Engine 'Stress'
Discussion
We're all familiar with the theory that a 5.0 v8 popping out a maximum of 250bhp will last longer than a 1.6 turbo that's been tuned to produce the same amount of power. Chatting about the merits of the different engines in the BMW 8-Series, a friend of mine said, "you'll never wear out a v12". You may often hear, "it may not have as much power as rivals but that engine is relatively unstressed compared to others" but how true is it?
Putting aside anecdotes and not going too far down the road of added complications like turbos or VANOS type systems, is there an actual scientific basis for the belief that an engine that produces much less specific horsepower than other similar engines will generally last longer?
Assume we're talking about everyday cars that aren't getting rallied about everywhere and where the engine will only hit the high notes on very rare occasions.
Putting aside anecdotes and not going too far down the road of added complications like turbos or VANOS type systems, is there an actual scientific basis for the belief that an engine that produces much less specific horsepower than other similar engines will generally last longer?
Assume we're talking about everyday cars that aren't getting rallied about everywhere and where the engine will only hit the high notes on very rare occasions.
Happy to be corrected by a more technical bod, but in principle the higher the pressure in the engine (i.e. higher specific power) the more force the engine internals have to deal with. Less force on the materials means the slower they will wear out.
A 6.0 V12 making 250hp would last for a very long time, whereas you rightly say a 1.6 4-pot turbo would wear much quicker.
A 6.0 V12 making 250hp would last for a very long time, whereas you rightly say a 1.6 4-pot turbo would wear much quicker.
I think its less true of modern engines.
A properly serviced anything will likely see 200k from the engine. Whether it gets to that mileage due to other things failing and not being worth repairing is another matter.
Even a superbike engine that revs to 14k and gives well over 100bhp/L will see 100k miles if its properly maintained.
A properly serviced anything will likely see 200k from the engine. Whether it gets to that mileage due to other things failing and not being worth repairing is another matter.
Even a superbike engine that revs to 14k and gives well over 100bhp/L will see 100k miles if its properly maintained.
It's not really about volume or horsepower and has more to do with the quality of the materials and engineering.
Like for like though, a lower tuned engine will run at a lower compression ratio which helps with thermal and will generally have a lower power band which helps with thermal and vibe.
And of course, a big engine with abundant torque to shove the car along will generally have an easier life than an engine which needs thrashing a bit.
Like for like though, a lower tuned engine will run at a lower compression ratio which helps with thermal and will generally have a lower power band which helps with thermal and vibe.
And of course, a big engine with abundant torque to shove the car along will generally have an easier life than an engine which needs thrashing a bit.
Often said about diesels which tend to rev a lot lower and produce more power lower down the rev range. The parts of the engine are physically moving around a lot slower which will cause less wear. You can get around it by better lubrication and using harder and/or lighter materials (e.g. lighter pistons) which while traveling faster produce less force on the wear surfaces (Honda vtec for example last quite well considering the high rev nature).
Generally the less revolutions on the engine the less wear, 1 min at 9000rpm would be more wear than 2min at 4500rpm etc. Most wear occurs in the first few miles as the engine oil is warming up so you would have to factor in the number of cold starts to get a reasonable comparison. A taxi that never stops for a 4hr shift and 500 miles would have a lot less wear on the engine than a granny driving 5 miles to the shops and back twice a week.
Generally the less revolutions on the engine the less wear, 1 min at 9000rpm would be more wear than 2min at 4500rpm etc. Most wear occurs in the first few miles as the engine oil is warming up so you would have to factor in the number of cold starts to get a reasonable comparison. A taxi that never stops for a 4hr shift and 500 miles would have a lot less wear on the engine than a granny driving 5 miles to the shops and back twice a week.
Edited by Crusoe on Wednesday 1st April 15:18
Crusoe said:
Generally the less revolutions on the engine the less wear
I think this is the key. A nice big petrol engine will move a car around at an unnecessary rate of knots with very low rpms, a little gutless engine requires many more revs to get anywhere. I bet if you compared the total number of engine revolutions in 100,000 miles in a Mercedes S600 and a Micra 1.0 there would be a massive difference, probably more than 2-1.Gassing Station | General Gassing | Top of Page | What's New | My Stuff