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Old 10-08-2007, 10:19 AM
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Default RPM Versus Wear

Ok, with a turbo system i can choose to create full power at 2500 RPM or the engine's rated power limit of 2800 RPM.

I can do this by adjusting boost, a very simple thing for me to do.

putting boost at higher than recommended amounts does not bother me as long as i keep intake manifold temps well below 160 F to protect against detonation.

The recommended boost of 31.5 means little if you understand air density.

On a 20F day, 31.5 creates way more power than on a 100 degree day, so setting the boost at take off at 31.5 without knowing the recommended temp means little!

So what be it, 2500 or 2800? for less engine wear
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Old 10-08-2007, 05:53 PM
SteveWrightNZ SteveWrightNZ is offline
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Default Re: RPM Versus Wear

If you are referring to a certificated engine, then I do not know.

If you are referring to an automotive engine, then I would say that you should choose your redrive ratio to place the engine in its correct power band. I don't think you will "wear out" an automotive engine in a plane, rather you will more likely damage it from mis-using it, ie trying to force it to make power at an RPM where it was not intended (by using boost ;-)

The same applies for boats - automotive engines either rot, seize up from lack of use, or die from sustained full-power operation rather than actual "wear".

Raising boost to higher than recommended levels *should* bother you, unless it's a diesel, or you have had appropriate race-mods made to the engine, and its' internals strengthened.

Again, I expect certificated aircraft engines are a different story completely, and I have no knowledge of that.

S
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Old 10-08-2007, 07:31 PM
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Default Re: RPM Versus Wear

Quote:
Originally Posted by SteveWrightNZ View Post
Raising boost to higher than recommended levels *should* bother you,S
Well, the recommended levels are based on control technology that is archaic at best, hydraulic slow as can be boost controls that are prone to over boost. a small intercooler and yucky cooling air flow.

I can control boost based on intake manifold temp and do it computer fast!

The levels i am talkin about are slim

the level of boost required to make the same hp at 2800 rpm and 31.5 and a manifold temp of ???? and 2500 rpm are not significant.

Detonation will not be an issue, I'll see to that with spark and im temp control.
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Old 10-09-2007, 11:18 AM
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Default Re: RPM Versus Wear

Probably 2-3 more inches would give you the same power at 2500 as at 2800. Loadings go up the square of the rpm so you'll have quite a bit less stress and loading on reciprocating parts at 2500. The engine is also more efficient running higher MAP and lower rpm due to lower frictional losses and lower pumping losses.
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Old 10-09-2007, 11:30 AM
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Default Re: RPM Versus Wear

I was pretty sure you would give that answer - thanks!

I'll compute the actuals and of course watch the Intake manifold temps closely.
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