K20 Rods in F23 Block?

Discussion in 'Naturally Aspirated' started by afaccord, Nov 7, 2011.

  1. afaccord

    afaccord Turbo noob

    I'm trying to find an affordable option for forged rods for the F23. It's been well established that K20 pistons can be a direct swap, but what about the rods?

    Here are the specs for both Crower's K20 and F23 rods:

    Part #.........Engine.......Length.......BE bore......BE width.......PE bore........PE width
    B93749B-4.....F23..........5.551........1.890.........0.780........0.866(22mm)... 0.780

    B93733B-4....K20A3.......5.453........1.890..........0.780.......0.866(22mm)... 0.780

    As you can see, the only difference is in length. The K20 rod is .098" or 2mm shorter than the F23 rod.

    I'm trying to answer two primary questions.

    1. Would the shorter K20 rods have the necessary vertical clearance in the F23 block, primarily at the bottom of the stroke?

    2. Somewhat unrelated, what is the correct way to calculate the compression of pistons rated 9:1 for the K20, when installed in an F23 block?

    I've been playing around with Zeal's compression calculator. Even if I tried to use the K20a3 forged pistons at 9:1, that wouldn't give me a 9:1 ratio with the F23 block and head, correct?

    The shorter length of the K20 rod in the F23 block would drop compression down considerably, right? The stock K20a3 piston @ 9.8:1 should have a -2.5cc dome from what I'm reading, while the off-the-shelf wiseco's for the K @ 9:1 should have a -8.3cc dome according to the calculator. Now if I used the K20a3 rod in the F23 block with the stock F23 piston, my compression would drop down to ~8.14, which I assume would be way too low to be practical on a street car. However, with the off-the-shelf Wiseco K20 piston at -8.3cc (per my calculation), compression would be up to ~8.69, correct? At this point, couldn't the head or block be safely milled or decked around 20-thousandths to bring compression up to almost an even 9:1, or where ever I wanted it to be?

    This doesn't take into account that the F23 combustion chamber is .5cc down from the K20's. Are there any obvious flaws or drawbacks to my logic? Is it possible to use the shorter rods with this block? I'm by no means an engine expert or machinist, so just slap me if I'm wrong, but please elaborate as to WHY this wouldn't work.
    Last edited: Nov 7, 2011
  2. afaccord

    afaccord Turbo noob

    From what I've read, using the shorter rods naturally increases side-load stresses on the cylinder walls, leading to ovaling of the cylinders and eventual loss of compression since the rings cannot seal a non-circular cylinder. That being said, this information was presented in the context of V8 engines using rods over 5% shorter than stock, while the difference between the K20a3 rod and F23 rod is only 1.4%. Is this really enough to cause concern?
  3. The_Beave

    The_Beave The Red Tape Avenger

    No. Look at the D-series engine. You have a 1.52 ratio on the D16s, and they can run fine for hundreds of thousands of miles stock. Even with a serious increase in power, they can take the abuse, as long as the tolerances are correctly selected to allow for things to do what they need to do.
  4. afaccord

    afaccord Turbo noob

    Cool. So, provided there's enough room at the bottom of the cylinder for the piston to come down on the shorter rod, there's no other foreseeable reason why this wouldn't work?

    LA PRESION New Member

    bisimoto makes f23 rods now..;)
  6. afaccord

    afaccord Turbo noob

    About a week too late. I purchased some Crowers and Wisecos... I even called and spoke to Julio just a few days before they announce this, but he never mentioned it. :thumbs down:
    Last edited: Dec 7, 2011

    LA PRESION New Member

    funny thing i called today for them and they told me it was only a limited time sale -_- lol..
    can you give me the price on the rods my buddy is building a f23 just looking for rods rite now, do you have a build thread?
  8. afaccord

    afaccord Turbo noob

    Build Thread

    There's no official page yet. Found a link on their Facebook page about half way down...

    "The long awaited F23 Bisimoto custom steel Long H-Beam rod with Custom
    forged piston with your choice of compression ratio and bore size!

    Combo for a limited time only $849!

    Upgraded wrist pins for 20+psi or high rpm NA setups +$40

    Upgrade pistons coatings: Ceramic barrier coatings for the piston crown, and
    moly-based friction reducing coatings for the skirt: 4 cylinders only. Takes 4
    business days to perform, and yields a 4% improvement in power in addition to
    anti-detonation qualities: +$160

    Give us a call at 888-922-6686 or email us at sales@Bisimoto.com

    Bisimoto Long F23 Steel H-beam rods features ARP2000 bolts, proper oiling holes,
    handles up to 800whp with proper tune and supporting parts

    Bisimoto Spec forged pistons are manufactured exclusively by Arias Pistons, with
    compressions ranging from 9:1 to an astonishing 17.0:1. These specialty pistons
    can accommodate up to 3mm oversize valves and strategically lightened to provide
    optimal weight savings without compromising strength intergrity. Gains exceeding
    8% have been documented with this piston technology in comparison to competitor
    shelf units."

    By: Bisimoto Engineering

    LA PRESION New Member

    yeah i seen it on there facebook page but wen i called today i asked the price for the f23 pistons and rods and they told me $1,201 :facepalm:
    but ill check out your f23 build, i'm building a all motor f22a my self with a b-series tranny..

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