The peak speed would be 785.4 inches per second.
Crank speed = (3?*5000)/60 = peak piston speed
This works out to 44.625 mph
You doubt oil protects the rings and cylinder walls from wear? Wow, man. I hope whatever kind of bullheaded reasoning process you use isn’t contagious.
TwinTurbo, thanks for the compliment.
EllyEllis, what I was getting at was that piston rings respond to compression in the combustion chamber by pressing outward. Additionally, as the piston slows down near TDC, the protection of the oil lessens (basically the ring “hydroplanes” on the oil at speed). This is why a worn engine will have cylinders that are “wider” towarsd the top.
What I was really driving at is–within reason, such as the highish crise RPMs of the OP–this is more a “fuel economy” concern vs. a “engine longevity” one.
(Certain exceptions do apply…I tend to keep my newly-acquired Honda CB350 =< 7500 RPM as much as possible, even though the redline is 10,500…because the thought of valve springs older than me is a bit unsettling!)
meanjoe, are you saying that you keep your car at 7,500 RPM while driving at speeds of 30, 40 or 50 MPH? As whitey says, if it is your preference, than keep it up. Have you been doing very long??
He’s talking about a small motorcycle that Honda built during the late '60s and early '70s, not a car.
That is not what I said, EllyEllis. You seem to have a hard enough time speaking for yourself. Please don’t try to speak for me.
By the way, EllyEllis, “<” means “less than.”
The Honda CB350 is a motorcycle with 325cc engine. Like many small displacement engines, it was designed to run at high RPMs, and can handle it with relative ease. The Honda CB350 was a two-cylinder motorcycle produced between 1968 and 1973, which makes it at least 36 years old.
Imagine a 36-41 year old engine that runs at 7,500 RPMs and hasn’t fallen apart. It must have been designed to operate at high RPMs.
Would someone please do the math how how fast the pistons of a 325cc engine have to move at 7,500 RPMs? I am just curious.
The Honda CB 350 engine had a 64 mm bore and a 50.6 mm stroke.
That would be about 2490 feet per minute average piston speed at 7500 RPM.
“Imagine a 36-41 year old engine that runs at 7,500 RPMs and hasn’t fallen apart. It must have been designed to operate at high RPMs.”
Or, it may have spent many years running at zero rpm while gathering dust in someone’s barn. How many miles are on the odometer and where are all the rest of the millions of Honda CB350s that Honda made? These were belly button bikes in the late 60’s, everybody had one.
Or, it may have spent many years running at zero rpm while gathering dust in someone’s barn.
That is certainly a possibility. There are a lot of CB750s from that era that get ridden and are still going strong. I feel lucky to have one of the last CB750s sold in the US. Now that it is broken in, it is running like a champ, even when I rev the engine.
Would someone please do the math how how fast the pistons of a 325cc engine have to move at 7,500 RPMs? I am just curious.
Well, the specifications show a cylinder stroke of 50.6mm/2in, so it would have a similar piston speed to the hypothetical 3" stroke at 5000 RPM.
So much of engine operations are specific to the application. The R-670 in a Stearman biplane produces max horsepower at 2,175 RPM; the motorcycle I mentioned is doing just a bit above idle at the same RPM. 4 5/8" stroke on the A/C engine…but that’s with each cylinder displacing 98 cu. in.!
The BMW 2009 M5 redlines at 8300 rpm,you can drive it like a little old lady you can run it as designed,the engine doesn’t care and BMW will not deny warranty for using the car as designed out to 50K. These are truly steetable F1 engines that can be driven by anyone who doesn’t even have a clue as to whats going on and the engine will not be damaged,lug it ,rev it its all been taken into account by the engineers.
Thanks everyone for your input. I gather, from all this info, that I should drive my vehicle harder so it will be “happy” and last longer.
How do you gather that conclusion based on this these responses? I think the reasonable conclusion is to drive your vehicle in a manner that you think will make it last longest based on how it was designed and built. The conclusion I draw is that each particular engine is crafted to particular specifications and tolerances, which vary from engine to engine.
In the simplest of terms, not all engines are created equal. Some are fragile and fly apart at high RPMs, while some are robust and are designed to withstand being driven at high RPMs.
How you choose to apply your “one size fits all” philosophy is up to you, but for many, this isn’t a “one size fits all” question or a “one size fits all” answer.
…and he calls me “slow.”
I still think that the finest engine made will last longer if driven slower!! A friend of mine has a new Chalenger with 180 MPH on the speedometer but it will probably last longer if he drives less than 180. I suppose he could drive it in ,say 3rd or 4th, and keep the RPMs up around 6000. It’s a 6 speed manual.
In that case, drive your car at 6 RPMs and let us know how long it lasts. You might need to lock up your torque converter first to force the RPMs that low, but according to your “one size fits all” belief, it should last forever. Let us know how it turns out.
I never said “one size fits all” but one thing does fit all, high RPMs are harder on an engine than moderate RPMs. But go ahead and drive at high RPMs and let us know how long it lasts.
I never said “one size fits all” …
Yes you did. You said:
I still think that the finest engine made will last longer if driven slower!!
Why don’t you prove it? Why don’t you lower your RPMs by starting out with your transmission in 3rd gear instead of drive? That would bring down your RPMs. Aren’t you sure that would make your engine last longer?
But go ahead and drive at high RPMs and let us know how long it lasts.
I already do, according to your standards. My regular commuting vehicle these days is a 2003 Honda CB750. At cruising speed on the highway, it operates at about 5,000 RPMs. Similarly, my four cylinder 1998 Honda Civic (with about 186,500 miles) operates at what you consider “high RPMs,” but it doesn’t have a tachometer, so I can’t tell you the specific RPMs.
I am already practicing what I preach because I am a man of my word. Are you a man of your word? If you are, get those RPMs down as low as you can by starting out in 3rd gear and tell us what it does to your car. My vehicles are holding up just fine. The Civic has been holding up just fine for 11.5 years. The CB750 has been holding up just fine for 6 years. I will let you know if they have any engine problems.
At least one of us follows his own advice. Let me know when you start following the same advice you dispense.
You should know by now that I drive nothing but automatics, I don’t know how I could start off in 3rd gear. Just where in the following statement did I say that “one size fits all”? “I still think that the finest engine made will last longer if driven slower!!”
Of course you can shift it to 3rd gear. I know you drive automatics, and they can be manually shifted to “2,” “3,” and sometimes “4” instead of “D.” Manufacturers include this feature so you can downshift when going down long steep hills. I am sure your engine qualifies as (in your opinion) one of the finest engines ever made, so why not try starting out in 3rd or 4th gear to keep your RPMs down? Come on. Practice what you preach, unless you have been talking out of your tailpipe this whole time. What are you afraid of? Are you afraid to find out you are wrong?
Well again you show you don’t know what you’re talkin’ about. If I put my vehicle in 1st it starts and stays in 1st. If is put it in 2nd it starts in 1st and will shift to 2nd. next up is drive and in drive it will start in 1st, shift to 2nd, 3rd, and on to 4th, or overdrive. The ooverdrive lockout is a button on the dash. As for being WRONG, didn’t you say that these were only preferences and NOBODY IS WRONG OT RIGHT?
I have had excellent luck with engines ever since I started driving for maximum gas mileage, which generally means shifting early.
280,000 on a '91 Geo metro, these cars only had a 1000 cc engine in them.
60,000 miles on a Suzuki DR 650 motorcycle, was still running strong but I wanted something else so I sold it.
91,000 miles on a Kawasaki ZRX1200 motorcycle, I still don’t have to add oil between changes. Even though this engine is redlined at 10,500 rpm, I almost never rev it over 4,000 unless I actually need all 115 horsepower to pass someone as fast as possible.
I’m not saying you should lug your engine but its just silly to use a gear that has your engine reving 2/3 to the redline when you are throttling the engine down to about 9 horsepower, i.e. obeying a 50 mph speed limit on level ground.