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Doc's Caddy Knowledge

Basic Engine Specifications

Tune-up Specifications

Year--Disp.-Fuel-Sparkplugs-Dist.-Timing BTDC-Intake opens-Idle speed











General Specifications

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Fastener Torque Specifications

Year-Disp.-Head-Rod-Main-Crank damper-Flywheel-Intake-Exhaust

' fit...60...30...35

Modifications and Swapping

Biggest gains in power output come with cylinder head work. Pre-'72 heads are small chamber 72 c.c. and are good for around 12 to 1 compression with race gas, the '73 and later heads have larger 120 c.c. chambers and are a better choice for a pump gas torquer with an 8.5 to 1 ratio. The best bet for a pump gas premium street torque monster is a set of '77-'79 425 heads, these offer an honest 10-1 compression ratio on both 472 and 500 engines. Big gains can be made by adding larger valves and induction hardened seats, the valve sizes can be boosted to 2.08/1.70 without worry of hitting the water jackets, and the usual porting, valve unshrouding, and minor bowl work, although the short-side radius should be left alone to avoid drastic differences in airflow. Roughly 20 horses can be gained by this work alone, and most of that comes from the larger valves.

Blocks should get the standard deburring, a drain hole can be drilled into the rear of the lifter valley for better drainback, also 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, a later block has 1/2 inch oil galleries for increased flow through the block, so it makes a good performance base. If the front cover has rust pitting from the water pump, it can be saved by sandblasting and filling the pits with JB Weld and then painting. One more thing about blocks, a 472 can be made into a 500 by swapping in the 500 crank and pistons, though on '68-69 engines a slight amount of notching is necessary at the bottom of the cylinder bores.

High Performance Tolerances

Crank endplay- minimum .008

Rod side clearance- .035

Top ring- .020

Second ring- .018

Cam degreeing benefits from advancing the cam timing 2 degrees, as these engines had a retarded cam in stock form for emissions. Attach the degree wheel to the crank with a 9/16 fine thread bolt.

The basic 472 and the later 500 engines both use a standardized Buick/Pontiac/Olds/Cadillac bellhousing pattern, so a Turbo 400 automatic will bolt right up to the back of the block, as long as the proper Cadillac flexplate and torque converter are used. The Turbo 425 front-drive automatic transaxle also fits these engines as used in the Eldorado, though a special dual-sump oil pan and pickup are used with these transmissions due to the needed halfshaft clearance. Any rear-wheel drive engine can be converted to front-drive, and vice versa if the proper oil pan and pickup are used, though 2 of the main cap bolts must be removed and swapped to mount the pickup's bracket. Another good thing about these engines using a Turbo 400 transmission is that a B/P/O/C patterned case can be stuffed 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 205, as fitted to some mid/late '70's Chevy 1 ton trucks, the 205 is a strong gear-driven transfer case and holds up nicely to the big Caddy's torque output.

When bolting these engines into most any application, use the stock-type Cadillac Eldorado engine mounts, oil pan, and associated pickup tube and fabricate a set of 3/8-1/2 inch plates to be bolted to the crossmember, the big Cad has the mount bolts roughly 5 inches ahead of where the Chevy mounts are when using the stock rear Turbo 400 transmission mount. For a 4x4 truck, the engine usually fits well with crossmember and framerail notches to clear the oil pump, if the truck originally ran a Turbo 350 transmission the crossmember goes back about 3 inches, and custom driveshafts will need to be made up to fit, these should run the large 1 ton U-joints for longest life.

In cars, the clearance problems are usually at the front crossmember, the exhaust manifold at the driver's side, and possibly the airbox on the firewall, though this can be dimpled with fibreglass or sheetmetal if necessary. Streetrods usually have sufficient room to drop the big Cad in, the fit is tight like with a big Chevy but the only change 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 '77-'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 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's side, this may help in routing the exhaust if it looks like a tight fit on that side.

Stock carbureted intake manifolds benefit from a 1 inch spacer under the carburetor, this will add around 15 horses. Because of the bathtub-type steel intake gasket, plate stock and exhaust tubing can be fabricated into a tunnel-ram style dual carb manifold, I built one of these to use the Quadrajets from 4.1 liter Buick V-6 engines, as two of these with straight linkage 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, encircle the ports to prevent an internal vacuum leak on both sides of the gasket.

The factory EFI system used from '75-76 on 500 cubic inch engines is a ported injection system which operates similar to the familiar Chevy tuned port injection, but appears like a large throttle body on an intake with separate fuel injectors. Each cylinder has it's own injector mounted in the intake runner near the intake gasket area with a common fuel rail feeding all 8. This system was also used through 1979 on Sevilles 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 system consists of 2 fuel pumps(1 in tank, 1 on chassis), the fuel filter, the fuel presure 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 2 main groups, one for cylinders 1, 2, 7, and 8, and the other group for injectors 3, 4, 5, and 6. All four injectors in each group open simultaneously, the 2 groups alternate in operation. The air distribution system consists of the throttle body 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(intake pressure), TPS(throttle position), MAT(air temp), CTS(coolant temp), and RPM(engine speed measured at distributor). The MAP sensor is housed in the ECU and a plastic vacuum line connects this 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, MAT located on the intake manifold and CTS located on the passenger cylinder head water outlet. The RPM sensor is on the distributor shaft under the cap assembly, it 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 4 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.

Point-type distributors are similar to the familiar Chevy, and use the same internal parts, however the internal shaft and the housing are Cadillac only. 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 the same as the Chevy, and the fuel injected has a square portion with a round 3 pin plug directly above the clamp area. Finally, the hold-down clamp used will depend on the distributor, they don't interchange so get the clamp when you get the distributor. Best choice for ignition wires would be a cut-to-fit set, as even the stockers do not fit quite the way they should due to the front-mounted distributor location.

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