what determines how high an engine can rev? whats the highest rpma stock 99-04 4.6 can handle safely?


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It's just how well the rods and crank will hold together when spun high, and how much power you actually make that high. A stock PI 4.6 stops making power above 5200 RPM so even spinning it up to redline is enough.

Stock safely? 6200 RPM is a good measure, though if you really wanted you could raise the rev limiter to 6800... but that's really pushing the FRAGILE stock internals. Again, you stop making power LONG before then.

 

The internals of the engine and heads are what determines how high you can safely rev. The stock 99-04 GT engines can rev to approx 6k safely. The cobra engines redline about 6800.