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Discussion Starter #1 (Edited)
I've been thinking of ways to get smoother power delivery at very low revs (like 1200-1600rpm).
The stock motors seem to pull through this rev range smoothly enough, but I've got another 60% or so more torque and that's where most of it happens. I can't use full torque below about 1700rpm without the engine lugging and shaking.
Lighter throttle application is fine (it trundles along a flat road in top at 1400rpm nicely).

I figure most of the vibration is the result of the torque pulses being further apart (thinking time here) at lower revs which gives more speed variation between each pulse.
As engine revs increase, this time shortens until it becomes smooth enough to not affect anything.

From the solidworks model I have of the flywheel, it weighs around 16kg stock and has a rotational inertia of around 335e6 gmm^2.
There is room to fit a ring inside the existing rim which can increase this by around 25% and increases the total weight to around 20kg.

So those of you who have experimented with lightening flywheels in other applications, how much difference did it make going the other way?
 

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Dougal: common practice on 4 cylinder rock crawlers is to bolt an Interia Ring to the flywheel to increase rotational mass and thus torque at low (read idle and slightly above). Jason Bunch of TriCounty gear in Pomona CA actually sells a kit for the AMC 4 cyl engine. It adds about 5-8 lbs to the fly wheel, and makes the engine much smoother at low revs.

I used a 168 tooth Flywheel off a 292 chev 6 complete with 11" clutch assy on my Mercruiser engine (181CI Chevy 4 cyl) and in bottom gear (93:1) it is imposssible to stall the engine with a load. That's with 35x15.5 Swampers and both axles locked and even standing on the 4 wheel 3/4 ton disc brakes! In fact one of my crawling techniques is to drag the brakes when climbing a rock to prevent wheel spin. This would not be possible without the big flywheel. All the time the engine runs happily at 750 rpms and is kept there by the Fuel Injection idle air control.

The heavyer flywheel makes all the difference, however the back side is considerably slower throttle response, especially off Idle.

Randy
 

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Discussion Starter #3
Hey Randy

Thanks for the info, do you know roughly what % increase you were dealing with?
Was there any rev range of lugging before which the heavier flywheel dealt with?

Looks like I'm at least heading in the right direction.
 

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I have no idea how to quantify the increase in inertia. Maybe one of our engineering buddies can calc it out. The Inertia Ring was about 1.5" wide (section view)and 1.5" high. it weighed about 5-8 lbs, but all of the weight was concentrated at the "outside" of the flywheel so it is much lighter than just building a mondo flywheel..

It would bolt to the flywheel in the spaces between the clutch basket contact areas. Then be relieved to span the areas where the clutch basket contacts the flywheel and clear the hold down bolts. Keep in mind the whole flywheel, pressure plate and inertia ring must be balanced together as one unit or the engine WILL shake like a dog shittin tacks. It then must be taken apart for reassembly, so dowel pins and match marks are an absolute "must do".

As far as the range of influence, it would be across the entire range, and I believe it would be a linier function. The purpose of the inertia ring is to maintain existing momentum, It "stores inertia", so it's effects would be seen as the engine is being pulled down with a load. If you are trying to accelerate with a load it would actually work against you as you have more mass to accelerate. A body in motion tends to stay in motion, a body at rest tends to stay put..

A point that needs to be made here is the fact that torque, and horsepower are linked together. They are not separate issues. If you don't have the power to pull a certain load you won't have the torque either. Torque is a function of rotational momentum. You must first rotate, which requires power then you get torque. With no rotation, there is no torque.

You could concievably have an 8 foot flywheel that weighs a ton powered by a 5hp motor.. You could get it spinning and then load it for a short peroid of time, and not see any real loss of RPM's and inertia . This is how a mechanical Punch Press works. Big flywheel, trip the clutch and the flywheel drives the press thru one revolution. However if you keep the load on the flywheel very soon the inertia (stored energy) is used up, and the burden of turning the flywheel and the load falls on the motors power., which is only sufficient to turn the flywheel, not the load.

The same holds true for an engine pulling a vehicle. Only in this case the power of the engine has to be more up to pulling the load than on a Punch Press, and recovering from loaded conditions must be continuous, as opposed to intermittent, so horse power must be present to continuously accelerate the load.

At 1200 to 1600 rpms these engines are just not making any real power. They have torque due to the rotating mass of the crank and flywheel, but without power constantly being applied in sufficient quantities, the load will win the fight, and the only thing a heavyer flywheel will do is slightly prolong the inevitable. The amount of time the Inertia Ring maintains your momentum may be sufficient for your needs, like in cresting a hill, but it only works in a continuous application , if the power is there to back it up.

This concept totally applies to you guys trying to pull higher gears at freeway speeds. You have to run the engine in the power band, that's all there is to it, trying to lug it below the power just won't work.

Randy
 

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Discussion Starter #5
I have no idea how to quantify the increase in inertia. Maybe one of our engineering buddies can calc it out. The Inertia Ring was about 1.5" wide (section view)and 1.5" high. it weighed about 5-8 lbs, but all of the weight was concentrated at the "outside" of the flywheel so it is much lighter than just building a mondo flywheel..

It would bolt to the flywheel in the spaces between the clutch basket contact areas. Then be relieved to span the areas where the clutch basket contacts the flywheel and clear the hold down bolts. Keep in mind the whole flywheel, pressure plate and inertia ring must be balanced together as one unit or the engine WILL shake like a dog shittin tacks. It then must be taken apart for reassembly, so dowel pins and match marks are an absolute "must do".

As far as the range of influence, it would be across the entire range, and I believe it would be a linier function. The purpose of the inertia ring is to maintain existing momentum, It "stores inertia", so it's effects would be seen as the engine is being pulled down with a load. If you are trying to accelerate with a load it would actually work against you as you have more mass to accelerate. A body in motion tends to stay in motion, a body at rest tends to stay put..

A point that needs to be made here is the fact that torque, and horsepower are linked together. They are not separate issues. If you don't have the power to pull a certain load you won't have the torque either. Torque is a function of rotational momentum. You must first rotate, which requires power then you get torque. With no rotation, there is no torque.

You could concievably have an 8 foot flywheel that weighs a ton powered by a 5hp motor.. You could get it spinning and then load it for a short peroid of time, and not see any real loss of RPM's and inertia . This is how a mechanical Punch Press works. Big flywheel, trip the clutch and the flywheel drives the press thru one revolution. However if you keep the load on the flywheel very soon the inertia (stored energy) is used up, and the burden of turning the flywheel and the load falls on the motors power., which is only sufficient to turn the flywheel, not the load.

The same holds true for an engine pulling a vehicle. Only in this case the power of the engine has to be more up to pulling the load than on a Punch Press, and recovering from loaded conditions must be continuous, as opposed to intermittent, so horse power must be present to continuously accelerate the load.

At 1200 to 1600 rpms these engines are just not making any real power. They have torque due to the rotating mass of the crank and flywheel, but without power constantly being applied in sufficient quantities, the load will win the fight, and the only thing a heavyer flywheel will do is slightly prolong the inevitable. The amount of time the Inertia Ring maintains your momentum may be sufficient for your needs, like in cresting a hill, but it only works in a continuous application , if the power is there to back it up.

This concept totally applies to you guys trying to pull higher gears at freeway speeds. You have to run the engine in the power band, that's all there is to it, trying to lug it below the power just won't work.

Randy
Thanks, adding 5-8 lbs to the outside is probably sufficient to double the polar inertia of the original flywheel.
I'm one of the resident engineers here so the maths and design details are well taken care of.

I'm running the Isuzu 4BD1T and my current problem is I have heaps of boost and torque at an rpm where the engine isn't smooth enough to use it all. This is why I'm considering a flywheel addition. If I can smooth out all the pulsation at that rpm then I can use that rev range a lot more. Essentially I'm out to cure a drivability issue I think I created with a turbo that produces lots of boost at lower rpm than Isuzu intended.
A larger turbo housing to reduce boost at that rpm would help too, but it's not the solution I'm really looking for.

The other benefits of a heavier flywheel will help in some places, the downsides (acceleration/decelleration) aren't a concern.

Thanks again for your help.
Does anyone know the weight and diameter of a 4BT flywheel? Just looking to compare against the Isuzu.
 

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A point that needs to be made here is the fact that torque, and horsepower are linked together. They are not separate issues. If you don't have the power to pull a certain load you won't have the torque either. Torque is a function of rotational momentum. You must first rotate, which requires power then you get torque. With no rotation, there is no torque.
Er, um... Torque is an applied force, and can exist without rotation. But no work is being done without movement. (Though in an engine, if it's applying torque but can't rotate, it's gonna be one of those days..)

Horsepower is what you get when you apply force that accomplishes work, and is the rate of doing that work.

Agreed, though. You don't get to pull more power from a flywheel, averaged over time, than what the engine can pump into it.

Thanks, adding 5-8 lbs to the outside is probably sufficient to double the polar inertia of the original flywheel.
I'm one of the resident engineers here so the maths and design details are well taken care of.

I'm running the Isuzu 4BD1T and my current problem is I have heaps of boost and torque at an rpm where the engine isn't smooth enough to use it all. This is why I'm considering a flywheel addition. If I can smooth out all the pulsation at that rpm then I can use that rev range a lot more. Essentially I'm out to cure a drivability issue I think I created with a turbo that produces lots of boost at lower rpm than Isuzu intended.
A larger turbo housing to reduce boost at that rpm would help too, but it's not the solution I'm really looking for.

The other benefits of a heavier flywheel will help in some places, the downsides (acceleration/decelleration) aren't a concern.

Thanks again for your help.
Does anyone know the weight and diameter of a 4BT flywheel? Just looking to compare against the Isuzu.
Hey, Dougal-

Does the 4BD1T have a plain crank pulley like the 4BT, or does it have a harmonic balancer like the 6BT? And is there a harmonic balancer available to fit it if it is plain?

I ask because a few weeks back I wound up having to replace the pulley on my 4BT, and all I had laying around to do it with was a low-mileage 1st gen 6BT harmonic balancer. (Pulley on the 4 had done a really bad rust job, and the result was all the ribs except very edge ones were being eaten off belts..)

The unexpected benefit is that the thing is noticeably smoother at idle / lower RPMs. In neutral, with my sub-spec idle setting (I think Scott measured it at about 700), my mirrors do NOT shake on the P-30. Drop it in drive while sitting still, and yes they still shake a small bit (but that's dropping to a 600RPM idle and "loaded"). And, even though I just added a good hunk of rotating weight, the engine also seems to rev a bit quicker.

And, thinking of that makes me wonder if the proposed flywheel mod wouldn't be more effective if the added weight had a "soft" connection to the original one in the same way the harmonic balancers are made with a rubber layer separating the two metal parts.. Yes, I know it'd be a bear to "tune", but .. ??

Just thinking out loud here..
 

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Discussion Starter #7
Hey, Dougal-

Does the 4BD1T have a plain crank pulley like the 4BT, or does it have a harmonic balancer like the 6BT? And is there a harmonic balancer available to fit it if it is plain?

I ask because a few weeks back I wound up having to replace the pulley on my 4BT, and all I had laying around to do it with was a low-mileage 1st gen 6BT harmonic balancer. (Pulley on the 4 had done a really bad rust job, and the result was all the ribs except very edge ones were being eaten off belts..)

The unexpected benefit is that the thing is noticeably smoother at idle / lower RPMs. In neutral, with my sub-spec idle setting (I think Scott measured it at about 700), my mirrors do NOT shake on the P-30. Drop it in drive while sitting still, and yes they still shake a small bit (but that's dropping to a 600RPM idle and "loaded"). And, even though I just added a good hunk of rotating weight, the engine also seems to rev a bit quicker.

And, thinking of that makes me wonder if the proposed flywheel mod wouldn't be more effective if the added weight had a "soft" connection to the original one in the same way the harmonic balancers are made with a rubber layer separating the two metal parts.. Yes, I know it'd be a bear to "tune", but .. ??

Just thinking out loud here..
Yes it's already got a two piece harmonic balancer pulley on the front. I know what you mean with the two piece softly connected flywheels too. The japanese are big on those in their smaller diesels. My work car (nissan YD22 diesel) has one, the flywheel in that is just off to get the clutch surface refaced.
I refuse to pull it apart, I know when I'm my own worst enemy and I need that sucker back on the road so I can finish off "the list" of projects on my 4BD1T powered 4wd.
But I'm not going dual-mass with this test. If I had an engine dyno and lots of spare time I would. But the 8 hours to pull and refit the engine with each flywheel mod is a good incentive to take the simple approach and get it right.

Just to clarify, at factory torque levels (330Nm) there is no vibration. When my right foot asks for more torque the vibration gets worse. If this will give me no noticable vibration at 2-300rpm lower than it currently happens I'll be very happy.
 

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Agreed, 8 hours + test time between each iteration would make for a heck of a long dev cycle..

I can't put my finger on exactly where, but I remember reading some time ago on a power / performance board for gassers where the power advantages of the harmonic balancer was being discussed (not just engine durability as a proper harmonic balancer can add useable power by it's action of damping / eliminating power consuming harmonics IIRC..). Now, the thing that sticks in my mind is the comment that was made about accessories (alternator, AC, WP, etc.), ones that are belt driven, also act to help dampen or counter vibration, too. Of course, they all consume more power than they return from the counteraction.

Now, take that bouncing around the noggin, combine it with your goal, mix liberally with rum and RC cola, and shake it in a brain that is radically short of sleep at the moment..

This may be silly, unworkable, dangerous, and downright stupid, but.. I like to leave the "box" at home and do my thinking down at the corner sometimes.

I can visualize where you add a drive point direct to the crank. I don't know what kind of space restrictions you're dealing with here, so I don't know if pulley / belt or rubber block straight through (like some of the cement trucks drive a hydaulic pump off the front of the crank directly) is gonna be workable, if either.. I'll assume pulley / belt, using standard V belts, not serpentine (though that could work, too..)

So, make a pulley that attaches on top / in front of your current harmonic balancer. You make a small flywheel / bearing support / pulley assembly that lines up, and use the old fashioned pry bar / jackscrew tension method for the belt(s) (for this purpose, an automatic tensioner may NOT be your friend, but a jackscrew "fixed" one might...). Bingo, you've added rotating mass, with a "soft" connection. If you're smart, that setup is going to have provision for 2 or maybe 3 V belts..

Why? Tunability. You can contol the "firmness" of the connection of the aux flywheel by varying belt count, belt tension, and even belt type. (If automotive type belts aren't "firm" enough, step up to fractional horsepower stuff, like used on mowers, tillers, etc..) If you made a straight-drive, then you can vary the dimensions and rubber type used in the "yoke" to do the same thing.

And, if you're thinking ahead, you might even make the flywheel part somewhat "modular" so that you can add / remove weight from it for tuning.

Of course, the fully optioned Evil Bastard™ model would have an electric clutch so that it could be engaged only when needed...

Yeah, I know, not as simple as strapping weight to the flywheel, and the first version is going to take more time than the flywheel mod, but a good thought exercise for me..
 

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Discussion Starter #9
Agreed, 8 hours + test time between each iteration would make for a heck of a long dev cycle..

I can't put my finger on exactly where, but I remember reading some time ago on a power / performance board for gassers where the power advantages of the harmonic balancer was being discussed (not just engine durability as a proper harmonic balancer can add useable power by it's action of damping / eliminating power consuming harmonics IIRC..). Now, the thing that sticks in my mind is the comment that was made about accessories (alternator, AC, WP, etc.), ones that are belt driven, also act to help dampen or counter vibration, too. Of course, they all consume more power than they return from the counteraction.

Now, take that bouncing around the noggin, combine it with your goal, mix liberally with rum and RC cola, and shake it in a brain that is radically short of sleep at the moment..

This may be silly, unworkable, dangerous, and downright stupid, but.. I like to leave the "box" at home and do my thinking down at the corner sometimes.

I can visualize where you add a drive point direct to the crank. I don't know what kind of space restrictions you're dealing with here, so I don't know if pulley / belt or rubber block straight through (like some of the cement trucks drive a hydaulic pump off the front of the crank directly) is gonna be workable, if either.. I'll assume pulley / belt, using standard V belts, not serpentine (though that could work, too..)

So, make a pulley that attaches on top / in front of your current harmonic balancer. You make a small flywheel / bearing support / pulley assembly that lines up, and use the old fashioned pry bar / jackscrew tension method for the belt(s) (for this purpose, an automatic tensioner may NOT be your friend, but a jackscrew "fixed" one might...). Bingo, you've added rotating mass, with a "soft" connection. If you're smart, that setup is going to have provision for 2 or maybe 3 V belts..

Why? Tunability. You can contol the "firmness" of the connection of the aux flywheel by varying belt count, belt tension, and even belt type. (If automotive type belts aren't "firm" enough, step up to fractional horsepower stuff, like used on mowers, tillers, etc..) If you made a straight-drive, then you can vary the dimensions and rubber type used in the "yoke" to do the same thing.

And, if you're thinking ahead, you might even make the flywheel part somewhat "modular" so that you can add / remove weight from it for tuning.

Of course, the fully optioned Evil Bastard™ model would have an electric clutch so that it could be engaged only when needed...

Yeah, I know, not as simple as strapping weight to the flywheel, and the first version is going to take more time than the flywheel mod, but a good thought exercise for me..
I like the way you think. I don't have enough space to try it though. Front pulley is about 10mm clear of a chassis crossmember.

Just one concern, you'd need to make sure the rubber layer in the pulley could take all the punishment you're intending to dish out to it.
 

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I like the way you think. I don't have enough space to try it though. Front pulley is about 10mm clear of a chassis crossmember.

Just one concern, you'd need to make sure the rubber layer in the pulley could take all the punishment you're intending to dish out to it.
That's the beauty... The pulley wouldn't be dual-mass, but just solid. Make 'em like auxiliary accessory drive pulleys that bolt on the crank with the same bolts as the harmonic balancer. The only rubber part would be the belts, and it wouldn't increase loading on your existing harmonic..

But, I sorta thought space might be the tripping point. Alas..
 

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Machman: your description of torque and horsepower is definately better than mine, in fact I'm going to use it in the future. My purpose in stating it the way I did was getting guys to understand torque and HP don't exist separately in any usable form. Maybe a torque wrench, but even a torque wrench has at least one half ass power hooked to it.

Guys here, and around "dieselland" in general tend to place way too much emphisys in Torque by itself.

My Dodge has 160HP/ 400FTlb, the horsepower is at 2500RPM but the torque peak is around 1600rpms. It will not pull a load at 1600 rpms. It will only maintain a given speed while pulling if the revs are in the 2000+ range where there is sufficient HP to maintain the torque that is being generated at 2000+ rpms. Which even though it is less than peak torque it is usuable. At 1600 rpms there isn't sufficeint power to continuously generate 400FTlbs. therefore that value is not usuable. It's like they load the dyno to peak torque but the engine is not required to maintain that load for any significant time period.

Lugging an engine can only be done effectively if the engines HP and torque curves are pretty much aligned throughtout the usuable power band. Then the load will dictate what speed it will be moved. If the curves are separated by significant margins of RPM's, then you must operate the engine where the power is, as That is what is actually allowing you to do the work, and attempting to operate where the torque is, is fruitless unless there is sufficient power to maintain the load.

An example from my past at SoCal Edison: A generator is spinning at 3600RPM to maintain 60cycles and a given load of x# watts. The torque on the shaft is fixed because the diameter of the turbine is fixed, and the rpms are fixed. As the load increases the only change possible is to add more power, otherwise the speed of the turbine deminishes and the frequency drops. There is no change in torque with this system, except if the speed changes, which they (the operators) and the governor will not allow. Effectively the operators control the throttle for big changes in load and the governor deals with minor fluctuations. All they are doing is adding more power.

Severe vibratation while lugging is the warning that you are operating the engine outside the normal power band. I think everyone can agree on this. It is also very hard on main bearings. Changing the balancing abilities of the engine will change the vibration to some small degree, however more than likely it will shift the ill effects to the next weakest component in the system.

This is what I see Dougal trying to do. And adding weight to the flywheel will change the operating characteristics slightly, but the engines power characteristics are what they are, and you can only expect so much work from it, unless you significantly raise the power, or lower the load,,,, by downshifting?

Randy
 

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Dougal,
When I first did my repower the 4BT came with a Chevy clutch set, so I used that and tilted the trans so the engine was vertical. Every thing ran smoothly, taking off from a start I didn't need to add any throttle and as soon as the engine was above idle the vibration disapeared.
Later on I thought I had a clutch problem, (slippage) could not figure it out so switch over to a clutch assembly from a 94 Dodge. Being curious I weighed both. I don't recall the exact figure but the Dodge clutch assembly (flywheel, pressure plate and clutch disk) was 5 pounds (2.2kg) less that the Chevy. What I did notice was that the Chevy flywheel weighed 62 pounds!(28.2kg) , and most of the mass was near the outside of the flywheel, whereas the 6B flywheel was almost like a flat disc. I hoped that 5 pounds would not make a difference, It did and it didn't. I now have more vibration at idle, more vibration accelerating from low speeds, and I have to use just a little bit of throttle to get the Scout moving from a dead stop.
You have it right, it's not just the total mass but where it's located on the flywheel.
 

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Machman: your description of torque and horsepower is definately better than mine, in fact I'm going to use it in the future. My purpose in stating it the way I did was getting guys to understand torque and HP don't exist separately in any usable form. Maybe a torque wrench, but even a torque wrench has at least one half ass power hooked to it.

Guys here, and around "dieselland" in general tend to place way too much emphisys in Torque by itself.

My Dodge has 160HP/ 400FTlb, the horsepower is at 2500RPM but the torque peak is around 1600rpms. It will not pull a load at 1600 rpms. It will only maintain a given speed while pulling if the revs are in the 2000+ range where there is sufficient HP to maintain the torque that is being generated at 2000+ rpms. Which even though it is less than peak torque it is usuable. At 1600 rpms there isn't sufficeint power to continuously generate 400FTlbs. therefore that value is not usuable. It's like they load the dyno to peak torque but the engine is not required to maintain that load for any significant time period.

Lugging an engine can only be done effectively if the engines HP and torque curves are pretty much aligned throughtout the usuable power band. Then the load will dictate what speed it will be moved. If the curves are separated by significant margins of RPM's, then you must operate the engine where the power is, as That is what is actually allowing you to do the work, and attempting to operate where the torque is, is fruitless unless there is sufficient power to maintain the load.

An example from my past at SoCal Edison: A generator is spinning at 3600RPM to maintain 60cycles and a given load of x# watts. The torque on the shaft is fixed because the diameter of the turbine is fixed, and the rpms are fixed. As the load increases the only change possible is to add more power, otherwise the speed of the turbine deminishes and the frequency drops. There is no change in torque with this system, except if the speed changes, which they (the operators) and the governor will not allow. Effectively the operators control the throttle for big changes in load and the governor deals with minor fluctuations. All they are doing is adding more power.

Severe vibratation while lugging is the warning that you are operating the engine outside the normal power band. I think everyone can agree on this. It is also very hard on main bearings. Changing the balancing abilities of the engine will change the vibration to some small degree, however more than likely it will shift the ill effects to the next weakest component in the system.

This is what I see Dougal trying to do. And adding weight to the flywheel will change the operating characteristics slightly, but the engines power characteristics are what they are, and you can only expect so much work from it, unless you significantly raise the power, or lower the load,,,, by downshifting?

Randy
Just a few clarifications Randy.
The power and torque curves are linked, power=torquexrpm, if you're working in metric (watts, Nm, radians/s) then the maths works straight up. If you work in english units (hp, ft-lbs, rpm) then there's a factor of 5252 that is thrown in to account for the different units.
If you have the torque curve, you can calculate the power curve. If you have the power curve you can calculate the torque curve. They are two different but interlinked ways of measuring the same thing (engine output), no amount of engine design or modification can move one curve relative to the other.

My engine currently produces around 520Nm from 1400rpm to a bit over 2000rpm.
At 1400rpm that 520Nm of torque produces 76 kilowatts of power. At 2000rpm it produces 109 kilowatts of power.
The torque is the same, but the higher rpm produce more power.

With your generator example, the rpm stays constant but the torque and power are what is changing. As you load up the generator the torque increases to deal with that load.

For the torque wrench example, while it's stationary there is no power being used and no work being done. But while turning a bolt there is power being used and work done.
The power is the torque to turn it multiplied by the speed it's turning at (divide by 5252 if you're in english units). The work done is the torque to turn it multiplied by the distance it turned.

It takes a bit of getting your head around, but there will be a "eureka" moment when you do.:beer:
 

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Dougal,
When I first did my repower the 4BT came with a Chevy clutch set, so I used that and tilted the trans so the engine was vertical. Every thing ran smoothly, taking off from a start I didn't need to add any throttle and as soon as the engine was above idle the vibration disapeared.
Later on I thought I had a clutch problem, (slippage) could not figure it out so switch over to a clutch assembly from a 94 Dodge. Being curious I weighed both. I don't recall the exact figure but the Dodge clutch assembly (flywheel, pressure plate and clutch disk) was 5 pounds (2.2kg) less that the Chevy. What I did notice was that the Chevy flywheel weighed 62 pounds!(28.2kg) , and most of the mass was near the outside of the flywheel, whereas the 6B flywheel was almost like a flat disc. I hoped that 5 pounds would not make a difference, It did and it didn't. I now have more vibration at idle, more vibration accelerating from low speeds, and I have to use just a little bit of throttle to get the Scout moving from a dead stop.
You have it right, it's not just the total mass but where it's located on the flywheel.
Thanks.
I suspected the 4BT's had heavier flywheels because they spin slower, you've just confirmed it.
My Isuzu flywheel is a featherweight 35lb compared to yours at 57 and 62.

Looks like some body-building supplements are needed. That flywheel needs some stout.:beer:
 

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I have been waiting for that eureka moment for 40 years and I still don't completely understand it. I will try to get the Torque= power x RPM function to work. I went to Edison Steam Generation school (30 years ago)which was the equivilent of a BS in 6 months. But these 2 exact concepts continue to elude me, as they did then, and I wouldn't hesitate to say 99.9% of people out there don't really understand it.

How do we account for the resultant torque increase when power goes up, as the formula only assumes a specific torque value? How do we calculate the increase of both torque and HP as rpms rise? Is there another formula or does one variable always have to be proposed? also what is the inverse function when power is known solving for torque, I couldn't get that to work at all.

I have a decent practical knowledge but sometimes a little more theory really helps with the understanding part.

ON another note:

How fast can your engine turn? I know almost nothing about the Isuzu engines. You keep talking about 1200,1600 and 2000 rpms. I am assuming this is a 3.9l Isuzu engine. I figure if the displacement is the same as a Cummins that the bore and stroke must be at least similar, and as a result I would conclude it should operate in a range of RPM's similar to the Cummins engine. Why not run the thing a little faster?

Guys here are running 4BT's up to 3200 RPMs and I would conclude they are probably getting substantial increases in power and torque just by doing this, although I haven't seen any numbers from the Gov Spring change.

If you saw the post about Mudweisers 4 bt running at 5100RPM and producing 650-700HP and 1200FTlb this power output is due in part to higher engine speeds right? Although I suppose the 75LB of boost and more fuel probably has something to do with it too.
 

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Discussion Starter #16 (Edited)
I have been waiting for that eureka moment for 40 years and I still don't completely understand it. I will try to get the Torque= power x RPM function to work. I went to Edison Steam Generation school (30 years ago)which was the equivilent of a BS in 6 months. But these 2 exact concepts continue to elude me, as they did then, and I wouldn't hesitate to say 99.9% of people out there don't really understand it.

How do we account for the resultant torque increase when power goes up, as the formula only assumes a specific torque value? How do we calculate the increase of both torque and HP as rpms rise? Is there another formula or does one variable always have to be proposed? also what is the inverse function when power is known solving for torque, I couldn't get that to work at all.

I have a decent practical knowledge but sometimes a little more theory really helps with the understanding part.

ON another note:

How fast can your engine turn? I know almost nothing about the Isuzu engines. You keep talking about 1200,1600 and 2000 rpms. I am assuming this is a 3.9l Isuzu engine. I figure if the displacement is the same as a Cummins that the bore and stroke must be at least similar, and as a result I would conclude it should operate in a range of RPM's similar to the Cummins engine. Why not run the thing a little faster?

Guys here are running 4BT's up to 3200 RPMs and I would conclude they are probably getting substantial increases in power and torque just by doing this, although I haven't seen any numbers from the Gov Spring change.

If you saw the post about Mudweisers 4 bt running at 5100RPM and producing 650-700HP and 1200FTlb this power output is due in part to higher engine speeds right? Although I suppose the 75LB of boost and more fuel probably has something to do with it too.
It can be hard to picture. But basically you've got three figures, torque, power and rpm. If you hold any one of those three steady, then the other two must vary together.
Draw them out in a triangle, power at the top, rpm and torque on the bottom points. Cover one and it gives you the relationship of the other two.

If your RPM stays steady (like a pump or generator situation), then torque and power rise together. 50% more of one results in 50% more of the other.
If your torque stays steady while RPM's rise, then power rises with RPM's. 50% more RPMs makes 50% more power.
This is where Mudweisers 5000+rpm come into play, double the rpm and you can double the power if you can keep producing enough torque at those rpms.

On most internal combustion engines the torque drops as RPMs increase, when your torque drops faster than RPMs are increasing your power starts dropping.

My Isuzu spins to 3600rpm (factory set). Maximum power at the moment arrives around 2500rpm because my exhaust sucks. A better exhaust system and it'll keep building power up to about 3000rpm. That'll give me just over 200hp.
But power isn't my concern, what I'm trying to acheive with the heavier flywheel is a drivability increase and reducing NVH. Basically making it smoother and easier to drive.
 

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Thanks.
I suspected the 4BT's had heavier flywheels because they spin slower, you've just confirmed it.
My Isuzu flywheel is a featherweight 35lb compared to yours at 57 and 62.

Looks like some body-building supplements are needed. That flywheel needs some stout.:beer:
A Pint of Guinness to the heavy flywheel:beer: OK 6 pack!
 

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If the driveability is your only concern then the flywheel will probably solve the issue. But even with the larger flywheel you will still beat the mains out of it by prolonged lugging, as that has nothing to do with balance.

Make sure when you attach the inertia ring to the flywheel that you use at least 3 and preferrably 6ea. 5/16 to 3/8 (8-10MM) dowell pins. (assuming the clutch basket contacts the flywheel in three places). These are absolutely necessary to decrease/remove the shear loads from the hold down bolts. We used 6 ea 1/2" Socket head cap screws (grade 9) to attach the ring. Also the dowels will index the whole thing back together (match marks!)after it's balanced, and as you probably know the whole assembly must be balanced in one piece minus the clutch disc, or IT WILL vibrate at ALL rpm's

Good luck

Randy
 

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Discussion Starter #19
If the driveability is your only concern then the flywheel will probably solve the issue. But even with the larger flywheel you will still beat the mains out of it by prolonged lugging, as that has nothing to do with balance.

Make sure when you attach the inertia ring to the flywheel that you use at least 3 and preferrably 6ea. 5/16 to 3/8 (8-10MM) dowell pins. (assuming the clutch basket contacts the flywheel in three places). These are absolutely necessary to decrease/remove the shear loads from the hold down bolts. We used 6 ea 1/2" Socket head cap screws (grade 9) to attach the ring. Also the dowels will index the whole thing back together (match marks!)after it's balanced, and as you probably know the whole assembly must be balanced in one piece minus the clutch disc, or IT WILL vibrate at ALL rpm's

Good luck

Randy
Despite all the myths and legends about blowing out main bearings with high load at low revs, I remain unconvinced.
The world is full of industrial and tractor engines which spend thousands of hours at full load and 1500rpm. Provided the oil pump and oil grade are up to it, there is no metal-metal contact in your main bearings.

Don't worry I'll have the connection details sorted (once I've figured out just how much weight I can fit in the space available). It's a large part of what I do for a living.
1/2" bolts are out, the flywheel is too thin to get sufficient thread engagement for such large fasteners with coarse threads. They'll be in the order of M6 or M8 and there'll be enough of them to do the job.
 

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Despite all the myths and legends about blowing out main bearings with high load at low revs, I remain unconvinced.
The world is full of industrial and tractor engines which spend thousands of hours at full load and 1500rpm. Provided the oil pump and oil grade are up to it, there is no metal-metal contact in your main bearings.
cut...
.
Dougal,
For the B series Cummins, lugging the engine is described by Cummins as full throttle below 1500 rpm for more that 30 seconds.
 
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