The Governor, the Stock Rod, and When Each Becomes the Problem

Two parts inside a Predator 212 decide how far it revs: a mechanical governor that closes the throttle around 3,600 rpm, and a cast aluminum connecting rod that was designed for an engine that never revs past that governor. People remove the first without thinking about the second. Here is what each one does and what the dyno says about touching them.

What the governor is

A flyweight on the camshaft gear pushes a lever that closes the throttle as rpm rises. Stock, it holds the engine around 3,600 under load — a pressure-washer speed. The throttle-stop screw is a separate thing: it limits how far the throttle opens at all. Removing the screw leaves the governor in place but lets the engine reach full throttle, and that engine pulls to roughly 4,700 rpm — which is the configuration Red Beard's Garage used for its stock baseline, 6.74 hp at 4,400.

That distinction matters in the simulator. "Stock governor in place" models the 3,600 engine; "governor removed" models the full rev range. Most first-mod owners are actually running the third case — governor in, stop screw out, about 4,700 rpm — and that is the option to use for a Stage 1 engine.

What pulling it gets you on a stock cam: nothing

The governor-delete sheet is the most useful pull in the series because it isolates rpm from power. Stage 1 kit, governor removed, billet flywheel adding 8° of timing, 18-lb valve springs so the valves would follow the cam past 6,000, a throttle plate, and the stock cam: 8.90 hp at 5,500 / 10.01 lb-ft at 4,100, with the sweep running to 7,200 rpm.

The same engine with the governor in had made 9.11 / 10.94. Freeing up 2,500 rpm of rev range gained zero horsepower and cost one lb-ft, because the stock cam's lift and duration stop filling the cylinder around 5,000 rpm and nothing above that has anything to give. Red Beard's said it on camera: there is no real point in the governor kit without a rod and a cam. The governor page on this site runs the same comparison on your parts list.

What the stock rod is for

The stock rod is cast aluminum, sized and lubricated for the rpm the governor allows. Once the governor is out, the rod is the part that decides how high you can spin the engine before it leaves through the side of the block. The usual practice in the small-engine world is a billet rod before sustained running much above the governed range, and every rod option in this simulator carries its own rev rating for that reason. ARC's rods for the Hemi and Non-Hemi also come in +.020" and +.040" lengths, which raise compression by moving the piston up — a small, free gain that comes with the part you needed anyway.

The rule in plain words: the governor is a rev limiter for a stock rod. Take one out, put the other in.

What the billet flywheel is actually for

Two things, and neither is the reason most people buy one. First, it is safe at rpm the cast flywheel is not rated for. Second, the ARC flywheels advance ignition timing (to 32° BTDC on the fixed versions; adjustable on the 6607-PH). On the Stage 2 sheet the +8° flywheel was part of a package that was horsepower-neutral, so do not expect the flywheel alone to show up on a dyno as anything more than a fraction of a horsepower. It is a safety part with a timing bonus, and the simulator's flywheel option treats it that way.

The order

1. Governor in, stop screw out, Stage 1 kit — about 9 hp, 4,700 rpm, stock rod is fine.
2. When you are ready for a cam: rod first, then governor out, then flywheel and springs, then the cam. The cam and springs guide picks the grind; the order that works page lays out the sequence.
3. A rev-limiting coil once the engine can actually reach the cam's ceiling. The simulator lists coils by their hard-cut rpm; pick one under your rod's rating, not over it.

Put the engine in the calculator with the governor option that matches what you actually have, then switch it. If the horsepower line does not move, the sheet above is why.

Sources: Red Beard's Garage — Road to Horsepower Ep. 2 (vaL4-d5Fz70), governor-delete kit on a stock cam, inertia dyno corrected to 29.92" / 60°F; Ep. 1 (tQjitfEMDxM) stock baseline. Rod and flywheel ratings from the manufacturers' catalog listings used in the simulator.

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