The fastest sleeper car I ever heard about was probably also the ugliest - a 1955 Ford 4 door that belonged to a mechanic at a garage I worked in the summer after high school. Every inch was dented, rusted or scraped. The rear doors were welded shut. The guy was running the Ford Tunnelport 426 c.i. engine that Mario Andretti used to win the 1964 Daytona. Hotter cams and bigger carbs than Andretti, too, since it didn't have to run all out 500 miles without breaking. He had dual differential gears - 4.11 for the street, 5.20 for the strip. The car could pull wheelies, just like in F&F; he had wheelie bars for the strip. The frame was cross welded (first time I ever heard of sub-frame connectors). Before freeways, he drove from San Jose to Napa in under an hour (about 80 miles). He used to race for pink slips (and made money selling the cars back to the owners). The car got stolen from his mom's garage while he was in 'Nam. I only got to see the pics. When I knew him, he was putting a Carrera engine from a car that had crashed at Nürbergring into a beat-looking 914. This guy was the king of sleepers.

 

This reminds me of two very fast sleepers I read once in Popular Hot Rodding.

Street legal: A 1985 Cadillac Fleetwood Brougham D'elegance with a built up 500ci Caddy engine, 175 shot nitrous, cutouts, and white wall slicks. 12.99 et's totally stock looking. The ultimate sleeper I think.

Not so legal: A 1964 Chrysler Imperial stripped down to the frame! "The Incredible Hulk". With slicks it ran 9.90 et's!!

 

Around the same time I was working in that shop, I knew a guy who built AA fuelie dragsters. His wife's grocery car was an 11 second '69 Camaro. It sounded like it, though.

My mom's next door neighbor at the time had a '39 Ford split window coupe, very nice, chocolate brown, moon hubcaps. It had a Chevy 327 with Corvette fuelie heads, but no headers since it wouldn't clear the steering box and he didn't want to relocate it, so it was very quiet, which fooled everybody. That car ran mid to low 11's. I remember his daughter's boyfriend giving a Challenger with a 6-pack a 3 car lead off the light, then the driver's jaw dropping when we blew by ....