Generic question on longevity of modern automotive engines at high load
Generic question on longevity of modern automotive engines at high load
(OP)
This is a "what-if" question - asked mainly out of curiosity, not because I need to implement any of the scenarios mentioned.
Consider a modern European hatchback designed for fuel efficiency and low price - so low displacement turbocharged engine is the order of the day. Say, 1.0-1.5 liter 4-cylinder petrol engine making 100-200 bhp with turbo. And in a car that weighs about 1200kg. Top speed of around 200 km/h.
Question 1 - imagine the car is driven for several hours daily on the Autobahn, at its top speed. How long would it be expected to last? Which component would fail first? Are cars of this size even designed with enough natural cooling capacity to withstand several hours of full throttle operation?
Question 2 - imagine the same automotive engine, but this time driving a stationary load (like a generator or water pump), or used as a boat inboard engine, or an aircraft engine. In each case assume the engine has sufficient cooling (via cold water supply or oversize radiator), no unnatural axial loading on crankshaft (i.e. propeller thrust loads borne by thrust bearing not directly loaded on crankshaft), and engine spends all its time at 80-100% of rated power. How long will it last this time, and which component fails first?
Reason I'm asking is because modern automotive engines strike me as taking advantage of the fact that full power is used only briefly in a car's typical operation, so they have very impressive specific power figures (over 100hp/liter) - but I can find no data on how durable they are when producing high power for extended periods of time. I'm hoping some automotive engineers can shed light on this question.
P.S. This being my first post, I should probably introduce myself and provide some background. I'm from Malta, have a B.Eng in mechanical engineering and a masters in materials engineering. My current job is package development for a semiconductor assembly plant, main focus being R&D of novel MEMS device assembly processes.
Consider a modern European hatchback designed for fuel efficiency and low price - so low displacement turbocharged engine is the order of the day. Say, 1.0-1.5 liter 4-cylinder petrol engine making 100-200 bhp with turbo. And in a car that weighs about 1200kg. Top speed of around 200 km/h.
Question 1 - imagine the car is driven for several hours daily on the Autobahn, at its top speed. How long would it be expected to last? Which component would fail first? Are cars of this size even designed with enough natural cooling capacity to withstand several hours of full throttle operation?
Question 2 - imagine the same automotive engine, but this time driving a stationary load (like a generator or water pump), or used as a boat inboard engine, or an aircraft engine. In each case assume the engine has sufficient cooling (via cold water supply or oversize radiator), no unnatural axial loading on crankshaft (i.e. propeller thrust loads borne by thrust bearing not directly loaded on crankshaft), and engine spends all its time at 80-100% of rated power. How long will it last this time, and which component fails first?
Reason I'm asking is because modern automotive engines strike me as taking advantage of the fact that full power is used only briefly in a car's typical operation, so they have very impressive specific power figures (over 100hp/liter) - but I can find no data on how durable they are when producing high power for extended periods of time. I'm hoping some automotive engineers can shed light on this question.
P.S. This being my first post, I should probably introduce myself and provide some background. I'm from Malta, have a B.Eng in mechanical engineering and a masters in materials engineering. My current job is package development for a semiconductor assembly plant, main focus being R&D of novel MEMS device assembly processes.





RE: Generic question on longevity of modern automotive engines at high load
RE: Generic question on longevity of modern automotive engines at high load
2. Similarly for generator or marine propulsion, provided that the installation is properly engineered.
In the specific case of generators, Diesels in particular thrive at sustained power levels of 60 to 90 pct of maximum rating, and develop congestion in various forms at lower power levels.
In the specific case of aircraft propulsion, the maintenance schedules for piston engines are so rigorous that none of the parts have a chance to get old, and even the established manufacturers have no experience with really high-time engines. They don't know how to build one because they've never, ever, been forced to do so.
Emissions- related durability testing has forced evolution of car engines that will last for 100,000 miles, and has forced evolution of design tools and manufacturing techniques that allow rapid development of new engines with similar prescribed durability.
The question you may have meant to ask is, 'What happens after 100,000 miles or equivalent?'.
I don't think anyone really knows. Big ol' 'Merican engines used to cruise well beyond that, given even minimal maintenance, but they can't meet the increasingly crazy emissions regs.
My personal suspicion is that new generations of tiny engines, their power level and effective displacement and internal stresses magnified on demand by turbochargers, will meet the statutory durability requirements. ... and then explode, as every part reaches its carefully calculated fatigue end of life at the same time.
It won't matter which part actually fails first, because collateral damage at high power will take out the remainder of the engine, or there will be no fatigue life left in the surviving remainder. It won't be worth repairing a failed engine, because every part in the junkyard will be within minutes of its end of life.
There won't be a need for junkyards, because everyone will be forced to buy either a brand new engine or a new car when the engine grenades.
<tangent>
Big ol' engine example:
I was not long ago involved in the zero-time rebuild of a pair of Waukesha natural gas engines retrieved from a junkyard (for $25,000 each), which will run at 900 rpm for the next 35 years providing up to 350kWe each, on an unattended oil platform in the GOM. The bare engines weigh 20,000 lbs. each, so they might be a little impractical for a hot rod. They do make a nice chest-thumping bark when you fire 'em up, though.
</tangent>
Mike Halloran
Pembroke Pines, FL, USA
RE: Generic question on longevity of modern automotive engines at high load
A little out of date now but IIRC, Triumph engineers in the 60s were aiming for engine survival of 50 hours at full power.
Against this, 100,000 miles @ 30 mph average would give 3,333 running hours (though dependent on ownership, might never actually see full power use). I also always think it is interesting to compare the running hours at higher average speeds (45 mph average drops the hours to 2,222), which perhaps goes some way to demonstrate why a relatively young, but high mileage car (implying it's done longer runs at higher speeds) is usually a less troublesome buy than an older, low miles car and will run to a higher mileage before failure.
This would also help to explain why big countries (US, Oz, mainland Europe etc) seem to report higher survival mileages than we UK Island Monkeys, where opportunities to sit at high cruising speeds for long periods are more limited.
I realise there are alot of sweeping generalisations here, but my personal experiences in almost 30 years of used car ownership have shown that well maintained high mileage cars remain reliable to very high mileages and it's rarely the engines that fail first.
Another wrinkle is how powerful the engine is in the first place, which obviously goes a long way to dictating how far up its power band it will be operated. I suspect that manufacturers are well aware of this and build their small engines tougher/hp than their big ones.
My first car was a Citroen Dyane with a 602cc flat twin and 29 snorting horses. That was driven with two throttle positions, on or off, and high rpms were needed to maintain progress. It could only manage just over 70 mph flat out so I can safely say that that car did get operated at full power for quite substantial chunks of time. It was admitting to 97k miles when I got it and I added about 5k more. It was still running when sold, but was showing signs of wear!
My current car is a '96 Audi A6 with a 2.5L I5 TDI. It is rated at 140 hp and while it has seen full power use on plenty of occasions, I don't think I've ever managed to hold full power for more than about 90 seconds continuously and then only when overtaking trucks on long hills. It just isn't possible (in UK at least) to hold full power for any longer without running out of road or seriously breaching speed limits. This car is now approaching 256k and engine-wise gives the impression that if I keep doing the scheduled maintenance, it'll double that. The body won't last that long though!
My feeling is that that car engines at least, cold starts, temperature cycling and lack of maintenance kills far more than the actual mechanical wear of hard use. Plenty of engines get scrapped in perfect working order too - I've recycled a few in my time.
Cheers
Nick
RE: Generic question on longevity of modern automotive engines at high load
But, that engine has much lower maximum revs than, say, a CBR600, even though its cylinder is smaller than those in the 600.
I have heard of a street ridden CBR600 in the southern US with over 260,000 miles on it (> 400,000 km) and it has reportedly never been apart.
I recall one of the UK magazines years ago ran a Honda Fireblade at top speed at MIRA for (I think) 24 hours and then tore down the engine, and found no wear. That engine made about the same power from its 900cc as you are suggesting from a bigger engine and did it with no turbo ... it did it with revs, which is generally tougher on everything.
I'm quite sure that nowadays, engines are designed for continuous operation at maximum power while remaining within the bounds of infinite fatigue life on the materials. Lack of maintenance is what usually kills them.
RE: Generic question on longevity of modern automotive engines at high load
thread108-150335: automotive engine performance
You can go there to see the answers.
B.E.
You are judged not by what you know, but by what you can do.
RE: Generic question on longevity of modern automotive engines at high load
{"Ford EcoBoost" problems}
will provide a _lot_ of reading material.
It appears that they fell just a little short of the mark, durability-wise,
and will have to add some iron, or fix some software.
Mike Halloran
Pembroke Pines, FL, USA
RE: Generic question on longevity of modern automotive engines at high load
Mike, tbuelna - do you have any idea of the longevity of an automotive engine converted to run an experimental aircraft, in terms of hours between overhauls? I'm aware of a lot of air-cooled VW beetle engines powering homebuilt microlights, and I was wondering whether it would be possible to capitalise on modern cheap, lightweight high-power turbocharged engines for an experimental microlight. Aerospace engineers will be well aware of the advantages of turbos at altitude, though with this being an automotive engine I don't know how it would cope with flying at altitude design-wise. And I'm not familiar with maintenance schedules for automotive conversions on experimental aircraft - does the owner/pilot have to come up with a suitable schedule himself, or maybe copy one from an existing similar certified piston engine?
Nick - my first car was a Ford fiesta/fusion. 1.4 liter NA petrol with 80bhp. Used to use full throttle quite often. My current car is an Alfa Romeo MiTo - 1.4 liter turbo petrol with 135bhp and MultiAir (for those not familiar with the term, MultiAir is a hydraulic valve actuation system whereby power control is done by variable intake valve duration [early intake valve closing or late intake valve opening] instead of a throttle body. That way the pumping losses are eliminated and they claim a 10-15% improvement in fuel efficiency and specific power compared to conventional (throttle-bodied) petrol engines). I barely ever have the room to use full throttle for more than 20 seconds at a time, and that's only at 2am when the roads are empty! Same engine with a bigger turbo is offered in the QV model with an output of 177bhp. So curious as to whether such an engine would make a practical experimental aircraft engine or whether it would have durability problems since getting 100hp/l means quite a high BMEP, and you'd have to run it all day at 5000rpm to get all 135 horses...
Brian - with regards to full power operation - so assuming fatigue life is infinite, is the cooling system in the car usually sufficient to permit continuous full throttle operation? Or will the engine slowly start to overheat?
Berkshire - thanks for the link. Seems a reasonable assumption is 2000 hours at full throttle, and Diesels are more suitable than petrols for extended high-power running?
RE: Generic question on longevity of modern automotive engines at high load
RE: Generic question on longevity of modern automotive engines at high load
Aircraft usage demands a whole lot of considerations that are not present in an automotive application. The average aircraft piston engine is air cooled ... it's a whole lot easier to get that to pass FMEA (failure mode effects analysis). They have redundant ignition systems, etc. In my last car, once upon a time, I had a coolant hose spring a leak while on the motorway. While the car came home on a tow truck after that happened, it did in fact come home. If that happens 2 km up in the air while you are crossing mountains or a big lake ... consequently, no comment from me on the advisability or suitability of an automotive engine in an aircraft.
RE: Generic question on longevity of modern automotive engines at high load
I never understood why aviation laws stipulate dual ignition systems (14 CFR Part 33, Subpart C, § 33.37). It's not like the ignition system is the least reliable part of the engine, at least with modern solid-state systems, in my limited experience. The CFR still permits the use of one fuel injector per cylinder (for engines that use them), one fuel pump, one oil pump, one cooling system, one radiator, one alternator, and one timing belt. So why would they be so hard on the ignition system, and require drilling two holes per cylinder for the spark plugs to make the engine qualify for certification (a requirment that an unmodified automotive engine can't meet), when they still permit single points of failure (like the single oil pump, whose failure would disable the whole engine)?
RE: Generic question on longevity of modern automotive engines at high load
Through industry links, I have heard that some aspects of the cooling system have been designed without much thought to manufacturing processes and the rate of degradation of the cooling system internals (casting debris, swarf, products of corrosion), resulting in coolant not necessarily being where you would like it to be.
I had a look at a sectioned display 1.0 Ecoboost - the pistons were reminiscent of racing pistons of not so long ago - very short, almost non-existent skirt. The rods, from what I could see, were nothing special - the I-section was what you'd think typical for a production engine. I gather that nearly all rods these days are laser scribed and snapped across the big end, but I also hear the odd story about b/end bolting causing failures owing to inadequately developed bolt types/torques/torqueing methods.
One has to consider that the Ford Ecoboost is currently at 100bhp/litre and the next iteration will probably be 120bhp/litre. It's not so long ago that these were racing outputs from engines that had little durability capability.
Many years ago, I was involved with the testing of truck engines in the range 254 to 380 cu in and the baseline test was, after a thorough oil consumption bed-in, 55 min at full load, rated speed, followed by 5 min at idle, no load. This was continued for at least 1000 hours and in some cases 1500 hrs.
Of course, there was no thermal cycling going on, as you would get in real use.
Bill
RE: Generic question on longevity of modern automotive engines at high load
The lightweight pistons in the 1.0 EB stand to reason. That engine is an inline-three with no counter-rotating balance shaft. Keeping the pistons light keeps vibration in check.
RE: Generic question on longevity of modern automotive engines at high load
Bill
RE: Generic question on longevity of modern automotive engines at high load
The thing about the 1.0 EB that has me concerned, is the timing belt running in oil.
RE: Generic question on longevity of modern automotive engines at high load
B.E.
You are judged not by what you know, but by what you can do.
RE: Generic question on longevity of modern automotive engines at high load
RE: Generic question on longevity of modern automotive engines at high load
RE: Generic question on longevity of modern automotive engines at high load
I have two friends with RV's using the 6 cylinder boxer layout with an Eggenfellner reduction gearbox. The gearbox is controversial, people either love them, or hate them, and factory support is spotty. I will contact them this Saturday. I am doing a weight and balance for one of them, I will ask the specifics on displacement and horsepower. I have another friend with a Kitfox with a belt drive reduction 4 cylinder inline motor. He has not reported any problems with his, other than that the unit is a bit heavy for his aircraft.
B.E.
You are judged not by what you know, but by what you can do.
RE: Generic question on longevity of modern automotive engines at high load
I actually have a friend who built an X-air microlight a few years ago. He spent €10,000 on the aircraft and €30,000 on a two-stroke two-cylinder Rotax (about 40-60bhp I think) to power it. From the little time I spent with it, the engine is not terribly impressive. Quite hard to start (prop spins but engine doesn't fire), though reliable enough once it's actually started. Sadly an automotive power plant wouldn't come anywhere near the light weight of this one due to being 4-stroke and liquid cooled. Probably the best bet would be an air-cooled motorbike engine, but not too convinced one would last long at a constant 10,000rpm...
RE: Generic question on longevity of modern automotive engines at high load
LMF5000-
The duty cycle of a recip piston aircraft engine is far different than a typical auto engine. The auto engine operates most of its life at light load and low speed operation. The recip piston aircraft engine has a duty cycle (ground-air-ground cycle) that involves a short period of high speed, high load operation during take-off and climb, followed by extended periods of operation at 60%-70% speed and full load. So it seems likely a recip piston auto engine used in an aircraft would have significantly reduced MTBR due to mechanical/thermal fatigue issues in many of its components.
RE: Generic question on longevity of modern automotive engines at high load
Your friends price for a 50hp Rotax engine sounds off by a factor of 10. The highest price I can find is about 7000 euros for a 503, or 582 ,or similar with a gearbox and electric start .
B.E.
You are judged not by what you know, but by what you can do.
RE: Generic question on longevity of modern automotive engines at high load
RE: Generic question on longevity of modern automotive engines at high load
The Subaru engines they are using in the RV 9's are 3 litre 6 cylinder boxer engines generating about 180 to 200 horsepower through a reduction gearbox using an MT electric constant speed 3 blade prop.
B.E.
You are judged not by what you know, but by what you can do.
RE: Generic question on longevity of modern automotive engines at high load
Thanks for getting back to me. Interesting how they both use horizontally opposed engines - as are certified engines. Perhaps they have the advantage of being lighter because of less balance weight?
Anywhay, very interesting that they use an electric constant speed prop. I didn't know they existed until you mentioned it. Only ever saw planes with fixed pitch and hydraulic CS props.
RE: Generic question on longevity of modern automotive engines at high load
When most all ignition systems used breaker points. They always were the weak point in the system, also the high tension components could be bothersome as well, all items that make redundancy a good thing. It would have been much more difficult to use 2 spark plugs per cylinder using one distributor or one magneto than it is with 2 or more.
2 spark plugs on an aircraft engine should be a necessity especially in the old days, with the higher TEL concentrations used then. Spark plug fouling was pretty common. And saying nothing about the efficiency increase with the extra ignition source.
As far as I know any durability testing on automotive engines using 100% plus of rated power are all done using precisely controlled conditions on a dynamometer. I've also questioned if the cooling system and exhaust system in the average car would withstand full power output for extended time. I think the average car uses maybe 20% of max hp in normal driving.
RE: Generic question on longevity of modern automotive engines at high load
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Generic question on longevity of modern automotive engines at high load
I've heard it said before that revving an engine with no load is dangerous. The (non-technical) sources I read allege that the harmonics that would otherwise be dampened by the load are instead allowed to run free and stress the engine. Personally I've never exceeded 4000 revs in neutral. I hear the modern VWs also have a drastically reduced rev limit in neutral or with the clutch pressed - though whether this is to prevent damage, or actually meant to be a primitive form of launch control I don't know.
RE: Generic question on longevity of modern automotive engines at high load
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: Generic question on longevity of modern automotive engines at high load
Norm
RE: Generic question on longevity of modern automotive engines at high load
RE: Generic question on longevity of modern automotive engines at high load
RE: Generic question on longevity of modern automotive engines at high load
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: Generic question on longevity of modern automotive engines at high load
----------------------------------------
The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Generic question on longevity of modern automotive engines at high load
RE: Generic question on longevity of modern automotive engines at high load
RE: Generic question on longevity of modern automotive engines at high load
RE: Generic question on longevity of modern automotive engines at high load
----------------------------------------
The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Generic question on longevity of modern automotive engines at high load
More abusive than I care to subject any of my cars to.
Norm
RE: Generic question on longevity of modern automotive engines at high load
- Steve
RE: Generic question on longevity of modern automotive engines at high load
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: Generic question on longevity of modern automotive engines at high load
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Generic question on longevity of modern automotive engines at high load
Course it's based on the speedometer being connected to the driven wheels not the other axle ;)
RE: Generic question on longevity of modern automotive engines at high load
----------------------------------------
The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Generic question on longevity of modern automotive engines at high load
B.E.
You are judged not by what you know, but by what you can do.
RE: Generic question on longevity of modern automotive engines at high load
I just skidded into a kerb with my car. Right front tyre hit pavement while steering was at full left lock to try and counter the skid. Forward speed at impact was well under 30km/h.
Car is now pulling slightly to the right. Needs 15 degrees of left steering input to go straight. Steering wheel returns to perfectly horizontal position when released with car moving.
Hit tyre is holding pressure fine (and is within 0.5psi of left one). Rim is scratched but not bent. Control rod looks visually straight, same as one on other side (didn't check wishbones). Acceleration and braking don't affect the pull. Wheel balance is subjectively fine (no vibration) at up to 60km/h (didn't risk going faster).
Can you experienced gentlemen please provide some suggestions? Would a simple wheel alignment likely work?
RE: Generic question on longevity of modern automotive engines at high load
B.E.
You are judged not by what you know, but by what you can do.
RE: Generic question on longevity of modern automotive engines at high load
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: Generic question on longevity of modern automotive engines at high load
How unfortunate. So a wheel alignment shop won't be able to bend things to cancel out the problem?
RE: Generic question on longevity of modern automotive engines at high load
B.E.
You are judged not by what you know, but by what you can do.
RE: Generic question on longevity of modern automotive engines at high load
Sounds like you bent the steering arm on the right side knuckle just a little (BTDT, left side).
If that is in fact the case, it'll be easier and far better to get it replaced rather than trust straightening it out, and I doubt that a repair/alignment shop would accept liability for straightening it anyway.
Norm
RE: Generic question on longevity of modern automotive engines at high load
The right wheel is also about 1cm closer to the back of the car than the left wheel is (i.e. can only fit 4 fingers between tyre and mudguard on RHS compared to 5 fingers space on LHS).
This car has a basic MacPherson strut suspension - single shock absorber on top, control arm (wishbone) on bottom. Like so:
I will be un-bending or replacing the wishbone and doing an alignment afterwards. Could something else be bent as well, besides the wishbone, to be causing the lateral displacement of the wheel towards the back?
RE: Generic question on longevity of modern automotive engines at high load
After the shop did their inspection did they mention suspicions of damage beyond the control arm?
How sure are you (how sure >>can<< you be ?) that the wheel was not displaced prior to whacking the curb?
Was the skid on dry road, wet road, gravelly road, snowy road, or icy road?
On snowy surfaces I practice quickly winding/unwinding steering lock when the front wheels skid. Each time we pass from straight thru maximum traction to skidding it pulls the front end a little bit more. My daughters yell when I drive like that on snowy days, but then each of them have driven straight into poles and trees, and I have not. yet.
RE: Generic question on longevity of modern automotive engines at high load
Skid was on glassy tarmac on wet road (wet from dew, it was 1am). Don't think you have the stuff overseas, but here in Malta some roads are coated with this cheap shiny high-glass tarmac with very poor grip. To make matters worse this was a sharp hairpin bend up a 30-degree incline and the road was barely two lanes wide between kerbs. Course there were no road lights so in the darkness I didn't realise how far I was far from the apex, went to take the turn a little faster than I should have (well, at least I know that now...) and steering lost all self-aligning resistance - i.e. the front wheels lost all grip. No tyre skidding noise either. I instinctively applied full lock to the left and pressed the brake but there was not enough space to my right and the rim banged into the kerb. Then the car bounced left and the tyres regained traction, so now it was heading straight into the wall on the left, but I managed to correct that in time and get it straightened.
I've never driven in snow. I suppose the grip level would be similarly poor (considering I'm using summer tyres). Funny thing is I had taken this car to a small race track in Sicily and had no trouble going round every bend with tyres screeching (correcting the understeer with extra steering input). It's FWD so has a natural tendency to understeer when the grip limit is exceeded but it's very neutral and easy to control. It also has traction control, torque vectoring and the other modern driver aids, but since it was in "dynamic" mode (aka sport mode) at the time they were not operating as agressively as in "normal" or "all weather" mode.
RE: Generic question on longevity of modern automotive engines at high load
The left wheel was not impacted, so using this wheel's values before and after the alignment, I can see what they've changed:
Half-toe increased from -40' to -5'
Camber reduced from -17' to -34'
Caster reduced slightly from +2*56' to +2*40'
Would any of these account for the increased steering effort? Power steering motor is fine because steering is very light when parking, it's only with speed that it stiffens up.