I have never really understood the physics behind this. More air permits more gas to maintain the same mixture. More gas = more boom = more power. I don't see how adding in more air, whether by adding a CAI, or hood cut out, or whatever, to achieve a bigger explosion, can in any way improve fuel economy. The hypermiler guys who tune their little 4-bangers for max MPG actually prefer hot air in the intake and MORE restrictive intake boxes so there will be less air and less gas.
Maybe I'm just dense... but can someone explain this to me?? How is getting more power and spark in the combustion chamber supposed to improve your MPG?
The easier it is for an engine to make power, the more efficient it is. An engine that makes more torque/power at a specific RPM than another engine of similar displacement will be more efficient - it can move the same weight with less effort.
This has absolutely nothing to do with the hood vents though. The hood vents have nothing to do with the intake. They only give hot engine bay air a route to escape, as they're in a negative pressure zone and therefore have no "ram air" effect.
Also, mr_didgers has already discussed that in practical terms, CAIs have no effect on everyday closed throttle fuel mileage. Under closed loop conditions the ECM will adjust the throttle opening based on MAF readings in order to only allow the specific amount of air that will maintain the stoichiometric ratio of fuel/air. If a CAI allows more air through, then the MAF will detect this and the throttle body will close more to compensate. It is only under open loop conditions (WOT), where the ECM switches to fuel tables rather than MAF and O2 sensor readings, that the CAI is allowed to shine.
'09 MSM G8 GT - Premium, Sport, Sunroof - since 9/18/08
Performance: Roto-Fab CAI; Corsa catback; VMS Tune; DBA 4000 slotted discs; Hawks Performance Ceramic pads
Interior: SAS/GTPprix Digital Gauges; Interior trim by CAA; Homelink-visor; Blendmount/Invisicord mounted V1/Dashhawk
Exterior: 3M 20% CS Tint; TSS custom darts; splash guards; Roto-Fab engine bay; Klearz sidemarkers; Spencers 5000k lows/3000k fogs
Misc.: Billet Prototypes catch can; full V-LEDs LED swap
Last edited by rez0nance; 08-31-2010 at 08:54 AM.