ak diesel driver
6.5 driver
I thought knife edging was to slice thru the oil easier more so than weight
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Cams & cam regrind discussion as a performance adder
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buddy
Active Member
Yeah, thats what knife edging is for, it accomplishes both though. The funny thing is when people want their crank trimmed to be like an airfoil thinking that airplanes cut through the air. But the entire purpose of an airfoil is to create drag to generate lift. Supersonic jets with more thrust can use the knife edge wings because they generate lift from thrust and higher speed.
ak diesel driver
6.5 driver
actually they generate lift from angle of attack and thrust/speed
JiFaire
Land Mine Finder
Ok, I get that... so lightening (assuming forged is lighter than cast, which I'm not sure about) and trimming the crank could affect spin-up (rpm acceleration) - but that's a torque function, not a power function - it still wouldn't have anything to do with the 'higher rpms and efficiency' part, right?
JiFaire
Land Mine Finder
part of the equation - then there's that annoying bernoulli thing...
robzombie4551
robzombie4551
The heavier it is the more energy it stores. Heavier is better for heavy vehicle/ high torque applications.
Lighter weight is good for high rpm applications. Light weight vehicle/race applications.
You are right that they will rev faster,but in our application not really wanted/needed.
We need the added weight/stored energy to move our 6/8000 lb. vehicles. And the fact that we don't see the high side of 4000 rpm, hopefully.
My big block buick/455 has one heavy a$$ flywheel and that is a torque monster and only goes to 4,500 rpm stock and 7,000 rpm built for street strip in my case.
buddy
Active Member
Some of us may be wanting to go past 4000rpm, and some already do. In which case the less resistance from weight being off center on the crank can help, because to spin that weight faster and faster takes more and more power and it resists change in speed up or down. Its heavy to be strong, and the counterweights are huge to help lower stress on the crank, but with stronger material it doesnt have to be made the same way.
So yes it can be more efficient and run higher RPMs easier if there is less resistance to spinning the crank. The heavier the rotating the assembly the more energy it takes to spin it, and is taken away from the wheels. That doesnt matter much on the camshaft since it doesnt have anything far off its center, but on the crank it has huge offset counterweights that stick out far.
So yes it can be more efficient and run higher RPMs easier if there is less resistance to spinning the crank. The heavier the rotating the assembly the more energy it takes to spin it, and is taken away from the wheels. That doesnt matter much on the camshaft since it doesnt have anything far off its center, but on the crank it has huge offset counterweights that stick out far.
JiFaire
Land Mine Finder
If you say so ... if it wasn't balanced, I would agree, but unless the resistance increases as a function of RPM, then mass shouldn't matter to a rotating assembly. I would think that oil resistance would be a much bigger factor. In any case, have at it... I'll watch with great interest..
I am curious how much weight difference there would be between forged and cast... never seen specs on that.
I am curious how much weight difference there would be between forged and cast... never seen specs on that.
buddy
Active Member
Its simply physics, although the theoretical and applied mechanics and mechanical engineering lessons help too.
robzombie4551
robzombie4551
I was talking about flywheel weight. Which we don't want to be to light.
You are right that lighter reciprocating mass. IE crankshaft, uses less energy .
Here is an article that helps explain the pros and cons a little bit.
Crank Materials and Construction
Essentially, the range of crankshaft materials runs as follows: billet steel, steel forgings, cast steel, nodular iron, malleable steel or (in some cases) cast iron. If we were to produce one crankshaft design and reproduce it in all these materials, the order of strength would approximately follow this same list. While cast cranks are typically less expensive than forgings, they can be produced in shapes not available with forgings. But dollar for dollar, forged cranks tend to be the better method of manufacture, certainly with respect to high output durability.
Often a subject of discussion and frequently believed to be critical in the design, modification and service life of a crankshaft, is how fillet radii are configured. If we were to perform a stress analysis test that included all other design features and conditions of a given crankshaft, fillet radii could be considered the most critical factor in overall design and/or modification procedure. There is belief among crankshaft manufacturers that the use of fillets of non-constant radius—sometimes called “non-circular” contours—is preferred over those of constant radius. Worst case, this is an area worth discussing with your engine builder or crankshaft manufacturer of choice.
Lightweight vs. Heavyweight Rotating Mass
Let's talk about transient torque. For purposes of this discussion, transient torque is a measure of how quickly an engine can accelerate (including under load) through its useful rpm range. Stated another way, under sudden conditions of WOT, how fast it will span from low to high rpm. From a measurement standpoint, this is torque as measured on an inertia dyno: not a so-called “accel” test as performed on an engine dyno whereby there is a controlled unloading of the power absorption unit. This is real-to-the-track” torque and it relates to an engines ability to overcome its internal resistance (inertia) to gaining rpm.
Based on these considerations, it is fair to say crankshafts don't normally operate at constant rpm. They're either accelerating or decelerating. Their resistance, in either case, includes static weight and dimensional landscape (stroke length, location and distribution of mass, etc.). Technically speaking, in a dynamic environment, crankshafts are continually changing potential energy into kinetic energy. So what, you say? Well, these are all factors that go right to the issue of how much torque is available at the output end of a crankshaft—and need to be considered for power optimization.
From a practical standpoint, acceleration of a “heavy” crankshaft absorbs more torque than one of less weight, thereby reducing the amount of net torque available to accelerate the car. But there are trade-offs in terms of durability, flexibility and potential longevity that should be considered when trimming crankshaft weight. Furthermore, it’s not all about weight. Placement of weight, relative to a cranks axis of rotation, is also important. For example, the moment of inertia (resistance to a change in state of rotation or acceleration/deceleration) increases as weight is moved away from the axis of rotation. Even between two crankshafts of the same total static weight, the one with more weight near its axis of rotation will exhibit less resistance to a change in rotational speed; it has a lower moment of inertia. Keep this in mind when adding “heavy metal” to crankshaft counterweights during the process of dynamic balancing.
Finally, where total crankshaft weight may relate to overall flexibility, it's best to err on the side of stiffness, if this can be accomplished by selecting a crank that trends toward stiffness in combination with durability and lightweight. Involved in making these type of choices, torsional vibration or deflection becomes another important issue.
You are right that lighter reciprocating mass. IE crankshaft, uses less energy .
Here is an article that helps explain the pros and cons a little bit.
Crank Materials and Construction
Essentially, the range of crankshaft materials runs as follows: billet steel, steel forgings, cast steel, nodular iron, malleable steel or (in some cases) cast iron. If we were to produce one crankshaft design and reproduce it in all these materials, the order of strength would approximately follow this same list. While cast cranks are typically less expensive than forgings, they can be produced in shapes not available with forgings. But dollar for dollar, forged cranks tend to be the better method of manufacture, certainly with respect to high output durability.
Often a subject of discussion and frequently believed to be critical in the design, modification and service life of a crankshaft, is how fillet radii are configured. If we were to perform a stress analysis test that included all other design features and conditions of a given crankshaft, fillet radii could be considered the most critical factor in overall design and/or modification procedure. There is belief among crankshaft manufacturers that the use of fillets of non-constant radius—sometimes called “non-circular” contours—is preferred over those of constant radius. Worst case, this is an area worth discussing with your engine builder or crankshaft manufacturer of choice.
Lightweight vs. Heavyweight Rotating Mass
Let's talk about transient torque. For purposes of this discussion, transient torque is a measure of how quickly an engine can accelerate (including under load) through its useful rpm range. Stated another way, under sudden conditions of WOT, how fast it will span from low to high rpm. From a measurement standpoint, this is torque as measured on an inertia dyno: not a so-called “accel” test as performed on an engine dyno whereby there is a controlled unloading of the power absorption unit. This is real-to-the-track” torque and it relates to an engines ability to overcome its internal resistance (inertia) to gaining rpm.
Based on these considerations, it is fair to say crankshafts don't normally operate at constant rpm. They're either accelerating or decelerating. Their resistance, in either case, includes static weight and dimensional landscape (stroke length, location and distribution of mass, etc.). Technically speaking, in a dynamic environment, crankshafts are continually changing potential energy into kinetic energy. So what, you say? Well, these are all factors that go right to the issue of how much torque is available at the output end of a crankshaft—and need to be considered for power optimization.
From a practical standpoint, acceleration of a “heavy” crankshaft absorbs more torque than one of less weight, thereby reducing the amount of net torque available to accelerate the car. But there are trade-offs in terms of durability, flexibility and potential longevity that should be considered when trimming crankshaft weight. Furthermore, it’s not all about weight. Placement of weight, relative to a cranks axis of rotation, is also important. For example, the moment of inertia (resistance to a change in state of rotation or acceleration/deceleration) increases as weight is moved away from the axis of rotation. Even between two crankshafts of the same total static weight, the one with more weight near its axis of rotation will exhibit less resistance to a change in rotational speed; it has a lower moment of inertia. Keep this in mind when adding “heavy metal” to crankshaft counterweights during the process of dynamic balancing.
Finally, where total crankshaft weight may relate to overall flexibility, it's best to err on the side of stiffness, if this can be accomplished by selecting a crank that trends toward stiffness in combination with durability and lightweight. Involved in making these type of choices, torsional vibration or deflection becomes another important issue.
buddy
Active Member
Nope, you missed the point, its physics. Go put a baseball on the end of a rope and try swinging it in a circle, then increase the length of tte rope, then try spinning it faster, then go put a brick on the end instead. I am guessing you get tired a lot faster because of all the energy you have to use to swing the heavier brick faster and faster. It takes more engery to spin more mass at a longer arm. it even says it in that article
"From a practical standpoint, acceleration of a “heavy” crankshaft absorbs more torque than one of less weight, thereby reducing the amount of net torque available to accelerate the car."
The weight and length away from the center on the crank is just as important as the weight of the pistons when it comes to reducing rotational mass to make it more efficient.
People change out pulleys for crying out loud. Because lighter pulleys use less engine power to turn. Those lighter pulley things are a joke to me, to unlock 10hp on a 500hp engine.
"From a practical standpoint, acceleration of a “heavy” crankshaft absorbs more torque than one of less weight, thereby reducing the amount of net torque available to accelerate the car."
The weight and length away from the center on the crank is just as important as the weight of the pistons when it comes to reducing rotational mass to make it more efficient.
People change out pulleys for crying out loud. Because lighter pulleys use less engine power to turn. Those lighter pulley things are a joke to me, to unlock 10hp on a 500hp engine.
ak diesel driver
6.5 driver
your talking about stroke with that analogy. and a shorter stroke motor generally accelerates faster
JiFaire
Land Mine Finder
I remember my physics and although I'm getting on in years, the mech engineering courses tend to stay with one. Thanks for the lesson, though.
In terms of hp to accelerate to RPM, yes, that's the whole point of inertial resistance. In terms of sustainable rpm, it's more important to attend to the constraints of dynamic balancing than it is to reduce crankshaft inertia... as rpm increases, the deflection caused by even slight amounts of rotating assembly mass needs to be absorbed by the countervail weight of the crank, or else things twist and flex... not good.
I tend to agree that knife-edging would lower rotational resistance, but it's a questionable amount of gain... race drivers tend to avoid going too far in this practice because of repetitive failures for questionable gains. On the other hand, full-system dynamic balancing allows for greater rpm without sacrificing stability.
http://www.eatonbalancing.com/blog/category/balancing/
In terms of hp to accelerate to RPM, yes, that's the whole point of inertial resistance. In terms of sustainable rpm, it's more important to attend to the constraints of dynamic balancing than it is to reduce crankshaft inertia... as rpm increases, the deflection caused by even slight amounts of rotating assembly mass needs to be absorbed by the countervail weight of the crank, or else things twist and flex... not good.
I tend to agree that knife-edging would lower rotational resistance, but it's a questionable amount of gain... race drivers tend to avoid going too far in this practice because of repetitive failures for questionable gains. On the other hand, full-system dynamic balancing allows for greater rpm without sacrificing stability.
http://www.eatonbalancing.com/blog/category/balancing/
buddy
Active Member
Like mentioned earlier in the thread, thinking outside the box. When your crank got 4, 6, 8 times or whatever it is harder, stiffer, stronger because of materials, then you could look at what realistic changes in its design could be done and still not break it.
the problem is disputing the simple fact that it takes more energy to spin a heavier mass with a larger arm.
the problem is disputing the simple fact that it takes more energy to spin a heavier mass with a larger arm.
buddy
Active Member
Here is Banks applying the theory to the DMax
http://www.hotrod.com/techarticles/engine/hrdp_0609_banks_performance_duramax_diesel/photo_02.html
He also seems more concerned with shedding the oil than the impact of the crank into the oil. I guess so the oil isnt adding weight to the end of the weights.
http://www.hotrod.com/techarticles/engine/hrdp_0609_banks_performance_duramax_diesel/photo_02.html
He also seems more concerned with shedding the oil than the impact of the crank into the oil. I guess so the oil isnt adding weight to the end of the weights.
robzombie4551
robzombie4551
I know I posted it. I'm not arguing that point.
But you also need to consider that with a body of mass in motion IE: flywheel, that a heavier flywheel and the energy stored in it after X amount of RPMS takes less energy to accelerate it or keep it in motion.
Are we gonna compare the overall use of said vehicle? Drag race, DD/ or Towing. Each has their own specific needs for ultimate effeciency.
Also weight,gear ratio, and other factors depending on how accurate the mathematical equation you're working with.
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Ratman
6.5 Diesel NUTCASE
Yes indeed, -and it can also "store" more energy as well. I remember switching out the 8" balancer on my 283 SBC and swapping it out for one of those small 7-1/4's (or whatever they are) -and noticed a HUGE difference in throttle response and gained a few more R's on the top end.
Everyone involved and subscribed to this thread realizes we are opening up huge cans of worms in terms of effects (that moment of inertia has) on the amount of power it takes to accelerate/decelerate a given amount of mass. Add to that the complexities of varying RPM and "critical speeds" of various components, -and one quickly gets in "over their head in math" real dang quick.
The fact is, more mass, -or a longer moment arm WILL in fact take more energy to accelerate/decelerate, because it adds moment of inertia into the equation.
This is waaaay off topic, but the Pratt and Whitney 28 cylinder 4360 cubic inch radial engine employed bifilar weights on several crank counterweights (a floating type of counterweight specifically designed to deal with constantly varying balance issues by constantly adjusting itself). The engineers did this to intentionally offset any imbalance issues that would occur if the pilot rolled-on takeoff power if an aircraft sat on the tarmac too long and fouled plugs and was attempting to take off with several dead cylinders because of the fouled plugs.
Amazing stuff indeed.
I love this stuff....:agreed:
buddy
Active Member
I will certainly agree, that having it all balanced correctly is definately required, thats an assumption that its all balanced afterwards.
But since I dont plan on touching a crank, no real reason to discuss it. Although, it begs the question if you get a forged one, did they just match the shape and balance it, or did they match the counterwieght's weight? And CIL6 was planning to get a billet one which even if the same shape it would be lighter everywhere, much lighter.
I changed the crank pulley out in my Z28, it helped responsiveness a little, but worst thing I ever did to it. It then underdrove all the accessories. It was a size difference as well as mass. The crazy thing is when people pay big bucks for just lighter weight pulleys, not even underdrive ones.
But since I dont plan on touching a crank, no real reason to discuss it. Although, it begs the question if you get a forged one, did they just match the shape and balance it, or did they match the counterwieght's weight? And CIL6 was planning to get a billet one which even if the same shape it would be lighter everywhere, much lighter.
I changed the crank pulley out in my Z28, it helped responsiveness a little, but worst thing I ever did to it. It then underdrove all the accessories. It was a size difference as well as mass. The crazy thing is when people pay big bucks for just lighter weight pulleys, not even underdrive ones.
JiFaire
Land Mine Finder
Yeah, I agree with much of that. The thing is, getting a billet crank that is lighter 'everywhere' won't work. It has to be the same weight in the right places to balance out the rotating assembly - which was the point of my earlier post - this is a system. The counters will be closer to the radial axis, but will be heavier, reducing the moment arm but retaining the balance so the piston/rod combo doesn't put torque on the crank.
That's what Eaton talks about with using heavy metal plugs machined into the counters...
As you say, matching the shape, balancing it, but with a different material won't solve things... the distribution of mass/force will be very different, while the distribution/force generated by the rotating mass will not have changed. Static balance vs dynamic balance.
That's what Eaton talks about with using heavy metal plugs machined into the counters...
As you say, matching the shape, balancing it, but with a different material won't solve things... the distribution of mass/force will be very different, while the distribution/force generated by the rotating mass will not have changed. Static balance vs dynamic balance.
3500GMC
What T F, over
And not to mention the firing order.. BBC: 18436572 - - 6.2/6.5: 18726543, exactly like the LSX GM gassers. Hmmm. Switch some injector lines around, maybe?