Most genset myths survive because people argue from the spec sheet downward. Argue from the mechanism upward — what the fuel does once it burns, where the heat goes, how the alternator answers a step — and the myths fall apart on contact. Here are three, taken at a like-for-like 660 kW. The Kohler-SDMO generator D830 is rated 750 kVA prime / 825 kVA standby (about 660 kW prime at 0.8 pf); the comparison is a Caterpillar C18-class set rated for the same ~600–700 kW band. Each section starts with the physics, then names the buying decision it forces.
Myth 1 — "Higher power density means it runs cooler in a tight room"
The claim: a compact, power-dense set packs more kW into less volume, so it must be the efficient, cool-running choice for a cramped plant room.
The mechanism says otherwise. "Power density" is a packaging metric; it tells you nothing about heat. The heat a set dumps into the room is the sum of four flows: jacket-water rejection, charge-air (intercooler) rejection, radiator airflow carrying it all away, and the alternator's own copper and iron losses. At 660 kW those flows are large and are set by the fuel burned (fuel ≈ load × bsfc), not by how tightly the box is packed. A denser set in fact concentrates the same heat into a smaller surface and a tighter airflow path — making cooling harder, not easier.
When this reverses: in a generously ventilated outdoor compound, cooling is never the binding constraint, and a more compact set genuinely saves you concrete and footprint cost. There, density is a real and fair advantage.
Myth 2 — "At this size, fuel maps are basically identical, so efficiency is a wash"
The claim: two reputable 660 kW diesels burn essentially the same fuel; arguing bsfc is splitting hairs.
The mechanism that breaks this is the shape of the bsfc curve, not its floor. Both engines have an efficient island, but it sits at a different load fraction for each, and your duty cycle decides which engine spends more time inside its island. Caterpillar generator publishes ratings developed for either low fuel consumption or low emissions — a tuning choice that moves the island. An engine optimised for emissions can carry a small bsfc penalty in the mid-load band where standby plants actually live.
When this reverses: for true emergency-only standby with under ~50 hours a year of running, fuel quantity is trivial and emissions compliance or maintenance interval should drive the choice instead — there, chasing bsfc is the hair-split the myth accuses it of being.
Myth 3 — "A bigger standby rating proves it will swallow a bigger block load"
The claim: the set with the higher standby kVA obviously accepts the larger sudden step.
The mechanism that governs block-load acceptance is independent of the thermal standby rating. Per ISO 8528-5, what a set can swallow in one step is set by the engine's torque rise and turbocharger response (how fast it can make fuel into torque without the governor losing frequency) and by the alternator's transient voltage dip and recovery. A set can have a generous standby rating and still accept only a modest first step if its turbo lags or its AVR has thin reserve. Standby rating is a steady-state thermal ceiling; block-load acceptance is a dynamics problem.
When this reverses: if you build the load up in small staged increments — a sequenced soft-start scheme or a programmed load ramp — no single step is large, the dynamics never bind, and the higher standby rating once again maps cleanly to "more capacity." Staging turns a dynamics problem back into a thermal one.
Topology/standards per the cited standards; all product ratings are manufacturer-stated values from the cited datasheets, current to 2026-06; derived/illustrative figures are labelled as such. This is not an independent head-to-head test. Kohler-SDMO is a brand affiliated with this site; competitor names are used for identification only.
