Howdy Folks -
Greg sent me an email that the Pulley issue had come up again on the forums, and I'd thought I would add my $0.02.
I have a 94 6-Speed, T04R setup, with all the usual suspects. To make sure I covered every possible upgrade avenue I went with a complete set of Unorthodox Pulleys (uncluding the replacement crank pulley). I chose to go with a TRD Twin Disk setup as part of the buildup, which includes a lightened flywheel. During a dyno session the *pressure plate* came apart - the rivets that hold the assembly together were pulled and twisted, and one actually got ripped out. Of course the normal stress element of a clutch is going to be the friction surfaces, the flywheel and disk so this was pretty odd - we assumed a faulty clutch from Toyota. Round 2: a new clutch, this time a Stage III RPS setup, sprung, with the Mueller lightened flywheel. Again, a few 100 miles put on the car for some break-in - car pulls fine - go to a _different_ dyno - BOOM, same problem - the PRESSURE PLATE comes apart the same way - like someone took the front and back plates and tried to twist them apart like an Oreo cookie!
Now we HAVE to figure that two clutches did not fail to do manufacturing defects in the same way - so we turned to debugging the problem that must have been resulting from the car. At one point we wondered if the motor had enough lost tolerance in the crank/bearings to cause a cavitation/vibration in the clutch assembly to cause the failure. Of course, that could have been a costly (well, premature since I am building a motor
) repair - and who knows, maybe the engine does have slightly out of spec tolerances that contributed to the problem - don't know, it has about 50K miles - but seems to run strong and shows no signs of leakage from the main seals.
OK, so as part of trying to get a solid answer before I dropped $3K on a new small block and installation, I put in a call to Rob Smith at RPS (used to work with Nissan's GTP team, FYI) and to Larry P at Sound Performance - both of who, IMHO, have a pretty established level of expertise in both Supras and drivetrains/clutches. As soon as Rob found out I was running an aftermarket crank pulley (without a harmonic dampener) he ID'ed it as the culprit - said that the combination of a lightened flywheel AND an undampened crank pulley can easily allow for VERY destructive vibrations to enter the crank, clutch (and related parts). He even suggested that I pull and cut open my oil filter to inspect for bearing shavings/particles to confirm no damage was done. Larry concurred about the crank pulley and said he didn't think to ask but was pretty confident that was the problem.
So off comes the Unorthodox crank pulley, on goes a new OEM Toyota part (about $225) my RPS clutch is put back together with a new pressure plate (I also got a new PP for the TRD setup which I'm keeping as a backup). Another few hunred miles are put on the car, and it then survives dozens of dyno pulls (on the original offending dyno!) and is still operating just fine with another 500+ miles, of which the last few hundred have been pretty abusive. I am still running the other pulleys in the kit.
For me, the bottom line is a *minimal* HP increase vs. possible damage to expensive clutch parts and/or (even worse) damage to the bottom end - is 8-10HP worth a $2500 bottom end? Also, when you get to single level, the extra HP is really inconsequential - does 600RWHP vs. 608 really mean anything? Hell, I partially did it for cosmetic reasons, so the performance add was not an issue at all. Grant has already referenced the articles by Rod and at the Dinan site - I tend to put more credibility in independent sources than the manufacturers claims.
Keep in mind: I have a ~650+HP car, with a G-Force ECU that raises the rev limiter to 7800RPM. Also of note, is the damage occured each time on the dyno (though two different models), so there could be something to the harmonics produced on a dyno vs. the street. There are certainly 6-speed owners with the full pulley sets who have not had any problems, but it's really in the specifics - Rob was very confident about the crank pulley, and it was replaced and the problem was solved - so there was *absolutely* something about my setup and the aftermarket pulley.
Hope this helps - this is just my obervations, things I was told by people I consider to have significant expertise about the problem, and the fix that ultimately resolved my problem.
Take care (and good luck to all the pulley users!)
