Quote:
Originally Posted by Paul Workman
The underlying supposition is fuel economy AND hp being the elements in the equation. But, those are some pretty big "IFs" thar! IF the same power, IF they drove the same, IF they get the same economy, IF they are the same physical size...Then hp/l would not be a factor. But, is that possible?
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There are tons of examples of smaller displacement not translating to smaller size, or better economy.
One of GM's, and supposedly the auto industry's, most efficient engines in terms of brake specific fuel consumption, was the "lowly" Buick V6. It's an ancient design that was often criticized for being of large displacement and old pushrod technology compared to its peers. In the late 90's it made about 200hp from 3.8L when Honda and Toyota were making that from 3.0-3.5L engines.
Was it less efficient? No. Was it less powerful? No. Was it heavier or larger? No. It just had more displacement. It also was a hell of a lot cheaper. People viewed it as inferior, and that matters for sales. The engine is gone now.
Look at the LS4 vs the FWD Northstar. The 303hp 5.3L LS4 gets substantially better fuel economy than the 300hp 4.6L L37, and it is small enough to fit in W-body/midsize cars. The Northstar could only fit in full size cars. Unfortunately they were never in the same car for a direct EPA economy comparison, but a look at a Bonnie GXP (probably the lightest car to get the N*) to something like a Buick LaCrosse Super (the largest car to get the LS4) and it is no contest.
It is not a big "If" to have a larger displacement engine that makes the same power as a smaller displacement one, while still having similar economy, size, and weight. DOHC setups are physically large and heavy. You may be able to do more with less displacement, but why do you need to? Take the space you saved in head size and turn it into displacement.
In spite of the low power/weight of something like the LS1/2/3/7, you would be hard-pressed to name a "smaller" production engine that makes the same amount of power as it, is lighter and physically smaller, and uses fuel as efficiently.