I have 2 new motors sitting outside my office, a 3800 with a traditional harmonic balancer and a 5.3 truck engine with a large hub and a thin flat belt pulley pressed over the hub with a rubber in between.
While this is a harmonic balancer they kept the outer ring to a minimum. It is about 1/4 inch thick.
I will go back to the BDS website and see agian what they say about harmonic balancers.
My feels about a harmonic balancer is that it dampens the fireing of the 8 cylinders. Each firing is seperated by a small amount of time and this causes a jerking motion in the crank, turtlevette said this already and I agree. These jerking motions or stricking of the crank causes vibration and the harmonic balancer just smooths out the jerking motion of the firing.

 

Back in the early '90s, I ran a 427 with a 8-71 Mooneyham blower, and the boys at Mooneyham told me the exact same thing. The blower and belt will take the place and act as a harmonic balancer.

 

Torsional dampers are tuned to damp the torsional vibrations at a relatively narrow frequency band (in the lower rpm range where an engine's torsional vibrations have the highest amplitude). I would be wary that the blower belt wouldn't effectively damp at these frequencies. I wouldn't feel comfortable removing the damper with an expensive engine possibly at stake.

 

So Weiand, BDS and Mooneyham don't know what they're talking about?

 

I feel the same way. I am getting nervous with NOT running a harmonic balancer. I already have the hub made and am having second thoughts.
I have alot of money in this engine and am really considering going with a harmonic balancer.

 

They do say I do NOT need one and BDS emailed me personally and said I would be fine without it and just use a hub for the belt drives. But I am still worried, my engine costs as much as most complete cars and I am seriously considering going with a full harmonic balancer. My engine is not a high rpm race motor and will see lots and lots of low rpm cruising miles.
I will probably take the safe way out and go with a harmonic balancer.

 

Why not ask them to explain why its not needed, from a vibration/harmonics viewpoint? This is from the BDS link posted above, seems to be a breakage issue with factory balancers.

"BDS crank hubs are made from 4100 series aircraft alloy hardened steel, designed to replace the stock factory harmonic balancer for blower applications only and are necessary for proper operation and longevity of the complete blower drive assembly. Factory harmonic balancers are not designed to handle the additional stresses of driving a supercharger along with the other accessories. They will normally crack or break near the keyway, break and come off the engine causing severe damage to the crank shaft, water pump, radiator, fenders or anything else near the front of the motor. After market harmonic balancers are capable of withstanding the additional stresses of a blown motor even in high performance applications. These highly effective harmonic dampeners are considerably heavier than the BDS steel crank hubs and therefore may not be desirable for all applications. Some modifications to the blower drive system are required in order for the lower drive assembly to bolt directly to the after market balancer. Since there are numerous configurations of after market balancers available, you will be required to send your after market balancer to us so that we may make the necessary modifications to the blower drive assembly. BDS also recommends using two keys along with the crank hub to prevent the hub from spinning on the crank snout. All BDS crank hubs come equipped with a stock size keyway and a ¼" keyway 180 degrees from the stock one. Key stock material is not supplied. Stock single keys are not adequate, especially if the blower drive ratio and RPM's of the motor are high. Using the stock keyway and a second ¼" keyway is highly recommended for all applications and two ¼" keyways are a requirement for high performance or racing systems."

A guy I used to work with ran at a small stock car track with out a balancer as a method to reduce rotating mass. Cheap way to allow the engine to rev faster. Never broke a crank, but he only ran the cars for a year at a time.

Jim

 

Norval maybe you should ask yourself this question, if I do run
a balancer will it harm my engine, you will probably answer no.
I don't know if you can get away without one but I would say
running a balancer won't harm your engine and if there were some
performance gain without a balancer it would be a tiney amount,
you have 540 cubes with a blower its not like you will be hurting
for power either way.

 

I don't know, and don't care! But for me it doesn't matter, I'll never have a supercharged engine.

 

Guys I am NOT taking the chance. A damper won't hurt anything, it could possibly save my crank and I will run one. I just destroyed one this week so I have to order another and leave it alone. Well cut another 1/4 inch keyway so I have 2 keys plus up the accessory mounting holes to 1/2 inch.
Thanks for the input guys.

 

I agree..they are designed to damp the torisonal shock vibration from the crank twisting and untwisting when the load is put on or released and this is most violent at the front of the crank.
It's the effect of the power stroke twisting the crank, accelerating that crank journal and twisting the crank and later snapping back.
The name harmonic balancer is not even correct, it's not a balancer..it's a damper. It usually works by friction, the stock ones use a rubber elastomer between the center and inertia ring, this gives a dampening/resistance effect to sudden radial speed of the crank just like a shock absorber dampens quick movement of the suspension and controls the spring. A bigger inertia ring has a larger efficient rpm range.

The viscosity/fluid dampers work just like the visco clutch on the fan, there's no bond between the inertia ring and the hub. The other type is the swinging pendulum type like the rattler.

The frequency of this is related to the engine rpm and at a certain rpm it will come into tune with the natural harmonic of a crank, and this is when you quickly kill the crank. This natural harmonic frequency is different for different cranks. Heavier cranks have a lower nat. frequency, stiffer cranks have a higher one, so best would be a lightweight stiff crank..maybe then you can elevate it out of the useable rpm band. Cast or forged, barrel drilled or not, even stuff bolted to it can change the freq. (as bolt on items may offer a sort of damping effect) A froged crank can accept more torsional vibration than a cast crank, this is a no brainer.

Stock damopers have a lower max rpm damppening limit than the expensive aftermarket ones.

IMO running a lightweight aluminium hub is foolish, run it hard enough and you will eventually see a fatigue failure in your crankshaft.

Also, think about the fact that it's mainly occuring at the front of the cam. These torsional vibrations are translated into the cam and will affect timing. I would think that this is even worse with a gear type drive since it's the most rigid, the chain drives snake aroudn at high rpm anyway. A good damper becomes very important.

Now...I don't see how the blower belt can do a good job at dampening these, iit may help some..but I would not want to risk a crank, I would run the dampener.

 

That's too bad. You will never really feel the power that only a supercharge be it turbo, blower or supercharger can give you.
This is my first blower motor, have run it for 7 years and I will never go back to naturally aspirated. You can't possibly get the power from a motor that a blower motor will put out.
If eventually the cops pull me off the road I will just install a different setup but it will be blown.

 

you destroyed your crank???

 

Sounds like a safety belt for your eng, you do not need it to run it but if something happens while it is running you will glad you have it.

 

How much of a HP gain will you really get out of not running it?
Seems to me (IMHO) that the gain is not worth the risk.

 

I think you would loose power, I think tests have shows larger dampers make more power.

 

For my situation, I will always be bound by the rules of whoever I'm racing with, and most classes don't allow forced induction if it wasn't there to begin with. Now maybe if I had a dedicated drag car, that would be a different story, but for autocross and road course time trials I'm limited by the rules.

It saves on my wallett, too.

Not to say that I wouldn't own a car with a blower, just that it wouldn't be in my autocross cars.

That said, I think FI is the future of internal combustion engines. I work for Eaton, I think the biggest supplier of blowers to the OEM's.

 

Some FAQ's from Fluidampr...

What is crankshaft torsional vibration?

Every time a cylinder fires, the connecting rod hammers the crankshaft, making it twist as well as spin. After every twist, there's a rebound as the crank unwinds. This twist/rebound cycle is known as torsional vibration and if not controlled, it will result in rapid bearing and crank journal wear and can lead to a broken crankshaft.

What's the problem with a stock damper?

Stock dampers are tuned for maximum effectiveness with a stock rotating assembly when it's spinning at low rpm's. When the pistons, connecting rods, or crankshaft are changed or modified, or normal rpm range is increased, the effectiveness of a stock damper is reduced.

What causes the inertia ring on a stock damper to move on a high performance street application?

In a stock damper, inertia ring slippage is usually due to deterioration of the rubber strip. As the stock damper ages, the rubber strip begins to crack and lose its grip, in essence it becomes "overworked." Also, rubber is a poor dissipator of heat. The more severe the crankshaft vibration, the more heat builds up. This causes the damping characteristics to change, which could lead to damper failure over time.

What are the key benefits of using a Fluidampr?

A good aftermarket damper protects your crank. Fluidampr is in a class all by itself, because it is designed to provide maximum control of all engine harmonic vibrations, regardless of the rpm at which they occur and regardless of the crankshaft's natural frequency. This translates to maximum protection of the crank, main bearings, related engine components and more consistent power output. Also, Fluidampr is maintenance and repair free. Fluidampr is effective on both race and street applications.

 

he cut the outer inertia ring off his damper because the blower manuf. told him he didn't need a damper.

I stated my opinion as to why i think a damper was important on page 1. I figured if you agreed and chimed in he would listen to you.

I'm just a poor little lamb who has lost my way......bah bah bah.

 

can you say...cracked crankshaft?? you will sooner or later.....
...redvetracr