Engine Gurus: Why No Crankshaft Damper?

[Pablo]

I see a lot of build ups on this forum with a focus on crankshaft and main cap strength. People spend big money on caps, girdles, and aftermarket cranks since that appears to be a weakness on our engines.

I don't often hear of people using a damper though. I also don't really understand why Buick didn't put a proper damper on our engines to begin with (as opposed to a solid balancer).

This seems to me to be very counter productive except but from maybe an economics standpoint.

Everything I have read has affirmed in my mind that a damper would seem to be a critically necessary component in engines like ours producing massive torque spikes.

heres an excellent article on Torsional Vibration
Torsional Vibration, by EPI Inc.

another on Torsional Absorbers
Crankshaft Torsional Absorbers, by EPI Inc.

and then there are a bunch more floating around online in more layman's terms on why Dampers are necessary.

So why don't people run them? Seems to me like it could make a cheap bottom end take as much abuse as a high dollar one without a damper.

Thoughts?

 

[1BADTT]

Very good point there Pablo. Subscribing...

 

[V6UnderPressure]

I subscribing as well.

 

[BetMinesFaster]

Subscribed.....

 

[Pablo]

Here's another quick link

Why Your Engine Needs A Good Crank Damper

"Curve 1 is a solid hub. Curve 2 is a damper that's too small for the job. Curve 3 is a larger damper that is getting the job done."

Thats quite a big difference in deflection. Curve three could probably withstand some pressure spikes from detonation and still keep it well below what curve 1 is.

 

[Eticket]

Pablo,

I'm only a guru in my mind, so take this for what it's worth. Everything about dampers you stated is OF COURSE TRUE. I think that EVERY BUICK engine builder on this site will recommend a BHJ balancer on every rebuild if the owner can do it.
However:

I think most relatively "serious" engines do have a BHJ balancer employed just as you are asking, especially when switching to a steel crank that's internally balanced anyway. We're talking about guys that really want to run Mid 10's and faster everytime they go to the track - and have the combo to do it.

It's commonly known that the main caps crack and break (from detonation) well before the stock crank does. This set-up with the stock balancer, all else being equal, can take you safely into the mid-high 10 range consistently. That's why the main caps/girdle usually come first. Having the rest of the car support the power is the other problem.

Putting a balancer on an engine and doing nothing else is kind of goofy.

If you're going to use a "real" damper on a stock engine, you have to pull everything apart to get it balanced. Are externally balanced - so the weight comes out of the balancer and the flywheel. Going through all of this trouble, you "mind as well" put main caps on it. At that point (IE if you're building a mid 10 sec or faster engine).. then mind as well use a steel crank $300-$600, steel rods $300-600, BHJ balancer $400 now (wow! was $200), and a sfi flywheel $50.

I think it's an "all or nothing" type of deal. Pick a range I'll say 10.6x's. Anything faster, then spend the $1000-$1500 on extra rotating assembly. AND the extra $000's on the rest of the combo to go faster then 10.6'x. We're talking bigger turbo, heads, suspension, and transmission.

I picked 10.6's because guys can do it with a single in tank pump, stock ecm setup, mild turbo, mild heads and cam, mild trans, and a GOOD driver that can 60 ft.

 

[KevinB]

I'd like to get a B H J one day. HAHA, that kind of rhymes

Last year my engine did fine w/o one. This year I'm starting off again w/o one. My car has a zero balanced stocker on it now.

 

[Pablo]

Pablo,

I'm only a guru in my mind, so take this for what it's worth. Everything about dampers you stated is OF COURSE TRUE. I think that EVERY BUICK engine builder on this site will recommend a BHJ balancer on every rebuild if the owner can do it.
However:

I think most relatively "serious" engines do have a BHJ balancer employed just as you are asking, especially when switching to a steel crank that's internally balanced anyway. We're talking about guys that really want to run Mid 10's and faster everytime they go to the track - and have the combo to do it.

It's commonly known that the main caps crack and break (from detonation) well before the stock crank does. This set-up with the stock balancer, all else being equal, can take you safely into the mid-high 10 range consistently. That's why the main caps/girdle usually come first. Having the rest of the car support the power is the other problem.

Putting a balancer on an engine and doing nothing else is kind of goofy.

If you're going to use a "real" damper on a stock engine, you have to pull everything apart to get it balanced. Are externally balanced - so the weight comes out of the balancer and the flywheel. Going through all of this trouble, you "mind as well" put main caps on it. At that point (IE if you're building a mid 10 sec or faster engine).. then mind as well use a steel crank $300-$600, steel rods $300-600, BHJ balancer $400 now (wow! was $200), and a sfi flywheel $50.

I think it's an "all or nothing" type of deal. Pick a range I'll say 10.6x's. Anything faster, then spend the $1000-$1500 on extra rotating assembly. AND the extra $000's on the rest of the combo to go faster then 10.6'x. We're talking bigger turbo, heads, suspension, and transmission.

I picked 10.6's because guys can do it with a single in tank pump, stock ecm setup, mild turbo, mild heads and cam, mild trans, and a GOOD driver that can 60 ft.

Thanks for your input E ticket, did I understand you correctly to mean that there are no external balance dampers?
I ask because I found this
FULL THROTTLE SPEED - Item Description Page

What's the problem with just slapping this on in place of your solid balancer on a stock type engine? Is there any reason you can't? (I honestly don't know)

Is it really that goofy to do when the damper is a bolt on deal and a crank, caps, girdle, etc require extensive and expensive machining?

I'm wondering what the graph above would look like if it were for a high boost TR engine. Seems like it would look significantly worse since our cylinder pressures are insane.

I understand that detonation pounds the main caps, I would have figured a damper would help combat the bending of the crank in a detonation event as well (of course detonation will kill your engine at this level either way)

I wish we had some legitimate test data showing what is going on down there.

 

[KevinB]

Just throwing this out there....

Last year my car did 120+ 1/4 passes and about 3K street miles. Eagle crank, K1 rods, girdle, etc, etc. All passes were low 10's and many high 9's. It had a stock balancer on it. I took the engine apart for inspection over the winter. Kinda mad I did b/c everything still looked great. Take it for what it's worth, just saying my car did fine w/o an aftermarket balancer.

 

[Pablo]

Just throwing this out there....

Last year my car did 120+ 1/4 passes and about 3K street miles. Eagle crank, K1 rods, girdle, etc, etc. All passes were low 10's and many high 9's. It had a stock balancer on it. I took the engine apart for inspection over the winter. Kinda mad I did b/c everything still looked great. Take it for what it's worth, just saying my car did fine w/o an aftermarket balancer.

Just playing devils advocate:

Maybe all those parts made up for the lack of a damper?

 

[Eticket]

Pablo,

You are right.. you can buy a BHJ for external balance.. but you can't balance it without the rest of the rotating assembly out of the engine.

"I guess" that a good machinist could take two balancers and duplicate a stock balance with a BHJ.. but I don't think they would probably do it or want to do it - nor does it account for the weight to weight differences between pistons/rods when an entire assembly is balanced properly.

I'm pretty much with KevinB though... the balancer is not even close to being the weakest link and definitely won't save a crank from detonation. I would use a BHJ if I were building a "serious" motor though.. it's just a preference thing at some point.

That graph you show.. we're probably talking about 1 degree in extreme conditions? and...we're talking about v6 that has a shorter crank and may or may not be affected by said harmonics at the rpms that we don't turn.

 

[pm87tb]

Subscribed.. good topic.

 

[Pablo]

"We never got to see the selection process in action. Without a damper most cranks will suffer torsional vibrations up to a degree or more of double amplitude (+/- 1/2 a degree). Steel, as opposed to aluminum, can withstand a certain amount of deflection indefinitely. However, after a certain point the hours and minutes begin to count against it.

Within the industry it is generally accepted that a typical V-8 can, at what appears to be the most important third and fourth order harmonics, tolerate about 0.4 of a Degree Double Amplitude (+/- 0.2 of a degree) almost indefinitely. These third and fourth order harmonics also seem to be the ones that have the greatest adverse effect on power. The object of the exercise then is to damp crank vibrations to something below this 0.4 DDA threshold. As can be seen from the graph on page 159 the ATI Super Damper did just that. Below 4,750 rpm the torsionals exhibited by the Scat cast steel crank were very low. This was not unexpected as cast steel, like cast iron, has higher self-damping properties than are seen with forged or billet cranks."


Just want to keep this going, I think its a good topic (I'm a little biased though)

E ticket, you have a good point about the shorter crank, but, do you think the insane cylinder pressures we run might negate any benefit to a shorter crank?

On the EPI-eng.com webpage they have a section on BMEP and cite some interesting examples from F1 and nascar.

A nascar engine at peak torque develops a BMEP of 219 psi, as I look at the waveforms on that first link i posted, I can just imagine how high the peaks are for that nascar V8.

Now consider that a typical Turbo Regal like mine is developing somewhere in the neighborhood of 615 ft lbs of torque at the crank (I dynoed at 500 to the rear wheels on a bad tune, 4800 rpm)
Doing the BMEP math, that comes out to a BMEP of 401 psi, significantly higher than even a nascar and Formula one engine. That's a lot of crank twisting force. If we were to drive for as long as they did at WOT I'm pretty sure all of our engines would be toast.

And If I am to understand things correctly, the fact that we are down two cylinders makes it worse since we have to develop the same amount of power with fewer combustion strokes per RPM. Kinda like riding a skateboard and maintaining speed with one really hard kick per second versus two lighter kicks per second. The skateboard (crank) accelerates and decelerates to a greater extent than it would with two kicks per second.

 

[bobc455]

Subscribed.. good topic.

Guys- Instead of making a post, just go to "Thread tools" at the top and subscribe without wasting thread space.

-Bob C.

 

[Alky V6]

A few points.

Vibration eats horsepower.
Our V6s have an inherent vibration characteristic that V8s don't suffer from.
Vibration over long periods will fatigue metal components. Where the level limits are, I don't know.
In Indy cars, the pan rail was used to mount the engine through the drysump oil pan. The pan rails would suffer from cracking due to vibration during long endurance runs.
The Buick Power Source book highly recommends a damper be used for high performance uses. You really can't ignore that one.
It would be interesting to see more data specific to our engines on this subject. Maybe some of the damper suppliers would have something.

I use an ATI and I noticed the inner weight has shifted rotational position last time I had it off. It was marked with a white marker by the manufacturer. I'll have to call them and find out if that is a problem. You guys got me thinking about it now.

 

[MSDGN]

Another reason for an aftermarket SFI approved balancer is that NHRA requires it for cars at 10.99 and faster...I'm sure a lot of tracks don't check but mine does...

 

[Eticket]

Pablo,

This is beyond me really. I was just trying to answer the economical question on damper vs steel main caps... etc. That's why I said that our motors may or may not suffer from those harmonics. I think your quote above mentioned that cast cranks have a tendency to damper themselves?

Don will take us over from here if we want to take this into getting the max HP from our engines. Don, one of the articles I read talked about the fluid dampers fluid getting too hot over time and settling back incorrectly?

this was probably a little more than my .02.

thanks!

 

[Alky V6]

Pablo,

This is beyond me really. I was just trying to answer the economical question on damper vs steel main caps... etc. That's why I said that our motors may or may not suffer from those harmonics. I think your quote above mentioned that cast cranks have a tendency to damper themselves?

Don will take us over from here if we want to take this into getting the max HP from our engines. Don, one of the articles I read talked about the fluid dampers fluid getting too hot over time and settling back incorrectly?

this was probably a little more than my .02.

thanks!

I am no expert on the different designs of dampers. I do recognize that vibration levels need to be controlled for maximum component life.

I haven't heard about the problem with the fluid damper. Interesting.

 

[turbofabricator]

Technically our cars do NOT have any torsional balancer at all. (hence the reason for this posting ) If you read the NHRA spec., it states "torsional dampners". So, there really isn't any reason to replace the front "Hub" with a SFI balancer. (per NHRA rules) I talked directly with the Division 6 tech diector years ago about this, and he said that "if it does not have a cast iron inertia ring, with a strip of elastomer between it and a cast iron hub, then it is not required to replace it." Each track can designate tougher rules than NHRA, though. The purpose of the spec is to prevent the cast inertia ring from exploding at high RPM. (and hitting the poor soul working the tree that night) But just "try" and explain it to a week-end "tek" (spelled that way on purpose) guy that. (last week I koodnt spel Tek inspektor, now I are 1)
Now........a good balancer is a good idea. There is ALOT of debate as to what kind of design is best. Most high end engine builders prefere the ATI balancer (non Buick) Fluid dampners are a problem at 7,000 rpm ( many say anyway). Do an internet seach on this topic, and spend a few months reading/learning.:eek

 

[Grumpy]

we went to the SFI stuff because we got tired of getting kicked out for running to fast and quick .. Some tracks check BUT like was said a LOT don't