Image Credit: Mecum.A 1966 Plymouth Belvedere convertible is already an uncommon sight, and this bright red example has received a substantial performance upgrade. Sitting under the hood is a dual-quad 426-cubic-inch Hemi V8 paired with a four-speed manual transmission.The combination gives the restored drop-top considerably more muscle than its understated Belvedere styling might suggest. A black convertible top, black bucket-seat interior, and period-inspired wheels complete the classic Mopar appearance.According to the Mecum auction listing, the car is heading to the auction house's Nashville 2026 sale, where it will cross the block on Friday, September 25. Mecum describes it as having undergone a frame-up restoration and highlights its Hemi-powered drivetrain among the major selling points.AdvertisementAdvertisementThere is an important piece of history behind that engine bay, however, and the Belvedere's VIN tells the story. Decoding it reveals what originally powered the Plymouth before someone decided this convertible deserved considerably more firepower.The 318 V8 Has Been Replaced By A 426 HemiImage Credit: Mecum.The centerpiece of the build is now Chrysler's legendary 426 Hemi. Mecum doesn't provide a horsepower figure for the engine, so we don't know whether it's received some aftermarket performance parts or not, but it punches out 425 horsepower even in stock form.Its factory 318 would have provided a considerably different driving experience from the dual-quad 426 currently occupying the engine bay.A four-speed manual transmission backs the Hemi, giving the convertible an appropriately engaging drivetrain. Power steering and power brakes should make the significantly upgraded Belvedere a little easier to handle away from a straight stretch of pavement.It Received A Frame-Up RestorationImage Credit: Mecum.The listing describes the Plymouth as having undergone a frame-up restoration, and the auction photos show a car presented in exceptionally clean condition. Its red bodywork is paired with a black convertible top and matching boot cover.AdvertisementAdvertisementInside are black bucket seats separated by a center console. The straightforward cabin retains the character of a mid-1960s Plymouth while complementing the much more serious hardware underneath the hood.Styled Road wheels wrapped in Diamondback Redline radial tires complete its current presentation. The combination gives the Belvedere the familiar period muscle-car appearance without distracting from its convertible bodywork.The Convertible Was Already An Uncommon BelvedereImage Credit: Mecum.Plymouth built the Belvedere in significant numbers during 1966, although convertibles represented a small portion of production, with just 2,502 examples built for the model year.The VIN begins with RH27, identifying this car as a Belvedere convertible, while the E engine code points to its original 318 V8. That makes this an authentic 1966 Belvedere convertible that has subsequently been transformed into a Hemi-powered build, rather than one of the highly valuable factory Hemi cars.AdvertisementAdvertisementThat's something collectors concerned with originality will care about. For someone interested primarily in the experience of a four-speed, dual-quad Hemi with the roof folded down, it could make the car considerably more approachable than a genuine factory Hemi example.It Crosses The Block September 25Mecum hasn't published an auction estimate for the Belvedere, leaving its eventual value up to bidders in Nashville. Its combination of an uncommon convertible body, extensive restoration, and desirable Hemi swap gives buyers several reasons to pay attention.Originality usually carries considerable weight at the upper end of the classic Mopar market, so the factory 318 history shouldn't be overlooked. This Belvedere offers something different: the looks of a restored 1966 Plymouth convertible with one of Chrysler's most celebrated engines sitting where that modest small-block used to be.
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