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How much can damping be improved via balancer swap?

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How much can damping be improved via balancer swap?

Postby 89vette » Tue Nov 05, 2013 6:39 pm

I have a relatively minor issue I'd like to improve. I have some engine vibration that would be nice to reduce/eliminate. While I could describe it as auditory side-effects of header/exhaust, several iterations of the exhaust system seem to show it's more likely from the motor. At one point, I ran a thread in Advanced Engine Tech -- which returned one negative opinion about the balancing technique. But, the builder stands by his method (of drilling the front counterweight with a 400 "offset" damper). He likes this option better than heavy-metal on the nose. Said he's done it to many engines w/o any failures. How can I argue with that? So...here's my question.

I'm running a Pro Race/Pro Sport balancer. It's got the 400-offset weight bolted in. It's about a $150 balancer...so better than the cheap PP brand/style. It LOOKS better than OEM engineering too. Of course, they make higher-dollar stuff like ATI Super Dampers. At 3 times the price, would damping be noticably improved over what I have now? It looks like they make a 7" damper for 400 motors.

I'd call my vibration centered on 1600rpm harmonics. I'm not sure I feel anything abnormal at 3200 rpms and I shift before 6400 rpms.

I'm running sidepipes that are mounted/rubber-isolated to the frame. This may be part of the issue (and how I can more easily feel it) though it's no where near what an exhaust pipe touching frame would be. I self-mega-ported my intake. Withouth having it flowed, who knows if/how much imbalance between tubes there might be...could that cause harmonic vibration?

I also notice a mild shudder as the moter sits down to idle. It seems more pronounced than the 219/219 cam would induce but I wonder whether some body shudder -- on the highway -- is related to this engine "imbalance". I'd say I can feel the shudder even when the motor is slowing rpms rolling down the highway.

That's why I'm considering if a balancer can improve the situation.

Both the ATI and Pro-Race balancers are elastomer construction. I've seen graphs on other types -- like dry friction (which make them look better). I probably have a size limitation of a 7" balancer.

With it being a Corvette with headers and sidepipes, the vibration is not out of character for the overall "theme" of the car. I'm saying most people wouldn't notice it. I'm just chasing an ideal after spending a chunk of change redoing the body, interior and motor on this car. Essentially, the exhaust is muffled by bullet converters and glass-packs. It barks pretty well but is fairly mild when babied. It's a 383 with 5.7" rods, Scat 9K crank, and Wiseco pistons. I'm running 10.25 compression with fairly agressive (stock-like) timing. I notice the vibration can be dimished by retarding the 1600rpm entires in my timing table.

I've considered welding old-style weights to the exhaust pipe to see what effect that has.

Thoughts?
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Re: How much can damping be improved via balancer swap?

Postby Dan Timberlake » Tue Nov 05, 2013 7:51 pm

Garden variety single mass dampers are for reducing torsional vibration of the crank. One end winding up / unwinding a half degree or more relative to the other. If there's a std shift flywheel attached to one end it stays pretty stable, and the big amplitude high frequency winding/unwinding mostly all happens at the damper end, which means a "damper" placed there will be able to see a lot of motion, many times per second, and suck out a lot of energy and convert it to heat instead of letting it build up as higher twist amplitudes. The problem rpm or resonant frequency will vary with the inertia of the hardware stuck on the ends.

Although primarily just the poor crankshaft is involved,twisting the night away in the main bearings, sometimes "coupling" causes a one directional vibration to show up in a new direction. Traditional torsional vibration is slightly inertia (piston acceleration means the crank is tugging or being tugged on) related, and strongly power related (no power = small firing pulses = minimal torsional excitation) so i'd tend discount anything you feel with closed throttle and low rpm as related to crank torsional vibration.

Visualizing torsional vibration is tough.

This highly fanciful video is worthless until the last half, when it shows their industrial "damping" elements distorting when shaft is oscillating torsionally relative to the heavy outer hub.
http://www.youtube.com/watch?v=VjcQvQRuLSY

This one is pretty good.
http://www.youtube.com/watch?v=JdSTGSJ90bw

Page 451 here Studebaker makes an effort to do it with 1950 technology. I believe what is represented is essentially the angle of flywheel flange relative to the snout key. If they remain at the same angle " "rigid" crank ) the plot is a circle. If the snout twists a degree behind the flange the curve goes inside the circle. When the snouts bounces a degree ahead of the flange the curve goes outside the circle. Because the traces have 4 external bumps I believe the crank makes 4 twists per revolution (at around 4900 rpm).

Here is another V8 engine's torsional response, displayed from 1000 to 4600 rpm.
"New rambler 327 V8" from the early 60s."
http://www.wps.com/AMC/Rambler-327/The% ... %20details)_files/v8-fig16.jpg
Note it also has high amplitude 4th order torsional vibration up over 4600 rpm.

Attached is an image from the SAE paper Chevy published about the 265.
Note the 4th order is again the big one, and occurs at a little higher (numerically) frequency than the others, up at 5300 rpm.

You could clamp weight to the headers as a test.
Did you ever try a different exhaust like I think you said you might?
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Re: How much can damping be improved via balancer swap?

Postby 89vette » Tue Nov 12, 2013 3:39 pm

Had the car in the air this weekend. My dad used to have long-large lead bars which I scoured the house for. No luck. I wanted to strap one to the exhaust. I considered strapping an industrial size pipe wrench to the exhaust to see how that dampened. Then ended up thinking of a different idea I might try.

I don't remember mentioning a different exhaust though I have considered pulling a center connector -- which would isolate the header/y-pipe from the [rubber-isolated] sidepipes. I really don't think that's the issue though since it wasn't a problem before stroking the 350.

Rather than hanging weights on the exhaust my new idea is to get some heat wrap and wrap the collector area. Then use a nylon strap and pull the headers together. By adding tension, I think it would dampen vibration.

I'm still not clear if another damper could help. Would it be a bad idea since the RA was balanced with the specific 400-style on the car? (I'm thinking about it again after taking a short-term class on vibration harmonics. The main things I got out of the "tutorial" were: Not to hold rpms in the range where vibration is highest AND that vibration can/does have a cumulative effect in bearing wear.)
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Re: How much can damping be improved via balancer swap?

Postby Kevin Johnson » Tue Nov 12, 2013 8:33 pm

Dan brought up torsional vibration and you mentioned having mega-ported your intake without flowing it. I am wondering if you are feeling the effects of unequal power pulses and then unequal pumping losses or engine braking when you decelerate with partially or fully closed throttle.

Do you have an automatic or manual? The latter would seem to me more likely to transmit engine braking imbalance to the chassis.
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Re: How much can damping be improved via balancer swap?

Postby Warp Speed » Tue Nov 12, 2013 8:47 pm

Kevin Johnson wrote:Dan brought up torsional vibration and you mentioned having mega-ported your intake without flowing it. I am wondering if you are feeling the effects of unequal power pulses and then unequal pumping losses or engine braking when you decelerate with partially or fully closed throttle.

Do you have an automatic or manual? The latter would seem to me more likely to transmit engine braking imbalance to the chassis.
:shock:
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Re: How much can damping be improved via balancer swap?

Postby Cubic_Cleveland » Tue Nov 12, 2013 8:51 pm

89vette wrote:Had the car in the air this weekend. My dad used to have long-large lead bars which I scoured the house for. No luck. I wanted to strap one to the exhaust. I considered strapping an industrial size pipe wrench to the exhaust to see how that dampened. Then ended up thinking of a different idea I might try.

I don't remember mentioning a different exhaust though I have considered pulling a center connector -- which would isolate the header/y-pipe from the [rubber-isolated] sidepipes. I really don't think that's the issue though since it wasn't a problem before stroking the 350.

Rather than hanging weights on the exhaust my new idea is to get some heat wrap and wrap the collector area. Then use a nylon strap and pull the headers together. By adding tension, I think it would dampen vibration.

I'm still not clear if another damper could help. Would it be a bad idea since the RA was balanced with the specific 400-style on the car? (I'm thinking about it again after taking a short-term class on vibration harmonics. The main things I got out of the "tutorial" were: Not to hold rpms in the range where vibration is highest AND that vibration can/does have a cumulative effect in bearing wear.)

You can get your new balancer mirror balanced to your existing balancer if you decide to buy another.
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Re: How much can damping be improved via balancer swap?

Postby Dan Timberlake » Wed Nov 13, 2013 2:18 pm

I think the vibration tutorial should have made it clear that although adding mass or tensioning something //might// reduce the vibration you are concerned with, it would not be as a result of "damping." Damping sucks out small gulps of vibration energy (motion) by converting it to heat by pumping oil thru holes, sliding surfaces to shear oil, sliding surfaces against friction, or distorting materials that create heat with internal material damping (like most rubber to some degree).

Is it the same exhaust system as before the engine was stroked?
You mention "several iterations of the exhaust system."
Does your system mount like this?
http://corvettes.about.com/od/customiza ... aust_6.htm

Regardless
I think your exhaust system and it's mounting and maybe your engine/trans mounts are binding or are not soft enough in the directions necessary to handle the motion of the engine.
If by chance the way the exhaust is mounted to the engine and the car has created a torsional resonance of the engine //assembly// at 1600 ( or 4X1600 if firing pulses are what's driving it) then changing stiffness and or mass can re-tune the resonance to another frequency so there might be less amplification at 1600, but again that is not damping.

Tuning that causes Rough running may cause pulsing torque and increase the motion at 1600 rpm , but that is almost certainly neither a balance or torsional damping issue

Looks like the original chambered side pipes were secured only at the very end by a flexible strap, allowing several feet of pipe to flex and absorb motion with plucking on body panels.
http://www.ecklerscorvette.com/diagram/ ... dex/id/35/
http://corvettepartsworldwi7-px.rtrk.ca ... t_s/79.htm
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Re: How much can damping be improved via balancer swap?

Postby Dan Timberlake » Wed Nov 13, 2013 2:35 pm

89vette wrote:Had the car in the air this weekend. My dad used to have long-large lead bars which I scoured the house for. No luck. I wanted to strap one to the exhaust. I considered strapping an industrial size pipe wrench to the exhaust to see how that dampened. Then ended up thinking of a different idea I might try.

I don't remember mentioning a different exhaust though I have considered pulling a center connector -- which would isolate the header/y-pipe from the [rubber-isolated] sidepipes. I really don't think that's the issue though since it wasn't a problem before stroking the 350.

Rather than hanging weights on the exhaust my new idea is to get some heat wrap and wrap the collector area. Then use a nylon strap and pull the headers together. By adding tension, I think it would dampen vibration.

I'm still not clear if another damper could help. Would it be a bad idea since the RA was balanced with the specific 400-style on the car? (I'm thinking about it again after taking a short-term class on vibration harmonics. The main things I got out of the "tutorial" were: Not to hold rpms in the range where vibration is highest AND that vibration can/does have a cumulative effect in bearing wear.)

===========

Hi 89, over on the Advanced Engine tech forum back in November you said '
"Disconnecting the collector pipe "extensions" from the side pipe inlets will [likely] be my next step. I'm 99% sure I can lessen my ability to feel said low-rpm-tremor with better isolation. I'm planning an exhaust change in the not-to-distant future anyway."
Others recommended practical tests like coasting down in neutral, etc.

Has any of that happened?

regards,

Dan T
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Re: How much can damping be improved via balancer swap?

Postby Dave Koehler » Wed Nov 13, 2013 3:50 pm

A lot of us have learned the hard way that you can't use aftermarket motor mounts on the modern FWD cars. OEM only guarantees zero complaints.
Wonder if that scenario has any play in this application?

Making a Rolls Royce out of a Corvette must be a daunting task.
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Re: How much can damping be improved via balancer swap?

Postby Kevin Johnson » Wed Nov 13, 2013 4:15 pm

Dan Timberlake wrote:Tuning that causes Rough running may cause pulsing torque and increase the motion at 1600 rpm , but that is almost certainly neither a balance or torsional damping issue


It is a torsional damping issue but not one that is solvable with a crank damper. The firing order in even a smooth running sbc inherently introduces rocking couples along the central axis of the crank and bisecting it from front to rear. This came up in a recent discussion about a Pontiac V8 engine that had an oil pickup that kept breaking loose. In flat four engines when the power output is increased the rocking couple increases. Subaru engines have a well known propensity for breaking pickup tubes when tweaked.

An engine is a big air pump and when the same assembly is working against a closed or closing throttle plate the imbalance of gas flow in an unevenly ported engine will also introduce -- or better, accentuate -- these torsion based rocking couples.

I agree that engine and transmission mounts and the way that the exhaust is mounted are the most likely paths to address this but softer mounts are a compromise in other respects.
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Re: How much can damping be improved via balancer swap?

Postby vincenelson » Thu Nov 14, 2013 2:09 pm

So you stayed with the external balanced motor set up with weight at the hermonic balancer and the weight on the flywheel? I just did a 454 bbc external balanced. I calculated all the bob weights and had a local shop spin the crank. When we took the engine off the stand to install the motor into a boat, I had too much help at the wrong time.....the crank flywheel flange did not have the dowel and my help installed the flywheel with the external weight one tooth off. We had a noticeable vibration at around 1800rpm which seemed to go away around 4500rpm. I did not let the motor go out until we checked the flywheel being installed properly......so we corrected the problem and the vibration at 1800rpm went away. So do you have any weights on your flywheel and was it clocked correctly? Did you install the proper flywheel?
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Re: How much can damping be improved via balancer swap?

Postby 89vette » Mon Nov 18, 2013 11:55 am

I have not flowed my intake. I am certain there would be an imbalance because the mounting bosses interfere with the ports on some of the tubes. That has to disrupt air flow.

I have not disconnected the sidepipe center collector. If I could improve isolation of their mounts, it probably would help. And, yes, the same sidepipe system was present before/after 383 conversion.

I still have the 400-style external damper (pro race pro sport model). I'm running the stock DMF which has the "standard" 30-gram imbalance....same as an automatic flex plate. (Note, this is a riveted, non-movable weight.)

The vibration I have is no more than my DD Isuzu with 3.5L motor. That motor doesn't have a balance shaft -- though it does have a higher-than-normal-priced crankshaft. Reading on that subject leads me to the believe non-balance-shaft-equipped motors may be smoothed via crankshaft. In both my cars, I COULD conclude any/all vibration is coming from the exhaust config. I assume pipe shape,size,weight, curves, etc...all add up to the harmonics generated with varied rpm "notes". (FWIW, I've always wondered about vibration on my Isuzu too. It's a [factory] stroked 3.2L Isuzu engine. I've driven other 3.2L engines and I consider them smooth/vibration-free. So, either stroking, exhaust manifold, or exhaust config seems to alter the character of that setup. OTOH, maybe it's stroker crank affects vibration while "highlighting" the need for a balance shaft in that V6?)

I'm using stock motor mounts. Side pipes are isolated with conical rubber grommets mounted on both sides where the mounting bolts pass through the floor-pan's frame rails
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Re: How much can damping be improved via balancer swap?

Postby 89vette » Thu Nov 21, 2013 12:50 pm

Progress is moving slower these past couple of months. The car is in the shop after being hit by an underinsured driver. I'm still waiting to be offered a settlement. I'm also considering what suspension upgrades/rebuild to perform. I'm leaning toward complete front suspension while I’m at it. Basically, labor would be $350 to do upper/lower ball joints, upper/lower control arm bushings, tie-rod ends, and hubs. It’s a smoking deal really. But, that’s off topic….sortof.

Because it was hit, I have a second set of eyes to look for anomalies related to this discussion. None found. Seemed reasaonble to fish for other ideas....

While I’m thinking about it, do stroker motors have more vibration inherently? This thread is about a 383 but I also have a 3.5L factory-stroked Isuzu. It seems more harsh than it’s 3.2L sibling.
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Re: How much can damping be improved via balancer swap?

Postby Dave Koehler » Thu Nov 21, 2013 1:14 pm

NO
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Re: How much can damping be improved via balancer swap?

Postby Dan Timberlake » Thu Nov 21, 2013 2:49 pm

89vette wrote:...................
I'm using stock motor mounts. Side pipes are isolated with conical rubber grommets mounted on both sides where the mounting bolts pass through the floor-pan's frame rails


===
I'm not discounting the possibility of an out of index flywheel etc if your combo is externally counterweighted.

Well, with stock motor mounts the engine is free to wiggle quite a bit.

Unless those pipe mounts are V-E-R-Y soft, with lots of travel (1/2 inch each way?), the pipes are going to be tugging on floor pan frame rails as the engine rolls and heaves and pitches.
https://developers.google.com/maps/docu ... -pitch.png
http://www.formula1-dictionary.net/Imag ... _heave.jpg

Look at how FWD cars with transverse engines are cinched down and controlled in the "torque" direction with scientific struts and sometimes dampers for upper engine mounts, and there is still a flexible bellows in the exhaust near the engine, and possibly even a spring loaded ball and socket to decouple the wild wiggly engine from the exhaust.

I'd disconnect the pipe mounts, and remove the cones if they are positioned to snub the vertical pipe motions, rev the engine up and down a bit, and" see" how it all feels.
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