even though the swept volume will stay the same, tuning the engine can, and does need more fuel/air to make more power. after all an engine is really only a pump and the more air you can get in the more power you can make, note here i said air, not fuel, getting fuel in is the easy part, and only there to ignite the air, getting more air in is the challenge and without air, burning fuel is a waste of time. changing lift and duration of cams, going to larger valves and different port shapes and sizes is purely to help maximise flow so more air can make it's way inside. turbo'ed or supercharged engines are more efficient at this than naturally aspirated engines but none will achieve 100% capacity, most naturally aspirated engines can achieve at best 70-75% capacity, and mass production and machine line tolerances mean even less for std engines. obviously, once you have done all this work the thing will run lean so more fuel is required to achieve an optimum air/fuel ratio and thus optimum horsepower (this is after all the point of the exercise) so there must be more fuel and air being consumed by each cylinder to make more power. the waste from this has to go somewhere so a matching exhaust with the ability to allow the waste gases to travel freely away (let's not get into scavenging here)is needed. add to this high revs allowing less and less time to fill/compress/burn/empty each cylinder and it all gets too much for the std exhaust to deal with. larger bores are one way to do this, with the added benefit of being quieter, but clever design, like the "spaghetti" systems work very well too. more discussion........ |