Cadillac engine knowledge
by: 1168061567, 1168560980, CadDaddy42, Cobalt327, Crashfarmer, Crosley, Curtis73, DrChop, GSXMEN, IkoZd3, Jon, M&M CUSTOM, Techinspector1
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|Year||Disp.||Fuel||Horsepower||Torque@RPM||Bore x Stroke||Comp. ratio|
|Year||Disp.||Fuel||Spark plugs||Dist.||Timing BTDC||Intake opens||Idle speed|
Fastener torque specifications
Block casting numbers
- 1968-'69 472: 1486238
- 1970-'76 472 & 500: 1485200 (1486200 was used on some 1974-'76 500 engines)
- 1977-'79 425: 1609110
- 1980-'85 368: 1615255 Carb; 1620734 EFI
Crank casting number
- 1968-'74 472: 1486424
- 1970 500: 1495094
- 1971-'76 500: 1496793
- 1977-'79 425: 1609142R
- 1980-'85 368: 1609142
Stroke can be measured through spark plug hole if the engine will turn over.
- 1968-'74 472, 1977-'79 425, 1980-'85 368: 4.060" (less than 4-1/8")
- 1970-'76 500: 4.300" (more than 4-1/4")
Head casting number
Usually in the center of the head under the valve cover.
- 1968-'69 472: 1486250
- 1970 472 & 500: 1495950, 1497902, 1486250
- 1971-'73 472 & 500: 1497902
- 1974-'76 472 & 500: 6024493, 6024552
- 472 and 500 heads have the last 3 digits of the casting number in a recess under a center intake port, visible from the lifter valley with a mirror.
- 1977-'79 425: 1609112, 1609423 (last 3 usually on driver's front / pass. rear exhaust port)
- 1980-'85 368: 1615188, others unknown. The 4-6-8 head is substantially different than the regular head, and the rocker assemblies are not directly interchangeable.
A fairly comprehensive 2 page PDF ID guide with pictures (mostly on the 472/500 engines) can be found HERE. For a quick ID, on the second page there is a box shape shown on the rear of the 1977-later blocks to ID the smaller engines. Distinguishing a 1970-newer 472 from a 500 can only be done by crank number, stroke, or piston design, as all other parts are the same.
Modifications and swapping
The biggest gains in power output come with cylinder head work. Pre-1974 heads are small chamber 76 cc's and are good for around 12-13 to 1 compression when a flat top piston is fitted. Race gas, alcohol or propane fuel must be used.
The 1974 and later open chamber heads have 120 cc chambers giving compression ratios of 7.5-9 to 1 depending on the piston used.
Big gains can be made by adding larger valves. The valve sizes can be boosted to 2.19"/1.84" without worry of hitting the water jackets. The usual porting, valve unshrouding and minor bowl modifications will work, although the short-side radius should be left alone to avoid drastic differences in airflow. Roughly 20 hp can be gained by this work alone and most of that comes from the larger valves.
The 1977-'79 425 heads have 108cc chambers giving about 10:1 compression ratio depending on the piston used. The 425 heads have restricted air flow due to their port design making them the least desirable for modification. The head gasket is different as well.
Blocks should get the standard deburring. A drain hole can be drilled into the rear of the lifter valley for better oil drain back and a spillway can be added to the oval hole at the front of the block to better lubricate the timing chain and the camshaft thrust face. Incidentally, later blocks have 1/2 inch oil galleries for increased flow through the block, so it makes a good performance base.
A 472 can be made into a 500 by swapping in the 500 crank and pistons, although on 1968-'69 engines, a slight amount of notching is necessary at the bottom of the cylinder bores.
High performance tolerances
- Crank end-play, minimum- 0.008"
- Rod side clearance- 0.035"
- Top ring gap- 0.020"
- Second ring gap- 0.018"
The stock cam can benefit from advancing the cam timing 2 degrees, as these engines had retarded cam timing in stock form for emissions. Attach the degree wheel to the crank with a 9/16-24 fine thread bolt.
Some TH350 transmissions came with steel transmission cases in older military tanks and trucks; they would be best for mondo horsepower applications such as 1500+ hp cad engines. It's fairly easy to build a 2000 hp twin turbo Cad with 35 pounds of boost at 7:1 compression on alcohol. It's said the block can take it, but the cast crank might not be able to.
The basic 472 and the later 500 engines both use a Buick/Pontiac/Olds/Cadillac (BOPC) bell housing bolt pattern, so a TH400 automatic will bolt right up to the back of the block as long as the proper Cadillac flexplate and torque converter are used.
Front wheel drive
The TH425 front-drive automatic transaxle also fits these engines as used in the Eldorado, although a special dual-sump oil pan and pickup are used with these transmissions due to the required half shaft clearance. Any RWD engine can be converted to FWD and vice versa if the proper oil pan and pickup are used, although two of the main cap bolts must be removed and swapped for studs with standoffs to mount the pickup bracket.
4 wheel drive
Another good thing about these engines using a TH400 transmission is that a BOPC patterned case can be assembled with the Chevy 4x4 tailshaft and associated hardware for use in an off-road truck. The engine weight is approximately 600 pounds fully dressed and splits the difference between small and big block Chevy, so suspension modifications are not usually necessary. Transfer case choice for a 4x4 should be a NP205, as fitted to some mid/late 1970's Chevy 1 ton trucks. The NP205 is a strong gear-driven transfer case and holds up nicely to the big Caddy's torque output.
700R4 / 4L60 / 4L80E
The 700R4/4L60/4L80E can be good transmissions to use behind the Cadillac 472 and 500, due to the fact that you can run 4.11 gears and not over rev the engine with the overdriven 4th gear.
The 4L80E is a good transmission to use on the Cadillac 472 and 500, due to the strength of the 4L80E. The 4L80E normally requires a stand alone controller for automatic shifting and pressure controls. With a price tag of a CPU controller at $600.00 and higher, it's not a inexpensive swap.
- The following are for comparison's sake and aren't recommendations, per se. As with any large expenditure, research before spending!
For those who want the strength of a 4L80E without the need for an electrical controller, there is the Quadzilla for around $3400.00.
The Compushift ECM (Electronic Control Module) for the GM 4L60E/4L80E costs about $1150.00. A less expensive controller is the Optishift; cost for it is around $600.00. For about half that amount, the MegaShift™ Transmission Controller is available. It requires assembly and some knowledge of electrical circuitry, etc.
When bolting these engines into most any application, use the stock-type Cadillac Eldorado engine mounts, oil pan and associated pickup tube. Fabricate a set of 3/8 inch thick plates to be bolted between the crossmember. The big Cad has the mount bolts 3-1/2 inches ahead of where the Chevy mounts are when measuring from the stock Chevy engine to transmission bellhousing mating surface.
For a 4x4 truck, the engine usually fits well by using crossmember and frame rail notches to clear the oil pump. If the truck originally used a TH350 transmission, the crossmember needs to go back about 3 inches and custom drive shafts will needed. These should use the larger 1 ton U-joints for added durability.
There are different oil pumps for the big Cadillac engines. One faces forward from the block at a 45 degree angle downward. The next faces downward 45 degrees and points right toward the bottom of the crankshaft pulley. There is another, that has been described as pointing more outward than the first one described. These can all be interchanged, but make very sure to properly clean the oil pump and block mating surfaces and always use a new oil pump gasket. The correct gaskets are available from major gasket manufacturers, and should be about 0.005" thick. An oil pump gasket that is too thick will cause more oil to bypass the pump gears and allow more end play of those gears too, something you do not want.
The stock Cad oil pump spring can be shimmed using a Q-jet metering jet to boost oil pressure to about 50-60 psi. 10-12 psi per 1000 rpm is good. Make sure to prime the oiling system using an electric drill to spin the pump after you do this to check for proper operation of the pump and pressure bypass and to check the oil pressure psi.
RWD pans used a front-sump pan and pickup. The Eldorado used a rear-sump setup. Later 425 and 368 engines used a mid-sump style. The latter two pans are what you would typically use for most engine swaps.
If possible, use the front sump oil pan design to eliminate the longer pickup; this will help keep the engine primed instead of using a thicker motor oil.
In cars the clearance problems are usually at the front crossmember, the driver side exhaust manifold, and possibly the HVAC airbox on the firewall. This can be modified with fiberglass or sheetmetal if necessary. Streetrods usually have sufficient room to drop the big Cad engine in. The fit is tight like with a big block Chevy, but the only change usually required will be in motor mount placement. Most all vehicles requiring a rear-sump oil pan and pickup can use the Eldorado pan and pickup tube, or a mid-sump pan and pickup as found on the smaller 368-425 Cadillac engines of 1977-'79 vintage. Stock exhaust manifolds may be used, or aftermarket block-hugger style headers can be sourced from Sanderson. In most cases where a big block Chevy header can be used, the Chevy flanges can be removed and Cad flanges can be made up quite easily. The primary tubes may need a bit of tweaking to line up with the ports with this method. Remember that the front and rear drive exhaust manifolds are different for the driver side. This may help in routing the exhaust if it is a tight fit on that side.
The Cad engines do not fit easily in some GM chassis. Never fit the engine in without putting the exhaust manifold on first. Better yet, use a custom set of block hugger headers, as Cad parts are usually insanely expensive (but worth it in this case).
Stock carbureted intake manifolds can benefit from a 1 inch spacer under the carburetor, adding around 15 hp. Because of the bathtub-type steel intake gasket, plate stock and exhaust tubing can be fabricated into a tunnel ram style dual carb manifold. You can build one of these to use a pair of Quadrajets from 4.1L Buick V6 or 4.3L Chevy V6 engines, as two of these with straight linkage could feed the big motor quite well. The bathtub gasket can be reused by using a bit of Permatex to seal the block and head surfaces by encircling the ports to prevent an internal vacuum leak on both sides of the gasket.
The factory EFI system used from 1975-'76 on 500 cubic inch engines is a port injection system which operates similar to the familiar Chevy TPI. It is a throttle body centered on an intake manifold with separate fuel injectors, and resembles the EFI set-up used on NASCAR Sprint Cup cars ca. 2012. Each cylinder has its own injector mounted in the intake runner near the intake gasket area with a common fuel rail feeding all eight injectors. This system was also used through 1979 on the Seville as standard equipment and as an option on full size cars.
It consists of four main systems; the ECU, the fuel delivery system, the air distribution system, and the sensors which supply information to the ECU. The ECU is a pre-programmed computer that analyzes the sensor information and computes the exact fuel requirements based on that information. It supplies the proper amount of fuel by opening the injectors for a specific amount of time, which varies as the engine operating conditions change.
The fuel delivery system consists of two fuel pumps (one in the tank, one mounted to the chassis), the fuel filter, the fuel pressure regulator, the fuel rails and lines, and the injectors. The fuel system runs with a pressure reading of 39 to 55-95 PSI. A relief valve protects the system from excessive fuel pressure. The fuel regulator maintains the pressure in the fuel rails at 39 psi for proper injector operation. The injectors are divided into two main groups, one for cylinders 1, 2, 7, and 8 and the other group for injectors cylinders 3, 4, 5, and 6. All four injectors in each group open simultaneously, with the two groups alternating in operation.
The air distribution system consists of the throttle body assembly, the air filter assembly, and the intake manifold. The throttle body houses the fast idle valve and the idle bypass air passage. The fast idle valve allows extra air to bypass the throttle blades when the engine is cold and closes as it warms up. The warm idle is adjusted at the idle bypass air passage.
The sensors are as follows:
- MAP (Manifold Absolute Pressure)
- TPS (Throttle Position Sensor)
- MAT (Manifold Air Temperature)
- CTS (Coolant Temperature Sensor)
- Engine Speed Sensor (measured at distributor)
The MAP sensor is housed in the ECU and a plastic vacuum line connects it to the throttle body. The TPS sensor is mounted on the throttle body and is controlled by throttle blade movement. The MAT and CTS sensors are completely interchangeable. The MAT is located on the intake manifold and the CTS is located on the passenger cylinder head water outlet. The engine speed sensor is on the distributor shaft under the cap assembly and sends engine speed and fuel triggering information to the ECU. This system runs in open loop configuration without an oxygen sensor and is quite easy to transplant into any vehicle, as long as all the components are used. The ECU has a separate computer/engine wiring harness that is easily swapped from donor vehicle to the new vehicle with only four wires and one vacuum line needing to be hooked up to work properly. All of the servicing information can be found in Chilton's #8587 manual, which deals exclusively with Cadillacs from 1967 to 1989.
The stock EFI is not very good for performance applications, it does not keep up with aftermarket cams. You need to change the fuel injectors for high flow ones, and use a fuel pump with a return line. The stock EFI will only handle approximately 300 hp max, they're hard to find replacement parts for. There were more Cadillacs made with the 800 cfm Q-jet than with EFI. And what's worse is the EFI equipped engines didn't make much more hp then the carbed versions.
Distributor and wires
Point-type distributors are similar to the familiar Chevy and use the same internal parts, however the internal shaft and the housing are Cadillac-specific. Ignition parts for the HEI-style distributors are also the same as the Chevy engine uses, with a few exceptions. First, like the points distributor, the shaft and housing are Cadillac only. Also, the distributor will differ between carbureted and fuel injected engines. The fuel injected distributor has a position sensor under the main body that tells the computer the engine speed and when to trigger the proper injectors. If you're not sure what distributor you have, the carbureted version looks similar to the Chevy distributor. The fuel injected distributor has a square portion with a round 3-pin plug directly above the clamp area. The hold-down clamp used will depend on the distributor. They don't interchange, so get the clamp when you get the distributor.
Many people have complained about the Cadillac HEI distributor having too much advance. One option is to go to a modified Chevy distributor cut down to fit the Cadillac engines. Many cars, especially the GM F-body, will not allow the hood to close with the HEI distributor in place. You can cut the stock HEI unit down about 2 inches and have it clear everything if you know how to measure and cut correctly. Always reshape the end of the distributor shaft to fit into the oil pump shaft. If cutting and welding the distributor shaft, be careful to not warp it.
Best choice for ignition wires would be a cut-to-fit set, as even the stock ignition wire sets may not fit quite the way they should due to the front-mounted distributor location.