Redblock crank pulley weight comparison

jamesincJames (@jamesinc) Oz Volvo Ice Fortress
in Articles & Guides 7441 / 409joined Jul 2013
Starting this off, here is a B21/23 3-belt pulley, coming in at 1910g. Made of steel, third pulley V can be removed. Note a lot of the mass is up around the belt track.

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Here is a KL Racing 3-belt underdrive alloy pulley. The mass is less than half, and the smaller diameter means that mass takes less energy to accelerate.

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bgpzfm142240Joe

Comments

  • 174 / 18joined Feb 2016
    Awesome stuff, thanks for the info
  • Vee_QueVee_Que (@Vee_Que) South Eastern suburbs Melbourne.
    7336 / 36joined Jul 2013
    The underdrive means your alternator and water pump don't run at the right speed if the car is a daily driver.
  • 320 / 14joined Jan 2015
    Dampener + mass is a friend of your crank on stock internals.
    Vee_Que
  • jamesincJames (@jamesinc) Oz Volvo Ice Fortress
    7441 / 409joined Jul 2013
    Keep in mind this is a weight comparison thread
    Ghettobird
  • Angus242164Angus (@Angus242164) Western Victoria
    1495 / 50joined Jul 2013
    The original pulley isn't a dampener/harmonic balancer in this case, the B21 and B23 had the type pictured which is a steel centre hub with pressed steel pulley plates bolted to it.

    The centre hub does seem to have more mass than is required for it to act simply as a belt pulley. Then again, maybe Volvo engineers didn't know how to design things any differently. A 240 door weighs twice as much as one from a Datsun.

    It's a clever design, allowing the same centre hub to be used with single, twin or triple groove pulleys depending on the accessory belt drive arrangement.

    B230's have a harmonic balancer made from two cast iron pieces with a layer of bonded rubber between them.
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  • edited October 16 320 / 14joined Jan 2015
    The original pulley isn't a dampener/harmonic balancer in this case, the B21 and B23 had the type pictured which is a steel centre hub with pressed steel pulley plates bolted to it.

    They also use a forged crank with larger journals and fewer counter weights that can take the torsional flex caused by power strokes. And why would Volvo change it when they revised the redblock? It certainly wasn't cheaper. Not saying it would lead to crank failure on the cast (less flexible) B230 crank, but on a 4cyl that you may want to rev, the engine will be alot more happy with the torsional vibration dampening than it would be with a kg less to spin up imo.

    In theory.

    In reality, she'll be roight :p

    Also I thought that was a B230 crank pulley pictured, my mistake. As you were.
    Vee_Que
  • 174 / 18joined Feb 2016
    so what exactly would be the benefits and drawbacks of a lighter weight+smaller pulley? I was thinking of getting one for my NA b230f
  • Angus242164Angus (@Angus242164) Western Victoria
    1495 / 50joined Jul 2013
    With the B230 they went to lighter rods, smaller bearing surface area, harmonic balancer, and after a year or so, a heavier flywheel.

    I think they were chasing a smoother engine, and probably a fuel economy improvement.
    Samman88
  • jamesincJames (@jamesinc) Oz Volvo Ice Fortress
    7441 / 409joined Jul 2013
    so what exactly would be the benefits and drawbacks of a lighter weight+smaller pulley? I was thinking of getting one for my NA b230f

    I'm not an expert on the importance of the damper in the B230 pulley, but looking around online it seems there's a large number of people using lightened pulleys with no damper, and having no noticeable running or longevity issues. The damper is designed to absorb harmonic resonance at particular RPMs, and it's commonly asserted that unless you're using a boat or some application where you set the RPM and leave it there for long periods of time, the damper is probably not that important.

    In terms of mass, you want all the rotating components to have as little inertia as possible (with exception of the flywheel where you want some mass to make the engine transmit power smoothly to the transmission).

    The moment of inertia of any component in the rotating assembly is a function of its mass and the distance from the centreline of rotation, so mass further away from the centreline requires more torque than mass near the centreline. Thus, reducing moment of inertia reduces the energy needed to accelerate the crankshaft.

    The other changes would be a reduction in work done turning the coolant pump and alternator, which would mean more power going to the transmission. You might need to tweak your alternator and thermostat to compensate for those changes.
  • Vee_QueVee_Que (@Vee_Que) South Eastern suburbs Melbourne.
    7336 / 36joined Jul 2013
    The lightened flywheel you're going to run will be pretty good already @Klaptrap24
  • bgpzfm142bgpzfm142 (@bgpzfm142) near Katoomba NSW
    2240 / 132joined Feb 2014
    I was reading somewhere online that the change from B23 to the fist iteration of B230 (with centre thrust, piddly little main and big end bearings, floating gudgeon pins, and horrible rods) made the reciprocating assembly weaker, and the engines would not live long beyond 7400 RPM or so without a great big fat old heavy damper on the end of the crank.

    Now, as we all know, the revised rear thrust B230 with the bigger rods, etc, is quite a different beast. The Penta cranks were forged but the car engines' cranks were still cast, however the weakest of them was still stronger that the earlier failed 'low friction engine' experiment of YM 84-87. Even so, by the time of the L block, the H rods, etc, made the whole engine a lot stronger, yet the fitment of the heavy crank pulley persisted.

    An underdrive pulley is going to be very useful in applications which see sustained high RPM usage - i.e. track cars. They're going to be pretty ordinary for daily driver duty because you're not going to be using 4500 to 7000 RPM for sustained periods going to and from the Coles car park - well, not unless it's been a real beach of a day. They will help in slowing your water pump pulley speed down to avoid cavitation of your coolant, and avoid frying your battery from your alternator being revved harder than typical.
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  • serkserk (@serk) Queensland
    68 / 21joined Aug 2015
    ClassicSwede 5 rib underdrive pulley
    V6ejWsJ.jpg
  • 174 / 18joined Feb 2016
    ClassicSwede 5 rib underdrive pulley
    V6ejWsJ.jpg

    300g lighter than the KL Racing one...what kind of application would the ClassicSwede one suit?
  • jamesincJames (@jamesinc) Oz Volvo Ice Fortress
    edited October 28 7441 / 409joined Jul 2013
    You'd need to convert your belt setup to serpentine drive

    Edit: the other benefit of a serpentine setup, other than reduced belt drag, is that you have to replace all pulleys - alternator, water pump, p/s, a/c, and presumably you'd replace them with lightweight billet pulleys like the above, so you'd end up shaving a bunch more weight off, probably.

    On the downside I imagine it's hard to make it work nicely. I've never tried, but there's not many posts on the Googles about people doing it.
  • Vee_QueVee_Que (@Vee_Que) South Eastern suburbs Melbourne.
    7336 / 36joined Jul 2013
    It involves adding an idler, probably an 850 one and you'd run an underdrive water pump too.
  • RaebirdRaebird (@Raebird) Springfield Lakes, Qld.
    385 / 17joined Jan 2014
    @jamesinc have you worked out what size belt to use with this?
    360GLT - Soon to be AQ171 powered!
  • jamesincJames (@jamesinc) Oz Volvo Ice Fortress
    7441 / 409joined Jul 2013
    Not yet, it'll get fit sometime before the end of the year
  • RaebirdRaebird (@Raebird) Springfield Lakes, Qld.
    385 / 17joined Jan 2014
    Not yet, it'll get fit sometime before the end of the year

    All good, I have mine fitted to my car now, will just have a guess 😂
  • jamesincJames (@jamesinc) Oz Volvo Ice Fortress
    7441 / 409joined Jul 2013
    Just wrap some rope around and measure it, that's how I'll do it
  • RaebirdRaebird (@Raebird) Springfield Lakes, Qld.
    385 / 17joined Jan 2014
    Yeah that's probably what I'll do.
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