Once again I clean up another turbo thread. And 2 users got time out time.

You may all resume with the tech talk.

 

I don't see how boosting will net better gas mileage. Sure, tuning helps tremendously, but even when not in boost, the turbo is spinning and adding air to the intake charge. With more air comes more fuel.

Boost pressure doesn't necessarily make more power. Air density does. The more dense the air the more oxygen molecules in a given volume.

If gas mileage were my main concern, I would build a higher compression NA engine. If power were my main concern, turbo it for sure.

 

Your right that with a given amount of air needs a given amount of fuel. You need to maintain the same A/F ratio, When turbo a 100hp car and make it a 200hp car you now have 100hp with roughly half the rpm of the 100hp car. This is where the fuel saving come into play. It takes less effort to spin the motor at 3000rpm than it does 6000rpm so you get more power from less air and fuel.

While boost pressure is a relative term measuring the restriction of airflow, when you add air through forced induction you are getting more air flow in the same system and will have more pressure or boost. It is possible to loose boost by doing heads and cams and gain power because you now have more airflow with less restriction.

If gas mileage were my main concern, I would build a higher compression NA engine. If power were my main concern, turbo it for sure.[/QUOTE]

 

If you are looking at 2 different types of cars with different gear ratios, then you are correct, generally the car with the lower cruising rpm will have better mpg. However, turbo charging a jeep has no effect what so ever on its gear ratio. Therefore at any given speed the rpms stay the same turbo or not. Any increase in gas mileage by not having to press the gas pedal as hard will be negated by the increased air flow which allows for more power at less throttle.

Sorry I should elaborated more. I was actually talking about boost pressure in regards to temperature. Colder air is more dense than hot air, so at the same boost level colder air contains more oxygen.

You are correct that less restriction= more power, however boost isn't lost with cams or head work, it is just more easily consumed by the engine.

 

This thread is so off point. The information being posted doesn't even make sense. I can not believe someone would say if you double the horsepower the RPMs when driving would be half. The only advice I would give is don't waste your money on a turbo or supercharger, if anything put a V8 in it.

 

Im not sure if you refering to my comment but I DID NOT say the rpms would be halfed when driving. I said you get twice the power at half the RPM. There for you accelerate much quicker. You have more power at lower rpms to climb hills so you dont need to spin the motor up as much to maintain speed.