what is the redline for a 225. and what is best shift RPM for the engine. and what is best for racing.

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225 Slant Six [Super Six]

Depends, depends and depends, but not necessarily in that order.

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Joshua

on what?...

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225 Slant Six [Super Six]

Plenty.

If you want a good answer you'll need to ask a good (meaning specific and detailed) question.

One answer, whether or not I fully understand the question as you have asked. A healthy 225 in stock form is almost impossible to over rev under load. Remove the load though and all bets are off. The reason being a 225 under load will not spin fast enough to do itself harm. You'll get bored from the lack of further acceleration and shift. Chances are excellent you'll shift before 5000 RPM. 4500 RPM may even be too late for optimum results with a stock engine.

Also, this question has been asked and answered in depth in this very forum.

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Joshua