3800 series II or III swap into 79 deville?
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RWD 19xx-1984 DeVille and Fleetwood,
1985-1996 Fleetwood and Brougham Forum Discussion, 3800 series II or III swap into 79 deville? in Past Cadillac Vehicle Discussion; I was thinking of trying to swap a Buick 3.8 V6 into my Caddy and see how close I can ...
  1. #1
    ferrisworld is offline Cadillac Owners Fanatic
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    3800 series II or III swap into 79 deville?

    I was thinking of trying to swap a Buick 3.8 V6 into my Caddy and see how close I can get to 30 mpg highway. I figure the series II and series III are the most efficient, but I know I read somewhere about an 80s box caprice with the 3.8 got 29 highway. Any ideas? I don't care if it's slow.

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    Stingroo's Avatar
    Stingroo is offline Wagon/Audio Enthusiast
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    Re: 3800 series II or III swap into 79 deville?

    The wiring would probably be a pain. It'd be interesting. Even a Series II supercharged 3800 can net you 26-28 highway if you drive it lightly - and 240 horses.

    Then again, an LS motor could also get you close to 30 mpg highway if left stock, and would give you a LOT more torque to move the beast (plus V8 rumble... can't go wrong there.).

  4. #3
    ferrisworld is offline Cadillac Owners Fanatic
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    Re: 3800 series II or III swap into 79 deville?

    Yeah but the LS would cost more.

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    cadillac kevin's Avatar
    cadillac kevin is offline Cadillac Owners Master
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    Re: 3800 series II or III swap into 79 deville?

    you might be able to eek 30 mpg out of a vortec 350 or lt1 dependent on gearing and tune. You could get mid- high 20's easy as long as you kept your foot out of it, so it wouldnt be impossible to get 30 mpg out of either motor (with proper trans and rear gearing choices of course and maybe slightly smaller injectors)

  6. #5
    CBodyFan is offline Cadillac Owners Fanatic
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    Re: 3800 series II or III swap into 79 deville?

    One of the reasons that Cadiilac's reputation tanked in the 80s was the lack of performance and reliability of the fuel economy-orientated engines: the V-8/6/4, Olds diesel, Buick V6 and the 4.1 V-8. During the first fuel embargo Cadillac sales were affected least among the full-size cars because Cadillac owners could afford the gas. The 80s saw Cadillac owners switch to Lincoln Town Car or the German makes, never to return. By switching from the durable and quiet 425 to a V-6 in a car of still ample proportions you'll just be repeating Cadillac's past mistakes. Why not use the money to have a more fuel efficient car for daily driving and leave the Coupe DeVille for leisure driving?

  7. #6
    Stingroo's Avatar
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    Re: 3800 series II or III swap into 79 deville?

    Look at the 5.3 liter LS motors. They're surprisingly inexpensive, relatively speaking.

  8. #7
    cadillac kevin's Avatar
    cadillac kevin is offline Cadillac Owners Master
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    Re: 3800 series II or III swap into 79 deville?

    the 3800 is a reliable engine, but there is a noticeable weight difference between a box caprice and a fleetwood brougham. also, the caprice likely had the 3.8 in it (from the 80's), which is not related to the 3800 family.
    that being said, the 3800 will have to work harder than usual to pull a 5000 lbs car.
    fwiw the 3.8 used in the 1980's was awful in larger cars, and most of them ended up being junked in a few years due to overheating issues on hilly terrain (too much strain on the underpowered engine). they were great on fuel mileage, but awful with respects to performance and reliability. Although, it wasn't the engines fault it was installed in a car it was never design for.

  9. #8
    brougham is offline Cadillac Owners Master
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    Re: 3800 series II or III swap into 79 deville?

    Youd be better off building a 350 for gas mileage. You might not car if the car is slow but that also means worse fuel mileage. If the 3.8 would work half decently in a larger car like the Cadillac and delivered good fuel mileage it would have been an option during the 90s.

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    jayoldschool is online now GM RWD V8 addict
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    Re: 3800 series II or III swap into 79 deville?

    The 80s Caprice didn't get the 3800. It got the 4.3 V6. I had an 88, with OD (you could get it earlier without OD, the TH200). Got good mileage, but not 30mpg...

  11. #10
    cadillac kevin's Avatar
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    Re: 3800 series II or III swap into 79 deville?

    Jay, didnt some b-bodies also come with the 3.8 (IIRC lesabres did in the early 80's but I could be mistaken)

  12. #11
    Stingroo's Avatar
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    Re: 3800 series II or III swap into 79 deville?

    A 4.3 is a 350, without any of the benefits of being a 350.

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    jayoldschool's Avatar
    jayoldschool is online now GM RWD V8 addict
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    Re: 3800 series II or III swap into 79 deville?

    All the power of a four cylinder, with the fuel economy of a V8!

  14. #13
    ferrisworld is offline Cadillac Owners Fanatic
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    Re: 3800 series II or III swap into 79 deville?

    Well let's see. My Deville weighs about 4750 lbs right now. I figure I could get that down closer to 4000 with some work, plus the smaller engines like the ls-1 or 3800 weigh a little less than the 425. The Caprice did have the 3.8 I think until 86, but it seems it was only available with a three speed, so I doubt it got the 29 that I had read about somewhere. fueleconomy.gov rates it at 24 mpg highway. I can't use a 5.3 because it's a truck engine and I live in California, and the FWD car 5.3 is tough to convert to RWD I think. I kind of still like the idea of the 3800, because a lot of the bigger German cars can be had with smallish engines in Europe that they don't offer here, like the 730i or whatever. but I'll probably just save until I can do the LS-1. I guess it makes the most sense over the 3800 or even the LT-1, since, if you're going to do the work, you might as well get the best engine the first time.

  15. #14
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    Re: 3800 series II or III swap into 79 deville?

    I live in CA and was under the impression that cars covered by smog (1976+) could only have their engine replaced with an engine that was available in that model at the time it was built.

  16. #15
    Stingroo's Avatar
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    Re: 3800 series II or III swap into 79 deville?

    Silly Californian laws.... what is this "emissions" crap?


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