Crank pulley

[Gismo R]

I've heard that aftermarket underdrive crank pulley are not very good for our cars due to balancing of the crank. But I'v also heard that they are good mods and free up a little power. I'm just wondering if getting an aftermarket crank pulley is worth the possible(?) risk or not.
Thanks

[William]

My opinion is that is should be one of the last things you should do when modding your car.  I'll eventually have one for my SR20.  Mike Kojima (contributing writer for scc) thinks and UD pulley on an SR20 is not something to be concerned about.  On a KA24 I don't know.  It is only half-counterweighted compared to an SR crank which is full counterweighted.  You will here people swear by their UD pulley's and people who swear at them.

[Jeff240sx]

Im one that swears at them!  Our Ka is a stroker motor, and there is such a long stroke an a ton of pressure at the combustion chamber, and our crank will wobble.  If you take the harmonic balancer (attached to the crank pulley) off, bad things will eventually happen.

Other guy:  How sure are you SR20 cranks are fully counterweighted?  That would add a ton of weight to the crank, a reciprocating part, and drag down the redline.  I thin they are half counterweighted also... but not 100% sure.

-Jeff

[sykikchimp]

It doesn't matter if they are counterweighted or not, b/c the underdrive pulley's for the SR can accomodate the harmonic balancer.  Besides thats NOT what he was asking about.

Techincally there is a certain amount of strain created on the engine by having a lightweight pully that can't accomodate the damper.  With out the damper you will have more crank flex.  I haven't seen anyone yet say their engine blew up due to their pully or that they have found adverse effects to them.  Of course that doesn't mean that it didn't have some underlying effect, but then again ANYTHING cuold have an underlying effect.  
The only thing I would recommend if you get one is to replace the front crank seal while you are there.  Its cheap and relatively easy since your gonna have the pully off anyway.  Check the back crank seal as well, just to make sure near are leaking or cracked.  These are probably gonna be the most likely place that something will break and cause damage (which will be because of a loss of oil coming out of the seal, and slung all over your motor from the pully)

The correct way to lower reciprocating mass around the Crank (without actually doing work on the crank) is to get a lightweight FlyWheel.

[240sxtreme]

there are people who have had the underdrive pulley's for over 20-30-40k miles.  I've had mine on for more then 10k now.  

and a flywheel...well, if you want to get nitpicky, a flywheel could be seen as a negative due to the fact that on stock gearing, you could go below your powerband when shifting.

I've got both of them. &nbsp;If and when I blow my engine, I'll let you know &nbsp;<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt=':D'>

[AceInHole]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (Jeff240sx @ April 04 2002,01:34)</td></tr><tr><td id="QUOTE">How sure are you SR20 cranks are fully counterweighted? That would add a ton of weight to the crank, a reciprocating part, and drag down the redline. I thin they are half counterweighted also... but not 100% sure.</td></tr></table><span id='postcolor'>
if i'm remembering correctly, the SR crank is fully counterweighted (going to not even look for the pic of it... i'm just really sure). &nbsp;

Fully counterweighting the crank adds weight, but that weight is near the rotational axis, so it won't amount to much (in comparison to the drivetrain itself). &nbsp;the effect of a fully counterweighted crank vs. a half counterweighted crank is less harmonic disturbance, less crank "snaking", and ultimately strength/ balance to rev higher.