Forced induction confusion? I need some clarity!

[Faultline]

The confusion I have has to do with the power created in an engine w/fI.I formerly was under the impression that power was created.Primarily because the cooler ,and compressed air ,going into the engine by itself ,created better compression in the engine. So without anymore fuel delivered into the system,you would magicly have more power.My only experience with turbos are with diesel trucks. The same engine naturally aspirated getting 8mpg ,gets 11mph with a turbo.Plus,the turboed truck has more power. But!!!! everything im reading on these pages about forced induction is telling me that with the forced air , your getting more o2 into the engine allowing you to burn more fuel,which gives you more power.so maybe it is both. but , how much of each?. I realize that knowbody turboes for better fe, but is more fuel needed to create more power when force inducting air?good vibrationsFaultline

[NovaResource]

If you don't add more fuel you will blow up the engine. This is why nitrous has a bad reputation. Old systems didn't add enough fuel to the added oxygen (the "O" on "NO2"). This caused a lean condition in the engine and BOOM, engine damage. Current nitrous systems are much better and when installed properly, they work fine.An engine requires approx 12:1 to 15:1 air/fuel ratio. That is, 12 parts air to 1 part fuel (to 15 parts air to 1 part fuel). To maintain that ratio, as you add more air, you must add more fuel or a lean condition will occur. Because the oxygen in nitrous is added after the MAF (mass air flow sensor) you must add fuel. Turbos and superchargers pump more air but that air goes past the MAF so the computer knows how much extra air is going into the engine and adds more fuel via the injectors (or in the case of the Vibes supercharger, a 5th fuel injector).The reason you get better mileage is because the added torque requiring less rpms and smaller throttle openings to move the vehicle. However, the air/fuel ratios remain the same.

[Faultline]

Thanks for the reply, that simply clears it up for me. . You also cleared up the question of weather the vibe SC has the 5th injector like the TRD SC says it has. Or is this just assumtion?It also baits the question in my mind: How much boost can you allow from either a turbo,or SC,and still be able to use stock injectors in our vibes? (1zz). At what point could they not be delivering enough fuel for the amount of air going into the engine, I wonder?Good vibrations Faultline

[andrewmva]

NovaResource: good reply!!! it is all anout tuning... proper AF ratio and an effecent system... to make more power it does require more fuel... and if you put a turbo on and mash it all the time you will EAT fuel....but if you just cruise around you can actually bet BETTER MPG. as for the factory injectors... depends on the set-up

[Yoda]

If what you and nova are saying is true, why is it that no engines become more fuel efficient on the EPA city or Highway cycles when they are turbocharged or supercharged (except for some turbodiesels)? I bring up the EPA cycle to remove all possible sources of variation. I would even consider a European or Japanese cycle. To compare personal experiences, however sincere, is not very scientific or reliable. I can see why a turbocharger could theoretically be more fuel efficient, but not a supercharger: Running a smaller throttle opening reduces efficiency (brake specific fuel consumption). This means that smaller throttle lowers power more than it lowers consumption. Also, the supercharger is using useful work from the accessory drive to compress the air - this process is always less than 100% efficient. Please don't flame me - I'm honestly just looking for answers. I do agree that in some small windows it is possible for a supercharged engine to be more efficient - Like if the N/A engine has to go into fuel enrichment to cool the engine and control knock to produce the same hp levels as the supercharged engine can produce at stoich. (without enrichment).

[MadBill]

The main reason either a turbo or supercharger vehicle might get better EPA economy is that the manufacturer might choose to raise the gearing to take advantage of the increased torque. The part throttle losses compared to normally aspirated might be small (OEM superchargers often operate with a bypass, drawing as little as 1/3 HP at cruise) or even slightly positive for turbo, due the re-claimed exhaust energy.