Joined: Aug 02, 2006
Posts: 705
Location: McLean, VA, USA
Posted:
Thu Feb 08, 2007 12:05 am
A common assumption among car enthusiasts is that if one adds some device to the engine that gives him extra say 10% power, his car will consume 10% less fuel if he does not use the extra power. Seems logical, yes? Would have been, if performance mods were increasing the amount of work produced per unit of fuel burnt. But they don’t. Not to any noticeable degree.
What they essentially do, they allow engine to burn 10% more air/fuel mixture. All of them, be it I/H/E or any of the chargers. Intake allows more air to be sucked in on the full throttle, headers and exhaust reduce the amount of exhaust gases left in the cylinder on the full throttle and thus allow more air in, and chargers just plainly push air…They do not increase the amount of work produced by any single unit of fuel.
Another argument can be made that stock intake and exhaust are just too restrictive and thus consume significant amount of engine power to suck air in and expel gases out. This is definitely true, but performance mods noticeably ease those restrictions only for high rpm full throttle and close to this. Under normal driving conditions pumping losses on partially closed throttle are way higher than all other pumping losses combined. And this is how we actually can regulate how much power engine is producing. Remember, on idle ALL engine power goes to offset pumping and mechanical losses.
Now, why I was telling turbo may give you better fuel mileage? Because to compress the air turbo uses part of fuel energy otherwise wasted, hence it produces more amount of work per the fuel unit burnt. But, the way aftermarket turbos are done normally, you will never see any fuel mileage gain. Riching it out and retarding ignition timing hurt efficiency badly.
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