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Old 01-09-2012, 02:50 PM   #21 (permalink)
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Originally Posted by redpoint5 View Post
Also, why haven't gasoline engines been DI from the beginning...
There have been direct-injected gasoline engines for quite a while; see the 1954 Mercedes 300SL (the coupes were the famous "Gullwing" cars). These systems were based on modified diesel injection systems of the era.

Similar Mechanical Fuel Injection systems were used on a number of early sports cars, like the Porsche 911 (starting with the 911E in 1968), the BMW 2002tii (starting I think in 1972?), and a number of Alfa Romeos and other Italian cars. (The Porsches used Bosch MFI pumps; the BMW used a Kugelfischer system, and the Italians used systems by Spica.) Some quality time with Google can show you how complex they truly were.

MFI was also used on quite a number of race cars in the 60s and 70s.

Some American cars used a very simple fuel injection system in the 60s, but it didn't really make a huge impact on the mass market. (Google "corvette fuelie" for one example.)

All of these bar the last were relatively expensive and difficult to tune, as well as only providing a moderate amount of control over the air-fuel mixture. Even the "simple" system used on the American cars was more expensive and more finicky than the carburetors of the day.

Carbs were much simpler, much less expensive, and offered reasonable driveability and easy tuning.

Electronics have only relatively recently progressed to the point where the very precise mixture control offered by modern-style DI could be supported reliably. (Even then it isn't necessarily as reliable as we could want. Google up "MINI high-pressure fuel pump" to see a common failure point on DI MINIs.) Solenoid valves (electrically-operated valves) that can deal well with the 1000+ PSI that DI requires have been very expensive until recently, especially ones that can last like we expect our cars to last these days.

...As often is the case, the primary answer to a question that starts "Why do they..." is: Money.


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