Four-speed dual-quad Positraction 409

“Four-speed” equals four-speed floor-shifted standard transmission, the pinnacle of hotrod transmissions in the late ‘50s and early‘60s.
The Borg-Warner T10 was the first four-speed car transmission available. It debuted in the ’56 Corvette, but quickly gravitated to other GM product lines, e.g. the ’57 Chevrolet and Pontiac.
It also shifted with a manual floor-shift lever, much more direct than shifters on the steering-column.
Hot-rodders had been converting their column-shift cars to floor-shift for years.
A four-speed just added another gear, sporting practice.
I think it was an adaptation of a three-speed transmission, and shifter-linkage was outside the gearbox.
An alternative was automatic transmission, but it sapped power to run pumps, so wasn’t as efficient as standard transmission.
Automatic transmissions also relied on hydraulics, so the engine had to rev fairly high to get a decent rate of acceleration.
Slip-and-slide with PowerGlide. (PowerGlide was Chevrolet’s automatic transmission.)
Automatic transmission did not shift as quickly as a manually-shifted standard transmission, although that advantage degraded.
Now drag-racers use auto-tranny. It’s usually faster than a manually-shifted standard transmission.
“Dual quads” equals two four-barrel carburetors, quite a bit of carburetion at that time.
Now single four-barrel carburetors are available with higher intake-rates than dual quads.
But in 1960 dual-quads were pretty strong.
I remember a high-performance SmallBlock Corvette engine available with dual quads.
With dual-quads an engine can move a lot of intake-air, and thereby be very powerful.
“Positraction” was a special differential design to offset wheelspin.
Dump the clutch in a drag-car, and one wheel might start spinning. Differentials being what they were, to accommodate different wheel rates as car rounded a corner, would transfer power to the spinning wheel, while not much would get to the wheel that hadn’t broken traction.
Positraction stopped wheelspin, and delivered equal power to both drive-tires.
A car with Positraction didn’t burn up one side with wheelspin.

A 409.

“I wonder how many realize how significant the 409 was when it debuted for the 1961 model-year?” I commented to my wife.
“Probably anyone else from that era interested in hotrod performance,” she said.
Detroit had been flirting with 400 cubic-inch displacement for years.
Ford had an engine at 390 cubic-inches, and Mercury had an engine at 430 cubic-inches.
But it was a stone.
It seemed no one wanted to take hotrod engine displacement over 400 cubic-inches.
But then Chevrolet bored and stroked their 348 cubic-inch truck-block to 409 cubic-inches.
The 400 cubic-inch barrier had been jumped.
And it was Chevrolet that did it, not Pontiac or Oldsmobile or Ford.
Humble Chevrolet with a killer motor!
Everyone wanted a 409, the car that beat all competition.
I remember Bill “Grumpy” Jenkins racing a 409 Chevy at Cecil County Drag-o-Way in northeastern Maryland.
He always won. Nothing could beat his 409.
That is, until Chrysler debuted its 426 Hemi motor, at which point Grumpy switched to a Hemi.
My brother-in-Boston, very much a Chevy-man, claims the 409 is the first “BigBlock” motor.
Not exactly.
The 409 is mega displacement, but not the same block-casting as later “BigBlocks.”
The 348 cubic-inch truck motor was also called a “BigBlock,” but it’s not the same casting as the “BigBlock” introduced in the 1966 Corvette at 396 cubic-inches. (That engine was later expanded to 454 cubic-inches; and is no longer installed in cars.)
Later BigBlocks had special cylinder-heads, almost a Hemi, with splayed valves.
The 409 wasn’t that.
Its valves were at the same height like the Chevy SmallBlock.
And it wasn’t the same casting as later BigBlocks.
It was its own design, unrelated to the SmallBlock or later BigBlock.
Of interest was that all 409s were essentially custom-made.
Bore a 348 out to make it a 409, and you’re asking for casting porosity.
Tiny air-pockets might be in the cast-iron that could leak coolant through the cylinder-walls.
Every 409 had to be manually checked to make sure it wouldn’t leak.