<ul><li><a href="http://dinancars.com/whitepapersFile.asp?ID=5">Check it out...</a></li></ul>

I believe the pulley on the 1.8T is just a solid piece of metal - no rubber damper involved.

I'd surmise the engineering bore in mind material composition along with the mass of the pulley.

Correct - but its still just a metal pulley. I have mine sitting next to me after putting on the ECS UDP - its just a hunk of metal. There is no rubber to act as a harmonic balancer.

The mass of the flywheel serves as a damper on that end of the crank. Lightening the mass at the front end will result in less dampening at that end.
Whether that is a real issue on the 1.8t I can't say but I do note that when a light weight pully is used with a LWFW, steady idle (especially with the A/C compressor running) is a distant memory.

That is simply not correct:

My idle is completley steady running a 15lbs LWFW and a UDP.

LucasGChips has the same setup and his idle is likewise rock solid - as is AXE's with the same set-up. (as do others).

In fact the UDP with the LWFW seems to run a lot better than just a LWFW - its more balanced.

If you run a LWFW with a stock pulley your unbalancing things a lot more - period.

Further to this: I did over 100kms city driving today in 37 degree celsius heat with the A/C on the whole time - and perfect idle.

...the different weight of a manual flywheel or an automatic adapter plate. Also, there's atill going to be a dampening (stabilizing) effect because of the loading of the rubber belt driving the alternator, A/C, P/S, etc. While the ETKA does call it a "vibration damper", there is only one part number for manual, auto, and with or without A/C. However, the 3.0L looks to be a different technology for the larger displacement engine. Perhaps the inline, four-cylinder 1.8T, which also doesn't need the counter-rotating balance shaft of the 2.0L, doesn't need the traditional harmonic balancer either.

Per the Bosch Automotive Handbook, 5th edition, page 407: "Vibration dampers are required to reduce the crankshaft's torsional vibrations to acceptable levels (e.g. bonded rubber vibration dampers or viscous vibration dampers)." The stock 1.8T doesn't have either so it's not a critical element. The V6, on the other hand, has much different torsional forces. Again, Bosch says, "the torsional vibrations of the resonant system...become increasingly critical with higher numbers of cylinders." This, along with the movements associated with V6 engines (page 403), and that end pulley is far more critical.

Bottomline: feel free to lighten that pulley on the 1.8T (keep the same diameter) but don't mess with the V6.

The link will show you the extremes VW/Audi will go to to resolve this problem.<ul><li><a href="http://www.sae.org/automag/techbriefs/11-2003/1-111-11-29.pdf">See last page for ICD</a></li></ul>

058 105 251 D without A/C
058 105 251 E for with A/C

Along with a different crank there is a different damper for the AWM. Could one even get an AWM in the US without A/C?
The 2.7t and 2.8 both call for a single damper part number and make no distinction between automatic or manual.

Bottomline . .feel free to run a lightweight pulley but expect decreased dampening on that end of the crank and expect to have no idle if you are also running a LWFW<ul><li><a href="http://www.impexfap.com/partlist.cfm?getpart=43529&amp;43528&amp;70949&amp;43528&amp;43529 &amp;75381&amp;PARTNUMBERSEARCH=058105251#part43529">Apparrently VAG is very proud of this damper</a></li></ul>

Folks who've cited issues with idle were running lighter wheels than 15lbs. IIRC ~12 lbs.
It simply is true :) that mass is effective as a damper. The mass of the flywheel performs a dampening function on that end of the crank. The farther from the flywheel the greater the effects of torsional 'vibration'.

See the comments from Mat in your previous thread on this subject. His comments echo those of other folks who added a lightweight pulley to a 12 lb LWFT set up.<ul><li><a href="http://forums.audiworld.com/performance/msgs/71074.phtml">http://forums.audiworld.com/performance/msgs/71074.phtml</a</li></ul>

I cant speak to the effects of running a UDP with a 12lbs. LWFW - but I now know from experience(and the experience of LucasGChips, AXE and others) that there is NO issue with a 15 lbs. flywheel.

As I said - mt idle is ROCK SOLID - even with AC on. And LucasGChips and AXE have the same setup as me and likewise have no issues.

Perhaps the 12lbs. flywheel is that little bit too light - that idle stability becomes an issue?

Running a 15lbs. LWFW and UDP is great - car revs freely, feels great and is easily St. driveable. Personally, I cant see the need to go lighter to 12lbs. I know a couple of ppl who have had 12 lbs. and found it too light.

What? NO comments about the Bosch literature? The engineers have already spoken for the new 1.8T. You need to stop being so old school. :)

wheel did but it is fine. As Mat indicated .. it is likely the combination of total dropped mass that gives idle issues.

e.g., . .. means exempli gratia "for example" .. and it is not enclusive. Had the intent been meant to provide exclusivity it would have been i.e., id est ... means that is, that is to say, or in other words.
I am really not old school . . well I am old ... I just think it is a bad idea to take dampening mass from both ends of the crank.

...there was any kind of rubber boundary layer involved, more than four cylinders, or much higher displacement. However, even Porsche has removed most of the weight in the new 3.8L 911 engine front pulley (aka vibration damper):

"Higher combustion forces produce more power but also more torsional crankshaft vibration, so Porsche engineers have integrated a vibration damper in the pulley at the end of the crankshaft. Conventional vibration dampers are made of cast iron but Porsche engineers devised an aluminum damper that reduces weight by some 3.3 pounds (1.5 kg) while controlling vibrations to a level even lower than the 3.6-liter engine."

Unfortunately, it doesn't specify if it's solid aluminum or still uses rubber. More significantly it upholds the conclusion that dampening is not merely a function of weight. In the case of the 1.8T there has been progressive changes in design in line with Bosch's research since 2000. The pulley now plays a much less critical part in vibration damping, if any, and the name still applied to it might be viewed more as a legacy designation that an actual statement of current functionality.

this kind of tells me it has some kind of counter weight effect. ie heavier on one side then the other. the light weight pulley probibly lacks this feature.

I know mass and weight are technically different but we're not talking about astrophysics here. It's an item on the near surface of the earth with a gravitational constant affecting the planet. It's been shown that weight (and, hence, mass) is not the essential factor for an inline, 4 cylinder, under 2L engine. Heck, Porsche showed it wasn't even about a larger, 6 cylinder, high HP engine when they shaved all the weight off theirs. Bottomline, at least for the 1.8T (and not other Audi engines): Light &lt;&gt; bad.

Are u saying that light is bad? or that light is not bad for the 1.8T?

What I find amazing is that most of the ppl here spouting advice either a: Dont have one on their car or have never tried one and b: Use examples of non Audi engines as the basis for their arguements.

We are not discussing BMW's inline 6 or Porsches Boxster 6 - both of which are totally different engine configurations to the inline 4 pot 1.8T Audi engine. So any comparisons to these engines is completley IRRELIVENT.

I am still waiting for someone to explain to me why neither myself, LucasGChips or AXE (all of whom run UDP's with 15 lbs. LWFW) have NO idle problems (even with AC on) and no other problems at all to speak of with this combination. In fact, all 3 of us agree that car is more balanced with this combination. Its common logic.

If you lighten the flywheel you are unbalancing the crank. Easiest way to bring it back into balance is lighten the other end - i.e. the Pulley. We are not talking scientific balancing to the gram - just closer to balanced than it would otherwise be.

The oscillatory harmonics and balancing in an inline four are very different from V6 or inline six engines. That's why I differentiate them from the 1.8T. All taken together light weight pulleys are not bad for the 1.8T (the &lt;&gt; symbol is equivalent to NOT EQUAL) as you've proven in actual usage. Further, no one is taking into consideration the dampening effect of the rubber drive belt and the constant pull it exerts in one direction on the pulley.

<A HREF="http://www.e31.net/engines_e.html">Engine Vibrations</a> and <A HREF="http://www.eng-tips.com/viewthread.cfm?qid=107602&page=1">Eng-Tips.com Thread</a>