Engine Revs per Mile vs. Wear

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The same engine at 65mph cruise (with virtually no load), will wear faster in 4th gear at 4500 rpm, than 5th gear at 3000,......but you cannot compare different engines this way. There are too many different design differences.
 
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I had a 1989 Subaru Justy w/ a 5.11 final drive. Turned 4,000 rpms at 70 MPH. It had 132,000 miles on it when I sold it, still got the same mileage as when new, and burned less than a quart of oil in 3,000 miles. Is this PROOF that you don't need low gears to make the engine last forever? No, it's not, but given my experience, I sure don't worry about it. Dave
 

tpi

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Its a good question-I can't answer. Crankshaft stroke has effect on piston speed and distance of piston travel. I've had examples of buzzy four cylinder engines turning 4000 @ 70 MPH which lasted well over 100K miles without any noticeable change. Newer vehicles with overdrive tend to run relaxed engine speeds on cruise-even the small 4 cyls. My 4 cyl. Camry turns about 2900 RPM @ 80MPH. It would stand to reason that reducing needless engine revolutions (but not lugging engine) would increase component life-including belts and accesory bearings. Anyone have results of a study?
 
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My 5.3 Vortec turns around 1,800-2,000 rpm at 75-80 mph or so. My LS1 can go up a 7% grade at 60 mph turning just over a grand! I love this engine, it has some torque to it!
 
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Yeah ! torque is the only way to go. I dont care about the engine wear, I know for sure that my earing wears a lot faster when I drive a typical four banger !! 150 hp at 5500rpm, [Thumbs Down!] I had a Malibu 97 with a 3.1, and I drove an Accord with their vtec 4 banger and technology or not a 4cyl is a 4cyl .I'll take the 3.1/3.4 with their pushrod and leaky manifold anyday before those turbine wanna be !
 

tpi

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quote:
Originally posted by Baveux: I dont care about the engine wear, I know for sure that my earing wears a lot faster when I drive a typical four banger !!
OK. I drive a 99 PSD pickup, 2000 RPM @ 70 MPH. 500 ft-lbs of [email protected] 1600 RPM. It is great! I can't hear the Camry engine @ 80 MPH. In fact can't hear much noise at all. IMO you can't broad brush 4 cyl. noise.
 

Kestas

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I don't know about others, but it completely amazes me that a design such as a piston engine can cycle up and down for billions of cycles and show neither appreciable ring wear nor high oil consumption. Beyond the number of cycles, the top compression ring in the piston by design forces more pressure outwards when there is more pressure produced by the combustion chamber, such as during acceleration. This has a significant effect on wear. So, not just rpm, but the higher number of stop-and-go's is another variable in this issue. That is one of the reasons why highway driving is considered the "easiest" on an engine. This is also why Ford's FIE 300-hour test (I believe) involves equal amounts of max rev and max load/full throttle for dyno evaluation of an engine.
 

tpi

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Amazes me too. Probably two biggest factors in engine life are amount of fuel burned and number (and severity)of cold starts. Assuming proper maintenance. The revs/mile would impact amount of fuel burned. Easiest on engine would be steady cruise with throttle cracked, with few cold starts. That would also correlate with the best fuel economy.
 
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What I wonder, is say you have a car that is a 4-cyl turning 4000 or so RPM doing only 70. Now are the results of the wear going to be about the same as my 3.1 at it;s (electronic) top speed of 107, which is only turning at 3800? Or is the bigger 3.1L causing more wear (not that there is any accurate way to really compare it) because it is producing more power than the much smaller, weaker 4 cyl? That's what I love about American cars, they have torquey motors and the big V8's (man I wish I had an LS1 powered vehicle) produce gobs of power, even at very low revs.
 
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If high RPM alone would cause significantly more wear than low RPM, then I should have worn out all my engines relatively fast. [Wink] What causes a disproportionate amount of wear are high load conditions with not high enough RPM. Just look at some BMW motors. Best thing to keep them happy for a long time is to drive them like you stole them. What I see a major contributors to engine wear are - cold starts - short distance driving - lugging the motor - wrong oil (like A1-rated oil in a motor that requires A3) ... and towing a boat behind your Yugo. [Razz]
 

driven2services

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Yep...that's one of the reasons my Cherokee has 200,000 miles and has never had anything major fixed nor does it have any problems now. I have to be going about 95mph before it will go up over 5k and hit the rev limiter... [Cheers!]
 
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Every engine revolution is considered a wear cycle, so you want to minimize total engine revolutions to maximize engine life. In particular, piston ring and cylinder wear is normally a function of mean piston speeds. Mean piston speeds in turn depend both the rpm range of the engine as well as the piston stroke. This is why high rpm, race motors tend to be "over square" designs, with large bores and short strokes. Of course, this assumes the pressures between parts are the same in all cases ....In the case of a high rpm, DOHC four cylinder engine, you many have many load cycles, but relatively low loads. One advantage of a four valve/cylinder head for example is that the valve masses are small, hence you can get by with lighter valve springs. Smaller valve springs reduce the pressure between the cam lobes and the valve lifters, compared to an eight valve head that functions in the same rpm range .... TS
 
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Hi, this is an interesting topic and many details have been covered But this is worth noting; 1 - German car makers have geared high in top for decades taking into account the Autobahn factor. When their cars were exported with the same gearing many buyers complained about the difference between gears 4 and 5 ( or 3 & 4 in older vehicles ). And the lack of top gear performance Their engine's life generally became legendary 2 - Heavy trucks were once geared with 60mph in top being in a 2900 to 3200 range range Some engines had a first in-frame rebuild life of around 120000 miles In order to increase fuel economy and etc. and along with other technical advances ( including lubricants and cooling systems ) these engines now run around the 1450 to 1650 rpm range First in-frame rebuilds can be at 600000 miles or more Wear can certainly be directly traced to fuel consumed as has been stated earlier - with some technical provisos! Regards
 
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The Camry 4 cyl engines have a balance shaft. They also have overdrive. really smooth and quiet. Some of the GM 4 cyl engines are called rock crushers by professional mechanic magazines. GM is too cheap to use balance shafts
 
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Their are so many factors that play a role. THe material used, the heat treatment and other surface treatment, loading, clearances, tolerances....... These factors listed above are why a well made 4 cylinder can turn 3100RPM doing 75 MPH and still out last in some cases an engine that turns 1800 RPM's traveling at the same speed! THe vechiles emission controls and lube system play huge role as well! Injector aiming, block stiffness, harmonics etc...... It has to be a total package aproach or your durability is going to be hit and miss!
 
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240 hp at 8600 RPM :thumbsup: My hearing wears out when "torquey" harleys rev their engines constantly (what's the deal, don't they have idle?) Compare the value/condition of Honda Accords vs. Chevy Luminas or anything similar, both on the street and in the used car market. If you are worried about engines lasting, look at how many trouble-free miles actually get put on them in the real world, instead of how many revs per mile they do in the theoretic world.
quote:
Originally posted by Baveux: Yeah ! torque is the only way to go. I dont care about the engine wear, I know for sure that my earing wears a lot faster when I drive a typical four banger !! 150 hp at 5500rpm, [Thumbs Down!] I had a Malibu 97 with a 3.1, and I drove an Accord with their vtec 4 banger and technology or not a 4cyl is a 4cyl .I'll take the 3.1/3.4 with their pushrod and leaky manifold anyday before those turbine wanna be !
 

Mal

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Just wondering! Has anyone found a correlation between engine revolutions per mile and engine life in miles? In top gear and at road speeds, some smaller 4 cylinder engines turn over lots more times per mile than some of the bigger V-8s and V-6's. Do the slower turning engines tend to last longer? Or is the wear so minimal under normal operation that maintenance, number of cold starts, short trips, etc. have more to do with wear?
 
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[QUOTE]Originally posted by S2000driver: [QB] 240 hp at 8600 RPM :thumbsup: Never man never ! [Wink] Who needs to shift constantly, to stay in the upper power band just to be able to move with the traffic. You can get all the 4 banger with turbo , blower,or with 56 valves per cyl that you want you will never be pushed back in the backrest like in the good old days. Cubic inches and torque rule [Cheers!]
 
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For a family sedan, Ill take the american car with the v6 over the japanese car with a 4 cyl. For me, having tourque with an automatic is imperative. I have driven Camrys and they are smooth and quiet, but guess what, so are Malibus and Tauruses. That said, Baveux, you have obviously never been pushed back into your seat by a 4 banger with a large turbo attached to it.
 
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I like engines that make the power on their own with out the need for a turbo or SC. That is why I like the LS1 because it comes stock with 310-350hp NA. So you can get 4 bangers that make that with a turbo and other mods but then you can get a small or big block that is all engine and makes 3 times the power that turboed 4 cyl. could make. I'll always take a low reving torque monster over a 8,000 rpm 4 banger anyday! BTW I smoked a Eagle Talon last night which I think had a V6 in it.
 
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