Re: 12 valves?

Posted by Hal (WA) on March 13, 2008 at 14:30:34 from (66.45.175.118):

In Reply to: Re: 12 valves? posted by Bob M on March 13, 2008 at 10:12:04:

Some Dodge Colts (actually manufactured by Mitsubishi) also had 3 valve per cylinder engines too. The second intake valve was very small. It was my understanding that the small valve carried a different mixture of air/gas than the larger intake valve, and the whole idea was to deal with hydrocarbon emissions while still using a carburetor. I don't remember if the small valve controlled a richer or a leaner mixture than the larger valve.

My 79 Colt hatchback got very impressive gas mileage and ran real well. But I remember that later I had some carb trouble with it, and it was one of the most complicated carbs I ever worked on.

A few years later, the emission standards got more restrictive, and the manufacturers decided to go to computer controlled electronic fuel injection. I am sure that move was one of the reasons that vehicle prices went up so much, but in my opinion, going to injection was overall a good move.

Dealing with the emissions regulations forced the manufacturers to change their products, which they did in gradual steps. I think they continued to use carburetors on lots of models because it was cheaper, and allowed them to put out a lower priced vehicle. But as complex as the carb on that Colt was, I bet the carb was one of the most expensive components on that car, and probably not all that much less expensive than the later fuel injection.

A buddy of mine had an early 80's Datsun pickup with a 4 cylinder engine that used 8 spark plugs. He never mentioned that it had more than 2 valves per cylinder, but I remember the engine as looking fairly exotic at the time. He claimed to get well over 20 mpg with that pickup in normal driving, which was better mileage than others were getting with their mini-trucks. The other thing I remember about that pickup was that it rusted worse than anything else around other than 73-76 Chevy pickups, which must have been the absolute low in Detroit's rust protection.

Some later vehicles had more than 2 valves per cylinder, like the GM Quad 4, and the 4 valve versions of Ford's 4.6 OHC V8. I think that most of them were given the extra valves so the smaller displacement engines would yield more horsepower. If you check the specifications on most of the 4 cylinder engines currently produced in cars, almost all have 4 valves per cylinder, and give horsepower ratings that exceed what lots of V6's did 10-15 years ago.

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