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Old 04-07-2019, 11:38 AM   #41
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> ....Are you paraphrasing P.T. Barnum (.......”born every minute.”)?
It's a myth. Barnum historians say he never said it.

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Old 04-07-2019, 11:42 AM   #42
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Yea, but Steve L and RockyBob did. Sort of. :-)
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Old 04-07-2019, 02:53 PM   #43
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Back when farm tractors had 35 HP and could plow a field, that was Torque.
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Old 04-07-2019, 03:54 PM   #44
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Those 35 HP tractors were all about gearing as much as anything, heh.

yes, HP is torque * RPM * scalefactor.... and yes, max HP is great, but its generally at a very high RPM you do NOT want to be cruising at unless you're going top speed, which you probably shouldn't be doing when towing.

when I'm towing, I'm usually around 2000-2500 rpm with my Tacoma 4.0, or 1500-2000 rpm with my Ford 7.3 diesel. it doesn't matter what my HP is at redline, I'm not going there except for very brief moments when accelerating hard.

The Tacoma 4.0L V6 had like 235HP at 5200 RPM and 266 lb*ft of torque at 4000 rpm, but its cruising revs were around 2500-3000, anything above that got pretty noisy. I'd find myself in 4th or even 3rd (out of 6) going up grades with the 3000-ish lb Casita 16.

That powerstroke only has 250 HP at 2700 rpm, but its got 525 lb*ft of torque at 1600 rpm. I can maintain speed in top gear at 60 MPH up most grades while towing a 4500 lb E21.

so yeah, for towing I want torque at low to moderate RPMs.
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Old 04-07-2019, 05:24 PM   #45
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It's a myth. Barnum historians say he never said it.

Harold
Perhaps, but I made my point. And whether he said it or not, it is appropriate and true.
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Old 04-07-2019, 07:25 PM   #46
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Hp

We have the 3.5 ecoboost Ford Expedition 2018 We will be pulling an Escape 21 this Summer Without trailer we are doing 70mph at 1500 rpm my other tow vehicle Sequoia with a v-8 would be at 2200 rpm
The difference is Ford has 470lb of torque at2500 rpm this is almost in Diesel territory
BTW I get 25mpg vs 18 mpg different Hp and torque in the new Ford
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Old 04-08-2019, 08:01 AM   #47
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Thanks Raspy! For your quote. “The point is, you can adjust the torque with gearing. Horsepower is what accomplishes work. Practical designs take into account the real world use of things. It's not valid to simply say torque does work.“ I’d add that maximum rated horsepower is only available at a particular engine rpm, so that best performance is obtained when gearing allows the engine to run at that rpm.
Consider a vehicle on a long climb up a grade, with wide open throttle. If the gearing only allows the engine to reach peak torque rpm (which will be less than peak horsepower rpm) the pulling power of the vehicle will increase — the vehicle accelerate — if you downshift so that the engine can wind up to peak horsepower rpm. More horsepower is “What accomplishes work”.
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Old 04-08-2019, 10:31 AM   #48
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Rocky,
It is interesting that all of the engine powered things we use, cars, trucks, boats, tractors, airliners, etc, have some limit on their horsepower. We can't just pull an infinitely heavy load up a steep grade at any speed we wish.

Given that, and that most of the time, engines run at less than full rated power, and the fact that we want good fuel economy and we have to fit the engine into the vehicle, means we have to find a compromise that works best.

Running down the highway pulling a trailer, it's best if we are not at full throttle and full HP RPM. Not only is the engine less efficient there, it is also under much more stress and it's annoying to the operator. So designing it with enough torque to do the normal job at the normal RPM, makes sense. Some extra torque, at that RPM, makes the experience even better. The result of that is that there is more power at a higher RPM somewhere beyond the normal working RPM.

Old John Deere tractors, for instance, didn't have much power, but they operated at a speed that was pleasant to live with and they lasted forever. Cummins engines pull best at about 1800-2000 RPM and are easy to live with and economical.

So, as I mentioned, each machine should be designed to find the best compromise between absolute max power and real world drivability. Then they have some reserve power if needed.

I recently drove a new Honda Civic with a CVT tranny. What an annoying thing! Every time I asked for a little more power, it would gear down and run the engine up to full HP RPM. A huge response to a casual request. A sledge hammer to kill a fly. I'd rather be in the fat part of the torque curve and let it speed up without all the drama, just as the Cummins does when in the Sierra. It leans into the load with torque and pulls like a locomotive.

As you get a higher and higher HP to weight ratio, performance becomes so interesting. The weight of the vehicle becomes less of a burden. A couple of examples are my KTM 495 dirt bike. At any time, a twist of the throttle and the tire speeds up. It doesn't really matter if it has traction or not, or what gear it's in. It is famous for digging trenches and spending long periods with the front end off the ground. My buddy used to have a '65 Plymouth with a built 426 Wedge. It accelerated harder in third gear than the lower gears because that was where it finally began to hook up. The body was just a tin can tied to a stick of dynamite. Very impressive and a huge amount of fun! I had a built 427 Chevy in a 19' flat bottom drag boat. That boat would literally jump out of the water when I punched it. Few things are more exciting than that boat, approaching a marina, and finding the throttle is stuck wide open! Yikes.
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Old 04-08-2019, 12:40 PM   #49
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Oh the complexities! The rpm that allows maximum horsepower doesn’t mean that maximum horsepower is being produced, just that for that particular gearing and vehicle speed the engine needs to spin at that rpm. As is obvious, only when the throttle is wide open and the rpm is right is max horsepower being produced. I wonder if the CVT design is a simple “increase rpm to max hp rpm and hold until needed vehicle speed is reached.” That’d be simpler than continuously adjusting rpm, although I agree it would be really annoying.

My 3.3 liter (202 ci) Santa Fe engine has changed my mind about high revs. Six speeds with red line of 6500 produces 290 hp. With moderate acceleration it happily spins to 4500 or even 5000 without much noise at all. By redline you hear it, but it isn’t alarming. My previous Jeep with 4.7L sounded much more obnoxious at 3500 rpm. And yet the SF drive train is warranted for 100K. (BTW, at 45000 miles and 4800 miles with the current oil, it’s used absolutely no oil. I don’t understand how they do that)

A long, long time ago I read an epistle about piston engine design. What I remember was the statement that the thing that most normal engines had in common was “peak piston velocity”. Supposedly from tiny short stroke babies to giant stationary engines was this velocity. Seemed reasonable to think that for engines with the same anticipated life that the peak speed of the compression rings might be constant. So 3 inch stroke of a 3.3 liter spinning at 4000 might be no worse than the a 6 inch stroke at half the rpm.
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Old 04-08-2019, 03:38 PM   #50
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The longer the stroke, the faster the piston speed for a given RPM. Now days, engines are becoming more and more oversquare, to the point that the stroke is sometimes only about 70% of the bore. Pistons are becoming lighter by making them into short disks. Even the new 7.3 Liter Ford V-8 that is a heavy duty engine, has very short pistons. These type engines will happily rev all day.

I don't know how they make them so oil tight either. Each of my three Cummins got oil changes at 10,000 mile intervals and none of them ever used a quart between changes. Sheesh. Cool.
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Old 04-09-2019, 07:51 AM   #51
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I don't know how they make them so oil tight either. Each of my three Cummins got oil changes at 10,000 mile intervals and none of them ever used a quart between changes. Sheesh. Cool.
The 4.0L in my FJ Cruiser doesn't seem to use any oil at all in 10,000 miles, even using thin 0W-20 synthetic as specified by Toyota. And this is after 100,000 miles (I just changed the oil at 100K the other day).
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Old 04-09-2019, 09:59 AM   #52
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I've looked at piston ring design, casually, for a long time and am amazed at not only what they do, but at how little oil is required to lube them and the piston. There is a tricky balance where the ring is scraping the cylinder wall, and tilting slightly on each stroke to seal, and it's need for lubrication. Too much oil left on the cylinder wall will allow burning of oil, too little will cause heavy wear. The film left on the wall is exposed to the full power stroke heat and pressure and the heat absorption through the cylinder wall to the coolant. The film has to be thin enough to be invisible to this, but still lube the rings. It has to not burn off the relatively cool cylinder wall while exposed to the high pressure fire. Impressive.

It has taken many years of heavy development work to refine ring design to get it to where it is today. When you think of materials rubbing against each other, it's interesting that a cast iron or steel ring can scrape a cast iron cylinder wall and not wear significantly over so many cycles and under so much heat and pressure. Especially considering that the ring tilts slightly to keep a sharp edge against the wall for excellent sealing. When rings are made, they are ground in a shape that is not round such that when pinched down to fit in the bore, they apply equal pressure all the way around against the wall. Now, some of them are made of spring steel and some are chrome plated.

Designers are constantly looking for and addressing friction points in the engine to increase power and efficiency. I wonder what percentage of overall engine internal friction comes from the rings? Cylinder deactivation is currently used to improve mileage, but only has limited benefit, partly because the pistons are still running up and down in the bores, but not producing power. Honda Pilots I looked at were available with and without cylinder deactivation and the mileage difference was only 1 MPG. I suppose it factors in to Ecoboost efficiency too, where a smaller engine has inherently lower internal friction, but can be boosted to act like a much larger engine. This takes the stress on the rings to a whole other level. Recently, a Ford engineer was discussing the merits of the new 7.3 V-8 and stated that the rings are very durable and the same design used in turbocharged engines.

One of the most sure ways to damage or ruin a diesel engine is to wreck the rings. This happens with the use of ether. Too much ether causes such a sudden and extreme pressure rise that it literally drives the rings down hard enough to break them and break the piston ring lands. After that happens, or as it happens over time with more ether use, the compression is so reduced that the engine becomes harder and harder to start. This requires even more ether to start and finally the engine is junk.
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Old 04-09-2019, 12:13 PM   #53
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I had to read that last paragraph at least 3 times before i realized you meant ETHER not either
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Old 04-09-2019, 12:43 PM   #54
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I had to read that last paragraph at least 3 times before i realized you meant ETHER not either
John,

Thanks. How did that happen?
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Old 04-10-2019, 11:03 PM   #55
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my kid's diesel army truck has no glow plugs, instead it had an ether based cold start system. he's never charged the ether system, instead just cranks it til it coughs over.

its a 14L old cummins 6 cyl, non-turbo.
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Old 04-11-2019, 09:29 AM   #56
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So consider a typical engine; six cylinders, 2000 revolutions per mile. That means 12,000 piston strokes per mile or 12,000,000 per thousand miles or 60 million strokes in a 5000 mile oil change interval. Given that there has to be at least SOME lubricant for that top compression ring for each stroke, it seems impossible for an engine to consume virtually no oil between changes — yet many modern engines seem to do that. And they do it for well over 100,000 miles. Ring design is really incredibly advanced.
Google says there are about 19,000 drops in a quart. So, if each piston stroke allowed even one thousandth of a drop of oil (a millidrop?) to be burned, by 5000 miles the engine would’ve burned over 3 quarts of oil.
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Old 04-11-2019, 09:38 AM   #57
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An engine guru at a machine shop I used long ago told me that ring friction was such a power loss that some racing folks would remove a ring to increase available hp. I don’t remember for sure but think it was one compression ring. He also pointed out that valve train losses were about one third of hp. Turns out that while it is easy to turn a valve train at slow speed because the valve spring forces balance out, at typical engine rpms they don’t balance out.
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Old 04-11-2019, 03:53 PM   #58
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my kid's diesel army truck has no glow plugs, instead it had an ether based cold start system. he's never charged the ether system, instead just cranks it til it coughs over.

its a 14L old cummins 6 cyl, non-turbo.
I remember an old coot telling me one time that the diesel engine should only be able to "smell" the ether. No liquid, ever. Any more than just a whiff, was dangerous. He was right. I've seen a lot of people use ether and not many of them ever use it correctly. And I've seen the carnage as a result. Gas engines, on the other hand, can run on it without damage.

I had a Perkins in my boat. It's pre-heat system was to push a button next to the ignition key, that opened a valve that allowed fuel to trickle into the intake manifold. At the same time, an electric heating element heated up that would ignite the trickle of fuel and start a fire in the intake manifold. Then you'd crank the engine, which would draw the fire into the cylinder and fire the engine. Another way to do this is to simply point a burning propane torch into the air intake at the manifold. Or even more crude, light a small piece of diesel soaked paper and drop in into the intake while cranking.

The whole "diesel starting" problem is another interesting aspect of combustion chamber design. Pre-combustion chamber engines are inherently hard to start because there is so much cold surface area compared to the overall volume in the chamber, that the cold walls absorb too much heat before injection occurs. The key reason for this is that the smaller the overall volume of a container, the greater the surface area of that container, per volume. More cold surface per heated volume. It's why direct injection diesels start easier, even with lower compression ratios, than pre-combustion engines, with their small combustion chambers. Direct injection engines have a greater radius to the cold surface than the pre-combustion design and less surface area per volume to cool the compression heat.

It seems to be part of the reason why ducks can leap from high nests in trees and fall to the ground unharmed. They are so small that they have a much larger surface are per volume than larger animals. More surface area means more drag per volume, so their terminal velocity is quite low. Of course, they are covered in down to add more drag. A bit off topic, but the volume vs surface area is an interesting relationship with all of it's side affects.

A square house with four equal length walls, has less overall wall area than a rectangular house with the same interior floor area. So, a square house should be easier to heat than a rectangular one.

Even though, at idle, a diesel has much more air than needed for combustion, it is never too lean to fire. Conventional gas engines can get so lean they will not run, even though they have barely more air than required to burn the fuel. In the diesel, the injection is the ignition timing. The chamber is already filled with superheated air. At the actual injector nozzle orifices, pure fuel begins to enter the chamber. There is no air in it and it is too rich to burn. Across the chamber, away from the injection point, there is pure air and it is too lean to burn. But somewhere in the middle, as the fuel atomizes and mixes with the charge air, and heats up to the ignition temperature, it ignites where the ratio is right and burns all available fuel that is within the required air/fuel ratio and not below the ignition temperature at the cylinder wall surface.

The oil left behind on the cylinder wall by the rings is too thin to be affected by the heat of combustion. The top two rings in gas engines are compression rings and are designed to seal on their way "up" and hold compression on their way "down". The oil ring has the remove enough oil that the two upper rings can't scrape oil in front of them on their way up, that would then burn, even though they are designed to not leak in that direction. It's hard to see how the system can work as well as it does. Then consider two stroke engines that are lubricated by a 50-1 fuel/oil mist. It doesn't take much oil to form a wedge that can hold parts apart to prevent wear.
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Old 04-11-2019, 04:00 PM   #59
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An engine guru at a machine shop I used long ago told me that ring friction was such a power loss that some racing folks would remove a ring to increase available hp. I don’t remember for sure but think it was one compression ring. He also pointed out that valve train losses were about one third of hp. Turns out that while it is easy to turn a valve train at slow speed because the valve spring forces balance out, at typical engine rpms they don’t balance out.
Interesting. Thanks. That is part of the reason we have to find a better engine design than the piston/poppet valve engine.

Achates is addressing the valve train problem with opposed pistons. And I want to personally boycott any overhead cam V6s. I had no choice with my Rubicon though. Get the V6 or don't get the Jeep. Hmmm. I thought about it for a while.
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Old 04-11-2019, 10:38 PM   #60
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Just wondering if it’s OHC V-6’s or is it Jeep? My 2000 Grand Cherokee (V-8) was never a prize with multiple annoying to aggravating failures before the transmission failed at 120k. OTOH, both the 3.8L and 3.3L Hyundai engines with variable timing OHC’s have never had any engine related issues. The 120k still has original plugs. Nice thing about Hyundai is the 60k bumper-to-bumper warranty; I had a steering wheel replaced under warranty at over 40k because there was a 1/8 inch chip in the steering wheel plastic, and an entire seat belt replaced because the little plastic button broke off. Call me a Hyundai fanboy, I guess.
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