Revving in neutral is bad, but... ??

[road_rascal]

My Taurus has a limiter for neutral and park and won't go past 3500 rpms. Not sure about the Windstar but I'm guessing it's the same setup.

 

[rpn453]

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My Taurus has a limiter for neutral and park and won't go past 3500 rpms. Not sure about the Windstar but I'm guessing it's the same setup.

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I think that's there to protect the transmission from idiots.

 

[Lonnie]

I think you know when your are out of line with engine speed in neutral or with the clutch in. If not, please, only drive on Sunday morning and never in rush hour traffic. The life you save might be James Dean's.

 

[Palut]

What's the difference between pistons being unloaded because of revving to redline in neutral, and pistons being unloaded at redline at the top of the exhaust stroke, or unloaded when at redline but completely off the throttle?

 

[biomed_eng_2000]

Rev matching is fine, engines are design for that.

Extended no load high rpm is better than if high load at that same rpm.

 

[moribundman]

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I was always told that free revving in neutral was bad, but that was heaps of revs (like near redline).

Explained to me that the types of cars that I was driving (old), had likely been driven by more gentle fol, and would have a ridge of either metal or carbon at the top of the bore.

Revving unloaded may allow the ring to contact that ridge, upsetting the rings, or braking them.

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Well, the con-rods stretch increasingly with RPM, whether at idle or under load. Happens often that some kid buys a granny car that's never gone near full speed, and when he takes that thing out on the Autobahn and breaks the rings at the aforementioned ridge in the cylinder wall going 120 in a car that's never seen 70 in all of its life.

I also heard that redlining an engine at idle was not recommended for anybody but heros and fools. The technical explanation, which sadly escapes at this moment, was quite plausible. Let me put on my thinking cap...

 

[DriveHard]

Some will argue that at light load high RPM that there is less pressure pushing down on the cylinder, and that allows the con rod to stretch more than normal (higher stress). Pretty sure that argument is [censored], as I sure do hope that the least amount of pressure on the piston is during intake. Same RPM, nearly the same vacuum pressure on the piston - loaded or unloaded during the intake stroke. I don't see any difference between loaded and unloaded revving as far as internal stresses go.

 

[mechtech2]

Drive Hard - Me too. [Even though I have been previously fully indoctrinated that free revving is a horrible thing.]