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1978 Cadillac sedan de'Ville
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Hello everyone, i have a 78 SDV that i would like to get more power and performance from. I just met a guy nearby who recently totalled his 73 coupe and has offered to sell me the 472 motor and tranny for $650. It has 38k on it and ran/drove great he said. Also had tune up done recently as well as intake gasket, alternator, starter, and pointless ignition. Basically looking for opinions as far as the praticality and difficulty of the swap, is it worth the work? Is this a good deal? Any info in regards to what ill be in for if i do buy. I always look to this forum for any and all things caddy and truly respect ur opinions. Thx so much in advance!
 

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95 FWB 81SDV 96 FWB 94 Fleetwood
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The 73 already had the lower compression motor , not a whole lot more power than your low compression 78 , but some. If you put some higher compression pistons in it you would feel a difference . But I think the 73 still had small dish heads that are better heads. The transmission in the 73 is a long tail shaft and the 78 is a short tail shaft. you can change the tail , but the transmission has to come apart. Starting in the early 70's they started making the TH400 transmissions cheaper and weaker. So many parts in the older trans are better and stronger.The old trans drum pistons were made of aluminum , thats good , later went to stamped steel , cheap... The cases kept getting lighter and lighter. Kept taking material out.
 

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1980 FBC
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My vote is swap it.

The 472 is nowhere as anemic as most people believe. Almost every part is the same as a high compression 472.

The difference in numbers is gross verses net horsepower ratings.

Forget the transmission. Keep yours. If it works OK just replace the pump seal while the engine is out.

The weight of a 472 in your car will make it feel like there's more car. It's a great feeling.

You will want a posi eventually because you will be spinning the right rear tire on wet roads when you apply the gas pedal.

That swap was first made known to me from a junkyard interchange manual back in 1982 or so. Relatively easy, especially with what you have to start with.
 

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78' 425ci = 180 hp @ 4000 RPM, 425 ft/lbs @ 2000 RPM, compression 8.2 to 1 & 100lbs lighter
73' 472ci = 220 hp @ 4400 RPM, 365 ft/lbs @ 2400 RPM, Compression 8.5 to 1 (was 10 to 1 in 1970)

HP to weight ratio
Stock 425ci 4200 lbs 180 hp = 23.3 lbs / hp
With 472ci 4300 lbs 220 hp = 19.6 lbs / hp
Modified 425ci 4200 lbs 214 hp = 19.6 lbs / hp
Modified 425ci 4100 lbs 209 hp = 19.6 lbs / hp

The problem with the 73' is the compression is dropped down.
The 78' was designed more for emmisions & fuel economy with less weight & cubic inches.
78' actually is rated with 60lbs more torque, which helps with highway gears & heavy cars.
But the 73' has 40 more HP.

That's factory new numbers, not engines 40-50 year old engines.
Few things could be off that would reduce these numbers.

It's debatable which one is better.
Most would probibly go with the 472.
Too bad it's not just a few years older, because then it would have much better power.

But if you already have a 425 installed & running.
The real question is it worth the time, $650 for the engine, plus misc costs for the swap.
I would argue it's not worth the trouble.
Also depends on the condition of your stock engine.
Depending on the condition & value of the car a orignal engine adds more value.

For 34 HP you're better off making improvements to what you have.

Some gains to be had with better carb tuning & distributor advance curve.
Better exhaust. Better intake. Maybe a cam.
Take 100 lbs off the car, you only need 29 hp to equil the 472.
Lightening the car slightly helps acceleration, braking, handling, and MPG.

All these engine designs are so old that if your wanting a lot more power it's more cost effective to get something more modern or sigh more popular aka Chevy.
Aftermarket performance parts are about 3X as costly as the most popular carbed V8's.
 

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1980 FBC
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There's no replacement for displacement.

A little compression increase does not make the engine all that more powerful.

When all is said and done a low compression 500 cube with a working EGR and good carbonator calibration is way better than any of this series of engines for overall driving on pump gasoline. That includes the high compression versions.

Anyone who believes advertised horsepower ratings to be very accurate should buy the Brooklyn Bridge.

Installing any speed parts on a Cadillac today is VERY expensive.

If the original poster simply wants more effective acceleration, the engine is not the first thing to change. The rear axle is.

The 2.28:1 gear ratio really cuts down on the 1/4 mile and zero to sixty performance of these cars while producing great highway economy.

Second area is exhaust. Even a hi performance single exhaust will make a large difference from a factory 1977-9 setup.
 

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"No replacement for displacement"
Agreed.
But with the older stock V-8's noticing 45 to 50 ci is hard to tell by the seat of you pants.
Good example 305 vs 350 Chevy in a Caprice or even 1/2 ton truck.
Or a 350 vs 403 Olds in a full size.
Same with a Pontiac 350 vs 400.

I remember one Pontiac dealer getting away with scamming people on the engine size.
They would order a new underhood sticker & place it on top of the old.
Don't remember if they changed other decals emblems.
Couldn't alter the VIN but back then most people wouldn't know.
Until the engine needs major work & the ordered parts don't seem right.

Also agree there are better ways to make power for the same time and money.
 

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82 CDV, 89 Brougham, 88 Brougham d'Elegance, 79 CDV, 73 Fleetwood Eldorado
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Hello everyone, i have a 78 SDV that i would like to get more power and performance from. I just met a guy nearby who recently totalled his 73 coupe and has offered to sell me the 472 motor and tranny for $650. It has 38k on it and ran/drove great he said. Also had tune up done recently as well as intake gasket, alternator, starter, and pointless ignition. Basically looking for opinions as far as the praticality and difficulty of the swap, is it worth the work? Is this a good deal? Any info in regards to what ill be in for if i do buy. I always look to this forum for any and all things caddy and truly respect ur opinions. Thx so much in advance!
I'm currently driving a 79 CDV 7.0, and a 73 Eldo 8.2, I understand the lackluster of a stock 425, and the joy of a 500. Here's how I see it, what I've done, and plan on in regards to my 425. All I've done to my 79 CDV 425 other than buy a preformance tuneup, is ALL new exhaust, headers from cad co, flowmasters, no cats, dual exhaust with H pipe. That woke my car up significantly, because now it can breathe, an engine is an air pump, so it needs to move air and exhaust as easy as possible. The plan is to put in a better cam, a cad co intake manifold, and a Holley sniper efi carb then ill be done. Parts alone I'm looking at about $2500-3k, and labor to help with the efi $200 or closer to 2k if I paid a shop for it all . My exhaust cost me 2k, I paid a shop. Everyone told me to scrap my 425 and go to a 472 or 500, if you build a 425 it will cost the same as a 472 or 500, a 425 will never achieve the same power as a 472 or 500,... all valid points. But where I am its hard to find a 472 or 500 in or out of a car for under $1200-1500, who knows what problems it has ($), money for parts to install and driving, then theres the preformance add ons so its efficient... if you're like me you know the 425 you have been driving it, its paid for, installed,... I dont want a race car I just want a woke car. Even if all you did was open up your current exhaust, a good tuneup, rebuilt your carb, and put in a new cam, your car will be a totally different car, costs the same as doing it to a 472 or 500 but without the extra work and expense; plus you keep the car that much closer to original. Dont get me wrong I'd still buy the 472, but the 425 is a good engine and more than enough, with a little work and money, to make your deville go like never before.
 

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1978 Cadillac sedan de'Ville
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Discussion Starter #8
Big thanks to u all for ur opinions and suggestions! My final decision is gonna be to just stick with my 425. At the end of the day i never heard or saw the 472 run or drive and my experience is that these days people arent always too honest, especially in instances where money is made. More importantly tho, my 78 has been nothing short of an absolute pleasure dating back to 04 when i picked it up. In the 15+ yrs now that ive owned it there has been a couple few stints where i thru the cover on n parked it for extended periods, up til few months ago i had it parked at a friends house for well over a few years. Everytime ive gone back to start driving it again it has fired right up. As far as work ive had to do to it mechanically as long as ive had it has only been alternator. It doesnt leak oil, but it does leak trans fluid pretty bad...im workin on it today some n was thinkin i may go grab a new trans pan gasket n see if that helps. Back to power n performance tho, ive been having a hard time locating the parts id like locally (seattle), which r a pair of 472/500 exhaust mani, 472/500 dual plane intake mani, i heard these will open it up n help it flow much better, im currently working on puttin together some kind of exhaust setup, id really like tru duals but for now i just wanna make it rumble or sound like a hotrod so i think imma cut the orig out n buy some piping from local parts store n just run straight pipe with a dynomax muffler a friend gave me many many years ago thats been ridin in the trunk probly over 10 yrs now, or i might instead just grab a cherrybomb glasspack from store too, n i have no welder so ill have to clamp it all up, im just really desperate for some change on it, if i hold off til i find the parts id like, hell i feel like itll remain stock for years to come
 

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82 CDV, 89 Brougham, 88 Brougham d'Elegance, 79 CDV, 73 Fleetwood Eldorado
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Big thanks to u all for ur opinions and suggestions! My final decision is gonna be to just stick with my 425. At the end of the day i never heard or saw the 472 run or drive and my experience is that these days people arent always too honest, especially in instances where money is made. More importantly tho, my 78 has been nothing short of an absolute pleasure dating back to 04 when i picked it up. In the 15+ yrs now that ive owned it there has been a couple few stints where i thru the cover on n parked it for extended periods, up til few months ago i had it parked at a friends house for well over a few years. Everytime ive gone back to start driving it again it has fired right up. As far as work ive had to do to it mechanically as long as ive had it has only been alternator. It doesnt leak oil, but it does leak trans fluid pretty bad...im workin on it today some n was thinkin i may go grab a new trans pan gasket n see if that helps. Back to power n performance tho, ive been having a hard time locating the parts id like locally (seattle), which r a pair of 472/500 exhaust mani, 472/500 dual plane intake mani, i heard these will open it up n help it flow much better, im currently working on puttin together some kind of exhaust setup, id really like tru duals but for now i just wanna make it rumble or sound like a hotrod so i think imma cut the orig out n buy some piping from local parts store n just run straight pipe with a dynomax muffler a friend gave me many many years ago thats been ridin in the trunk probly over 10 yrs now, or i might instead just grab a cherrybomb glasspack from store too, n i have no welder so ill have to clamp it all up, im just really desperate for some change on it, if i hold off til i find the parts id like, hell i feel like itll remain stock for years to come
I'm 100 miles north of you, good luck finding local/in state.
Here's what 2.5" duals with h-pipe and super 44 flowmasters on a stock 425 sounds like...
PS: it's my car
 

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Don't underestomate the value of a quality custom / semi custom exhaust.
Some of the parts store exhaust accesories like adapters are overpriced junk.
They don't seem to carry much for hangers.
Sometimes parts are not an exact size where there is never a good fit between pipes.
Being able to expand, bend, weld, having a good selection of supplies to use, & a skilled installer is priceless.
Not that many are skilled exhaust craftsman.
An exhaust shop might have 0 to 1 great person.
Most are parts installers that can do minor modifications, small sections, & adjustments.
 

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1978 Cadillac sedan de'Ville
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Discussion Starter #11
I'm 100 miles north of you, good luck finding local/in state.
Here's what 2.5" duals with h-pipe and super 44 flowmasters on a stock 425 sounds like...
PS: it's my car
Yeah thats the kinda sound im lookin for! Funny thing is id watched that video a handful of times before even registering on this forum, small world huh? Lol. Badass caddy man! I need to post up some pics of what im workin with n let yall see mine
 

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1978 Cadillac sedan de'Ville
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Discussion Starter #12
There's no replacement for displacement.

A little compression increase does not make the engine all that more powerful.

When all is said and done a low compression 500 cube with a working EGR and good carbonator calibration is way better than any of this series of engines for overall driving on pump gasoline. That includes the high compression versions.

Anyone who believes advertised horsepower ratings to be very accurate should buy the Brooklyn Bridge.

Installing any speed parts on a Cadillac today is VERY expensive.

If the original poster simply wants more effective acceleration, the engine is not the first thing to change. The rear axle is.

The 2.28:1 gear ratio really cuts down on the 1/4 mile and zero to sixty performance of these cars while producing great highway economy.

Second area is exhaust. Even a hi performance single exhaust will make a large difference from a factory 1977-9 setup.
I keep seeing the issue that is the rear axle in every discussion i come across while searching the web for knowledge n info on my car. Could u enlighten me on what i should be looking for when it comes to this plz? N where i would find it? How much damage am i lookin at cost wise? Keep in mind id still like to be able to drive on the highway somewhat comfortably, thank u in advance, all of u have been more than helpful and without u guys im all alone on this stuff, it means alot
 

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95 FWB 81SDV 96 FWB 94 Fleetwood
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If you were to change the gears in your rear end you have 2 choices that would use your same carrier. A 2.41 or a 2.56 ...you could change the whole rear end but these parts are getting harder to find.
 

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1978 Cadillac sedan de'Ville
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Discussion Starter #14
If you were to change the gears in your rear end you have 2 choices that would use your same carrier. A 2.41 or a 2.56 ...you could change the whole rear end but these parts are getting harder to find.
Yeah id like to try n stay on the less spendy/easier install side of things due to being poor n only average mechanical skill, any idea what a job like that would cost? Thank u much!
 

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1980 FBC
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Not much performance improvement from changing to 2.56 but that's what fits the existing hardware as The Dr. said.

Back in the 80s I latched on to a full size Chevy drum to drum posi. IIRC it was 2.73:1 which is just where the car started to really wake up. Installation was not straightforward and I landed up with a smaller bolt circle on the rear rims.

I've converted a number of HT-4100 cars and one 1982 V6 car to 425 and 500 C.I. engines. The job usually includes swapping the factory 3.41? 3.42? (don't know) or 3.23 to a 2.28 or 2.41. A few times I would complete the engine and leave the original axle for a few weeks.

Acceleration was amazing compared to the 2.28 but one could not launch from a dead stop without lighting up the right rear tire.

Not at all sure what rocks I would look under if I needed a 3.xx posi these days but it would most likely be under a newer Toadmaster, Capche or 93-96 Fleetwood.
 

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Posi complete posi axles are always take of the cars right away around here.
Between some say they weren't always the strongest, the posi upgrades, & disk brake upgrades they are popular.
Still see waggons with posi's but they aren't exactly the same.
 
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