1972 Plymouth GTX / Roadrunner Vs. 1994 Impalla SS with 20’s

A 1972 Plymouth GTX and Road Runner running a modified 318 small block, re-sleeved to accept 340 pistons, takes on a 1994 Impala SS riding on chrome 20s and a factory 260-horsepower LT1. Comments from nearly two decades of viewers confirm the budget build held up long after the cameras stopped rolling. Watch to see why the Impala’s driver stopped smiling by the end of the run.

Everyone at the track expected the lowered Impala SS on chrome 20-inch wheels to win before the two cars even staged. Its owner had spent real money on wheels and stance, and the tired-looking Mopar in the other lane was running an engine most people would call a parts-store afterthought, a 318, the small block Chrysler built by the millions and rarely takes seriously. What nobody in the stands knew was what had been done to that 318 under the hood, and by the end of the run, the Impala’s driver wasn’t smiling anymore.

The 318 Nobody Respects

Chrysler’s 318-cubic-inch small block has a reputation as the engine that came in grocery-getter Furys and work trucks, rated for modest power and even more modest expectations. This particular 318 broke that stereotype by being bored and re-sleeved to accept pistons from the much larger 340, a swap that let the builder run higher compression and a more aggressive cam than a stock 318 block could ever survive. It’s the kind of budget engineering that muscle car forums still argue about: is a heavily modified small block cheating, or is it exactly the kind of ingenuity that built the performance-parts industry in the first place.

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From a Small Carb to 780 CFM

According to the car’s owner, the engine originally ran on a modestly sized carburetor before a 780 Holley replaced it after this footage was shot, a change that alone added an estimated 25 to 35 percent more horsepower. Comments from more than a decade after the original upload confirm the same short block was still running strong with a 340 Torker intake and that 780 Holley, proof the combination held up over the long haul rather than grenading itself the way many big-carb-on-a-small-motor builds eventually do.

20-Inch Wheels vs. a Warmed-Over Small Block

The 1994 Impala SS represented GM’s return to a genuine performance sedan after nearly two decades away from the nameplate, built around a 260-horsepower LT1 V8 borrowed from the Corvette and Camaro. GM paired that LT1 with a 4L60E automatic and a specific low, limited-slip rear end tuned more for highway cruising than drag-strip launches, a detail that likely cost it precious tenths against a car built and geared specifically to leave the line hard. Dressed on 20-inch wheels, it looked every bit the part of a serious street car, and on paper its factory power output should have handled a re-purposed grocery-getter engine without much drama.

Why the Edelbrock Was the Right Call

The owner specifically credits an Edelbrock intake, sized around 625 cfm, for giving the engine the response and drivability that a bigger, more aggressive setup would have sacrificed. Rather than chasing peak horsepower on a dyno sheet, the build prioritized a combination that pulled hard through the whole rev range and stayed streetable enough to be driven to the track and back, a philosophy plenty of budget-build Mopar guys still swear by decades later.

A Build That’s Still Being Talked About Nearly Two Decades Later

What stands out about this matchup isn’t just the outcome, it’s how long the video has kept finding new viewers; comments range from people watching it for the first time to the same commenters returning fifteen and seventeen years after their first viewing to check in. That kind of staying power is rare for a home-video-quality street race clip, and it speaks to how satisfying it is to watch an underestimated engine make good on a bet nobody else believed in.

The GTX and Road Runner Body That Started It All

The Mopar wearing this small-block surprise is a 1972 Plymouth, wearing the GTX badge in its new life as a Road Runner options package — the standalone GTX model had already been retired the year before, when Chrysler pulled the plug on the high-compression engines that defined it. The GTX name had debuted in 1967 as Plymouth’s answer to the GTO, always paired with big-block power as standard equipment, which makes finding one running a small-block substitute like this all the more unusual for the badge’s own history. By 1972, insurance costs and tightening emissions standards had already begun gutting the muscle car market that produced cars like this one, which makes a well-sorted survivor still running hard on the street thirty-five years after this video was filmed even more noteworthy.

The Sleeper Car Tradition

Cars like this 318-powered Mopar sit at the heart of sleeper culture, vehicles deliberately built to look unremarkable while hiding real performance under the hood, precisely so moments like this one happen. The tradition goes back to factory sleepers of the muscle car era itself, when manufacturers occasionally dropped big engines into plain-Jane trim levels specifically to catch buyers and competitors off guard. This 1972 Plymouth, worn-looking paint and all, fits that lineage perfectly, and it’s exactly why the reaction in the video matters as much as the elapsed time.

Budget Builds vs. Bolt-On Culture

This matchup captures a tension that still exists in the muscle car community: the value of clever, budget-minded engineering against the appeal of writing a check for bolt-on performance and curb appeal. The Impala’s owner invested in wheels and stance; the Mopar’s owner invested in machine work most spectators would never see just by looking at the car. Both approaches have their place, but this particular afternoon belonged to the guy who spent his money where it actually made the car faster, which is exactly the kind of result that keeps this video getting shared in Mopar forums whenever the debate over engine swaps versus curb appeal comes up again.

What This Small Block Proves About Chrysler Engineering

Mopar’s small-block family shared enough architecture across the 273, 318, and 340 that swaps like this one were common practice among budget-minded builders throughout the 1970s and 1980s, long before crate-engine kits made big power a credit-card purchase. Pulling this kind of result out of a 318 rather than simply dropping in a factory 340 or 360 took real machine-shop knowledge, and it’s exactly the sort of hands-on problem solving that separates a genuinely quick small block from one that just sounds good revving in a driveway.

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