Harmonic balancer?? Why have one??
Melting Slicks
Joined: Mar 2004
Posts: 3,472
Likes: 18
From: Lake Ozark, MO
interesting theories....Dodge Neons carry a big hunk of iron bolted on just under the radiator support, looks like the back half of a pick axe. Designed to stop harmonics transmitted from the engine in cracking the frame - or so the Chrysler engineers say. Most of us ricers remove the 11lb weight because it make take 300K miles (whick car will never see) before it does. Norval, you engine may be in same boat, it will only last 300,000 miles with a partial damper.
Melting Slicks
Joined: Jan 2006
Posts: 3,028
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From: North NJ
Definitely get your crank double keyed for the supercharger. I beleive the keys go on opposite sides and are almost twice the size of the standard key. This is a must with blown motors.
IMO I beleive you made the wise choice to run the dampner...too expensive to risk.
IMO I beleive you made the wise choice to run the dampner...too expensive to risk.
Thread Starter
Race Director
Joined: Nov 2000
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From: Waterloo ontario Canada
Originally Posted by Twin_Turbo
you destroyed your crank???
I have since changed my mind and will pick up another one tomorrow and have the keyway cut. I run two keyways, one 3/16 and one 1/4 inch.
I also degree the wheel with a dividing head.
Drifting
Joined: Oct 2003
Posts: 1,486
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From: Big Pine Key FL
Doesn't the mass (and friction) of the rotors in the blower and the blower drive belt do essentialy the same thing as the rubber bonded ring of a damper (provide a damping term that prevents resonance)?
His motor is internally balanaced and would use neutral FW and damper if he was to use the conventional approach.
I have a SAE paper I saved somewhere on the use of gilmer style belts for damping crankshaft induced harmonics in the valve train... It did a fantastic job on the math.
In any event this is not new engineering ground..
His motor is internally balanaced and would use neutral FW and damper if he was to use the conventional approach.
I have a SAE paper I saved somewhere on the use of gilmer style belts for damping crankshaft induced harmonics in the valve train... It did a fantastic job on the math.
In any event this is not new engineering ground..
Thread Starter
Race Director
Joined: Nov 2000
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From: Waterloo ontario Canada
Originally Posted by 84rzv500r
Doesn't the mass (and friction) of the rotors in the blower and the blower drive belt do essentialy the same thing as the rubber bonded ring of a damper (provide a damping term that prevents resonance)?
The belt is cogged and 4 inches wide so it doesn't slip even when cold, It would have to jump teeth like a timing chain.
If you run the belt anywhere near tight cold once hot it would put too much load on the front bearing.
Le Mans Master
Joined: Aug 2000
Posts: 6,362
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From: Brazos TX
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84rzv500r, you are correct about belt drives not transmiting harmonics (such as to the valve train when used as a cam drive). The point is that it doesn't transmit them not that it damps them at the source. Therefore, a blower belt drive with not damp anything (or very little) from the crankshaft.
Race Director
Joined: Dec 1999
Posts: 16,945
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Originally Posted by turtlevette
i hate pressed-on sht. They should have splined the front of the crank. Then there wouldn't be all the brain damage pulling it off and on.
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Drifting
Joined: Oct 2003
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From: Big Pine Key FL
Originally Posted by burners
84rzv500r, you are correct about belt drives not transmiting harmonics (such as to the valve train when used as a cam drive). The point is that it doesn't transmit them not that it damps them at the source. Therefore, a blower belt drive with not damp anything (or very little) from the crankshaft.
Are we just interested in NOT letting the harmonincs in the crank reach some natural frequency that the crank would resonate at?
As TT points out it's the press fit of the damper to the crank that transmits the vibrations in the crank to the damper to be absobed by the elastomer in the damper?
I guess I dont know why the cog belt and the rotors dont approximate the rubber and the ring on the damper.
(BTW) for a street engine I'm not suggesting omitting the damper...
Some how I think were gonna end watching suspension bridges in the wind
Or start talking about engine configurations, crankpin spacing, cross-plane vs inline, and perfect primary balance
Melting Slicks
Joined: Feb 2003
Posts: 3,053
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St. Jude Donor '03,'11
Originally Posted by 84rzv500r
As TT points out it's the press fit of the damper to the crank that transmits the vibrations in the crank to the damper to be absobed by the elastomer in the damper?
:
:
i had a brain fart
Drifting
Joined: Oct 2003
Posts: 1,486
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From: Big Pine Key FL
Originally Posted by Twin_Turbo
I think you would loose power, I think tests have shows larger dampers make more power.
So the smaller diameter and lighter damper the more observed rwhp and the faster the motor would rev.
Isnt that also one of the reasons for the 180 degree crank so that you dont have to have the counterweights to bring the motor back into balance. (90 degree cranks are the norm for cross plane or V configuration engines)
Another thought I think turtlevette brought this up... Dont stresses concentrate at the edges ? hence the reason for peened and polished rods and bigger radii on the journals? maybe norval can get a raw forging and machine the crank for less potenial to crack...
Last edited by 84rzv500r; Nov 9, 2006 at 10:53 PM.
Melting Slicks
Joined: Jul 2000
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From: Beacon NY
Originally Posted by yellow 72
The harmonic balancer, or vibration damper, is a device connected to the crankshaft to lessen the torsional vibration. When the cylinders fire, power gets transmitted through the crankshaft. The front of the crankshaft takes the brunt of this power, so it often moves before the rear of the crankshaft. This causes a twisting motion. Then, when the power is removed from the front, the halfway twisted shaft unwinds and snaps back in the opposite direction. Although this unwinding process is quite small, it causes "torsional vibration." To prevent this vibration, a harmonic balancer is attached to the front part of the crankshaft that's causing all the trouble. The balancer is made of two pieces connected by rubber plugs, spring loaded friction discs, or both. When the power from the cylinder hits the front of the crankshaft, it tries to twist the heavy part of the damper, but ends up twisting the rubber or discs connecting the two parts of the damper. The front of the crank can't speed up as much with the damper attached; the force is used to twist the rubber and speed up the damper wheel. This keeps the crankshaft operation calm.
Le Mans Master
Joined: Aug 2000
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From: Brazos TX
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There is a difference between transmitting and absorbing. A belt doesn't transmit for the same reason that tapping on metal with a hammer transmits the energy but tapping on a rope doesn't.
Aluminum rotors on a blower won't have the amount of mass that a damper has and the long belt isn't going to transmit a damping effect, especially in a timely manner. A damper is for damping and a blower is for blowing. I would certainly run a damper on a street engine but not on a drag race engine.
You are correct that less rotating mass will show more HP but the difference for a street engine isn't worth snapping the crank in half. Dare I bring up the debate; torque is going to be slightly more relevant in this case. You can loose the rotating mass in other areas and be way ahead of the game. Things like wheels, tires, and brake rotors will have a more profound effect on rwhp than removing the balancer.
Aluminum rotors on a blower won't have the amount of mass that a damper has and the long belt isn't going to transmit a damping effect, especially in a timely manner. A damper is for damping and a blower is for blowing. I would certainly run a damper on a street engine but not on a drag race engine.
You are correct that less rotating mass will show more HP but the difference for a street engine isn't worth snapping the crank in half. Dare I bring up the debate; torque is going to be slightly more relevant in this case. You can loose the rotating mass in other areas and be way ahead of the game. Things like wheels, tires, and brake rotors will have a more profound effect on rwhp than removing the balancer.
Last edited by burners; Nov 10, 2006 at 03:51 PM.
Drifting
Joined: Oct 2010
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From: Chester Virginia
If you are talking about a blown motor with supercharger aren't you of necessity also talking about substantially higher rpms that the pistons go up and down and the crank is spun around? At 5,000 rpm's these are microseconds. At 750 rpms they are longer periods between when power is applied through cylinder explosions by definition. The longer the time before an explosion on the other side of a crank from a piston on the other side "balances" the force of the first explosion it seems to me, non engineer, that you would likely have more harmonics to deal with. Once the rpms get way up there the time lapse is so small that the forces would tend to balance each other with such tiny intervals that the physics of transmitting non equal tortional forces would just about disappear for all practical purposes it seems to me.
Just my two cents worth. What might be true for a street engine's general range of use might be totally different for a high rpm motor like one that's blown would be. Throw more air and gas in to use it you got to move it through and that means rpms up it seems to me.
I'd think the two states of inherent vibration would be very different.
Lance...just two cents worth of theory.
Just my two cents worth. What might be true for a street engine's general range of use might be totally different for a high rpm motor like one that's blown would be. Throw more air and gas in to use it you got to move it through and that means rpms up it seems to me.
I'd think the two states of inherent vibration would be very different.
Lance...just two cents worth of theory.
Intermediate
Joined: Dec 2010
Posts: 41
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I have not read all of this thread but I use to have an 82 with a 502 with 8-71 bds blower. Only ran a crank hub. put many street miles with no problems. BDS told me that the belt and pullies would make up for the damper.
If I knew how upload photos I would post some
If I knew how upload photos I would post some
Race Director
Joined: Nov 2002
Posts: 12,142
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From: Taylor Michigan
the serious supercharged engines run a small front hub of steel and not a cast iron balancer that can come apart, Street engines need belts and pulleys to drive all the extra junk and a balancer fits the bill to attach them so they can look good at the local car shows or so called bragging rights....most real fast race cars dont have fenders or drive in trays hanging on them.....
