Like so many of Smokey Yunick’s projects, the Reverse Torque Special is surrounded in myth and legend. Let’s see what we can sort out.
In American oval track racing, there’s a very old idea with almost mystical appeal: reverse engine rotation. We’ll let Yunick himself, in his autobiography, Best Damn Garage in Town (Indy racing volume, p.22), describe the theory behind it:
“Look, if you’ve got a front engine car with rear wheel drive, open the door and leave it wide open, and then start engine without putting it into gear, goose the motor good. Notice how driver’s door raises up and right side of car goes down (this conversation is for circle track left hand turns only). With conventional engine rotation, you’re transferring weight to the right side of the car—when you turn left the weight goes there anyway. The idea of reverse rotation is, when you accelerate hard the weight comes to the left front and left rear, and pulls weight off of the right front. This more evenly distributes weight across the chassis, increases your lateral traction on the front and back end. You go faster.”
That’s the gist of it: Most modern passenger car engines rotate counterclockwise as viewed from the flywheel. (There’s no critical reason; it’s mainly a convention.) If we could reverse the engine’s torque and thus the torque reaction on the chassis as well, then theoretically we can improve load distribution for the left-hand only turns of American oval tracks. And that was Smokey’s plan with his entry in the 1959 Indianapolis 500. The Reverse Torque Special was a Kurtis-Kraft 500H featuring a special trick. Its Offy engine and drivetrain were modified to rotate in the opposite direction.
The Reverse Torque Special on pit road at the Indianapolis Motor Speedway in May, 1959.
How did Smokey accomplish this feat? Actually, on a traditional Indy roadster it was fairly straightforward. The classic tool-room engine, an Offy four-banger could be configured to run in either direction without any particular difficulty—most of the directionally critical components could be mirrored. (In marine and aircraft engines, so-called reverse rotation is totally commonplace.) Meyer & Drake records indicate that Yunick simply specified reverse rotation when he ordered engine no. 210 from the company. (As reported in Offenhauser: The Legendary Racing Engine and the Men who Built it, by Gordon Elliot White, Motorbooks International 1996, p. 190.) What price premium Yunick may have paid for this feature is not recorded.
From there, the remaining challenge was to reverse the drivetrain to match. In most normal rear-drive axles, you will find the ring gear on the left side of the pinion, supporting conventional engine rotation. But Halibrand, the manufacturer of the quick-change axles used in Kurtis roadsters, also offered mirror-image units with the ring gear on the right for use in FWD and 4WD racers. Otherwise Identical to the standard quick-change, these were known as “Front QC” units. (Current racing axle suppliers continue to offer the necessary components to this day.)
So we don’t know exactly how Smokey did it back in 1959, but we can say this much: There’s no reason he couldn’t have assembled his seemingly esoteric reverse-rotation special entirely from ready-to-wear components. Any clever mechanic could do it, it seems, and Smokey was as clever as they came.
Tommy Ivo’s 4WD, four-engine Buick Showboat dragster used a Halibrand Front QC unit to drive the front wheels.
So how did the Reverse Torque Special perform? Quite respectably: Veteran Duane Carter qualified the car 12th and finished 7th, running competitive speeds and averaging over 133 mph for 500 miles. The reverse torque principle didn’t embarrass itself, but then it didn’t really distinguish itself either. The clear evidence is that engine rotation isn’t terribly critical either way. And that’s no doubt why the reverse-rotation concept, as seductive as it might seem, has never caught on in oval racing in all these years. Let’s take a closer look.
The traditional rear-drive live axle with its torque and reaction forces.
Just as Smokey described, engine-driveline torque produces an equal and opposite reaction upon the chassis, lifting the left side of the body, pushing down on the right side, and redistributing the load to the outside of the corner in a left-hand turn. Which is not good, all things considered.
Torque reaction also lifts the right end of the rear live axle and pushes down on the left, with the axle housing forming a sort of lever. On a typical car developing oh, 300 lb-ft of crankshaft torque, there might be 75-120 lbs. of force loading one end of the axle and unloading the other. (Or, maybe why your vehicle’s right rear wheel spins helplessly when you’re stuck in the snow.) But for oval racing at least, this redistribution is in a nominally helpful direction—from the outside to the inside tire.
And note that reversing the engine’s rotation does not cancel the reaction forces in any event. It simply reverses them. And in the case of the forces acting on the axle housing, it’s in the wrong direction for oval racing.
When we get to the bottom line, the forces involved are not great enough to justify the cost and bother of reversing engine rotation. Much the same effect can be achieved simply by cranking in a bit of chassis preload with a few turns of a wrench—which is much faster, easier, and cheaper, we have to admit.
So alas, Yunick never built another Reverse Torque Special in his successive attempts at Indy, nor did anyone else of note. (As far as we know.) We salute the man who had the independent mind and competitive spirit to try it in the first place.
A rear axle assembly with independent rear suspension.
As a final note, on contemporary road and race cars with independent rear suspension, lateral torque reaction isn’t an issue. The axle’s center housing is bolted rigidly to the chassis, and the two axle shafts are articulated with universal joints. There is no beam axle housing and no lever arms to load one end of the axle and unload the other.
Smokey Yunick fan? Read about his infamous 7/8 scale NASCAR Chevelle here.
Smokey Yunick at the Optron with a small-block Chevrolet.
Long ago, I installed a “hot” reverse rotation cam in a Corvair engine that was destined for a Karmann Ghia with the stock VW transaxle, it was a real sleeper.
Great explanation, Bill. Thinking of the era when tires were skinny and drivers were wide, it’s hard to envision laying down much traction with simple engine rotational torque. In fact it is hard to imagine one of those monsters laying down a 10/10ths lap on those iron wagon wheels. I do give them credit for trying something interesting, which has been legislated out of what we once called “racing” …
I had heard that he ran some stock car engines in reverse also – Hudsons if my memory is correct.
A decade or so ago reverse rotation engines were often used in Sprintcars. Reputedly it made them drive harder off the left rear and less stagger could be employed. Though it seems to have gone out of fashion now.
CHAP Racing
You are correct that a beam axle reacts the torque increasing left side load. However, the independent rear suspension with the differential mounted to the chassis the engine torque is applied through the chassis and reacted by the springs at the rear. That takes care of the rear, but at the front or at the engine the torque force is equal and opposite and applied to the chassis. With independent rear, the reaction is balanced within the chassis. With the beam axle, the reaction to 300 ft.-lbs. on a 72″ wheelbase would be 50 lbs. down directly on the left wheel and -50 lbs. on the right. Also the equal and opposite torque at the engine attachment through the chassis applies 50 lbs. to the right and takes 50 lbs. from the left. This reaction is shared by the front and rear wheels. So on the scales, the load on the RF & LR increases 25 lbs. per wheel while the LF & RR loses 25 lbs. per wheel or 100 lbs. of cross weight or wedge.
Yes, this is a very old trick, but I don’t think (with all due respect) Smokey was the first to do this. I believe that John Bandimere Sr. did it with an early OHV Caddillac in the early fifties.
According to smokeys book he made the parts to turn the motor in reverse. Engine #210 was not purchased until 1961 This car ran in the 1959 Indy 500