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Any mod that allows more air and fuel to pass through an engine means you have to increase the restriction of same air flow to produce the lower levels of power that are required in most normal cruising operation.
Which engine would get better mileage, all other things being the same?
1. A 20 cubic engine running at 80% of max load without fuel enrichment.
2. A 1000 cubic engine running at 5% load.
Alfa Romeo grand prix engines circa 1950 produced 390 HP at 10k RPM, out of 90 cubic inches, but got 2 MPG when racing. Compare that to a restrictor plate NASCAR racer getting close to 6 MPG at Daytona at 180 MPH, out of a basically 60+year old engine design.
Low RPM, low manifold vacuum, no fuel enrichment is where you get the most power PER UNIT OF FUEL CONSUMED.
The key component is the per unit of fuel consumed, which will seldom be decreased by allowing more air in and more exhaust out in the same size engine.
regards
Mech
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