3SX or other non-OEM Custom Crank Pulley vibrations vs STOCK CRANK PULLEY smooth ???

[ilian51378]

Shoot, I just installed an UD 3SX pulley a week ago and drove the car about 20 miles with it. Well, guess what? I am replacing it with the stock one tomorrow!

[J. Fast]

I'm going to the garage to pull out and drive my 700whp street car with now 70k miles on an unorthodox pulley...

[IPD]

I'm going to the garage to pull out and drive my 700whp street car with now 70k miles on an unorthodox pulley...

if it didn't sit well with ray p., then it doesn't sit well with me either.

[mb3000]

I'll swap back to OEM after I shatter a crank.

[J_Parker]

I'll swap back to OEM after I shatter a crank.

I can't say I'm worried about it either, I've never run anything but since owning a 3/S and never had any problems.

[BaadVR4]

There are literally hundreds, if not thousands, of papers/treatises/etc/etc/etc addressing the issue of torsional vibration in crankshafts in internal combustion engines. Here is the simplistic, Wikipedia version:

Torsional vibration - Wikipedia, the free encyclopedia

I am probably not going to convert anyone to abandon their solid pulleys, but I feel honor bound to try.

Torsional vibration dampeners are used by every OEM automobile manufacturer. Every Nascar engine has one. All NHRA Pro Stock engines have one.

I promise you, if there were no reason to use a torsional vibration dampener instead of a solid pulley, none of these engines would have anything other than a solid pulley.

Mitsubishi (or Ford or Nissan or Toyota or Chevrolet or Dodge or any other OEM) would NEVER install a $30 dampener when a $2 pulley would do. NEVER.

And none of the world's race car engines would have a dampener unless it were absolutely required. Especially not when theirs go for $1000 plus each.

As for "indisputable" evidence, just read the papers. You could start with the failures of the ABC Motors Co. "Dragonfly" engine sold to the British military in 1917. Here's an excerpt:

"Crankshaft torsional vibration has been a problem with
aircraft engines since before World War I.
Crankshaft torsional vibration happens because each
power stroke tends to slightly twist the shaft. When
the power stroke subsides, the crankshaft untwists.
One would think that something as massive as a
crankshaft would not twist significantly, but any piece
of metal always deflects a bit when a force is applied,
and when large amounts of power are generated, the
forces can become huge indeed. The effects of
torsional vibration can be amplified by a phenomenon
called torsional resonance. Each crankshaft design
has a natural torsional frequency like the note of a
ringing bell or sound of a vibrating guitar string. If this
natural frequency coincides with the torsional
frequency of the crankshaft, the effects can be
devastating, resulting in broken crankshafts, lost
propeller blades, sheared accessories, and stripped
gear trains.
One of the first major scandals in British aviation
began in April of 1917 and involved torsional
vibration. Granville Bradshaw, chief designer of ABC
Motors, Ltd., secured a production contract from the
British Air Board for a new engine, the Dragonfly.
Bradshaw was a better salesman than engine
designer. The Dragonfly had not even run at the time
it was procured. When it did run, it was a miserable
failure because Bradshaw had managed to design its
crankshaft with a resonance exactly in the operating
range. By the time the contract was cancelled, 1147
of the engines had been built. This episode upset
British air-cooled engine development for years."

Just my 1.5 cents worth.

You will not feel a solid pulley. Some people don't think the negative effects are substantial, while others wouldn't be caught dead without the OEM dampener.

I've yet to find indisputable evidence that proves solid pulleys will destroy cranks, so until I do I'm not going to bother swapping mine out.

[i3igpete]

in my field of work (crankshaft and camshaft dynamics analysis) its not even a question of whether to use one. I can personally say I've designed dampers on everything from indian 1 cylinder scooters, to earnhardt-childress racing engines, to cummins locomotive diesels, to wartsila monsters. As in, I have the models, the test cell crank twist data, and a few prototypes on my desk.

but armchair experts will be just that.

[Zaroth]

in my field of work (crankshaft and camshaft dynamics analysis) its not even a question of whether to use one. I can personally say I've designed dampers on everything from indian 1 cylinder scooters, to earnhardt-childress racing engines, to cummins locomotive diesels, to wartsila monsters. As in, I have the models, the test cell crank twist data, and a few prototypes on my desk.

but armchair experts will be just that.

You are certainly the best person to comment in a thread like this. What will be the negative side effects of a solid pulley on an engine like ours with forged cranks. Will it eventually shatter the crank or just deform it maybe?

[BaadVR4]

And why in the world would you say "I'll swap back to OEM after I shatter a crank."? Maybe your engine will be the "one" that survives for xyz cycles without breaking anything. Maybe it won't. It's kind of like saying "I have lived in my house for 10 years. It hasn't flooded, so if my house floods, I'll get flood insurance". Too late.

The anecdotal fact of any given engine making X amount of HP surviving Y length of time does not change the fact that crankshaft torsional vibration exists, it is hazardous to engine longevity and there are numerous ways to minimize (if not eliminate) the potential for damage. There are solutions other than OEM dampeners. And OEM dampeners were designed for OEM parameters, not the parameters of a 700 AWHP behemoth at 35psi boost.

To those of you who claim there is no benefit to a properly designed dampener and/or no risk in a solid pulley, I ask: Why did you replace OEM internals with lighter/stronger aftermarket products? How much will it cost to rebuild your 700 (or 500 or 400) AWHP engine?

The potential damage from torsional vibration (and the solutions to prevent it) have been known since before WW1. There is no new science. No new balancing technology or material breakthrough to magically eliminate the problem.

I readily agree there are numerous types/brands of dampeners available, and the merits (or lack thereof) can be argued in order to determine the optimum device for any particular application. I will even agree that there are a multitude of small engines manufactured without dampeners. None of them are turbocharged automotive OEM engines.

Here you have the statement of a man who makes his living providing analysis and solutions for this exact problem. Would you say his education, experience and solutions are wasted and useless because he is solving a problem you know doesn't exist because it hasn't happened to you/your engine? Yet?

Just my 1.5 cents worth.

in my field of work (crankshaft and camshaft dynamics analysis) its not even a question of whether to use one. I can personally say I've designed dampers on everything from indian 1 cylinder scooters, to earnhardt-childress racing engines, to cummins locomotive diesels, to wartsila monsters. As in, I have the models, the test cell crank twist data, and a few prototypes on my desk.

but armchair experts will be just that.

[n2nsanity]

Wow, little too much info here. I have a generic udp (got from someone else for cheap) and I'd swear it is somehow causing my belt and other pulleys to chirp and squeal. Before reading this last page, I was already planning on testing with the oem pulley back on to see if that helped. Now, I'm just going put the oem back on and leave it.

BaadVR4, just out of curiousity, what's this about aftermarket dampers? Don't believe I've seen or heard of them before.

Also, when you have a block from one car, heads from another, and crank from another, which pulley should you use? The one that matches the crank? Is any oem pulley enough? Do you need a custom damper at this point?