balance shafts or no balance shafts

[1990AWD]

Its seems as though a lot of people are removing their balance shafts and/or oil squirters. Why is this? And why do people also use n/t blocks on turbo cars? I realize the n/t block would be higher compression but what other advantages are there?

 

[TunaTalon]

Getting more horsepower by removing the balance shafts is old and accepted DSM lore but there is no hard proof of it.

All else being equal lower rotating mass will measure as more horsepower with inertial based dynos, but not with eddy current dynos that can apply a fixed resistance at a fixed speed. Once the rotating mass comes to speed only the negligible bearing losses affect measured horsepower.

However, with balance shafts all else is not equal. The balance shafts are eccentric masses with the imbalance calibrated to cancel out the imbalance of the engine. That's why the whole car shakes after BS removal. Engine power used to make the car shake does not get to the wheels.

Try this thought experiment:
Attach an electric motor to your DSM and drive the balance shafts with their eccentric load at about 5000 RPM until the car shakes as much as with the engine running at 2500 RPM. The amount of power it takes for the electric motor to shake the car is the amount of power that is lost to creating the vibration without the balance shafts.

 

[Calan]

The biggest reason for the BS removal (whether valid or not) is to avoid a potential disaster when the BS belt breaks and takes out the timing belt, and then the motor due to valves going through the tops of pistons.

 

[dsmfa9nutter]

The biggest reason for the BS removal (whether valid or not) is to avoid a potential disaster when the BS belt breaks and takes out the timing belt, and then the motor due to valves going through the tops of pistons.

Bingo. Doing a BSE kit has nothing to do with making tons of power.

People use NT blocks to get rid of the possibility of an oil squirter working it's way loose and losing all oil pressure in a high hp motor spinning very high rpms.

 

[webconnect]

1. Safer (Don't have to worry about b/s belt)
2. More horsepower due to friction, weight of the b/s
3. Higher oil pressure

 

[94awdcoupe]

Getting more horsepower by removing the balance shafts is old and accepted DSM lore but there is no hard proof of it.

All else being equal lower rotating mass will measure as more horsepower with inertial based dynos, but not with eddy current dynos that can apply a fixed resistance at a fixed speed. Once the rotating mass comes to speed only the negligible bearing losses affect measured horsepower.

However, with balance shafts all else is not equal. The balance shafts are eccentric masses with the imbalance calibrated to cancel out the imbalance of the engine. That’s why the whole car shakes after BS removal. Engine power used to make the car shake does not get to the wheels.

Try this thought experiment:
Attach an electric motor to your DSM and drive the balance shafts with their eccentric load at about 5000 RPM until the car shakes as much as with the engine running at 2500 RPM. The amount of power it takes for the electric motor to shake the car is the amount of power that is lost to creating the vibration without the balance shafts.

great post. good to see some intelligence in here. I never remove balance shafts from my builds. I do however have them nitrided with my cranks to increase the reliability.

 

[Calan]

Getting more horsepower by removing the balance shafts is old and accepted DSM lore but there is no hard proof of it.

All else being equal lower rotating mass will measure as more horsepower with inertial based dynos, but not with eddy current dynos that can apply a fixed resistance at a fixed speed. Once the rotating mass comes to speed only the negligible bearing losses affect measured horsepower.

However, with balance shafts all else is not equal. The balance shafts are eccentric masses with the imbalance calibrated to cancel out the imbalance of the engine. That's why the whole car shakes after BS removal. Engine power used to make the car shake does not get to the wheels.

Try this thought experiment:
Attach an electric motor to your DSM and drive the balance shafts with their eccentric load at about 5000 RPM until the car shakes as much as with the engine running at 2500 RPM. The amount of power it takes for the electric motor to shake the car is the amount of power that is lost to creating the vibration without the balance shafts.

Not to argue with your very informative post, but there has to be some power loss due to what's required to drive the shafts and the additional friction/loading of the BS belt. And I don't see the logic of "Engine power used to make the car shake does not get to the wheels". The engine's power output should be the same, minus BS drive losses...but more harmonic vibration is introduced which could add to the wear and tear (such as piston side loading for example)... right?

Or am I completely off the mark here?

Either way, I think for most people the slight increase in vibration is a small price to pay for one less potential catastophic failure.

My theory is that most people feel very little if any additional vibration in the first place, due to the motor mounts usually being shot.

 

[DSM1G90]

is to avoid a potential disaster when the BS belt breaks

I'd can see cam belts break more readily due to the massive stress that the belt uses by turning two cam sprockets, oil pump sprocket and being pulled by the crank pulley, absorbing the sudden impulse rotation of the crank when every piston is forced down during the power stroke along with the belt travel that the belt has to take around all of these pulleys, than a puny 10inch diameter toothed belt that is under slight tension by the roller tensioner and goes around two pulleys - which, the front BS sprocket has hardly any load behind it in the first place - and the whole thing operates in a simple elliptical circle.


When I did my belts, my T-belt was in worse shape than the BS belt-which I could have left in there. But, being respectable to my motor, I did both.

It's simply pointing towards the 'need for more power' than anything - which I agree: there is really no concrete evidence that removing BS shafts really aids in gaining additional power - maybe in the clutch-dropping, short burst takeoffs, but on the long run, I can't see it.

Course, in all with my comments above, really isn't fair to all since I don't drive like a race driver trying to beat that Honda, or Chevy at the light, but mainly drive around town and on freeways as a DD driver - but still love the knowledge that I have that available power when it's time for it to be used.

-DSM

 

[lacroixdp]

I agree with Calan's view on it - it not only reduces complexity in the motor, but it is two less moving parts to break that can cause a catastrophic failure in your engine (belt, bearings). In general, the less moving parts in your engine, the less things that can break and cause a failure. It is exceptionally rare, but I have seen spun balance shaft bearings before that have ruined an engine. The amount may be minuscule, but everything driven off your car's belt takes up some amount of power.

 

[cheap90gsx]

I'd can see cam belts break more readily due to the massive stress that the belt uses by turning two cam sprockets, oil pump sprocket and being pulled by the crank pulley, absorbing the sudden impulse rotation of the crank when every piston is forced down during the power stroke along with the belt travel that the belt has to take around all of these pulleys, than a puny 10inch diameter toothed belt that is under slight tension by the roller tensioner and goes around two pulleys - which, the front BS sprocket has hardly any load behind it in the first place - and the whole thing operates in a simple elliptical circle.


When I did my belts, my T-belt was in worse shape than the BS belt-which I could have left in there. But, being respectable to my motor, I did both.

It's simply pointing towards the 'need for more power' than anything - which I agree: there is really no concrete evidence that removing BS shafts really aids in gaining additional power - maybe in the clutch-dropping, short burst takeoffs, but on the long run, I can't see it.

Course, in all with my comments above, really isn't fair to all since I don't drive like a race driver trying to beat that Honda, or Chevy at the light, but mainly drive around town and on freeways as a DD driver - but still love the knowledge that I have that available power when it's time for it to be used.

-DSM

Not true, I've personally seen the front balance shaft belt tear into peices and nearly took the t-belt with it. Which I've also heared is very common.

edit- The car was being driven as a dd for work when the BS belt broke not being raced. Unaware of the age of the belt, but it not only snapped it separated from the teeth on the belt as well.

 

[DSM1G90]

You personally seen this belt be almost torn. How long was it in the motor and how was the motor used-as a DD, or a stoplight street racing machine?

A sudden jump in revs from 750 idle to redline can immedately put major stress and stretch on any belt esp. on a belt that has to spin up a sprocket that spins twice as fast as the crank in a split second (major, major torque resistance is created by the front BS shaft in that split second), and the BS belt, being as small as it is, can fail sooner than what it was designed for...

-why the probable reasoning of the BS removal...

Thus, I claim my above statement (as true, in my prespective), since I treat my motor in a rational conservative matter-no redline takeoffs, just casual DD driving.

DSM

 

[TunaTalon]

Not to argue with your very informative post, but there has to be some power loss due to what's required to drive the shafts and the additional friction/loading of the BS belt. And I don't see the logic of "Engine power used to make the car shake does not get to the wheels".

The engine's power output should be the same, minus BS drive losses...but more harmonic vibration is introduced which could add to the wear and tear (such as piston side loading for example)... right?

Or am I completely off the mark here?

If the balance shafts were balancED shafts you would be right on. However, the shafts are eccentric loads and out of phase with each other in the horizontal plane. Spinning the shafts causes the engine to vibrate at two times the engine RPM. The vibration is passed on to the chassis and causes the whole care to shake. However much power it takes to vibrate the car comes from the engine and does not get to the wheels. Yes it would take some little power to spin the shafts without the vibration effect. Your point about driving the belt is a good one not often mentioned but still a minor effect.

The power lost from the vibration depends on how the engine is damped. If the 4G63 were welded to the deck of the USS Missouri there would be no motion and no lost power. The chassis of my Talon does not remind me of any warship.

Side loading on pistons is a separate issue.

The harmonic imbalance does not affect any bearing loading. The negative effect of the vibration is the vibration itself. Not just the effect on the significant other but on other components attached to the engine. Vibration causes mechanical devices to fail.


For more see http://www.kidzuku.com/StrokeOrNot.pdf.

After all the math and words it is still an individual decision to keep or remove the balance shafts. With the BS belt in the trash, the timing belt is safer. There are many in line fours on the road without balance shafts.

 

[Colt4G63 also]

Just to clear up any misconceptions. I had my crank spin balanced at a machine shop, and I weighed my rods and pistons on a digital scale before I assembled them. Two of the rods were a little heavier than the other two, and same went for the pistons. I assembled the heavy rods with the light pistons, and ended up with each assembly being equal weight within about a couple tenths of a gram. I have no balance shafts, and no vibration. My s**t is smooth as silk, so don't be discouraged by talk of vibration.

 

[TunaTalon]

Static imbalance from mis-matched piston weight is a separate issue from harmonic imbalance from missing balance shafts. Harmonic imbalance is due to the geometry changing with crank angle and cannot be affected by static balancing.

Static imbalance will cause vibration at the base frequency of the engine RPM and harmonic imbalance will vibrate at two times the base frequency.

When I started the calculations for the StrokeOrNot document I expected to find that the vibration forces from mismatched piston weights would be much more than the forces from second order harmonics. Boy was I wrong. The imbalance forces exerted on the crankshaft from second order harmonics is about ten times the force on the crankshaft from pistons that are mismatched by 20 grams.

I still hold my olde cherished belief that piston weights in a performance engine should be matched. Closely matched. But now that I know that second order harmonics are applied to the crank in the same manner as static imbalance, and are ten times as great, I have to re-think just ignoring the harmonic imbalance.

 

[dsm-onster]

The engine wastes energy because it is an I4 and is inherently imbalanced. Vibrations occure with no bshafts and energy is lost. Affixing the motor to a ship would cause the ship to absorb the energy the energy still leaves the motor, but the ship moves very little. But still moves as much as the energy makes it move. The vibrations as kenetic energy convert to the kenetic energy in the ship, that you can't see because it is so big and heavy.

The same goes with the b-shafts. The energy converted to vibration has already left from a point where it can be converted to rotation through the drive shaft. The b-shafts are there to setup another vibration that is 180* out of phase with those initial vibrations. This proccess takes now twice as much energy: the initial energy lost to the vibrations of the block, and then the energy required to generate the vibrations that are 180* out of phase.

 

[zckry]

Is it necessary bad to run a block without oil squirters?
A local yard has a nice N/T block they are wanting to sell.

 

[dsm-onster]

that's another debate.

 

[zckry]

that's another debate.

Ah, I knew I was going to get an answer like that
Time to search away!

 

[TunaTalon]

The engine wastes energy because it is an I4 and is inherently imbalanced. Vibrations occure with no bshafts and energy is lost. Affixing the motor to a ship would cause the ship to absorb the energy the energy still leaves the motor, but the ship moves very little. But still moves as much as the energy makes it move. The vibrations as kenetic energy convert to the kenetic energy in the ship, that you can't see because it is so big and heavy.

The same goes with the b-shafts. The energy converted to vibration has already left from a point where it can be converted to rotation through the drive shaft. The b-shafts are there to setup another vibration that is 180* out of phase with those initial vibrations. This proccess takes now twice as much energy: the initial energy lost to the vibrations of the block, and then the energy required to generate the vibrations that are 180* out of phase.

The forces from the balance shafts are equal and 180 out of phase with the forces from the inherent imbalance of the I4. The equal and opposite forces are coupled through the rigid block and cancel out the vibrating motion. Without motion from the vibration there is no lost horsepower.

Even if there is vibration across a distance there may not be any horsepower lost. If the engine is suspended from perfect springs the energy from the downward motion would be stored in the springs and returned to the system on rebound. If the suspended engine were attached to a shock absorber (dampener) the energy absorbed by the dampener would be lost horsepower.

Now I’m off to make the Google servers smoke trying to find documents on the first principles of rotating eccentric loads and the effect of damping.

 

[lacroixdp]

If the balance shafts were balancED shafts you would be right on. However, the shafts are eccentric loads and out of phase with each other in the horizontal plane. Spinning the shafts causes the engine to vibrate at two times the engine RPM. The vibration is passed on to the chassis and causes the whole care to shake. However much power it takes to vibrate the car comes from the engine and does not get to the wheels. Yes it would take some little power to spin the shafts without the vibration effect. Your point about driving the belt is a good one not often mentioned but still a minor effect.

The power lost from the vibration depends on how the engine is damped. If the 4G63 were welded to the deck of the USS Missouri there would be no motion and no lost power. The chassis of my Talon does not remind me of any warship.

Side loading on pistons is a separate issue.

The harmonic imbalance does not affect any bearing loading. The negative effect of the vibration is the vibration itself. Not just the effect on the significant other but on other components attached to the engine. Vibration causes mechanical devices to fail.


For more see http://www.kidzuku.com/StrokeOrNot.pdf.

After all the math and words it is still an individual decision to keep or remove the balance shafts. With the BS belt in the trash, the timing belt is safer. There are many in line fours on the road without balance shafts.

That's an excellent paper explaining your point! It took me a little over 2 hours to read through the whole thing. Are you the author of that paper? I don't know your real name and that's all that's on the paper.
Edit: I just saw your other post saying you were. I for one appreciate the time you took to do that research and make an A1-quality research paper for the DSM community. I had a few doubts about building a stroked motor and this paper addressed them. Thank you!

 

[Calan]

I agree... I read through that whole paper before settling on my stroker build, although I admit I skipped some of the technical points

Nice work!

 

[TunaTalon]

I appreciate the kind words. Just proves that Obsessive Compulsive Behavior can be channeled to good use. Not that I'm car crazy or anything.

 

[dsm-onster]

It is a great article. As respects craziness. . . OCD isn't crazy, unless it annoys .

The forces from the balance shafts are equal and 180 out of phase with the forces from the inherent imbalance of the I4. The equal and opposite forces are coupled through the rigid block and cancel out the vibrating motion. Without motion from the vibration there is no lost horsepower.

Even if there is vibration across a distance there may not be any horsepower lost. If the engine is suspended from perfect springs the energy from the downward motion would be stored in the springs and returned to the system on rebound. If the suspended engine were attached to a shock absorber (dampener) the energy absorbed by the dampener would be lost horsepower.

Now I'm off to make the Google servers smoke trying to find documents on the first principles of rotating eccentric loads and the effect of damping.

You have to cause the force of the b-shaft to cancel out the force of vibration. Press your hands together as hard as you can. You're burning twice as much energy than if you just push with one hand and leave the other limp.

Now if the engine were suspended in perfect springs, it would just bounce forever and get more and more violent in movement as time passes while running. The force doesn't go back into the crank and cause circular motion.

 

[Colt4G63 also]

Static imbalance from mis-matched piston weight is a separate issue from harmonic imbalance from missing balance shafts. Harmonic imbalance is due to the geometry changing with crank angle and cannot be affected by static balancing.

Static imbalance will cause vibration at the base frequency of the engine RPM and harmonic imbalance will vibrate at two times the base frequency.

When I started the calculations for the StrokeOrNot document I expected to find that the vibration forces from mismatched piston weights would be much more than the forces from second order harmonics. Boy was I wrong. The imbalance forces exerted on the crankshaft from second order harmonics is about ten times the force on the crankshaft from pistons that are mismatched by 20 grams.

I still hold my olde cherished belief that piston weights in a performance engine should be matched. Closely matched. But now that I know that second order harmonics are applied to the crank in the same manner as static imbalance, and are ten times as great, I have to re-think just ignoring the harmonic imbalance.

Oh! I thought having the crank balanced would solve that. I did stay at a Holiday Inn Express last night, and I won't ever replace my harmonic balancer with a solid underdrive pulley.

 

[TunaTalon]

You have to cause the force of the b-shaft to cancel out the force of vibration. Press your hands together as hard as you can. You're burning twice as much energy than if you just push with one hand and leave the other limp.

We agree on the forces involved and are now debating the differences between force, energy, and power. I’ll hold my position that if the forces cancel motion then horsepower is saved because horsepower requires, force, time, and distance. I agree that the forces on the main bearings are not affected by the balance shafts.

For the last eight hours my head was forced down on a pillow by gravity. I have more energy now but I’m pretty sure no horsepower was generated by the force.