on the carbonator through some type of thermal switch which will not let the EGR come on with a cold engine.

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    terrible one's Avatar
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    Re: Does the '74 Eldorado w/500cid need premium?

    Well I think I'll just forget about it. It's not like it gets cold enough for it to come in handy here anyways. Plus it would mean getting the thermal switch and stuff.

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    Caddy112 is offline Cadillac Owners Member
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    Re: Does the '74 Eldorado w/500cid need premium?

    In my 77 Coupe De Ville, with low compression, it runs a hell of a lot better with premium gas and the timing advanced a little(where exactly I set it I do not remember). This car is picky, Amoco gas made it run so bad it was stalling all over the place, it likes Sunoco, Citgo, Shell and Texaco, have'nt tried anything else in it. Maybe the Amoco was just a bad batch of gas, but I am not taking that chance again, that was hell. In my experiences, carbureted cars can be tempermental, some will run just fine on regular gas, and others, regardless of high or low compression,will need premium to run right.

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