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1979 Coupe Deville, 1995 FWB & 6 Other Non-Cadillacs.
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I have been reading past threads on the 500 for months now. I really don't know what to do. I recently picked up my 80 which I am keeping all OEM/Bone stock. So now I want to modify my 78 for performance. Anyone on this forum that knows me knows I do stuff right...No shortcuts. I'd like to throw an early 500 in the 78 but can't find one close to me. On top of that, I plunked $2600 into my 425 b/c my original plan was to keep the 78 all stock/#'s matching. Is it possible to get serious performance out of the 425 or am I stuck with a BB paperweight that nobody wants plus the headache of finding and building a hi-power 500? I want my 78 doing this in the near future...
http://www.youtube.com/watch?v=JJ4tb-fzpIc
 
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If you seriously want to do that I would contact a pro like MTS or Cad Company. Anything is possible with enough cash.
 

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79 coupe deville d'elegance (76k og), 84 coupe deville
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114 Posts
i would love to take the 425 off ur hands but im dead broke. good luck with the sale.
 

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Wheelman, If you decide that you want to do that 500 thing, I will be interested in the 425 that will be left over, so please send an email my way if that happens.
 

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1977 Coupe (blue), 1977 Coupe (yellow), 1977 Coupe (green)
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One problem with the 425 is the intake. The stock unit is an updraft design, to allow hood clearance. There are alternatives for the 472 - 500. These may be made to fit the 425 by maching the port flanges, but I'm not certain of this. It's a matter of if the manufacturer puts enough material in the flange area.
 

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1981 Sedan DeVille Diesel
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I want my 78 doing this in the near future...
http://www.youtube.com/watch?v=JJ4tb-fzpIc
I wouldn't plan on it with a 425, or without an "invested" 500 build (not to mention the chassis mods in Shawn's Coupe). Don't mean to nay-say... :)

If you've got cash tied up in the 425 you may want to stay that course as you'd need to spend it all over again on a 500. If you're truly wanting big power numbers then go 500. I'm sure there's some built 425's out there but I just haven't seen 'em...

Weigh your power needs/budget. What all have you invested into your 425? You could try a cam, roller timing chain, 472/500 intake and exhaust manifolds, etc. and have a pretty fair running 425 I think. Not a 1/4 mile monster though....

Just my $0.02 :thepan:
 

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1979 Phaeton Coupe, 1990 Brougham d'Elegance 5.7 liter
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Yeah, if you did that with the Fleetwood, you'd have to run drag slicks and do all sorts of chassis mods to withstand that much power, not to mention the tranny. And it would totally take away from the panache that your car is overflowing with. Just build up that fresh 425 a little bit. One of the big block caddy sites sells a rebuild kit for the 425 called the 'ultimate 425' which just changes some key parts to make it all that it can be. I'd do something like that, and Rick had a modded 472 intake on his. There's a lot that can be done with what you have, you don't need a sprint car.

But if you're still thinking about selling it, disregard all that was said. :)
 
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