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[J_Hart]

I'm trying to find other options 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 -8.25cc (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?

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?

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.

[dvst8r]

No porn, no care.

[J_Hart]

Oops! My bad...





It's the best I could do from work.

[crxvtec91]

I'm trying to find other options 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 -8.25cc (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?

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?

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.

Super cheap way to build it, I like

[PhilStubbs]

I hope by "best I could do from work" that means you will step it up when you get home.

This sounds feasible, you could run a super high compression forged K piston to make up for the short rod, then have a fun street turbo motor with decent compression for drive ability.

[J_Hart]

Wiseco offers 9:1 K20's which would take decking and/or milling to keep it from being a limp dick in vacuum, but gives me plenty of flexibility to choose my compression.  CP has flat tops that would put me at 9.6:1 for a few bucks more.  I'm kinda partial to the wiseco's, but I guess it comes down to what ratio my tuner wants to play with... 

[Joseph Davis]

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

Not enough to worry about, run it.

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? 

Zeal's calculator should work fine.  All you need is compression height, dome height, and it all plugs together.

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?

It's presented in the context of V8 engines where any one piston weights three of any Honda.  Side loading is not now, nor has it ever been, a concern of a Honda distributor engine. 

Ever see a cylinder ridge in a V8?  Pretty common.  You almost never see them in Hondas.  No side loading.

[PhilStubbs]

That is true, I have yet to find a ridge in a Honda cylinder. I should be opening up a 300k mile D some time this week though. Maybe it will be my first.

[92CXyD]

That is true, I have yet to find a ridge in a Honda cylinder. I should be opening up a 300k mile D some time this week though. Maybe it will be my first.

My d15b8 (180k miles w/ abuse) had it little ridge in two cyl. but we are talking about <0.001" barely catching my finger nail, and it was not carbon build up. 

[ratcityrex]

You will be surprised on how little power u will loose going from 9.xx compression to 8.xx compression. Hell, I gained power. But it was .5 over and balanced and printed

[PhilStubbs]

I daily'd a stock length rod vitara D for a couple years. It drove fine out of boost. But if I was to dd a turbo car again, I would do it with more compression.

[ratcityrex]

With the tq the f makes u will be fine with 8.xx comp

[jabberwock]

Lower comp and lower torque?  Crank dat distributor

[J_Hart]

Rechecked my numbers and came out with something different.  THIS is why I don't do math in public.

Off the shelf K20a3 rods and 9:1 pistons .5mm over with NO decking or milling comes out to 8.7.   MONEY.

OT, looking at the SC50 T3/T04E for this engine.  The .48 ar trim would spool quickly, but would it be too small for modest power goals?  The .63 trim would have more headroom, but I think JD gets enough "fuck this piece of shit car" texts from me as it is.


Video of the day... http://youtu.be/WWCoGVdcYEI

[Joseph Davis]

You will be surprised on how little power u will loose going from 9.xx compression to 8.xx compression. Hell, I gained power. But it was .5 over and balanced and printed

Oversquare engine like B16 or LSx, gutless.  Undersquare engine like F23, does not lose significant power.

[jabberwock]

It's all in the dwell.

[crxvtec91]

I think this is in my near future. f block for $50 and k20a2 rods and pistons for $40

[Phate]

I think this is in my near future. f block for $50 and k20a2 rods and pistons for $40

Where are you finding k20 pistons and rods for $50?  Shit, I'd be happy with just a set of the pistons (from a k20a3) for that money.

[crxvtec91]

I think this is in my near future. f block for $50 and k20a2 rods and pistons for $40

Where are you finding k20 pistons and rods for $50?  Shit, I'd be happy with just a set of the pistons (from a k20a3) for that money.

Theres a few K guys by me, they just have them laying around and told me $50 im sure I could low ball them for $30

[Phate]

I think this is in my near future. f block for $50 and k20a2 rods and pistons for $40

Where are you finding k20 pistons and rods for $50?  Shit, I'd be happy with just a set of the pistons (from a k20a3) for that money.

Theres a few K guys by me, they just have them laying around and told me $50 im sure I could low ball them for $30

Well, depending on when my motor build actually gets around to starting (tax return maybe?), I might be needing a set of those (doing the stock K20a3 pistons on F23 rods setup).  I'll have to try to track down some people in my area that have built K20's.

[crxvtec91]

I think this is in my near future. f block for $50 and k20a2 rods and pistons for $40

Where are you finding k20 pistons and rods for $50?  Shit, I'd be happy with just a set of the pistons (from a k20a3) for that money.

Theres a few K guys by me, they just have them laying around and told me $50 im sure I could low ball them for $30

Well, depending on when my motor build actually gets around to starting (tax return maybe?), I might be needing a set of those (doing the stock K20a3 pistons on F23 rods setup).  I'll have to try to track down some people in my area that have built K20's.

If you cant find them, pm me and ill ask around locally.