Jon wrote: Do you guys think it is a good idea to replace the original damper just in case? How would a replacement be balanced to my motor? (340 forged crank)
If you regularly rev up to redline at full load, I'd say yes.
f you jsut drive around and give it the occasional blast, I'd say that's not necessary.
But I've been known to do unnecessary things just for peace of mind.
Just like I sometimes write long, almost off-topic posts in the middle of the night for no apparent reason (although this time, I have a reason. I've been holding my club's booth at an old car convention all day, and I've been asked if that car -an orange 70 challenger- was the car from "Starsky & Hutch". Twice today. I have to go back tomorrow).
The engine on my cuda was built 3 years ago, and has been used for rally and road racing, and drag racing. Not that we get that many drag racing events in France anyway. It also got around 7000 miles on the road.
Engine redlines around 6200, never been above 6500.
I did 4 full races this year, so probably around 40 runs.
The $80 damper installed by the engine builder just wasn't meant for this.
You can check from time to time that yours doesn't wobble. Mine gave clear audible warnings, at first during turns, then all the time, then it became obnoxious. On a small-block, the damper hitting the cast aluminum timing chain cover is a very cristalline metallic sound.
Had I known what to look for, I would have known, two weeks ago, why I had a hard time setting ignition timing.
Here's what I know about dampers (and it has expanded a great deal in the last 10 days).
OEM dampers are all elastomeric. That is, they're made of a center ring (which also serves as the hub), an outer ring, and a rubber bond injected/molded in between.
OEM dampers have no insulation, the rubber portion is exposed to elements, oil leaks, and any chemical that may happen to be around the front of the engine. Temperature cycles don't help either.
OEM dampers have no safety feature whatsover to prevent the outer ring from getting loose, once the rubber is too damaged to keep it seated.
OEM dampers are most often cast iron, which can crack, and may easily fragment under stress (you get the idea).
The main purpose of the vibration damper is to limit the torsion angle on the crank snout (the crank twisting on its axis), which is induced by the rods pushing on the crank throws during operation.
The damper also absorbs harmonic vibrations.
Balancing a cast crank is another function altogether, although it is also performed by the vibration damper (and converter weights) on cast-crank engines.
There are several types of aftermarket dampers.
Elastomeric (like OEM, and slightly different ones), fluid-based, and the TCI Rattler.
Let's start with the latter. One of the more recent marketing fads, the Rattler uses a harmonic damping principle which, though perfectly valid (and extensively used in jet engines), can only control vibrations in one axis. I don't know if it's an issue or not in a V8, which, by definition, is not balanced. That principle was patented by TCI for use in cars, hence the Rattler is currently the only model using this principle.
The Rattler is dimensionnaly identical to an OEM damper (which is better for pulley alignment).
Next, the FluiDampr family, which has been around for a decade or so, and was probably introduced as a (then) new marketing ploy to sell something new.
Principle : compared to the elastomeric damper, the fluid damper's hub and first ring is integral to the housing, and the second ring is enclosed inside it. Free to turn. Bathed in a silicon fluid.
Pros : the engine sees only a fraction of the damper's weight when accelerating, since the second ring is free-wheeling. It's very durable, being totally sealed. They're very durable, have degree markings up to 50° and every 90°, and I have one that's 10 years old at least on a big block.
Cons : The clearance for the secondary ring is really tight, and even a slight dent on the housing may pin the second ring in place and render the damper useless. There's no way to check for yourself that the ring is free to turn.
And last, the elastomeric damper. I've read that this is the most sound techinical principle (on a manufacturer's website which sells this type pf damper, of course). Which I would be tempted to believe, on a pure technical basis. After all, it is the OEM design of almost every damper on every combustion engine even today. For those of us who try to avoid cheap chinese-made junk (and I mean junk, there are some pretty nice Mopar parts made in Asia, but I have some pictures which say "Professional Products" sells real junk), there's an Australian firm which makes fair-priced dampers, in two street (one SFI-approved, one not) and one race versions. I helped install one on a small-block recently. Not in stock at the moment at Mancini's, though.
Most high-end elastomeric dampers nowadays are sealed, laser-welded, so therubber can't be contaminated. The casing may enclose the outer ring, so it can't fly off. The rings may be serrated, so they can't spin out of control.
BHJ also makes very good dampers (and fairly expensive ones).
Since inner mass has no useful purpose on a damper, their aluminum-center dampers look really good. Prices are awful, though. Non-SFI approved at 200 bucks, all the rest starts above 400.
The variant : ATI makes dampers with 2 or 3 steel rings, removable hubs, and the rings are held to the housing with rubber o-rings.
Several O-ring types are available to tune the damper to the engine (which is only really useful if you have unlimited access to a dyno).
Now, if I don't want to make this -
already off-topic- post far too long, let's just say the ATI design seems hands down the best design there is. Some OEMs use ATI dampers on their big crate engines.
They're rebuildable. The removable hub makes installation a breeze, and let's face it, they look cool. They have options for weird things (crank triggers, blower pulleys).
Now the cons, as unbelievable as that may seem. These guys seem to have engineered the best damper on the market, and they boldly state on their catalog that the hub is too long. They know it. They did it on purpose! You can machine it (they even give you the length to machine it to).
You are almost assured to have pulley alignment issues with that, and custom pulleys may be the only way to go if you get a 3-ring damper.
Yeah right. I need a damper on the engine before next saturday or my last track session of the year is cancelled.
I ordered a Pro-Race unit, which was backordered, and settled on a FluiDampr.
I already have one on a big-block, now I'll have one on a small-block too.
Whatever type you chose, I'd say the SFI approval at least give some insight into the intended use of the part.
Price-wise, I'd say good dampers start around 130-150 dollars. Below that mark are dampers like the one I had...
SFI approval does not mean the damper works as stated. Just that it can be spun at 12K RPM for one hour and still be there afterwards. Stop and go conditions, accelerations and decelerations, heat cycles, dirt, oil, none of this is part of the SFI test procedure.