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Old 11-07-2011, 08:25 AM   #1
afaccord
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Default K20 Rods in F23 Block?

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 by afaccord; 11-07-2011 at 08:27 AM.
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Old 11-08-2011, 07:20 AM   #2
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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?
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Old 11-08-2011, 07:33 AM   #3
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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.
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Old 11-08-2011, 08:33 AM   #4
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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?
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Old 12-07-2011, 12:09 AM   #5
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bisimoto makes f23 rods now..
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Old 12-07-2011, 05:50 AM   #6
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Originally Posted by LA PRESION View Post
bisimoto makes f23 rods now..
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 by afaccord; 12-07-2011 at 05:52 AM.
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Old 12-07-2011, 09:09 PM   #7
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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?
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Old 12-07-2011, 09:16 PM   #8
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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
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Old 12-07-2011, 09:46 PM   #9
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Originally Posted by afaccord View Post
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
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
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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