OBX Overdrive Pulleys. Yay or Nay?

[chefma70]

ive heard of lots of horror stories with aluminum pulleys esp like mentioned earlyier on long crank engines , but w/ that in mind ive also read that the 7m is a fairly well ballanced ,because of the way the cylinders are staggered in 3 pairs. i personaly have been runing a UR underdrive for 5 yrs and havn't had any problems ...........also i pulled this off of wiki hpe it helps ............... in inline six engine is in perfect primary and secondary mechanical balance, which can be achieved without using a balance shaft. The engine is in primary balance because the front and rear trio of cylinders are mirror images, and the pistons move in pairs. That is, piston #1 balances #6, #2 balances #5, and #3 balances #4, largely eliminating the polar rocking motion that would otherwise result. Secondary imbalance is avoided because an inline six cylinder crankshaft has six crank throws arranged in three planes offset at 120 degrees. The result is that differences in piston speed at any given point in rotation are effectively canceled.

wow..........please tell me that supra in your sig isint the one your torturing.....and my professor said anyone who uses wiki answers for thier research instantly gets a ZERO on thier report. Wiki can be change by anyone anytime and is the worlds most unreliable source of information. Anyone that says the words "my mechanic",i instantly dont listen to a word they have to say. Your suppostu be the mechanic and especially if you own a oldschool supra.this room smells like my cats litterbox

oem crank pully ftw!

 

[gofastgeorge]

Don't worry chefma70,
87tomanymods also has a thread started about making an electric turbocharger...........

http://www.supramania.com/forums/showthread.php?t=103443

 

[IJ.]

I hate to lay down some more poo, and I'm not trying to go against the theory of harmonic vibrations but I too ran an Unorthodox Crank pulley for roughly four years. The car was my daily driver and I did about 17K miles per year at the time.
My engine did finally let go, but due to the ringlands on #1 cylinder shattering. I missed a gear and overevved in third while making a pass. Now if a lightend crank pulley would cause that then that is what it was.
When I tore down the engine the rod and main bearings looked normal except for the metal shavings that scored them when the piston broke. I do have pics to show, but I"m not at my computer right now.
I didn't know then the dangers of running that kind of crank pulley back then. Now that I do I'm not doing it again. I'm going back to a stocker.
So, there's my contribution to spewing BS.

Care to explain how the above happened?

Been sitting here watching this TrainWreck in the making for a few days here...

It's NOT VIBRATION Harmonic or otherwise that the Damper is primarily trying to control.

You drive the car from the flywheel end of the crank, as each Cylinder fires it's trying to twist the crank and this deflection/windup/twist (steel is elastic) can be violent if left uncontrolled (no damper)

In high output engines the BANG is bigger therefore so is the deflection/twist, this is why ATI list their off the shelf Damper to xxxrwhp then spec a bigger diameter custom one for higher HP.

Think of the Damper as a Shocker for the Crank nothing more.