Balance shaft delete discussion.

[johnl]

If the vibrations are canceled, how are they still reacting?

I think I've plausibly explained this in my post #14

The main question here is does it matter?

In practical terms, not much, but the discussion is interesting.

If What is the short term effect?

Not much.

long term?

The same

I feel that in the real world it's all up to personal preference. If one wishes to remove the belt, shafts or both then so be it.

Agreed.

It will make a difference in engine performance and feel. We don't know if it will affect reliability, or do we?

Real world affects will exist, but in my limited experience will be very small. A sensitive dyno might pick it up, but it may well be within the dynos' margin of error.

I've never heard of BSs , or lack thereof, causing problems, other than if the belt breaks. It's certainly common for them to be deleted for race engine builds.

[Domesticated]

The Porsche guys I run with always run balance shafts. Porsche 944s and especially the uber rare swap from a 968. Ho took the shafts out of his 944 and it wouldn't rev up as high as normal and felt like ass. A few guys on the forums who road race said they lost top end power, so three don't do it anymore. I guess there's no physical proof I have on hand, but too many coincidences I've seen. I gave my opinion and my logic, so decide as you will.

And not that it adds to my credentials much, but I use 150k dollars of equipment made by LMS everyday to measure chassis and powertrain vibrations and I spend all day analyzing the data.

[johnl]

Good job describing that as I was thinking purely theoretically (vector math) the job of the balance shaft.

I'm afraid "vector math" is likely to be beyond me...

Simply, the balance shaft "spreads" the vibration energy through the block material instead of having the block itself vibrate. Looking at it from this perspective, by the time the vibration reaches any critical components, the magnitude is close to negligible right?

In the scheme of things the imbalance forces are relatively small. However, I suspect they would be significant enough that when designing the block to utilise BSs the engineer would have to ensure that the block is strong enough in and around the locations of the BS bearings that the forces don't eventually over time cause metal fatigue and create cracks in the casting.

[johnl]

The Porsche guys I run with always run balance shafts. Porsche 944s and especially the uber rare swap from a 968. Ho took the shafts out of his 944 and it wouldn't rev up as high as normal and felt like ass. A few guys on the forums who road race said they lost top end power, so three don't do it anymore. I guess there's no physical proof I have on hand, but too many coincidences I've seen. I gave my opinion and my logic, so decide as you will.

And not that it adds to my credentials much, but I use 150k dollars of equipment made by LMS everyday to measure chassis and powertrain vibrations and I spend all day analyzing the data.

Interesting, but first I've heard of such issues related to BSs, which isn't to imply they don't exist. However, since vibration is a minor order consumer of power, my suspicion immediately goes to something that might be affected by vibration rather than energy lost as a result of it. Maybe some sensor...?

Vibration can cause unexpected problems, an example might be DCOE Weber carburettors that are nearly always mounted with a flexible element between the carb and the manifold, or else high frequency vibration adversely affects how well they work. My racing kart has it's ignition coil factory fitted with very flexible rubber blocks because high frequency vibration causes problems with them.

As an aside related to power loss caused by vibration, I've had tyres on my kart that caused enough vibration that the kart became very unpleasant to drive at higher speeds (the whole kart vibrating quite badly at speed), balancing the offending tyre resulted in loss of the vibration, but no increase in rpm at the end of the straight (which equates to a higher terminal speed). If the vibration were causing a significant effective power loss, then I would have expected to see at least some increase in terminal rpm, was hoping I would, but didn't, disappointed...

[sonikaccord]

I'm afraid "vector math" is likely to be beyond me...

If you can understand vehicle dynamics, I think you can add some arrows together.

In the scheme of things the imbalance forces are relatively small. However, I suspect they would be significant enough that when designing the block to utilise BSs the engineer would have to ensure that the block is strong enough in and around the locations of the BS bearings that the forces don't eventually over time cause metal fatigue and create cracks in the casting.

That may be part of the reason why the B20 doesn't use them as mentioned above.

[johnl]

If you can understand vehicle dynamics, I think you can add some arrows together.

Throwing some arrows together and describing the same thing mathematically are not necessarily interchangeably easy...

That may be part of the reason why the B20 doesn't use them as mentioned above.

I somehow doubt it. The engine block will need to be designed for and be strong enough to use BSs, which is easy enough. I really think it's simply because the need isn't great enough to justify the added costs with a smaller capacity straight four, i.e. smaller capacity = lesser inherent vibration.

As an aside, apparently Mitsubishi holds the patent on counter rotating balance shafts, all other manufacturers who use them (including Honda and Porsche) pay a royalty to Mitsubishi.

[illinois_erik]

I somehow doubt it. The engine block will need to be designed for and be strong enough to use BSs, which is easy enough. I really think it's simply because the need isn't great enough to justify the added costs with a smaller capacity straight four, i.e. smaller capacity = lesser inherent vibration.

thats the point I was stabbing for, is the crv, civic, integra..customer base wouldnt need as much pampering as an accord/odyssey/prelude demographic so the added minimal cabin vibration wouldnt be as much as an issue for them thus the extra money in design and materials wouldnt be applicable. .2 liters isnt much and the blocks are relatively identical. The balance shafts were for the comfort of Granny in her new accord IMO.

[af_1132]

I think this might be the initial thread you were looking for, OP: http://www.cb7tuner.com/vbb/showthread.php?t=136259

Darkcloud started with a question about how the BS delete is related to emissions, and then people quickly started asking about the benefits to just a belt removal and then the whole shafts removal as well. It ends up moving toward a different conclusion than most recent threads on the topic, but the physics discussed is the same. It's definitely worth a thorough read.

[wagon-r]

Thanks for the thorough explanation, Johnl. I just gave the short-hand version.

One additional point. I used to work for Honda and worked with some of the R&D people. One of them raced Hondas. He also had access to Honda's test equipment. He told me that removing the balance shaft belt would gain 5 hp on an H22. Of course, the hp gain increases with higher revs and the F22 isn't going to match the 8000 rpm redline of the ITR. But we are still likely looking at 3-4 hp.

Not exactly scientific proof. But he knew more about modifying Honda engines than anyone I have ever met.

[johnl]

He told me that removing the balance shaft belt would gain 5 hp on an H22. Of course, the hp gain increases with higher revs and the F22 isn't going to match the 8000 rpm redline of the ITR. But we are still likely looking at 3-4 hp.

Not exactly scientific proof. But he knew more about modifying Honda engines than anyone I have ever met.

When I deleted my BS belt I couldn't feel any significant change in acceleration, but my 'butt dyno' may just not be sensitive enough. I won't doubt your friends numbers, I'm certain an effect exists, though "5hp" may mean different things depending on exactly where it's coming from.

It might be interesting to think about where the 5 (or so) hp is being 'gained'.

Deleting the BSs (by whatever means) reduces the rotating inertia, which will show up as a gain on an inertial dyno with the engine rpm rising, and be (I think...) a stable factor from low to high rpm (assuming the rate at which rpm change is constant, which is unlikely). This won't show up on a 'brake' dyno where the engine is held at a given rpm and resisted by a 'brake', because the rpm will be constant (rotating inertia becoming a non issue at constant rpm).

If the gain is a result of eliminating any parasitic loss caused by the power required to generate the 'counter vibration' created by the BSs, then this would show up on either an inertial or brake dyno, but would become a bigger factor as rpm rise higher and higher (i.e. start as a small gain at lower rpm and then linearly increase as rpm rise). Such a power loss (that we are trying to eliminate) is in effect equivalent to a 'pumping loss' as occurs from say pumping oil through the lubrication system, the energy required to move gasses into and out of the cylinders, or internal friction. Deleting the BSs (or stopping them from rotating) will also reduce any 'pumping loss' generated by the friction that occurs as the BSs rotate (i.e. oil drag in the BS bearings), though I think this will be a very minor thing.

In varying degree I think it will be both, i.e. power 'freed' to be 'seen' at the flywheel as result of eliminating BS inertia and as a result of not generating a 'counter vibration' (which requires an energy input). I think the inertial aspect is likely to be the substantially greater % of any HP gain (keeping in mind any gains won't be substantial).

Assuming the cars' top speed is not rpm limited (i.e. short gearing), an inertial HP gain will improve the cars' acceleration, but it won't increase it's top speed (because the rpm become stable at top speed as aero and rolling resistances become too great for the HP to overcome). A power gain caused by eliminating BS counter vibration will improve both the acceleration and the top speed because there is more HP to reach a higher terminal velocity, even when the rate of change in engine rpm slows down.

[owequitit]

Thanks for the thorough explanation, Johnl. I just gave the short-hand version.

One additional point. I used to work for Honda and worked with some of the R&D people. One of them raced Hondas. He also had access to Honda's test equipment. He told me that removing the balance shaft belt would gain 5 hp on an H22. Of course, the hp gain increases with higher revs and the F22 isn't going to match the 8000 rpm redline of the ITR. But we are still likely looking at 3-4 hp.

Not exactly scientific proof. But he knew more about modifying Honda engines than anyone I have ever met.

John L and your Honda R&D friends are spot on.

1) It has been dyno proven that a balance shaft delete is worth about 5 WHP on an H22. It will also allow it to rev faster by virtue of the fact ~16lbs of balance shafts aren't being rotated at 2x crank speed (the shafts in an H22 are running 16K RPM at the ~8,000RPM rev limit on an H22. That is a lot of mass and momentum.

The spin at 2x crank speed because the second order vibrations that make 4 cylinders vibrate happen 2x per crank revolution. By running the shafts at 2x crank speed, they are able to cancel out both 2nd order vibrations, resulting in a smoother feeling engine.

Honda's system was different than Porsche's (really Mistubishi, who licensed the technology to Porsche) because it allowed cancellation of the vibrations at all engine speeds, rather than just one specific engine speed.

As for the assertion that the shafts are there to protect the reciprocating assembly, this is not correct. In Honda's own technical manual available through Helm's on the changes to the 1990 Accord, Honda states that they are there to produce an engine that feels smoother to passengers.

The reason it doesn't protect the actual rotating assembly is because all thrust loads, vibration loads, etc on the rotating assembly are still there with the balance shafts. The balance shafts simply cancel them AFTER they are produced, but before they shake the power train assembly. Basically, the balance shafts are stopping them from leaving the block.

Most pure race duty Honda engine have the balance shafts removed because obviously the smoothness in the cabin isn't necessary and it is better to have the additional free HP and the extra revvability.

2) The balance shafts in a Honda are more for the NVH transmission into the chassis than they are for structural reasons. Basically, Honda was adding balance shafts to make the engines feel quieter and smoother in the cabin, so that their 4 cylinders were competitive with low power V6's of the time (such as the 3.1 OHV Chevy). By using these shafts in conjunction with active mounts, they were able to produce a powertrain that was as smooth as some of the lower end V6's and nearly as smooth as some of the top end V6's of the era.
The newer Hondas don't even put the shafts in the block, instead locating them in a separate assembly down in the oil pan of the engine to help smooth vibration. The K20Z is a good example of the difference. All of the original K20 engines with DOHC VTEC did not have balance shafts prior to the '06 Civic Si, where Honda added them to smooth the engine slightly. The K24 always had them because longer stroke and larger bore 4 bangers have larger 2nd order vibrations.

[johnl]

1) It has been dyno proven that a balance shaft delete is worth about 5 WHP on an H22. It will also allow it to rev faster by virtue of the fact ~16lbs of balance shafts aren't being rotated at 2x crank speed (the shafts in an H22 are running 16K RPM at the ~8,000RPM rev limit on an H22. That is a lot of mass and momentum.

I pretty much agree with your entire post.

Sixteen lbs is a lot of rotating mass, only ameliorated by the fact that the mass isn't disposed a long way from the centre of rotation. Since the BSs are rotating 2X crank speed this sixteen lbs is equivalent to thirty two lbs on the flywheel, but with a flywheel the mass (or much of it) is a fair distance from the centre of rotation so has a larger affect on the effective rotational inertia.

Placing X mass at Y radial distance from the centre of rotation will create Z rotational inertia. Moving X mass to 2xY radial distance will I suspect have a much larger affect than increasing rotational mass 2x, i.e. will create much more than 2xZ rotational inertia. It's likely there is an algorithmic progression in the inertial resistance of X mass the further it's moved from the centre of rotation, but I'm not certain. My guess is that inertia of the mass is likely to be dictated by the square of the distance of the mass to the centre of rotation, but I could be wrong (I'm no mathematician...).

When 'deleting' the BSs the only significant benefit of actually removing them is to eliminate the sixteen lbs of static weight (i.e. the entire car becomes sixteen lbs lighter, worthwhile in a racing car, but not noticeable in a road car). Just removing the belt alone will give all the benefits of deleting the BSs, other than kerb mass remains the same.

Neither removing the BS belt nor changing my flywheel for a much lighter one created any significantly noticeable increase in acceleration (though physics says an improvement must exist). The lighter flywheel did significantly improve 'revability' of the engine, and thus increased gear shifting speeds (especially when 'rev matching' for downshifts). I couldn't really notice any significant 'revability' difference with the BS belt removed.

[GenDBlade]

Well, unfortunately my computer was down so i wasnt able to respond after posting, but ive learned a good bit from this. thanks guys.