No replacement for displacement

No replacement for DisplacementThe saying there’s no replacement for displacement has probably been around since someone made an engine bigger than the other guys.  Given the technology in the early days of automobiles, there was no replacement for displacement.  But does that still hold true?

In the muscle car era, it still did.  Yes there were a few exceptions, like the 340 Mopar and the Boss 302 Mustang, but for the most part in the 60’s displacement ruled supreme.

All other things being equal, a larger engine will make more power than a smaller one.  However, all other things are rarely equal.  But if you look at displacement as the amount of air an engine can displace, then it still holds true.  An engine needs air (oxygen) to burn the fuel, and the more air you can run through an engine, the more fuel you can burn and the more power you can make.

For the sake of this discussion, we will assume that the efficiency of each engine is about the same.  So as long as you can pump the same amount of air through a small engine as a large one, you will make the same amount of power.  For comparison, look at a Chevy 572 crate motor with 720 HP at 6250 RPM.  Compare that to a Formula 1 engine, which makes about 740 HP at 18,000 RPM.  Which one would you rather have in your street car?  But from the other side, which one would you rather have in a purpose built road racing car?  The rat motor makes its power at an RPM that is usable on the street, versus at super high RPM.  But as you can see, if you can spin an engine fast enough, you can get enough air moving through it.  So no replacement for displacement, as long as you are talking air.

There are drawbacks to both sides.  The drawback to the big block is the size and weight of the engine.  Given that the minimum weight of the F1 engine is 209 pounds, versus the big block at 600+ pounds, maybe less if it has an aluminum block.  Either way, still considerably more, possibly 3 times as much depending on the parts used.

The drawbacks of the F1 engine would be the RPMs required to get that kind of power, and the durability.  A heavier slower turning engine will generally be more durable.

While most of us will probably not be installing F1 engines in our cars, there are other ways to get more air or oxygen into an engine.  Nitrous Oxide, Roots blowers and turbo chargers are all ways to get more oxygen into an engine to burn more fuel.  The drawbacks to them are more complex engines, and heavier internal components needed to get the same reliability due to higher cylinder pressures. And with nitrous, once the bottle is empty, the fun is over.

So to sum up the saying, there is no replacement for displacement, for simplicity, no there is no replacement.  You can get around it by finding other ways to get more air into an engine, but then you are talking displacement of air, not cubic inches and there isn’t a way around pumping more air through that I am aware of, so yes there is no replacement for displacement.


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