User Tag List

+ Reply to Thread
Results 1 to 16 of 16

Thread: crankshaft knife edging

  1. #1
    Spanner Monkey

    Join Date
    Dec 2011
    Location
    Cowdenbeath
    Age
    40
    Posts
    400
    Thanks
    32
    Thanked 17 Times in 16 Posts

    crankshaft knife edging

    as per title what are peoples views on this

  2. #2
    Racer Decade Plus User

    Join Date
    May 2012
    Location
    Camberley, Surrey
    Posts
    3,233
    Thanks
    5
    Thanked 353 Times in 339 Posts

    Re: crankshaft knife edging

    A lot of money for questionable / measurable returns. If you are turning large rpm in a wet sump engine with big budget.............buy a dry sump kit and vac. pump first!

  3. #3
    Mechanic

    Join Date
    May 2007
    Location
    Belgium
    Posts
    762
    Thanks
    45
    Thanked 36 Times in 36 Posts

    Re: crankshaft knife edging

    Less rotating mass, if balanced right should revv up quicker, for most engines not worth the hassle I guess ?

  4. #4
    Racer Decade Plus User

    Join Date
    Mar 2012
    Location
    Belgium
    Age
    56
    Posts
    2,118
    Thanks
    7
    Thanked 197 Times in 169 Posts

    Re: crankshaft knife edging

    I always like the idea of less mass, faster rotation, more power, quicker throttle response etc.. But if I take a Honda crank the next day I can only see they fitted a very heavy crankshaft in the S2000 (running 9K standard). They also fitted a much more heavy crankshaft in there "high power" version of the K24 engine compared to the standard (lower powered) K24 version. I once had the chance to open a Toyota (TTE) race engine. Build up with an endless budget and found again ....... a serious heavy, not sporty looking crankshaft.

    It makes me wonder all this mass lowering processes do add more power? Maybe opposite is true??? Maybe it's better to have a nice and balanced crankshaft instead of a super light vibrating piece of steel ? Maybe it's better to leave it all alone?

  5. The Following 2 Users Say Thank You to Dyno For This Useful Post:


  6. #5
    Racer Decade Plus User

    Join Date
    Jan 2008
    Location
    Up the garage
    Age
    43
    Posts
    2,775
    Thanks
    218
    Thanked 179 Times in 172 Posts

    Re: crankshaft knife edging

    I read of an engine tuner who welded weights onto cranks to make them heavier. Competitors always ridiculed his methods but he claimed that his engines were race winners and that his reason for making cranks heavier was that it helped with torque and throttle response in corners, much like a heavy flywheel.

  7. #6
    Spanner Monkey

    Join Date
    Dec 2011
    Location
    Cowdenbeath
    Age
    40
    Posts
    400
    Thanks
    32
    Thanked 17 Times in 16 Posts

    Re: crankshaft knife edging

    I would have thought the greatest advantage would be windage as the crank cuts through the air/oil mist. not the weight removal as lighter flywheel would have the same effect ?

  8. #7
    Bodger

    Join Date
    Oct 2013
    Location
    Suffolk
    Age
    47
    Posts
    194
    Thanks
    0
    Thanked 14 Times in 14 Posts

    Re: crankshaft knife edging

    The crank needs to well balanced for high revving engines
    It has little to do with weight when going for big revs
    The weight in the crank will help it hold momentum
    Like drag cars with there heavy fly wheels
    It won't add power but aid it's delivery in certain circumstances

    A lighter one will help revs be achieved quickly
    But the revs will return back to idle faster to due to less momentum mass
    Which is not the best if you car is heavy

    A good jap bike has lighter this and lighter that
    And revs very quick but a bikes weight is very little in relation to a car
    Hence why they say a bike engine kit car ain't to great unless
    It's mega light

    Knife edging on its own is a bonus
    Add strength by removing potential crack points
    Cut the oil = less drag = lower oil temps = less air reation
    = better oil return to pan = better oil pressure


    As always it really depends on the use

    I have lightened/balanced/knifed cranks in my pinto turbo
    My cosworth and I even had one in my gsxr 750

    Also they almost look to good to hind away inside a engine

  9. #8
    Spanner Monkey

    Join Date
    Oct 2008
    Location
    italy
    Age
    56
    Posts
    471
    Thanks
    21
    Thanked 40 Times in 38 Posts

    Re: crankshaft knife edging

    all perfect and I add also that it depends on the number of cylinders.

    The higher the number of cylinders, the lightest you can go
    The closer the gearbox ratios...the stroke of the engine...there are many variables
    I don't see really a must to have a knife edged crank.
    If I'm right I remember that Dave Walker wrote that he had gain on a Pinto (or was a xflow?) keeping the oil level at minimun and he presumed it was due to less drag on the crank.

  10. #9
    Racer Decade Plus User

    Join Date
    Mar 2012
    Location
    Belgium
    Age
    56
    Posts
    2,118
    Thanks
    7
    Thanked 197 Times in 169 Posts

    Re: crankshaft knife edging

    Quote Originally Posted by Turboman View Post
    I would have thought the greatest advantage would be windage as the crank cuts through the air/oil mist. not the weight removal as lighter flywheel would have the same effect ?
    I would be very pleased I would own a dyno who can measure the difference in power when you crank is cutting the oil mist or not. I'm willing to understand it is better to "cut" through the oil mist to prevent it from splashing it to the pistons and sending the oil rings more work. But even here I would like to see the difference. More like zero to nothing. Maybe an oil winding plate ? The "cutting" by itself should be not possible to measure.

    Anyway, I always try to put my energy and budget in the most "economic" way of making more power. This would not be my first option.

  11. #10
    Racer Decade Plus User

    Join Date
    Mar 2012
    Location
    Belgium
    Age
    56
    Posts
    2,118
    Thanks
    7
    Thanked 197 Times in 169 Posts

    Re: crankshaft knife edging

    In my opinion it is best to have a crank build up as heavy as needed for best balance. Less stress in the crank and block. If you need less rotating mass, reduce the flywheel.

    BUT, I can be totally wrong !!!! I have no prove at all.

  12. #11
    Racer Decade Plus User

    Join Date
    May 2012
    Location
    Camberley, Surrey
    Posts
    3,233
    Thanks
    5
    Thanked 353 Times in 339 Posts

    Re: crankshaft knife edging

    Its probably more along the lines of 'it LOOKS like it should work, it does no harm so why not' rather than having empirical evidence to support the theory.

  13. #12
    World Champion Decade Plus User alladdin's Avatar

    My 1st Project
    My 2nd Project
    Join Date
    May 2005
    Location
    s.wales
    Age
    60
    Posts
    9,200
    Thanks
    167
    Thanked 446 Times in 432 Posts

    crankshaft knife edging

    And shining parts sell 👍


    Sent from my iPhone using Tapatalk

  14. #13
    TURBOSPORT SPONSOR Turbosport Subscriber
    Turbosport Moderator
    Turbosport Administrator
    Graham's Avatar
    My Race Car
    My 1st Project
    Join Date
    Feb 2006
    Location
    Ely, Cambs
    Age
    56
    Posts
    25,099
    Thanks
    310
    Thanked 2,476 Times in 2,250 Posts

    Re: crankshaft knife edging

    Quote Originally Posted by alladdin View Post
    And shining parts sell ��


    Sent from my iPhone using Tapatalk
    oh yes dont they, ive got one engine here i built for a customer, it has loads of blingy really high spec parts in which which were really really not needed, all they have done it greatly contribute to emptying his wallet,

    BUT THEY LOOK GOOD

  15. #14
    Spanner Monkey

    Join Date
    Dec 2011
    Location
    Cowdenbeath
    Age
    40
    Posts
    400
    Thanks
    32
    Thanked 17 Times in 16 Posts

    Re: crankshaft knife edging

    This isn't something I am planning on doing but just wondered what others thoughts were on the subject. I remember a thread where Jason rwd fords said he had tested back to back and crank scrapers, and had shown a increase so wondered if anyone had proof this worked

    Thanks for replys

  16. #15
    Racer Decade Plus User

    Join Date
    Mar 2012
    Location
    Belgium
    Age
    56
    Posts
    2,118
    Thanks
    7
    Thanked 197 Times in 169 Posts

    Re: crankshaft knife edging

    Despite I've never tested myself, I believe more in crank scrapers as knife edging crankshafts. Not because of the knife edge, more about the lost of balance weight. The crank scraper, if it does not help it will not harm. Not the same for the knife edging.

  17. #16
    Racer Decade Plus User Forest_rallying's Avatar

    Join Date
    Feb 2013
    Location
    Derbyshire
    Posts
    2,438
    Thanks
    92
    Thanked 393 Times in 348 Posts

    Re: crankshaft knife edging

    We have had Holbay, Farndon and an early 84mm Millington Diamond twin web cranks in EN40 in our NA Cosworth engines over the years and not one of them was knife edged.

    We Rallied an Escort Cosworth GP A Turbo in the mid 2000s fitted with a Mountune spec engine which was fitted with a Std Cosworth crank which was knife edged.

  18. The Following User Says Thank You to Forest_rallying For This Useful Post:


+ Reply to Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts