I read up about the multiple displacement V8 a while ago (when your not using full power certain pistons shut down to help mpg) it seems like a great idea, but how come no one ever uses them? have they had problems with them? too expensive? also have there been any lines of vehicles that have used them? i know the new jeep cherokee has one.

 

i know my bros new 05 f150 has something like that, it has a second smaller radiator system and when the main system fails it switches to running on 4 cyclinders and uses the backup system, havent read on it but thats what i heard. i dont know how efficient it would be being that you still have to push the rest of the pistons and the ignition and fuel system would be expensive.

 

The first car I'm aware of that used it was a '81 Cadillac (8-6-4). When it was working right (which wasn't often), it felt like an extra "shift" when a pair of cylinders kicked in or out. What happened a lot is the computer couldn't decide how many cylinders to run, so the engine just stalled out while it was trying to make it's mind up. The system was so bad Cadillac offered a V6 as an alternate engine mid-year, and brought out the 4.1V8 the next year (which wasn't exactly an improvement).

The new chrysler system seems to work pretty well. Chebbie will offer a variable displacement 5.3V8 in the Impala next year- be interesting to see how it works out.