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average piston speed at 7800 is 25.74 m/s. That is F1-level on a cast piston.
For a rally application on cast pistons and rods, I'd stick to something like 7200 to 7300 . That corresponds to the piston speed of a K20 spinning about 8300 or 23.8 m/s.
That is near stock, but it will last. Make it 7500, but not higher on a stock bottom end.

Joe McCarthy once posted here 2013 about the K20a that is essentially using the same rod and piston technology.
"I'm basing that bit of advice on many years of experience of endurance racing stock bottom end K20's in the 25 hour at Thunderhill. If the rev limiter is set at 8,200-8,300 the engine will finish the race without exception. If its set at 8,600 one of the pistons will disintegrate by the 11-12 hour mark. At 9,200 I've seen stock pistons last under 10 laps. I can't even begin to count how many times I've seen people destroy perfectly good engines by doing this. I've also seen engines limited to 8,300 last through 2 complete seasons of endurance racing, which is about 100 hours total.
Its metal fatigue, which has 2 components, load and time. That's what determines the lifespan of any metallic part.
On the street the time span is SO short that a lot of people get away with over revving the engine for a long time, but its just a clock ticking off the seconds at that load level and eventually the piston WILL be destroyed."
That is some great information , I love reading his posts.
 

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Discussion Starter · #27 ·
PRB 02-04 K20a2


The 05-06 K20z1 Retainers may be flat. If the image is needed I can provide.
Thanks - I ordered SuperTech steel retainers and locks since the OEM locks on not available from Honda, according to my parts folks. They only had 20 available. I assumed that the SuperTech locks won't work with the OEM K20A2 retainers.
 

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Thanks - I ordered SuperTech steel retainers and locks since the OEM locks on not available from Honda, according to my parts folks. They only had 20 available. I assumed that the SuperTech locks won't work with the OEM K20A2 retainers.
Do you have a link to the valve springs you ordered ?
 

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I have thinking about Toda cams. I need to do a bit more research and compare them to other cams available. I am interested in them because of the oem quality they are known for. I want to compare them to Drag Cartel 2.2 endurance cams.
 

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Discussion Starter · #31 ·
Quick update - new Supertech retainers, seats, seals and locks in place and Toda springs are much happier....but there appears to be valve to piston interference with the new Toda C's. Cams spin freely, pistons spin freely but once we put the timing chain on it spins a bit and then binds...spins the other way and then binds again. The goal was to not open the motor and just drop new cams and springs in. The Toda C's have 12.5mm EX and 13mm IN lift....is that too much for a k24a or is something off indexing wise?
 

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do you have some images you can share with us?

I am interested in purchasing Supertech Ti retainers.

really want Ti valves on my wishlist on the next build
 

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Discussion Starter · #34 ·
Update - Finally got everything sorted and installed. Tuned on the dyno last night and netted 190TQ and 233HP at the wheels on 91 octane, VTC hit about 28/29 but is physically limited at 30. We played with the VTEC engagement between 4k-5k and 5K seemed to the smoothest point. It seems to top out at about 6700rpm and assume this is due to my 2.5" exhaust system...with a 3" exhaust system it should keep running to 7000+
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It seems to top out at about 6700rpm and assume this is due to my 2.5" exhaust system...with a 3" exhaust system it should keep running to 7000+
I had 2.5" exhaust systems on 290 hp engines for tuning, the difference is just a few lbft in quantity compared to 3" pipings, has nothing to to with what we see here. Something blocks, much more serious I assume. Could be from not optimal tune, a rare valve issue (floating, lash, ...) up to an non well sealing engine or just a simple fuel injector issue and something in the path of alternation of load. Much more serious as just a simple too small piping. Just my two cents.

I am open to check your calibration/WOT log for a second response for you. Do you have header design parameters for validation as well as the exhaust setup for me?
 

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Discussion Starter · #36 ·
I had 2.5" exhaust systems on 290 hp engines for tuning, the difference is just a few lbft in quantity compared to 3" pipings, has nothing to to with what we see here. Something blocks, much more serious I assume. Could be from not optimal tune, a rare valve issue (floating, lash, ...) up to an non well sealing engine or just a simple fuel injector issue and something in the path of alternation of load. Much more serious as just a simple too small piping. Just my two cents.

I am open to check your calibration/WOT log for a second response for you. Do you have header design parameters for validation as well as the exhaust setup for me?
Thanks for the insight. I would think the limit with just cams, header and intake would be 240-250whp on a stock k24A bottom end and head, no? Tune shouldn't be an issue, my tuner has a long history with Honda's, work(ed) for Singer Porsche tuning their cars and tunes on a daily basis. I can see if I get the WOT logs, if you're interested. If there's an issue I'd like to solve before the next rally.

Andrew
 

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I just had a look at the Pracworks website after suspecting this being a resonance issue.
RRC vs Pracwork (blue)
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They show on this EP3 (K20a2) the same 6500 rpm resonance as you. the next positive mode only starts getting active at 7500 rpm to about 8500 rpm.
You're stuck in the torque dip between 6500 and 7500.
On the other side, reving it only to 7000 will make your k20 last.
 

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I just had a look at the Pracworks website after suspecting this being a resonance issue.
RRC vs Pracwork (blue)
View attachment 106161

They show on this EP3 (K20a2) the same 6500 rpm resonance as you. the next positive mode only starts getting active at 7500 rpm to about 8500 rpm.
You're stuck in the torque dip between 6500 and 7500.
On the other side, reving it only to 7000 will make your k20 last.
I believe OP car is a k24a. Would that change anything?
 
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