Vvt And Variable Fuel - Corolland: the Toyota Corolla Forums

the other day i saw an old american car that said "variable fuel" on the rear end. only recently had i learned what vtec and vvti meant and so i was wondering that if variable valve timing adds only the right amount of fuel when needed why wouldn't an engine better benefit from variable electronic fuel induction than having to mess with the valve timing? a search of variable fuel only yielded aftermarket chips and whatnot, but i was not able to find any additional info. can anyone add any knowledge to the subect? it would be much appreciated. thanks

VTEC and VVT-i are only a part of the whole system. They mainly control actuation of the intake/and or exhaust valves (duration, lift). The ECU will determine how much fuel to add with input from the MAF or MAP sensor and intake air temperature. The variable valve timing doesn't add any fuel at all - it just controls the duration - basically how long during the cycle it stays open (duration) and far to project into the cylinder (lift) - on some models.

Actually most modern EFI system are very efficient - they constantly optimize the air/fuel mix for a given situation. But that can only give you so much - variable valve timing technology will allow you to extract more power and efficiency from the motor. By having variable valve operation - you can optimize the vehicle for low RPM and high RPM operation - places where just varing the fuel cannot achieve.

The moniker "variable fuel" could be just a model that can run on either gas or ethanol or some other fuel. Before the hybrids came out - engineers where experimenting with alternative fuels. Cars that could run on CNG, propane, ethanol, jet fuel, etc. Just do a search for "alternate-fuel vehicles".

Good Luck.

VTEC and VVT-i are only a part of the whole system. They mainly control actuation of the intake/and or exhaust valves (duration, lift). The ECU will determine how much fuel to add with input from the MAF or MAP sensor and intake air temperature. The variable valve timing doesn't add any fuel at all - it just controls the duration - basically how long during the cycle it stays open (duration) and far to project into the cylinder (lift) - on some models.
Actually most modern EFI system are very efficient - they constantly optimize the air/fuel mix for a given situation. But that can only give you so much - variable valve timing technology will allow you to extract more power and efficiency from the motor. By having variable valve operation - you can optimize the vehicle for low RPM and high RPM operation - places where just varing the fuel cannot achieve.
The moniker "variable fuel" could be just a model that can run on either gas or ethanol or some other fuel. Before the hybrids came out - engineers where experimenting with alternative fuels. Cars that could run on CNG, propane, ethanol, jet fuel, etc. Just do a search for "alternate-fuel vehicles".
Good Luck.

You've hit it head on.

induction1... I'd try doing an internet search for information on fuel injection, vairable valve timing and general informaton on how an engine operates. I applaude you interest in wanting to know how it all works and why.... but your missing some key pieces of information.

Modern engines are incredibly sophisticated and adapt to the environment and driving conditions. The only real restriction to further innovation is cost and safety and emissions regulations. Otherwise every car would have 7speed semiautomatic gearboxes, weigh 2000lbs and have 2.0L engines that made 300HP but still get 30mpg on the freeway.