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Discussion Starter #1
Some interesting engine info I found on pistonheads - - -

1.) The K-series engines are not nearly as reliable as the F-series when pushed to higher power levels and rpms. We've seen a large number of racers running stock block K-motors who've had pistons fly apart of oiling issues (oil pump cavitation above 8500 rpm) when running them at over 8000 rpms for extended time periods (1-2 races in road racing is all it takes). Under boost, it gets even worse. A stock block turbo S2000 on race gas will make 500+ whp all day long even under road racing conditions (I own one making 450 whp), try running over 400 whp regularly on a stock block K-series of any sort, especially on a road course and it won't last too long. The only place you have to worry about an F-series is with revs over 9200 rpm on a regular basis - upgraded retainers are needed at that point - but you'll need them on a K-series too above 8500 rpm.

2.) The F-series engines will make plenty of power with mods. The problem is that there aren't many cams out there that work for the F-series while there are a dozen manufacturers for the K-series. That said, a stock block/head K20 with a modified intake mani/intake/throttle body/cams and a good header/exhaust will make about 270 whp and 180 lbs-ft of torque on my dyno. An F20C with intake/header/exhaust and tuning (stock cams, stock cam gears, stock intake manifold) will make 250 whp/165 lbs-ft. Throw in cams (Hytech makes a great set) and adjustable cam gears and it will make 270 whp and 175-180 lbs-ft of torque without i-VTEC. Again, that's with a stock intake manifold still. Point being, both engines have similar peak power levels (and similar peak torque), but the F-series doesn't take as much to get there because it starts with a better head. The K-series has the advantage in midrange torque because of i-VTEC.

3.) Fully built race engines are tough to compare. We've made 290 whp and 200 lbs-ft of torque from a stock block F22 on pump gas with cams, ITBs, header/exhaust and tuning (we've done 270 whp on a blueprinted stock block, stock cams, stock manifold and stock TB F22 as well). We've made 300 whp from a K22 on pump gas with full internals and an intake manifold upgrade. That's close enough given that the K-motor had more done to it.

The simple summary? The F-series comes with a better bottom end and a better cylinder head. The only advantage the K-series has is the i-VTEC. Properly designed, the F-series has no disadvantage in peak power, only in midrange torque (i-VTEC). The only way a K-series can be as reliable as the F-series is with full internals and a modified oil pump.
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Add to that tougher pistons (forged) and con rods, injection molded and sintered cam follower/rocker arms, fiber reinforced metal (FRM) usage in the cylinder liners, specially designed and stiff valve springs (single element, round profile IIRC) and you've got an engine that is much more willing to rev than a comparable K-series engine.
 
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Discussion Starter #2
More information - - -

Critical differences between the K-series and F-series:

1) Cylinder head flow. The F-series head flows about 7-8% more air for a give lift level than the K-series. Valve size is slightly bigger on the F-series. Valve springs are stiffer as well. Factory retainers see highly increased rates of failure above 9100 rpm though.

2) Internal construction. The F-series uses robust forgings for pistons, rods, etc. The sleeves are a MMC (metal matrix composite) construction. The K-series OTOH, uses lower cost castings - understandable given that it is a much higher volume engine. This begins to pose an issue at higher rpms. Under extended use above 8000 rpms (say, in race cars), K20s have extensive issues with piston failure (citation - Derek Stevens of Hondata and Joe McCarthy from Prototype Racing). You can take a bone stock F20 and race it for a year running it between 8000 and 9000 rpm and have no internal failures.

3) Oil pump. Above approximately 8300 rpm the K-series oil pump begins to cavitate (citation - Jhn Grudynski at Hytech Exhaust). This can cause issues with oil pressure and overall oiling quality. The S2000 pump is good to at least 9500 rpm (as high as I've revved a stock block) and probably higher given the engine speeds achieved by a couple purpose built F20Cs.

4) VTC. A properly tuned K-series engine will always produce more midrange torque than an F-series of the same size. VTC makes a _huge_ difference in this area. In fact, in our experience, VTC allows a K-series engine to behave like a 5-8% bigger F-series engine below 6500-7000 rpm in terms of torque output and power curve.

5) Intake manifold. The RBC manifold found on the Euro-R and current Civic Si is the best flowing intake manifold on factory 4-cyl Hondas. It is far superior to the F-series intake manifold, which, according to Honda's SAE technical paper released back in 2000, was designed more for quick revving response while compromising overall power delivery, especially at the top end (primarily by using an extremely small plenum).

In essence, Honda took much of what they learned on the F-series and applied it where they could in developing the K-series. Both can trace roots to the H-series of old. The K-series embodies significant improvements in performance due to VTC, as well as an improved intake manifold. Reduced costs pose some issues in extreme situations, but those cost cutting measures and production compromises have had a minimal effect on achievable performance while making the engine vastly more available.
 
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Discussion Starter #3 (Edited)
Important for those with higher rev limits, especially on track and or with forced induction -

K20 - "We've seen a large number of racers running stock block K-motors who've had pistons fly apart of oiling issues (oil pump cavitation above 8500 rpm) when running them at over 8000 rpms for extended time periods (1-2 races in road racing is all it takes). Under boost, it gets even worse"

"Oil pump. Above approximately 8300 rpm the K-series oil pump begins to cavitate (citation - Jhn Grudynski at Hytech Exhaust). This can cause issues with oil pressure and overall oiling quality"

I know lots have had no issue, even on track, but worth noting.

When modding my FN2 with Flashpro I'm going to reduce the limit from 8600 rpm to 8400 rpm.
 

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Discussion Starter #6
Unfortunately I don't know when they were written, or even where. Someone had just posted it on pistonheads this year.

Has anything changed in the K20 to address those issues? I think the FD2 oil pump is a wise upgrade, but thought this was the same as earlier K20A pumps anyway?
 

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Discussion Starter #8
Have since been reading posts where oil pumps noted as fine to 8600/8700 rpm, in line with 8600 for valvetrain.

Makes sense as so many EP3's and FN2's running Hondata at 8600 rpm limit and been fine for years.
 
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Also when turbocharging a K I'd always be inclined to drop in a set of forged pistons and rods. This offsets many problems mentioned above.

You don't need as much revs when turbocharged to make stupid power either, this will bring the reliability up.
 

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Have since been reading posts where oil pumps noted as fine to 8600/8700 rpm, in line with 8600 for valvetrain.



Makes sense as so many EP3's and FN2's running Hondata at 8600 rpm limit and been fine for years.


Nuno ran a 8800rpm limit for a long time with spoon cams. I think with the FD2 pump you could have a limit of 9k but for reliability I wouldn't want to be going there often.

But no long term testing to prove this.

If your staying NA then uprated valve train would be a good idea as in one of the build threads Drag Cartel cams were making power far beyond what the stock valve train could take.


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