# Over-reving a diesel

**URL:** <https://community.cartalk.com/t/over-reving-a-diesel/19522>\
**Category:** Maintenance/Repairs\
**Created:** [September 13, 2008, 3:10pm UTC](https://community.cartalk.com/t/over-reving-a-diesel/19522 "2008-09-13T15:10:54Z")\
**Posts on this page:** 5\
**Page:** 2

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**Author:** ![circuitsmith](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/circuitsmith/32/40376_2.png) [@circuitsmith](https://community.cartalk.com/u/circuitsmith)\
**Post date:** [September 16, 2008, 3:17pm UTC](https://community.cartalk.com/t/over-reving-a-diesel/19522/21 "2008-09-16T15:17:47Z")

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“The energy is CONSUMED…”

Energy can be neither created nor destroyed. It can however be converted to mass.

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**Author:** ![B.L.E](https://avatars.discourse-cdn.com/v4/letter/b/848f3c/32.png) [@B.L.E](https://community.cartalk.com/u/B.L.E)\
**Post date:** [September 16, 2008, 5:22pm UTC](https://community.cartalk.com/t/over-reving-a-diesel/19522/22 "2008-09-16T17:22:44Z")

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Same situation here, over the years I have learned that if my wife wants my opinion, she’ll tell me what it is.

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**Author:** ![MrPhil](https://avatars.discourse-cdn.com/v4/letter/m/ecccb3/32.png) [@MrPhil](https://community.cartalk.com/u/MrPhil)\
**Post date:** [September 18, 2008, 1:26am UTC](https://community.cartalk.com/t/over-reving-a-diesel/19522/23 "2008-09-18T01:26:46Z")

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During WWI, a lot of airplanes were powered by 9 cylinder radial engines that had a stationary crank that was bolted to the plane’s firewall and the entire crankcase just rotated around the crankshaft. This resulted in the pistons just going around in a circle centered around the crank throw. These engines were no more efficient than conventional engines.

Just to set the record straight, these engines were known as “rotary engines” (not to be confused with the later Wankel). Quite a strange design, where the crankshaft was stationary, the crankcase and cylinders spun, the pistons went back and forth and around with the cylinders, and the prop was bolted to the crankcase. I think it was done to improve engine cooling, but the torque effects of that huge rotating mass could snap you into a spin if you weren’t extremely careful. Many a pilot died this way, and the rotary was abandoned not long after. Radial engines (think of a “Vee” design on steroids) lasted a long time, through WWII and the 50’s, until jets displaced larger prop planes. I think radials are pretty rare today.

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**Author:** ![Whitey](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/whitey/32/24680_2.png) [@Whitey](https://community.cartalk.com/u/Whitey)\
**Post date:** [September 20, 2008, 5:45pm UTC](https://community.cartalk.com/t/over-reving-a-diesel/19522/24 "2008-09-20T17:45:10Z")

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Where is the red zone on the tachometer? As long as the needle stays out of the red zone, no harm is done.

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**Author:** ![B.L.E](https://avatars.discourse-cdn.com/v4/letter/b/848f3c/32.png) [@B.L.E](https://community.cartalk.com/u/B.L.E)\
**Post date:** [September 21, 2008, 11:00am UTC](https://community.cartalk.com/t/over-reving-a-diesel/19522/25 "2008-09-21T11:00:26Z")

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I don’t think it’s that black-and-white.  
Over the years, I have come to the conclusion that there is no magic rpm where  
abuse suddenly starts any more than there is an altitude where outer space suddenly starts.  
One motorcycle manufacturer (Moto Guzzi) even puts a yellow zone ahead of the red zone so they appearently agree with me.

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