I agree 100% with the Wingman.

The only way that today's engines can produce more power and more torque (and they do) than earlier engines, and that is with today's common 8.5mm restrictors, non-conical headers and 3 chamber pipes is because the engines are way more efficient.

While the modern engines are CAD/CFD designed and will swallow a lot more air/fuel through them, a considerably greater percentage of that mixture is actually part of the combustion process - more fuel is actually burned, in other words, producing torque and since, power.

That will make an engine more fuel efficient since the actual car will be displaced a greater distance per unit of fuel since the fuel is being used more efficiently.

Earlier engines passed a lot more of the mixture directly to the exhaust system without going through the combustion process.

XE