LSx conversion in a 77-79 DeVille
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RWD 19xx-1984 DeVille and Fleetwood,
1985-1996 Fleetwood and Brougham Forum Discussion, LSx conversion in a 77-79 DeVille in Past Cadillac Vehicle Discussion; So I have been searching but I haven't come up with any threads on this, so if it's out there ...
  1. #1
    TheCadillacKid's Avatar
    TheCadillacKid is offline Cadillac Owners Member
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    LSx conversion in a 77-79 DeVille

    So I have been searching but I haven't come up with any threads on this, so if it's out there I apologize.

    Has anyone put an LS series engine in there 77-79 DeVilles or know of someone who had done it?

    I have a 2000 Camaro with an LS1, and it runs so well and is decent on fuel. I like having the 425, but let's face it, I'm getting like 6 miles to the gallon if I'm lucky.

    I figure an LS1 or a LS2 would be real nice for ever day driving. Just wondering about engine and transmission mounts/crossmember and drive shaft... I don't think oil pan should be an issue...

    Any thoughts?

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    cadillac kevin's Avatar
    cadillac kevin is offline Cadillac Owners Master
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    Quote Originally Posted by TheCadillacKid View Post
    So I have been searching but I haven't come up with any threads on this, so if it's out there I apologize.

    Has anyone put an LS series engine in there 77-79 DeVilles or know of someone who had done it?

    I have a 2000 Camaro with an LS1, and it runs so well and is decent on fuel. I like having the 425, but let's face it, I'm getting like 6 miles to the gallon if I'm lucky.

    I figure an LS1 or a LS2 would be real nice for ever day driving. Just wondering about engine and transmission mounts/crossmember and drive shaft... I don't think oil pan should be an issue...

    Any thoughts?

    There are a few guys who have done it on the impala ss forum. Stingroo is currently putting one in his wagon.

  4. #3
    77CDV's Avatar
    77CDV is offline Cadillac Owners Master
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    Re: LSx conversion in a 77-79 DeVille

    If you're only getting 6 mpg from your 425, there's something wrong. Even around town, this engine should be returning 10-12 mpg, and 15-17 mpg on the open road. Not stellar, I admit, but still. I'd personally address the issues with your 425.

  5. #4
    csbuckn is online now Cadillac Owners Master
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    Sting better post a link in the picture thread....or else....lol

  6. #5
    Bro-Ham's Avatar
    Bro-Ham is offline Cadillac Owners Connoisseur
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    Quote Originally Posted by 77CDV View Post
    If you're only getting 6 mpg from your 425, there's something wrong. Even around town, this engine should be returning 10-12 mpg, and 15-17 mpg on the open road. Not stellar, I admit, but still. I'd personally address the issues with your 425.
    The above is oh so very true. The 425 is one of the very best of the last true Cadillac engines.

  7. #6
    Stingroo's Avatar
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    Re: LSx conversion in a 77-79 DeVille

    Quote Originally Posted by csbuckn View Post
    Sting better post a link in the picture thread....or else....lol
    lol That is not a Cadillac Forum approved project. No fun to be had here for that type of stuff.


    Yes - you could LS swap it pretty easily. You could run a carb'd 6.0 and have a Cadillac worlds faster than GM ever intended, but then you get to go through the brakes, rear end, steering.... it never ends. As Smoky the Bear says: Only YOU can decide how far you want to go with your project and how much money you want to throw at it.


    ...well, those weren't his exact words, but I paraphrased.
    77CDV and talismandave like this.

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    cadillac kevin's Avatar
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    Quote Originally Posted by Stingroo View Post

    lol That is not a Cadillac Forum approved project. No fun to be had here for that type of stuff.

    Yes - you could LS swap it pretty easily. You could run a carb'd 6.0 and have a Cadillac worlds faster than GM ever intended, but then you get to go through the brakes, rear end, steering.... it never ends. As Smoky the Bear says: Only YOU can decide how far you want to go with your project and how much money you want to throw at it.

    ...well, those weren't his exact words, but I paraphrased.
    Thank god for the aftermarket given to us by impala ss guys

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    TheCadillacKid's Avatar
    TheCadillacKid is offline Cadillac Owners Member
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    I do love that 425 cubic inch under the hood of my 79 Coupe deVille... and yes I will be addressing the issues with it. The car has been taken care of for the most part over the years. The second owner had a fleet of cars and I think was having trouble keeping up with all of them. So she does need a complete tune up and I'm also going to completely rebuild the carburetor... I don't believe it's ever been touched. It brings back so much nostalgia when I get those secondaries to open up --love that sound!

    I wouldn't mind having the fastest 79 Cadillac Coupe deVille to torment my neighborhood a little more... but really would keep the LS1 or 2 stock and dare I say quite. I would even keep catalytic converters...

    It's just something I was thinking about, between the 3 cars I have I don't have the money for that project... yet!

  10. #9
    deVille33 is offline Cadillac Owners Connoisseur
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    Re: LSx conversion in a 77-79 DeVille

    Do not go through the Q-jet carb until you have gone through a complete tune up procedure at least once. The Rochester Q-jet is one of the most reliable units on your engine. Get a Service Manual for a '77 - '79. The described settings are similar throughout these three years ( with a few variations, but any will work on a base line ). Understand and follow the procedure as described, but, before you do, check all the vacuum hoses for leaks and cracks. The vacuum systems on these engines are extensive and have a major influence on how well your engine runs. Check all vacuum canisters and the dashpots that they hold the proper vacuum for the required amount of time. You would be surprised that people often go through the carbs when the dashpot motors are the main problem. Also check out your distributor. Sticky mechanisms, worn flyweight parts, and rust can effect the mechanical advance. A little dab of lithium grease will go a long way. Don't forget the Vacuum Advance canister.
    Then go through the settings for your Q-Jet. Get out your feeler (gap) gauges and check the settings. Hope you have a lot of patience, because the procedure can be tedious. If all your support units for the vacuum system are working properly, you should be able to get at least 16 mpg.

  11. #10
    larryinalabama is offline Cadillac Owners Fanatic
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    Re: LSx conversion in a 77-79 DeVille

    Ive alsways wondered what one of these would do on a 425.

    http://www.summitracing.com/parts/hly-502-20s/overview/

    But then the Qudrajet has an outstanding reputation.

    As far as taking a 425 out, that's a giant step Backwords.
    pompste likes this.

  12. #11
    deVille33 is offline Cadillac Owners Connoisseur
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    Re: LSx conversion in a 77-79 DeVille

    Bruce has been working with the factory injection system for the 425 for a long time now. He has been tweaking it in an attempt to get mpg over 20. This system does get the 425 better mpg than the Q-Jet, ( I think Bruce last recorded 19 ) but it is complex and needs understanding if you are going to install it on your car. The TBI system was the corporate answer ( experiment ) that soon was overshadowed by other more efficient means of fuel induction ( Tunnel-Port, EFI ). Perhaps the offering by Summit will give more than the Q-Jet without the complexities of the factory injection system, but the engine still has to be tuned-up and properly set up to get you there.

  13. #12
    Stingroo's Avatar
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    Re: LSx conversion in a 77-79 DeVille

    Quote Originally Posted by larryinalabama View Post
    Ive alsways wondered what one of these would do on a 425.

    http://www.summitracing.com/parts/hly-502-20s/overview/

    But then the Qudrajet has an outstanding reputation.

    As far as taking a 425 out, that's a giant step Backwords.
    Taking an ancient, carburbureted 425 cubic inch boat anchor out and putting in a modern all-aluminum power plant with fuel injection and the latest technology is a step backwards?

    But dropping $1200 on an ancient TBI-based fuel injection setup is a possible alternative?

    Yep. There we go. We're still on the Cadillac forum.

  14. #13
    the APEMAN is offline Cadillac Owners Fanatic
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    Re: LSx conversion in a 77-79 DeVille

    Quote Originally Posted by Stingroo View Post
    Taking an ancient, carburbureted 425 cubic inch boat anchor out and putting in a modern all-aluminum power plant with fuel injection and the latest technology is a step backwards?

    But dropping $1200 on an ancient TBI-based fuel injection setup is a possible alternative?

    Yep. There we go. We're still on the Cadillac forum.
    You would be correct if the modern engine had no cost.

  15. #14
    Stingroo's Avatar
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    Re: LSx conversion in a 77-79 DeVille

    Quote Originally Posted by the APEMAN View Post
    You would be correct if the modern engine had no cost.
    I'm still correct. For all intents and purposes, it's the best "step forward" you could ever take.

    Advancement costs money.

    Want your car to handle better? Spend money.
    Want your car to look better? Spend money.
    Want it to perform better? Spend money.
    Want it to be more efficient? Spend money.

    Doesn't matter how you achieve it, really. Money makes the world go 'round.

  16. #15
    larryinalabama is offline Cadillac Owners Fanatic
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    Re: LSx conversion in a 77-79 DeVille

    The whole problem is sort of like this......................

    Mustangs, Cameros, Firebirds and Corvettes are highly collectable......................but the New Ones are a whole lot BETTER.

    We RWD Cadillac collectors don't have a lot of options, as there will never be another one made, so a better new one is not going too happen.

    The 425 was a Fine Power Plant, only reason I suggested projection was a direct replacement for the carburetor, which should increase mileage and power slightly, as well as driveability and cold starts.

    As I see it, it wouldn't be worth the costs and trouble to try and make the car a 2014 running car. At least that's not why I collect them.

    IN my 1990 , on trips I have gotton as good as 24 MPG in my "throttle body" 350 Brougham, and even by modern standards that's exceptional.
    77CDV, pompste and talismandave like this.

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