does the lower compression of the 225 hp engine (possibly) lead to better gas mileage?
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Nope. For off-boost operation HIGHER compression would...
make more power for each amount of fuel burned and therefore offer better gas mileage.
FWIW, the slightly lower compression ratio of the 225 (vs 180) allows the extra boost to produce more power at full throttle without sacrificing durability. Under part throttle conditions, which is most of our cruising driving, the engine's effective compression ratio is very low, because only a fraction of the maximum air & fuel are being admitted to the cylinders.
For example, if it only takes 45 hp to maintain the car at some cruising speed, that's only 20% of the 225 maximum hp, so the engine only needs about 20% or so of its maximum airflow, and even less fuel.
Most fuel mileage differences between 180's and 225's are due to driving habits, assuming they travel the same roads. Oh yes, total vehicle weight and aero drag have direct affects on overall (city/highway) fuel economy. Coupes will get better mpg than roadsters!
My $.02
FWIW, the slightly lower compression ratio of the 225 (vs 180) allows the extra boost to produce more power at full throttle without sacrificing durability. Under part throttle conditions, which is most of our cruising driving, the engine's effective compression ratio is very low, because only a fraction of the maximum air & fuel are being admitted to the cylinders.
For example, if it only takes 45 hp to maintain the car at some cruising speed, that's only 20% of the 225 maximum hp, so the engine only needs about 20% or so of its maximum airflow, and even less fuel.
Most fuel mileage differences between 180's and 225's are due to driving habits, assuming they travel the same roads. Oh yes, total vehicle weight and aero drag have direct affects on overall (city/highway) fuel economy. Coupes will get better mpg than roadsters!
My $.02
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