MARKUS_P

Another question, who has bought a new damper and can say that it really improved engine operation?
Was it noticable that the engine ran smoother or something like that?
The body of my vette is still off the frame these days, maybe I should consider changing this damper until the body is on the frame again... it would be a lot easier..
I saw in the cataloques internally / externally balanced and 6.6" dia and 6 3/4" diameter.
I guess the diameter isnīt soooo important, as long as you donīt use a timing tape...
but internally balanced? I didnīt even knew that there are externally balanced engines....
Which balancer is the right one for my engine? 355 cui SB
Thanks

Gordonm

You want an internally balanced one. The external is for the 400 crank on a small block. You can internally balance a 400 crank butthats another story. I have a fluidamper on mine. I run a lot of rpm so I did it for insurance on the motor, I doubt it will improve performance it just makes the motor smoother. The streetdamper should be OK for most applications.

Lt1er

I use a 6 1/4 SFI Fluid damper. The ATI is also a good choice. I use an adjustable pointer which was another$27.

MARKUS_P

Just ordered the streetdampr, thanks

Eddie 70

How much for the Street Damper. I may do some engine work this winter and this would be one of those things while you are at it.

81vette

Below is a quote from the Scat site that I have been wondering about for some time. It is at the end of the "About Scat Cranks" article if you want to read the whole article. I know most of us are not driving race cars here, but most of us like to "quickly accelerate" our cars. With that in mind, is Scat recommending that we stay away from all dampers that use fluid inside the damper for reducing vibrations? Quote from article below:

"A word about vibration dampers

In our conversation, Tom Lieb gave us some great (though sure to be controversial) information about a subject directly related to the crankshaft and its survival in a race engine: vibration dampers. He was quick to point out that a very common cause of crankshaft failure is using the wrong damper, and is especially leery of any damper that has moving parts. "A damper is supposed to balance an engine. How can you do that when you have something moving on the damper?" Lieb went on to say "Any damper with moving parts, whether it is fluid or mechanical, is not recommended in a drag race engine. Anything that moves in the damper has inertia. When you quickly accelerate or decelerate the engine, that moving part of the damper slams one way or another and puts a lot of stress on the crankshaft. For an engine that runs in a very narrow rpm band and with very little change in engine speed, like an 18-wheeler or a car that drives on the highway at a constant speed, a damper with moving parts is fine, because it will find the frequency at a constant rpm and dampen the vibrations. But with a drag race engine that accelerates and decelerates fiercely, the engine will only have certain vibrations for a millisecond." For a drag racing engine, Lieb recommends the lightest, smallest damper possible, with an elastomer-type construction. "The rubber will sit there and hum, but it won't change location.""



[Modified by 81vette, 6:53 PM 12/28/2001]

Rocket Ron

I had the same advice from my machine shop guy. He has been building winning chevy race engines for 30 years. Also keep in mind that the street damper is not sanctioned for drag raceing so if you have a tendancy to jump on it once in a while you risk having a damper failer or worse.
I have seen an indexed sleeve that covers the stock damper.That is what I will be experimenting with on my next race engine.

MARKUS_P

:D
Sorry guys, just had to smile a bit.
Donīt take me wrong, I really respect the advise of somebody whoīs building race engines.
First of all mine isnīt a race engine. Max. power will be 430 HP with NOS, used one or two times a year at the drag strip.

Ok, now to pysics......
They say that they use silicone in the dampers right?
Silicone is much thicker than water, right?
OK, now imagine a fluid thicker than water, eg silicone, in a rotating chamber.
Our engines run at least with 900 rpms, so what is the fluid going to do?
The centrifugal forces are sooooooooooooo big, that the fluid will be immediately pressed out against the outer shell of the damper.
Further more the fluid will be distributed through the shell, so there should be no force creating weight that isnīt compensated by the same amount of fluid in the opposite of the damper shell.
Iīm not a damper constructor and I may be wrong in this case, but my common sense tells me what I wrote above.

I just found a little more info on this - please read

http://www.fluidampr.com/torsional_vibration.html

I posted the most important facts:
Another common concern is that fluid and mechanical dampers contain moving parts, which are believed to impede proper balancing of the crankshaft assembly. A fluid-type damper, such as Vibratech's FluidamprŪ, contains an internal inertia ring that is self-centering, even at idle speed, due to the balance of pressure and shearing forces in the viscous fluid that surrounds the ring. Also, every precisely machined inertia ring that goes into a FluidamprŪ is separately high-speed balanced during its manufacture in a robotic cell.

In elastomer dampers, the outer inertia ring is fixed relative to the mounting hub through a ring (or rings) of elastomeric material (usually rubber). These units must be balanced after assembly to correct imbalance due to any offsets between the inertia ring and the hub that are created by the imposition of the rubber ring between them (note the large balance holes on many of these dampers). An elastomer damper that is not balanced out of the box is not self-correcting at any speed.




[Modified by MARKUS_P, 6:58 AM 1/3/2002]

73 Teach's Pet

I had a mild flat topped pistoned 355 small block connected to a turbo 350 tranny using 2.73 open ended rear gears which was running high 14's. After I installed a Fluid harmonic balancer and full roller rocker arms, I dropped a consistent 3 tenths in the quarter mile and improved my MPH speeds a consistent 3 MPH. I just purchased a used Fluid harmonic balancer at Fall Carlisle for $50. I figure other than a little wear on the crank snout, which can be fixed by purchasing a wear sleeve, how can they really go bad, so I don't shy away from buying these expensive items used when they are offered at a considerable discount.
Hope the performance gain insight helps.
Be Cool!
"TEACH"

427V8

I think this guy has SOME good ideas but I think he is a little clueless about the physics of it all.

I agree with him that a pure drag car should probably use the smallest dampner possible, the question is what is possible?

As far as a fluid dampner 'slamming' one way or the other, I don't think a fluid dampner could 'slam' since it has nothing to slam against! ( i.e. the internal ring can rotate as far as it wants ) A rubber dampner however does have a mechanical connection to the crank and the further the inertial ring deviates from the static position the stiffer it becomes, so it would slam against the rubber?

What I do see as a potential problem with fluid dampners is the eddy currents in the fluid itself, ever take a raw egg and spin it? It doesn't spin very well, the fluid in the egg is the cause. That same egg when hard boiled will spin very nicely!

Me I have an 8" fluid dampner, I believe they are designed to do the job and have only a little parasitic loss

gkull

81vette It sounds like an excuse for junk crank manufactures. Don't blame the crank it had to be the damper :rolleyes:

I have owned a couple of high rpm race motors (9000 rpm) both equiped with 6 1/4 SFI fluid dampers and neither ever popped. One motor spent a whole year Sprint car racing without a teardown and was sold in it's still running condition.

I have a 79 L-82 which came with the bigger damper. At approx. 50K miles it broke from the inner to outer ring. I first noticed it when my dial in timing light was bouncing all over. I was thinking what the F***. Stock dampers just fall apart when subjected to 7000 rpm.

I was going to add that I buy all SFI rated parts because. You buy these parts for a lifetime and you just never know if some day you might want to go drag racing and you get turned down at the Tech Inspection Station because your not up to code.


[Modified by gkull, 8:57 AM 1/3/2002]

Frankenvette

If one were performing an engine rebuild for a mild 350 that is just for driving around and no racing, would one need to worry about SFI approved or use a quality oem damper?

Regards,

Jim

73 Teach's Pet

The question about the use of a fluid harmonic balancer on a mild street motor actually has two answers.
A. SFI is a safety inspection rating given to high performance components to give a rating of how tough or durable they are in regards to how well they perform at extreme measures, so an SFI harmonic balancer is not required for any mild street engine, or for even a mild street strip engine, which is why Fluid Dampers sells a non SFI spec fluid harmonic balancer and at a cheaper price because they do not have to be built to sustain the extreme rigors of racing applications
BUT, Fluid Harmonic balancers are advertised as being superior to reducing harmonic vibrations in the rotating assembly, which ultimately reduces friction, which reduces wear, and increases the longevity of the bearing and rotating assembly inside your engine. For a mild street application if you have gone to the extreme costs and trouble of rebuilding an engine yourself and want the components of your engine to have the longest possible life span, the use of a fluid harmonic balancer is a good performance part to acheiving that goal.
B. For street applications a fluid harmonic balancer is not a must item, hence an OE balancer is fine, but if a good buy on a used fluid harmonic balancer becomes available, such as the one I picked up at Fall Carlisle for $50, I would not hesitate to take advantage of its gains, but I personally would not go out and buy an expensive SFI new balancer for $230+ or even a non SFI spec. fluid balancer which run around $140+ new for the benefits on a mild street engine, unless I wanted to lengthen the longevity of my rotating assembly as far as possible. Older aged OE balancers are known to be prone to having the rubber come loose and the outer and inner seperate. This can cause inaccuarrate timing readings and other problems. These may be reasons to change over to an fluid harmonic balancer which is a solid construction unit and will not come apart. Also many fluid harmonic blalancers are degreed having the degree marks engraved in the outside ring which can help in setting up timing at times and does away with a need to purchase a timing tape which often flies off the balancer, ultimately wasting your money.
Hope that is a detailed enough pro's and con's reason of using a fluid harmonic balancer for a mild street application.
Be Cool!
"TEACH"

81vette

Thanks for everyone's input. I will stick with my original plan to use a fluidampr for my build-up. :cheers: