Cadillac engine knowledge

(Stroke can be measured through spark plug hole if it will turn.)

1968-'74 472, 77-'79 425, '80-'85 368: 4.060" (less than 4 1/8")

The biggest gains in power output come with cylinder head work. Pre-'74 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 '74 and later open chamber heads have 120 cc chambers giving compression ratios of 7.5-9 to 1 depending on the piston used. 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.  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.

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, 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 [[Pitted rust|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, although on 1968-69 engines, a slight amount of notching is necessary at the bottom of the cylinder bores.

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 to 1 compression on alcohol. It's said the block can take it, but the cast crank might not be able to.

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. For those who want the strength of a 4L80E without the need for an electrical controller, there is the [http://www.transmissioncenter.net/4L80E.htm Quadzilla] for around $3400.00.   

The [http://www.transmissioncenter.org/compushift_4l60e_4l80e.htm Compushift CPU] for the GM 4L60E/4L80E costs $1136.00. A less expensive controller is the [http://www.optishift.com/ OptiShift]; cost for it is around $600.00. For about half that amount, the [http://www.msgpio.com/manuals/mshift/4L60e.html MegaShift™ Transmission Controller] is available. It requires assembly and some knowledge of electrical circuitry, etc.

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 V-6 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.

===Distributors===

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 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 stock ignition wire sets may not fit quite the way they should due to the front-mounted distributor location.

Many people have complained about the Cadillac HEI distributors having too much advance. One option is to go to the Chevy distributor and cut it 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. Never cut and weld a shaft together, as it will warp it.