If Jay Leno waits around a parking lot so he can talk to you about your car, rest assured, you've done a hell of a job with it.

And that's exactly what happened here. 

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Leno intercepted Savant Young, the owner of this stellar 1973 Mazda RX-3, outside the Peterson Automotive Museum in Los Angeles. There, the famous gearhead learned that while the gorgeous gray coupe sports a rotary engine, the original mill has been swapped in favor of a unit from a second generation RX-7.

Extensive mods, including a bridge-ported intake, mean the engine has a lumpy idle and produces somewhere in the neighborhood of 400 horsepower. And for a car which probably weighs about as much as a loaded shopping cart, that's a scary amount of poke.

Now, General Motors Company's [NYSE:GM] venerable LS engine has been transplanted into virtually everything, including plenty of RX-7s. So it's really cool to stumble across swaps which go for creativity and authenticity over the—somewhat stereotypical—addition of American muscle.  

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Watch the video to find out more about Young's super-cool build.  

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