The 1958 model year was to be the last use of the old FirePower Hemi in the 300. The engine was still 392 cu in (6.4 L), but tuned to 380 hp (280 kW) as standard. Thirty-five cars were built with fuel injection and delivered 390 hp (290 kW), but the fuel injection system was troublesome and most cars soon had it replaced with the standard twin-quad carburetor setup. A 300D was driven to 156.387 mph (251.680 km/h) at the Bonneville Salt Flats that year, but only 618 hardtops and 191 convertibles were produced, in part due to a recession in the economy.
1959 saw the Hemi engines replaced by Chrysler's new Golden Lion wedge-head V8 at 413 cu in (6.8 L) displacement (which Chrysler called "lion-hearted"). Power output remained about the same at 380 hp (280 kW). The loss of the Hemi and the late-1950s recession meant sales of 522 coupes and 125 convertibles. Power swivel seats were standard.
The 1960 300F introduced a new, higher power 413 cu in (6.8 L) Wedge engine delivering 375 hp (280 kW) in standard form. To boost power at lower and mid rpms, a special "cross-ram" intake manifold was derived. Instead of the normal V8 engine central intake manifold with carburetor(s) on top, the cross-ram consisted of two pairs of 30 in (760 mm) long tuned pipes that criss-crossed so that each set fed the opposite side of the engine. The carburetors and air cleaners hung off the sides of the engine over the fender wells. These long tubes were tuned so that resonances in the column of air helped force air into the cylinders at those engine speeds. Also new were four individual, leather bucket seats with a full length console from dash to rear seatback. Swivelling front seats were fitted as standard equipment.
A special 400 hp (300 kW) "short ram" version was produced for competition; in this, the tuned portion of the stacks was only 15 in (380 mm) long (though the overall tube length remained at 30"), so that the resonant effect was produced at higher engine speeds. Only 15 "short ram" cars were produced; these were also fitted with the exotic but often troublesome French Pont-a-Mousson 4-speed manual transmissions developed for the Chrysler-powered Facel Vega. Approximately 4 of these "Special GTs" are known to exist, including one convertible and one with air conditioning; it is believed that 15 were originally produced.
The bodywork was also redone for 1960, using Chrysler's new lightweight unibody construction and given sharper-edged styling with outward-tilting fins that were visually separated from sides. The "toilet seat" trunk lid contributed to a demeaning opinion of the 300F and was done away with after this one year of production.
Sales increased to 969 coupes and 248 convertibles.
The 1961 300G saw another restyle. The grille, formerly wider at the bottom than the top, was inverted; the quad headlights, formerly side-by-side, were arranged in angled fashion, inward at the bottom, in a manner reminiscent of 1958-1960 Lincolns. Small parking lamps below the headlights were likewise slanted and V-shaped, and the front bumper was canted up at each end, scoop-like. At the rear, the taillights were moved from the fins to the tail below them, and the fins were made sharper-pointed. Power windows were standard.
Mechanically, the cross-ram "short ram" and "long ram" engines remained the same, although the expensive French manual transmission was dropped, and replaced by a more reliable and still expensive Chrysler racing manual transmission (referred to as 'option code 281'). There are currently only five cars with this transmission. Code 281 cars may have been built for the 1961 Daytona Flying Mile, although like the 1960 F Specials, no specific records were kept by Chrysler. Unlike the 300F Specials (which were randomly pulled from the line and upgraded for the Flying Mile), the 300Gs had a specific build code (281).