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Discussion Starter #1
why did the 425 drop so much horsepower from the 472 and the 500..i have always wondered that.cause the 500 has like 400 or so hp and the 472 had more than the 425..cause it only has 180 hp...does any1 know?
 

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You're looking at gross vs net hp mostly. The "400hp" out of the 500ci motor was gross HP. That's back when they measured HP with no aircleaner, no exhaust, no accessories, etc. Basically, the advertised numbers weren't realistic in the slightest...
That's also the 10:1 motor, not 8.5:1 compression like your 425.
In 1972 they switched to net hp, which is pretty close to what you actually see in the car. It's measured with the aircleaner on, accessories on, full exhaust, etc.
The low compression 472 only made 220 net hp, and the low comp 500 made 190-235 net hp, depending on the year.

The 425 doesn't make that little power once you put them on an even playing field.
 

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Discussion Starter #3
how much horsepower does the 6.0 litre 368 8.6.4 engine have?..by all the things i have read on the car i like it alot and i wonder how it runs and gas milage....my 425 is a gas guzzler but when i get a new oil change and all that its better on gas..did they only make that engine in 80 and 81?
 

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My Chiltons shows the 368 being used from '80 to '85. Probably only in the commercial chassis though. Hp was 140-145.
The V864 was '81 only. From what I hear, it was a good system, but the electronics as a whole sucked so the engine did not operate very smoothly. There are a few guys here with V864 cars who like them alot and get very good mileage (for a large car) with them.

Smaller engines generally get better mileage. They are also generally in lighter cars, and lighter cars get better mileage too. I wouldn't put a 368 in a 425 chassis though - probably too heavy and would just make the car slow.
Try a full tuneup and see what that does for your mileage, also make sure you keep your tires inflated to at least the numbers Caddy reccomends, or just run them at the max shown on the sidewall.
I consistently get 12-15mpg in my 472 with a mix of city/highway driving. Not a fuel miser, but it's pretty good for a 35 year old, 5500# car.
HOW you drive is also a big factor. Take it easy off the stoplights around town. If you are accelerating with traffic, you are using more gas than you need. In all the cars I drive I let everyone dash off the light while I accelerate more slowly. In town you'd be surprised how often you end up right next to the same people at the next light. If the road is open enough and traffic thins out enough to start moving, then I will just keep accelerating after everyone else has taken their foot off and slowly work my way up through a pack of cars, just cruisin'.
 

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Discussion Starter #5
oh some of those guys that have that car need to post some things about it i like that engine by the sounds of it!ive seen alot of pics to and i like it..another thing i have wondered is why did they ever even think of putting the 4.1 litre 6 cyl engine in such a huge caddy??? i bet that car didnt move at all..or did it??
 

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Discussion Starter #7
Thats Pretty Rad Cause I Like The Way It Cuts Off Cylinders To Save On Gas..i Like It..but On That 500 It'll Probably Still Be A Gas Guzzler
 

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The 368 was used in the same chassis as the 425 :)

in fact, in the '77-'92 chassis... nearly the same car... the Cadillac 425 and 368, also in V8-6-4 version, the Buick V6, Oldsmobile 350 diesel, Cadillac HT4100, Oldsmobile 307, Chevy 205 and 350 were used.

Really when you look at all that, the only 2 engines that were justified are either the 425 or the 350.... add to the fact that the 425 is unique and made by Cadillac, and is a big block.... and as far as I am concerned, the 425 is the only solid engine that is best in these cars. The 350 is pretty nice, but it is in everything. the 307 got the job done and was good on gas too... but it really lacked power and there was no aftermarket.

About the only thing bad on the 425's part is the gas mileage... but considering it is carburator and only 3-speed, the 13/16mpg my '79 with 93k miles gets really isn't too bad.... right around the same as most full size pickup trucks and SUV's..... and hell, my '79 DeVille probably sees more off-roading them most SUV's sold today.

The 425 really isn't all that bad, I used to knock it, but not anymore. Really, its an amazing engine that is only over looked because it simply isn't a 500. Why get a 425 when you can have a 500, ya know? but really its the smae thing. At the time they wanted a lighter engine that was better on gas and less emmissions, and it was.

Yeah 180hp from a 7.0L V8 is weak... but come on... 1977-1979 wasn't really the time for mega-power in any car... with a gas crisis on hand they were trying all they could to get the fuel mileage up. But remember, it isn't HP that gets these boats, or any vehicle moving, its torque. The stock 425 has 320ft-lbs of torque at 2,000RPM. That there is pretty healty and what gives these engines a nice wake up call.

The major thing holing back the 425-powered DeVilles are the 2.28 gears they came with. Come on...2.28? Chevy guys freak out with 3.11's. Put 3.11's on a 425 car and you'll be flying.. better hope you have Posi.

Plus, the real restriction on the 425 is the intake, cam and exhaust. Open up the intake with an open element air cleaner and a modified 472 intake manifold, put stock 500 exhaust manifolds on with true dual 2-1/4" exhaust with some nice hi-flow mufflers, and you already woke the 425 up. Get a better cam.... nearly anything is better then the stock granny-spec smog cam, and you already have a beast waiting to be let go..... though with the stock valve train you cam options are limited.

But the 425 isn't a dog....really, considering what it has to move, and how it does it, it is decently quick at it.
 

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Night Wolf said:
The 425 really isn't all that bad, I used to knock it, but not anymore. Really, its an amazing engine that is only over looked because it simply isn't a 500. Why get a 425 when you can have a 500, ya know? but really its the smae thing. At the time they wanted a lighter engine that was better on gas and less emmissions, and it was.

Yeah 180hp from a 7.0L V8 is weak... but come on... 1977-1979 wasn't really the time for mega-power in any car... with a gas crisis on hand they were trying all they could to get the fuel mileage up. But remember, it isn't HP that gets these boats, or any vehicle moving, its torque. The stock 425 has 320ft-lbs of torque at 2,000RPM. That there is pretty healty and what gives these engines a nice wake up call.

But the 425 isn't a dog....really, considering what it has to move, and how it does it, it is decently quick at it.
You hit just about every point. One to add is that the national speed limit was 55 MPH when the 425 came out. Cruise at 60 MPH verses 70 or 75 and the 425's fuel economy will increase quite a bit. The stuff about needing a certain RPM at cruise range verses the lowest RPM that you can drag a car with doesn't agree with my findings. The 425 is plenty happy in top gear on the highway at 1700 RPM.

Not only was the 368 used in the same exact chassis as the 425 but certain 368 equipped models were actually hevier than certain 425 models.

Yes the V6 was s l o w. Great for economy though. Durability was better than the other engine with the same displacement. That other engine ran much smoother when it ran though.
 

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Yeah, the 425 has no problem crusing at 1,700RPM.

I simply ment that I heard on the BB Cad's the best cruise RPM is the torque peak, so you gear accordingly.... for the stock cam that would be 2,000RPM, with the 2.28 gears that is right around 70mph... but at that speed you are now looseing MPG due to the drag of the car.

My best was 17mpg with the cruise set at 65mph, I am sure it would have gone up if I went slower but I really didn't want to go slower... plus the car likes 70+ more then anything less for steady highway driving.
 

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Discussion Starter #13
i have a question..i know that the 77,78,and 79 all have the 425 but i have always wondered since i have the 79 the last year they made the 425 is it more advanced or have a little bit more spunk because they had a couple years to look over the engine from the 77 to the 79..so would the 79 engine be a little more advanced cause its a later model engine of that car??
 

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Nope.

all 425's are the same.... the whole engine itself is pretty much as good as it would get, being that the big blocks have been around since 1968.

Of course putting a modified non-EGR 472 intake manifold on it or 500 exhaust manifolds would help alot...

but as far as the 425..... all the same. only differences were the Qudra-Jet vs. fuel injection versions... even the 425 in the FWD Eldorado was pretty much exactly the same.
 

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Discussion Starter #15
yea i always thought that they might have time to look over it and like advance it a little more..but the 472 manifolds will fit on the 425?
 

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bigblockcaddy said:
i have a question..i know that the 77,78,and 79 all have the 425 but i have always wondered since i have the 79 the last year they made the 425 is it more advanced or have a little bit more spunk because they had a couple years to look over the engine from the 77 to the 79..so would the 79 engine be a little more advanced cause its a later model engine of that car??
Different year 425's DO have differences. The engines are exactly the same but fuel system parts and calibration differ. Even timing proceedure changes.
 

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Discussion Starter #18
tripleyellow78cad said:
my 78 cd 425 is pretty powerful and fast for an old car , it only needs more power on large steep hills , like the i-5 grapevine hill to la
i live in ca,
yea my caddy runs great on streets and flatland..but when i go up north kickin it in overdrive i usually stay around 65-70mph but thats about all it will do going up mountains.
 

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bigblockcaddy said:
yea my caddy runs great on streets and flatland..but when i go up north kickin it in overdrive i usually stay around 65-70mph but thats about all it will do going up mountains.

There is no Over Drive on these cars.

My '79 has no problem going up any hills... stays in 3rd gear and just goes.
 
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