New member...425 questions
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500, 472, 425, 368 Discussion, New member...425 questions in Cadillac Engine Technical Discussion; Hello from a new member. I purchased a 52 Merc as a project. I aquired a '77 Caddy 425 engine ...
  1. #1
    The Butcher is offline Cadillac Owners Member
    Automobile(s): 1977 425 in a 1952 Merc (please dont shoot me)
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    New member...425 questions

    Hello from a new member.
    I purchased a 52 Merc as a project. I aquired a '77 Caddy 425 engine and transmission from a friend who scrapped the car which was junk. The engine and trans have around 60K on them. She ran when taken apart, but after giving it an exterior power wash, I decided to put a cam in and get the heads done.....may as well do it right. Anyhow, I am ready for reassembly, but am wondering (since this is a budget project) what cam I should go with for a bit extra power and sound, but that will be a good match to the stock heads and intake.
    Also, the rearend on my project is a GM with 3:73's.....I imagine this will be a good match for my engine?
    Any input is greatly appreciated

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  3. #2
    Angry Matt's Avatar
    Angry Matt is offline Cadillac Owners Enthusiast
    Automobile(s): (2) '81 FWBs, '86 Cutlass Supreme
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    Re: New member...425 questions

    The tranny is only a three speed, I have 3.23's with mine (472/th400) and I'm out of gear at just over 100mph. My only concern would be with the highway driving, your gas mileage is going to suffer and I don't like running my engine at high rpm's for a long period of time. Other than that, I think that rear will be nice and quick off the line.

  4. #3
    The Butcher is offline Cadillac Owners Member
    Automobile(s): 1977 425 in a 1952 Merc (please dont shoot me)
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    Brunswick, OH
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    Thread Starter

    Re: New member...425 questions

    Angry Matt,
    Thanks for the reply. Now that I know for sure (after doing some research) what tranny came with this 425 I can see that the lower gears made it the infamous torque-monster it was known to be. With my higher gears I can see it being quicker off the line and on normal streets, but may be a screamer at highway speeds. We will see, and if it becomes too stressful on the motor to ha ve these higher gears, then I change them out I guess.
    I appreciate the response back to my post. From what I understand, this motor as well as the tranny are basically bulletproof and a favorite among many hot-rodders.
    I should mention also, that the Caddy back in 77 weighed around 4500 lbs....? My Merc when finished will only weigh around 3200 lbs......I believe this factor will also make for one hell of a nice street rod even if I leave that big block alone and don't mess with huge expensive upgrades.
    Take care......look forward to others' feedbacks on my 425 big block...

  5. #4
    deVille33 is offline Cadillac Owners Connoisseur
    Automobile(s): 1977 Coupe (blue), 1977 Coupe (yellow), 1977 Coupe (green)
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    Re: New member...425 questions

    You may want to concider an overdrive unit. It depends on how much money you have to play with. An American Gear unit can set you back quite a chunk. There are some overdrive transmissions you can use, but again, your going to have to shell some out. If you bring your gearset down to 3.23 you'll still be reving this engine on the high end of it's range. How tall a tire can you run on the rear axle? Taller tire will help here, depends on how your car is set up. Standard tire size for these engines is comparable to a P225/75-15R, which is a relatively tall tire on it's own.

  6. #5
    BRUCE ROE is offline Cadillac Owners Fanatic
    Automobile(s): Eldorado
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    Re: New member...425 questions

    That trans should be fine, except the seals may be turning rock hard. Get new internal seals & gaskets for reliability; I would not touch the other internals. And put a new timing chain on the motor too. Bruce Roe CLC # 14630

  7. #6
    steelybill is offline Cadillac Owners Enthusiast
    Automobile(s): '85 Fleetwood FWD
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    Re: New member...425 questions

    That '77 Caddy likely weighed more than 4500 lbs. My '76 Coupe DeVille was 5300 lbs on the title. You should have a fun ride!!
    My '76 had a 2.67 ratio rear end.

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