Hello Fellow Enthusiasts,
I recently heard a story but am unsure of its truth. I was told that a guy my friend knew had his engine rigged up to run on two of his six cylinders. When he would race, he would reformat his engine to use all six cylinders. My friend was using terms such as "duece" and "links" as in he would "unlink" and "relink".

The engine that this was done to was a late 60s model Chevelle. I understand that in our current age cars/trucks can do this but is it possible to do this with an older car such as a 1970 Cutlass S?

 

A couple years ago, I saw a couple Honda CRX hatchbacks that were rigged to activate or deactivate cylinders. The more primitive one had a pendulum-controlled computer that would shut off two fuel injectors when they were not needed. Obviously, bumps, corners, and other conditions affected it, so the owner built an electronically controlled, far more complex system that also shut off two fuel injectors. The cars idled very poorly when the systems were activated, but would smooth out at higher speed.

I wonder if your friend was referring to cylinders or barrels? I've heard of the V8's with three, two barrel carburetors- sometimes they were called "six-packs", sometimes "tri-power", and I think I remember them being called "three deuces". It would be a simple matter to disconnect the linkage for two of the carburetors, leaving the third two-barrel to run the engine during normal driving. This would not deactivate any cylinders, however, as the third carburetor (usually the center one of the three) would still feed fuel to all the cylinders.

 

So you are saying that this would do nothing to help the overall fuel efficiency of the car?

 

It would probably help, but modern cars that do it don't gain a whole lot. There is some gain in MPG, enough to make it worth it I guess.
Doing it with carbs might cause fuel/air distribution issues, some cylinders run lean, some rich. Fuel injection can control the mixture much more precisely.

 

Disabling 2 of 3 carbs makes the engine run just like any other 2 barrel engine- but with all three carbs linked together, you increase the potential amount of air-fuel mixture that the engine can take in. This doesn't matter much for regular gentle driving, but stuff your foot to the floor and you'll feel the difference.

It's very difficult to make a multi-displacement engine by enabling and disabling carbs, because all of the cylinders draw fuel and air from a common manifold. Somebody in the late '70's (Cadillac, I think) used a 4-6-8 system where the V8 could switch between 4 cylinders for coasting, 6 cylinders for cruising, and 8 cylinders for power. The change was not in the fuel delivery system, but rather in the valve train. A solenoid activated or deactivated the intake valves as needed. The downside to the system is that the 4 cylinders that are running now have the added drag of the 4 cylinders that are not, kind of like pulling dead weight around, which I would think would really kill the efficiency of the idea.

 

The 3 2 barrel set ups of the 60s and 70s used progressive linkages to do just that. Under part throttle the center carb would be working, but under hard acceleration the 2 outboard carbs would open up. It's like most 4 barrel carbs. The front 2 (primary) barrels would operate under all driving conditions, but under more throttle the rear (secondary) barrels would open allowing more air and fuel into the engine.