Miles vs power loss

[Itchy]

Its said usually by blokes down the pub , that petrol engines lose power the more miles you put on them,

while diesels get more bhp as you cram more and more miles on them.

is this true?

And is there a general guide as to how much (not withstanding rebuilds and rebores etc) BHp you lose per say 10,000 miles?.

Any thoughts?

Ta
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[MarJay]

If anything you gain BHP if the engine is properly serviced.

Running/bedding in is an amazing thing.

Only if the engine is unhealthy/hasn't been serviced will it make less power.

Or, I suppose if it was poorly designed.

I'd be very surprised if a new Blade engine made less power at 10k miles than at 0 miles.

However a 100,000 miler might be less powerful, but I'd imagine that being more through neglect than anything else. A freshly serviced and FSH 100,000 miler would be fairly fit I'd guess.
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[mark83]

Its all to do with compression ratios.

Once you've worn the machine in, there's little more to be had in terms of power.

The engine will lose power because the compression ratio will fall.

BMW actually do compression ratio tests for their brand leaders, and I heard a 7 series loses only 3% after 10 yrs!

Might not be completely accurate though.....
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[Pete.]

It shouldn't lose much if any of it's power throughout it's serviceable life. Obviously piston rings wear and will need replacing but modern engines are generally very long lasting.
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[Dom_]

I can't see a 100k miler with FSH making more bhp than a 5k miler tbh.
Wouldn't the lads at motogp be using old blade engines if thats the case.

[MattHirst]

[0ddball]

Race engines are a different story. They are built to reach their peak after a very short run in time and be knackered after a few hundred miles.

With a production engine there's no reason a 50,000 miler shouldn't make the same power as a 5,000 miler. The engine itself doesn't wear much if it's looked after properly. You might have problems with other components though at that milage. Injectors can varnish slightly, fuel pumps get tired, exhausts carbon up ect.

I don't think it will apply with bike engines as they are made for performance from the word go but some car engines will not make book power untill they have about 30,000 miles on them. So some can gain more power as the milage goes up, especially if you thrash them.

[MarJay]

[colin1]

i know its true that cars lose bhp as they age in some cases (although not all)
top gear did a thing about it

i suspect its also true of bikes to some extent

[Kickstart]

Hi

Would expect a diesel to loose power just as much as a petrol engine.

Don't think bike engines are designed to last that long. Yes they will gain some power as they run in, but that isn't that long.

With miles the bores wear, the rings wear (both reducing compression), jets become worn / clogged, spark plugs get contaminated, valve clearances go out, cams wear (reducing the time valves are open slightly), etc.

Taking care of an engine will reduce this, but it is still wearing (mainly from cold starts).

All the best

Keith
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