The Infopages

Day after day, we get calls from people who have a Cad motor but are unable to tell what year/model they're looking at. Since many 472s and 500s use the same , and the later (425 and 368) engines look similar, as well, you'll have often to have a look deeper than the block casting numbers to finally determine which species of torque animal you have there. For more detail, and pictures, please visit the technical section of our web site at http://www.cad500parts.com/tech.

The first step is to ID the block. The block casting number is found at the rear of the engine, between the intake manifold and transmission bell housing, right next to the oil pressure sending unit. The casting number is the raised, cast in number on the passenger side. Some blocks have a number stamped in this area, as well, but these numbers cannot be reliably decoded.

All ‘70-’76 472 and 500 engines should have a block casting number ending in 52xx or 62xx (referred to as the ‘5200’ block). The ‘68-’69 (and a few rare ‘70 472s) use a block that looks identical at first glance, but bears different casting numbers, has smaller oil passages and does not have clearance for a 500 crank. Fine for a mild street engine, but unacceptable for a serious performance engine. The 425 and 368 blocks have a slightly larger timing cover and a box shape in the casting to the rear of the intake on the driver's side.

Pistons:

The ‘68-’70 472" and ‘70 500 engine have the 10:1 (or 10.5:1) pistons which have a swirl-chamber dish that resembles either a ‘squashed peanut" or a big fat "butterfly". Do not assume your high lift cam will work with those pistons! In 1971 the compression was dropped to 8.5:1, with the piston design having a rectangular "soapdish" 47cc pocket. The ‘74 model introduced the new large chamber heads, and maintained the 8.5:1 compression ratio. The ‘74 472 sported a unique true flattop piston. This ‘74 piston has no swirl chamber, no valve reliefs, not even the 8cc depression of the ’74-’76 500" piston (round dish, approx.. 1/8" deep). [You cannot interchange 472 and 500 pistons due to the different compression heights].

Crank:

Most 500 cranks have a casting # ending in ‘93 or ‘94, next to the 4th main journal.

Most 472 cranks have a casting # ending in ‘24, found on the 3rd counterweight.

The 425 crank is the same stroke as the 472 crank, and is physically interchangeable, but cannot be balanced effectively due to the drastic weight difference caused by the bore size.

Heads:

The cylinder head casting numbers can be difficult to find. In some cases, the full 7 digit number will be found on top of the smog rail, or between the rocker supports. In most cases, the last 3 digits can be found on the bottom of the head under one of the center intake ports. The 425 heads (casting number ending in ‘423) usually have the last 3 digits on top of the #2 and #7 exhaust ports.

From ‘68-’73, the heads were of the 76cc small chamber design. These heads have 3 casting numbers, ending in ‘250, ‘950, and ‘902. All ‘68/’69 and ‘71-’73 cars should be equipped with a smog pump from the factory, while the ‘70 cars were not. The ‘250 and ‘902 heads are equipped with built in smog rails, while the ‘950 heads were not. Not all ‘250 and ‘902 heads were drilled for smog rails, if they were installed on a non-smog ‘70 car, even though the extra material is in the casting. A common misnomer for the ‘950 heads are that they are "hi-po" (high performance) cylinder heads; they are not! The ‘70 500 was rated at more horsepower because it had 10:1 compression, not because of special heads. The ‘950 head has a 76 cc chamber just like the ‘250 and ‘902, but differs in design by not having a smog rail cast between the pedestal support towers. Don't be fooled by the "hi-po" myth. If you are restoring a 1970 Eldorado, however, you'll want to have the ‘950 heads to be factory correct. And, not because of flow, many racers prefer the ‘950 head as it weighs about 3 lbs. less than the other heads. If you want to pay more for ‘950 heads, because they're lighter, or "cleaner" (no smog rails), OK; but don't let them be passed off to you as factory high performance. ‘68-’69 472" and ‘71-’73 472 and 500" motors came with either ‘250 or ‘902 cylinder heads. Though the reference books indicate a drastic horsepower loss in 1972, they changed the way they rated horsepower, with the actual horsepower of those later motors much closer to to the actual power of the ‘70 500 (see the dyno pages for details).