I did this "thread" on "www.500CID.com" a few years ago, & it's "archived" on
"www.cadillacpower.com". The 425 Cadillac engine is "only" @ 40 lbs. heavier
than a stock sbc. The heads are a bit restrictive in stock form & will require some porting in the intake ports especially. The stock exhaust manifolds are a bit "concave" due to clearance issues with the stock '77-'79 front upper control arms in the Cadillac cars that they originally came in. But like others have said, they will respond very well with the same "hot rod" work as the 472 & 500's do. To do the "Stroker 454" thing, first, a Caddy 500 crank (4.304") stroke is needed. Then, a set of Oldsmobile (mid to late '60's) 425 c.i. (6.998" long) the Olds 7" connecting rods will be needed also, along with a set of EGGE Machine Company .040" over Oldsmobile 350 pistons will be needed too. The stock Olds 350 pistons are 4.057", so + .040" makes them a 4.097" diameter. A stock Cadillac 425 bore is 4.082" so, with a .015" over sizing will bring the bore of a 425 Caddy engine to 4.097" So let's do some math here, 4.097 X 4.097=16.785409 X 4.304 = 72.2444 X .7854 = 56.740751 X 8 = 453.926 rounded off to 454 c.i.. That's actually closer than a Chevy 454 Big
Block engine. When it comes to exhaust, either a stock set of Caddy 472's or 500's will fit, along with the stock 472 or 500 intake manifolds. The heads don't interchange though. The 472's & 500's have different size water passages that don't align with a 425 block. Other than that, the engines are very simular. Valve covers, oil pans water pumps, oil pumps & flex plates all
are interchangeable. So are the distributors & front belt pulleys. The 500 (4.304") cranks might require some re-balancing due to the difference in piston weight. The stock Caddy 500 pistons are huge & heavy. The Oldsmobile
.040" over pistons not quite as huge or heavy. And, depending on what vehicle the engine might be going into, a "custom" oil pan may have to be
made up by cutting at least two, the one made for the car or truck that the engine's going into & the 'pan that came with the Caddy engine then welding the Caddy oil pan's gasket flange section onto the oil pan that fit's the vehicle's chassis. But, getting off track here, back to the crank. The connecting rods, pistons, crank & block WILL have to be assembled at a machine shop because it's not a simple "bolt in". The parts MUST all be assembled & balanced precisely or the engine won't run for long (if at all).
The rest is just as simple as any other engine build. The heads (& especially
the valve train) will need to be "upgraded" as with all Caddy engines, the stock valve train components are lacking (at best) for performance & should
be replaced with either a set of Cad Company Shaft Rockers (cheaper) or a
Shaft Rocker set from MTS (Maximum Torque Specialties). The latter of them
are a bit pricey though (Like, well above $500 per set, with out push rods)
where as the Cad Company sets are $450 per set with push rods. The "best"
Cams are either the Lunati "Voodoo" cam (part # 10940702) or the MTS # 15
cam. The Lunati will have to ordered directly from Lunati, as no "parts vendor"
sells them. The MTS # 15 will have to be ordered from Maximum Torque Specialties directly. They don't sell their products through "Summit Racing Products" or Jegs Parts. Nor are the parts available through any Auto parts
stores either. All of the other parts, i.e. bearings, gaskets, seals, bolts, timing
gear sets & soft plugs or, ("freeze plugs") are available almost everywhere.
"www.cadillacpower.com". The 425 Cadillac engine is "only" @ 40 lbs. heavier
than a stock sbc. The heads are a bit restrictive in stock form & will require some porting in the intake ports especially. The stock exhaust manifolds are a bit "concave" due to clearance issues with the stock '77-'79 front upper control arms in the Cadillac cars that they originally came in. But like others have said, they will respond very well with the same "hot rod" work as the 472 & 500's do. To do the "Stroker 454" thing, first, a Caddy 500 crank (4.304") stroke is needed. Then, a set of Oldsmobile (mid to late '60's) 425 c.i. (6.998" long) the Olds 7" connecting rods will be needed also, along with a set of EGGE Machine Company .040" over Oldsmobile 350 pistons will be needed too. The stock Olds 350 pistons are 4.057", so + .040" makes them a 4.097" diameter. A stock Cadillac 425 bore is 4.082" so, with a .015" over sizing will bring the bore of a 425 Caddy engine to 4.097" So let's do some math here, 4.097 X 4.097=16.785409 X 4.304 = 72.2444 X .7854 = 56.740751 X 8 = 453.926 rounded off to 454 c.i.. That's actually closer than a Chevy 454 Big
Block engine. When it comes to exhaust, either a stock set of Caddy 472's or 500's will fit, along with the stock 472 or 500 intake manifolds. The heads don't interchange though. The 472's & 500's have different size water passages that don't align with a 425 block. Other than that, the engines are very simular. Valve covers, oil pans water pumps, oil pumps & flex plates all
are interchangeable. So are the distributors & front belt pulleys. The 500 (4.304") cranks might require some re-balancing due to the difference in piston weight. The stock Caddy 500 pistons are huge & heavy. The Oldsmobile
.040" over pistons not quite as huge or heavy. And, depending on what vehicle the engine might be going into, a "custom" oil pan may have to be
made up by cutting at least two, the one made for the car or truck that the engine's going into & the 'pan that came with the Caddy engine then welding the Caddy oil pan's gasket flange section onto the oil pan that fit's the vehicle's chassis. But, getting off track here, back to the crank. The connecting rods, pistons, crank & block WILL have to be assembled at a machine shop because it's not a simple "bolt in". The parts MUST all be assembled & balanced precisely or the engine won't run for long (if at all).
The rest is just as simple as any other engine build. The heads (& especially
the valve train) will need to be "upgraded" as with all Caddy engines, the stock valve train components are lacking (at best) for performance & should
be replaced with either a set of Cad Company Shaft Rockers (cheaper) or a
Shaft Rocker set from MTS (Maximum Torque Specialties). The latter of them
are a bit pricey though (Like, well above $500 per set, with out push rods)
where as the Cad Company sets are $450 per set with push rods. The "best"
Cams are either the Lunati "Voodoo" cam (part # 10940702) or the MTS # 15
cam. The Lunati will have to ordered directly from Lunati, as no "parts vendor"
sells them. The MTS # 15 will have to be ordered from Maximum Torque Specialties directly. They don't sell their products through "Summit Racing Products" or Jegs Parts. Nor are the parts available through any Auto parts
stores either. All of the other parts, i.e. bearings, gaskets, seals, bolts, timing
gear sets & soft plugs or, ("freeze plugs") are available almost everywhere.