The Cadillac Series 90 for 1938 was essentially a Series 75 with a V-16 engine. Even though the wheelbase was 330mm shorter, the bodies were equal or larger in all dimensions than previous Cadillac V-16's. This was accomplished by fitting the nearly flat engine low in the frame and partially behind the line of the firewall. V-16's were distinguished from the counterpart V-8's by a coarser pitch eggcrate grille, fender lamps, and streamlined louvers on the hood side panels and all fender skirts.

The new V-16 engine was of L-head, short stroke square design, cast-en-bloc, with 135 degree Vee. With each block in running balance, the engine was basically a twin-eight. Dual accessories included carburetors, oil bath air cleaners, manifolds, distributors, coils, fuel pumps, and water pumps. The fuel pumps were interconnected so that either one could supply both carburetors if needed. Only the left hand distributor contained breaker arms; the two arms being electrically independent but operated by a single eight-lobe cam. The right hand unit acted only to distribute the high tension voltage to the spark plugs in the right bank. A cross pipe connected both exhaust manifolds and fed into a single down-pipe at the left. The generator was placed low in the Vee and was driven by an internal rubber ring in the fan hub acting on a driven wheel on the generator shaft. This arrangement allowed for fan speeds less than engine speed and generator speeds nearly twice engine speed - it lasted only one year.