Rebuilding a 425 any suggestions for better HP?

[guyrobert]

I recently bought a 1979 425 that I hoped would require a minimal freshen up (timing chain, water pump etc.)
However after the leak-down test it is clear it will need a total rebuild.
I would like a little more HP, but as it is going in a stock 1979 Coupe DeVille Phaeton I am not planning on going too crazy.
The rebuild will start next week, I am thinking to thave the block and heads decked to improve compression, possibly change the cam, and have a bit of port work done. Is there anything I am missing?
I want the engine to appear all stock when done.
Thanks in advance for you help.
Robert

["Cadillac Kid" Greg Surfas 15364]

Robert,
By all means the easiest, least expensive way to up the HP would be to use a 472 (short block, heads and intake manifold) as a replacement for the 425.  Besides having a relatively unlimited choice for added performance equipment, if you use the 425 oil pan and pick up, the oil pump as well as rocker arm covers, the change will be invisable to ALL but the most knowledgeable observer.
That is what I did in my 79, using an MTS #5 cam, flat top pistons and large chamber heads. Resultant 9:1 compression ratio puts the HP about 50 above what the 425 would put pout.
Greg Surfas

[guyrobert]

I was looking for a 472 or 500 block for some time and I couldn't find anything around here.
I was hoping for a quick fix if the 425 I did buy would have been in better condition.
The engine in the car runs really well but burns a lot of oil.
I am kind of down the 425 path rebuild now so I will keep doing research on what will get me the best bang for my buck(s)!

[35-709]

Take Greg's advice --- don't expect a lot out of the 425.  If you are near Florida, I have a good 472 out of a '73 that you could talk me out of.  Will need overhaul, carb, flywheel, and ignition.  472s and 500s, however, should be easy to find.

[35-709]

Oops, I see you are in Vancouver, BC.  Kinda far away.   

[J. Skelly]

Robert,

In addition to what you propose to do, make sure the Quadrajet is professionally rebuilt.  A lot of people like to dog this carb, but when tuned properly it gives good service. 

[Scot Minesinger]

You can buy a 472 intake manifold (that has been modified internally for better performance or not), cam and improved heads (ported with large valves) from MTS in CA and they will ship to you, rather than using a "good used" 472 engine.  Also, get rid of the smog pump with a revised set of pulleys from MTS if it had one.

The 472 engine parts will make your Cadillac look very nearly stock, run smooth at idle, and have some more punch.

[35-709]

There is a fellow (believe he is in California) over at the Cadillac & LaSalle Club Modified Chapter that has a rebuilt 472 for sale.  Do not know his asking price, but could possibly help put you together with him.

[TJ Hopland]

Have you tried contacting MTS or CadCo and see what they have for advise and parts?

At one time the 425 was a popular motor to do an eco power build on.  I think a lot of guys would do them for daily driver truck swaps.  I never did it myself and it was long enough ago that I don't remember the details.  I think the peak of those builds went back the Al MTS of Wisconsin days what 15-20 years ago now?  LS engines were too new at the time to be an option like they are now.  Seems like maybe he even sold a kit for those builds.  I remember drooling over one in a catalog for the dually I had at the time but back then I just didn't have the money.   

 

["Cadillac Kid" Greg Surfas 15364]

Robert,mnto
With all the information above I am sure you now have both feet firmly planted in mid air.  The 425 motor had almost 100 pounds of cast iron removed (from the 472/500) as part of the vehicle downsizing in 1977 and they took most of that Iron out of the motor's web, vastly reducing the strength.  While more than adequate for a stock motor, much any (if it were available) performance enhancing parts would move the motor to borderline oin strength and durability.  This is what a few of the folks that tried improving this motor found out. Any custom pistons would be custom (read that over $1,000.00) and cylinder heads are unique to the 425 so off the shelf modified 472/500 inch motor heads would not work.
That said, I think you will find that Eddge is just about the only one making replacement (stock compression) pistons, so that also might be costly.
IF your 425 needs to be rebuilt I believe it will be more costly than the previously discussed route of buying either a rebuild able or a rebuilt 472 and going with that.
I have the 425 that came out of my 79 "Paris" which after losing the transmission, spun the thrust bearing on the crank.  I am putting it together using a 472 crank, rods and an MTS #5 cam, but it will be a stock motor for my cousin's 1200 pound roadster.
Greg Surfas
Greg Surfas

[guyrobert]

Wow, Lots of solid info! I will keep researching 425 builds, I am not looking for anything but street use.
And because as I mentioned in my other thread on visual differences between the 368 and 425 you can get a solid running Caddy 77-81 well under $5K around here I would like to keep my budget at about $5K on the build.
I will attach a picture of the engine I bought.
I will keep everyone posted on the route I go
Thanks

[guyrobert]

Robert,

In addition to what you propose to do, make sure the Quadrajet is professionally rebuilt.  A lot of people like to dog this carb, but when tuned properly it gives good service.

Great tip and fortunately I have 2 rebuilt Quadrajets at hand, one on my current engine and one on the shelf

[bcroe]

Wow, Lots of solid info! I will keep researching 425 builds, I am not looking for anything but street use. 

While you are at it, go through that TH400 (unless yours was recently done). 
Bruce Roe

[guyrobert]

I have just found a 1970 472 about an hour and 1/2 away. It doesn't have the exhaust manifolds, would the ones from the 425 cross over?

["Cadillac Kid" Greg Surfas 15364]

Yes
A actually you have to use them (425 manifolds). Clearances under the hood are tight
Greg Surfas

[TJ Hopland]

77 they changed the front suspension a bit so they had to slightly squish the exhaust manifolds to clear.   The new suspension was also why the new oil pan and oil pump/filter design.    Anything specific to fit your car can be swapped from the 425 to the 472 if the deal goes through.  68-69 there were some differences but 70 should be fine.

70 should not have a smog pump but would be dual groove AC/PS so both a plus and minus.
70 should not have an EGR intake.
70 should be a high compression motor so it should make some good power but will need the best gas you can find.   

[bcroe]

I reduced 0-60 by a second by converting my TH400 transmission
to switch pitch.  Bruce Roe

[guyrobert]

I put an offer in on the 472, I will have a pile of parts with two 425's and one 472 if I can get it for the right price...
My hope for a cheap and quick swap with the 425 for $1,500  or so seems to have gone out the window 

["Cadillac Kid" Greg Surfas 15364]

Robert
You will need the following 425 parts for this swap
Oil pan oil pick up oil pump exhaust manifolds.
You will need a modified HEI distributor since the advance curve from your 425 is way off. I would suggest you decide whether or not the motor (if not 1970)’will use an AIR pump. The choice of pulleys can then be made. Greg Surfas

[guyrobert]

Ok the gentleman with the 1970 472 accepted my offer so I will get it picked up this week I am sure that I will need more tips and advise as the build progresses.
I had already bought a bunch of parts for the 425 rebuild so hopefully some will cross over. Again I will keep you posted!