8-6-4 Motor
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500, 472, 425, 368 Discussion, 8-6-4 Motor in Cadillac Engine Technical Discussion; Hello, I'm new to this forum, but I am very pleased to have found it. As my name sugjests I ...
  1. #1
    Caddy_freak's Avatar
    Caddy_freak is offline Cadillac Owners Member
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    8-6-4 Motor

    Hello, I'm new to this forum, but I am very pleased to have found it.

    As my name sugjests I am a Cadillac freak, I've had Many different Caddy's over the years, but never one with the 8-6-4 motor. Well now I have one. It's a 1981 Fleetwood brougham D'elegance and it has 90,000 miles on it and seems to run well, it has been modified to run on all 8 all the time. The car is emaculate and is definetly a keeper. It was kept in a Garage when not driven and was well taken care for by previous owner.

    How good/Bad are these motors? I know less than nothing about them.
    Some people have told me that I should have a tow truck follow me around everywere I go! It can't posibly be as bad as the HT4100 can it?
    I've blown up plenty of them.

    I plan to drive it localy for a year or so, then swap a 350 chevy and turbo 400 trans in it next year. when I do swap should I go with Carburator? will computer adapt to throtle body on chevy motor?
    will it starve for fuel?
    Any comments/advice/oppinions would be most appreciated

    Thank you

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  3. #2
    elwesso's Avatar
    elwesso is offline Cadillac Owners Master
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    Re: 8-6-4 Motor

    The 8-6-4 is a solid engine.... Not perfect, but decent..... The only problems I know with it are the 8-6-4 solenoids..... But since you bypassed that I dont think youll have a lot to worry about..... The main thing is maintenance...... That will determine its reliability......

    Im not really sure on your other thing, but I dont think it will adapt...... You'll have to disable teh computer all together! Or I suppose you could get a FI kit for it (ive seen plenty on ebay, Im thinking of putting one on a 327 in a boat).....

  4. #3
    Ultra Slow is offline Cadillac Owners Fanatic
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    Re: 8-6-4 Motor

    THe 8-6-4 motor is great...I think it had a bad rap due to public stupidity... The HT4100 came after the 8-6-4 and was the websters definition of "junk"... I think people got confused to what was what and cadillac was not going to correct them as they were selling 4100's not 8-6-4's.

    The motor itself is as excellent as any 69-80 big block cadillac engine. The 8-6-4 part is not that bad, but the EFI is a bit of a pain. The idle problems are notorious from the "servo" that controlled the idle and the poor developed firmware in the computer. The best way to fix that is to take out the check engine lamp and set the servo to a good idle and leave it there. Its not what you want to do in a perfect world, but it works like a champ. You may have to reset it in winter/vs summer as there will be no AC idle kick up with this disabled.

    As far as reliablity... I had an 81 8-6-4 myself... Drove it to 120K... No issue other than idle. I put a switch to turn on/off the 8-6-4... Was a blessing when you got low on fuel, but never ran it unless I was pushing the fuel limit... I sold the car to a friend who drove it to over 250K... He sold it to his friend who is known for trashing anything he gets his hands on... I still know the car and it has over 500K on it with nothing but waterpump changes and very minor work. THe car is not kept up, looks like hell, but does not fail.....

    8-6-4... one of the most reliable engines ever built in this country.... NOT to be coufused with the HT4100.... The single worst engine in the history of GM.....

  5. #4
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    Re: 8-6-4 Motor

    Here's an idea. If the fuel injection acts up, the commercial setups still had displacement on demand, but they were carbureated. As far as how well the engine is built, I can vouch for that. My car has the first year for the block design, and it is extremely well built and reliable. Now the electronics on the other hand.....

  6. #5
    Caddy_freak's Avatar
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    Re: 8-6-4 Motor

    Well I feel much better about my car today, thanks for the info.

    I also read as many other threads as I could yesterday as I'm getting familliar with this forum, and seen many other post about this motor. I am very pleased!
    My car does however have this Funky idle That you mentioned, but not all the time. I checked the codes and the only one it had was code 33,

    It has a small exaust leak at passenger side manifold, so that will be the next thing I hit. Hope I don't brake any bolts in block!

    The motor runs extremly well and since it turns out not to be a lemon motor, I will delay my engine swap, might as well get all I can out of this one first.
    I will consider the idle fix mentioned above, thanks

  7. #6
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    Re: 8-6-4 Motor

    Thanks caddy freak i get it now. I think i want one now.

  8. #7
    Cadillac Pat is offline Cadillac Owners Member
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    Re: 8-6-4 Motor

    Welcome Cadillac freak, I'm Cadillac Pat (caddyforme on ebay).
    Please read my posts under anything here to do with the V8-6-4 as I have left a lot of valuable info.
    The V8-6-4, and all other 368's suffer from some of the same problems of early GM engines, but not as much as some others. Take the Olds 403 for example-it has "windowed" (a hole in the web) main bearing cap webs to reduce weight. This greatly affects it's strength and limits it's performance potential. GM didn't care about later performance upgrades like installing better heads and a 425 crank to utilize it's 4.351" bore to make an engine of over 500 cubic inches. The 368 suffers from small main oil galleries, which limits it's rpm and therefore it's performance potential to stock or slightly over stock. Additionally, it has scalloped heads and oil pan rails. "Scalloping" refers to removing metal between the bolt holes on the outside edge of the heads and oil pan rails to reduce weight.
    My favorite car (besides my '81 Coupe with a '72 500), is my '81 V8-6-4 Coupe which has 190,000 miles. I have heard of numerous cars easily making it over 200,000 miles. Have you ever heard of a 4100 making it to 200,000 miles? Maybe so, but they are few and very far between.
    Since the 368 has smaller oil galleries, routine maintenance, such as regular oil changes every 3000 miles and a quality filter are imperative. In the winter, I change my oil every 1000 miles, but I don't drive it much, mainly to work and back. Changing the oil myself is about $10 and worth every penny.
    As far as replacing the engine with a SBC, that is the wrong way to go. Because any stock 368, 425, 472 or 500 has more torque than your average SBC (i.e. not an LT-1, LS1 etc.), it is your best bet. Additionally, you can use the fuel injection system from the 368 on a 425 (abeit maybe not with the V8-6-4 system, but I intend to upgrade my 368 which is about the same thing) if you use bigger injectors (85 lb/hr if your car doesn't already have them) and/or the bigger Chevy 454 670 cfm throttle body. To install this, you will have to either modify the intake to accept the bigger throttle body or use a carbureted intake and throttle body adapter.

    Pat

    Quote Originally Posted by Caddy_freak
    Hello, I'm new to this forum, but I am very pleased to have found it.

    As my name sugjests I am a Cadillac freak, I've had Many different Caddy's over the years, but never one with the 8-6-4 motor. Well now I have one. It's a 1981 Fleetwood brougham D'elegance and it has 90,000 miles on it and seems to run well, it has been modified to run on all 8 all the time. The car is emaculate and is definetly a keeper. It was kept in a Garage when not driven and was well taken care for by previous owner.

    How good/Bad are these motors? I know less than nothing about them.
    Some people have told me that I should have a tow truck follow me around everywere I go! It can't posibly be as bad as the HT4100 can it?
    I've blown up plenty of them.

    I plan to drive it localy for a year or so, then swap a 350 chevy and turbo 400 trans in it next year. when I do swap should I go with Carburator? will computer adapt to throtle body on chevy motor?
    will it starve for fuel?
    Any comments/advice/oppinions would be most appreciated

    Thank you

  9. #8
    Caddy_freak's Avatar
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    Re: 8-6-4 Motor

    Well thank you Cadillac Pat, pleased to meet you.

    I will read all that you have written about the v8-6-4 motor as soon as finnish writing this, I'm sure I will find lot's of good stuff.

    I'm sure JJHOMER83 will read your post and go research on your past postings too, as we were disscusing this very subject yesterday.

    http://server.madisonross.com/~cadil...ead.php?t=4766

    I am very interested in reading all I can about the v8-6-4 motor, and all caddy motors for that matter

  10. #9
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    Re: 8-6-4 Motor

    Just a word on a 8-6-4 and HT4100 . I have to say from my experience, that 368 8-6-4 is a much better engine for a caddy. I used to have an 83 HT4100 Eldo and that was a disaster. I know that maintainance is a key, but there was always something going on with a HT, not to mention the head gasket leaks all the time (despite using GM sealers). I know I probably had a bad luck buying a poor maintained HT4100 engine,but still... it was just too much for me.
    About the 8-6-4. On the 8 cylinder mode this engine should do well. It requires less maintainance and is little bit more powerfull and has more torgue.
    I just got one and Iam glad it isn't HT4100.

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