Stock 1970 426 HEMI engine dyno.

After a four-year restoration, this numbers-correct 1970 426 Hemi finally hit the dyno — but a later update reveals the pull you’re watching wasn’t even the engine’s true number. Rich carburetors likely left ten to fifteen horsepower on the table. Watch the pull and find out what almost got missed.

Four years is a long time to spend chasing one number on a dyno graph, but that is exactly what it took to get this 1970 426 Hemi back to the pull you are about to watch. The engine had been apart, rebuilt, and reassembled across a restoration that stretched over four full years, and when it finally roared back to life on the dyno, the numbers told a story that was almost, but not quite, complete. There is a wrinkle buried in the update notes that most viewers scroll past, one that means this legendary engine still has horsepower left on the table.

The Engine That Needs No Introduction

The 426 Hemi needs no introduction to anyone who follows Mopar history, but its origin story is worth repeating anyway. It began life as a NASCAR homologation engine, built to dominate stock car racing in the mid-1960s, then detuned just enough for street legality in 1966, built around hemispherical combustion chambers that gave it both its name and its reputation for making power other big blocks simply could not match. Chrysler officially rated it at 425 horsepower, a number widely understood even at the time to be conservative for marketing and insurance reasons, which is part of why the Hemi remains the most mythologized big block Detroit ever produced, decades after the last one left the factory.

⚑ Featured Gear

Start Car Conversations →

As an Amazon Associate I earn from qualifying purchases.

Four Years, One Engine, One Dyno Pull

Getting a stock-spec Hemi back to its factory dyno numbers is a far more demanding project than building a modified engine for maximum output. It means sourcing correct casting numbers for the block and heads, period-correct carburetors and intake manifold, original-style ignition components, and holding machining tolerances that match what left the factory rather than what performs best on paper. A four-year timeline reflects exactly that kind of parts hunting and precision machine work, prioritizing correctness over shortcuts at every single step, even when a faster and cheaper path was available.

The Update That Changes the Story

Buried in a March 2021 update to this video is the detail that changes the whole story: the carburetors were later rebuilt and found to have been running extremely rich during the original dyno pull, likely costing the engine ten to fifteen horsepower it was fully capable of making. Carburetor tuning is notoriously the last and most finicky step in extracting a big block’s true number, more art than science even for experienced tuners, and this update is a reminder that even a picture-perfect restoration can leave real performance on the table until the details are dialed all the way in.

Why Stock Numbers Still Matter to Restorers

None of that diminishes why builders chase numbers-correct restorations in the first place. A stock-spec dyno pull, even an imperfect one, preserves exactly what these engines delivered from the factory floor, which matters enormously to Mopar collectors chasing authenticity over raw output. Four years of work went into proving what a real 1970 426 Hemi could still do, and the fact that there was even more left to find, hiding in a set of over-rich carburetors, only adds to the engine’s mystique rather than taking anything away from it.

What Comes Next for This Engine

What happens next for an engine like this is almost always more dyno time, since a builder who has already invested four years chasing correctness rarely stops at “close enough” once a specific shortfall has been identified. A re-jetted or professionally re-tuned carburetor setup would be the logical next step, and it would not be surprising to see a follow-up video from this same build showing a second pull with the missing ten to fifteen horsepower finally accounted for, closing the loop on a project that has already spanned four years of work.

Watch the full video and share your thoughts below.

Republished by Blog Post Promoter