CBX Racing

CBXs, new bikes, old bikes, cars, trucks, general chat, off topic, this is the place to post it.
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Warwick Biggs
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Re: CBX Racing

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Time for tennis and something different.

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Re: CBX Racing

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Was any engine ever designed with more compromises than the CBX?

Irimajiri san, the author of that design admitted that conflict within Honda over packaging caused problems, not the least being the V shaped inlet ports. Because of the angles each cylinder fuels differently. On the production bikes he was able to partly compensate with the internals of the airbox and employing vacuum carbs.

Irimajiri also stressed the importance of tuning the exhaust on the CBX, something that had previously been more associated with 2 stroke engines. He adopted two 3 into 1's. EMS your point about the 6 into 1 on the CBX is well taken.

These two issues, differential cylinder fueling and tuning the exhaust for resonance both entail complex challenges on a race bike employing straight thru' carburettors and requiring maximum ground clearance. The most obvious is that looking at air/fuel ratios across the rev range on a conventional dyno has limited use because with only one sniffer they are merely an average of the 6 cylinders while the difference between #'s 3 &4 and 1&6 are likely to be significant. This is all very different to the average 4 cylinder m/c engine.

Roly is over at the track this w/e for the Hartwell club races and he brought some 0.5 mm spacers to put under the carb needles to test Bito san's theory about running lean. Modern fuel injected race bikes can easily accommodate individual cylinder tuning using computers and sensors. Attempting this manually by trial and error with the CBX is difficult.

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Re: CBX Racing

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This is exactly why I'm planning to convert my street-ridden CBX to EFI, and why that plan includes retaining all of the OEM intake tract.

Good luck getting it sorted out.
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Re: CBX Racing

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That seems like a sensible mod Phil. If you combine the efi with Lambda sensors tapped into your exhaust headers then you will be able to tune each cylinder individually.

In theory, with the right software this could be achieved automatically with an ecu.

It is easy to imagine a modern CBX with efi, electronic throttle, titanium valves, variable valve timing, variable valve lift (8 cams!), digital coil over plug ignition, balanced light weight crank, Carillo rods, quickshifter, slipper clutch and liquid cooling and lean sensitive traction control. In fact a V6 CBX RR could be built in time for the last ICE to roll off the production line.

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Re: CBX Racing

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Several CBXes have been converted to FI. The unequal lengths of the intake tracts remained a challenge in all of them. It's the air that's the issue, not the fuel.

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Re: CBX Racing

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Warwick Biggs wrote:
Sun Mar 07, 2021 5:23 pm
In theory, with the right software this could be achieved automatically with an ecu.
In practice, I don't think that any ECU for an all-new engine combo has ever been dialed in "automatically". From what I've seen, a lot of custom EFI setups get to the point where they idle OK and run well at WFO, but suffer with stuff like off-idle and midrange street manners. I'm not confident about complete success, but it's something I want to do so I'm gonna take a crack at it.

I like the idea of having the data from 6 individual lambda sensors, and 6 individual MAP sensors. The MAP sensors are not difficult, but finding a place to put a lambda sensor in each header pipe that both fits and looks decent/stealthy seems like an almost insurmountable problem. I have an emotional attachment to my one-off, handmade header and don't want to hack it up too much. I think that maybe I could go with 6 external thermocouples to measure header temps, plus one lambda sensor to measure overall AFR. If the overall AFR is good and every header is at the same temp, that's probably a good compromise. I could have flat thermocouples strapped on the outside for tuning, and then remove them once I felt OK about how the bike runs.

I honestly just had the temp sensor idea now as I wrote this up, but did a little search and found this - so maybe I'm not out to lunch.
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Re: CBX Racing

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I imagine the temperature sensor would be more useful than a temperature gun that only works with the bike at standstill Phil but would be expensive by the time you fit 6 of them and then buy the gauge. They may indicate too lean or too rich but not the cause. They will also spoil the look of the 6 clean headers altho' not as badly as 6 18mm lambda sensors. Maybe you could make a feature of them and have them anodised bright red.

EMS, as we know, the V port head was an unfortunate compromise to accommodate carbs and you would not need it if the motor were to be injected. My suggestion was a clean sheet design. You could have equal length straight ports with the injectors placed close to the valves, thus avoiding the air differential.

Maybe some form of forced induction with an airbox would help to overcome the V port air problem? The bare CR's dismantle the designer's original compensatory airbox design. Maybe playing with longer velocity stacks for cylinders #3 & #4 in a ram air pressurised airbox would help? Who knows? Has anybody ever tried it, I wonder?

My current problem is that the CR's are running pretty well everywhere except from 3,800 rpm to 4,200 rpm where it is way to rich (lambda is showing 1.05 @ 4,000 rpm). That is a big hole in the middle of the power curve.

Playing with the ignition curve was ineffective and it seems odd that the fueling elsewhere is OK around 0.8 + or -. Suspicion is falling on the Delkevic 6 into 1. It would not matter if I could keep the revs above this point but the motor is also not producing much power over 8,500 rpm and with 2 heavy braking first gear corners at Mac Park its difficult.

It would also help if I had the cam specs apart from knowing they have been ground off the baseline so I could slot them. Where are you now Hugh?

I asked James Fisher who successfully races a CBX in the UK how he manages the CBX fueling/air issues. He and his old man have 15 CBX's between them. I'm paraphrasing his Ginsbergian response with, "Ommm!"

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Re: CBX Racing

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Warwick Biggs wrote:
Tue Mar 09, 2021 2:14 am
I imagine the temperature sensor would be more useful than a temperature gun that only works with the bike at standstill Phil but would be expensive by the time you fit 6 of them and then buy the gauge. They may indicate too lean or too rich but not the cause. They will also spoil the look of the 6 clean headers altho' not as badly as 6 18mm lambda sensors. Maybe you could make a feature of them and have them anodised bright red.
By using thermocouples clamped on the outside, they could be removed once the per-cylinder trim is tuned. 6 EGTs and one WBO2.

But with the thermal mass of the header pipes, the EGT sensors would be very slow to react. I don't know if the idea has any merit or not.
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Re: CBX Racing

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Back to the Lump and I've made a few more changes to be track tested at the w/e. I've lifted the needles a smidgin with some 0.5 mm washers under the circlips on Roly's suggestion and to test Bito san's theory that the throttle running on is as a result of top end leanness. I have also fitted a more substantial spring to the linkage to ensure it closes firmly when I back off the throttle and hit the brakes.

I've replaced the shorter dogbone on the rear Wilbers shock with the longer version that I had made thus lifting the back by a further 12 mm. After loosening off all the exhaust bolts and pushing up the headers I've removed the muffler and am running a straight thru' un baffled exhaust. If that doesn't work I will remove the mid collector, just leaving the headers. It will be very loud!

After changing the front fork oil I tried something I haven't done for a long time and pumped 15 psi into the forks. Coincidentally this immediately raised the front by 12 mms. Roly reckons this will just produce cavitation under race conditions and stuff up the damping but we will see. This is certainly a cheap way to increase ground clearance if it works.

Changed oil (10W60 MA2 JASO) & filters, torqued and re-lockwired everything and ran it in the workshop OK. But will it make the hole at 4,000 rpm worse? I'll let you know.

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Re: CBX Racing

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The changes worked and nothing was scraping at a brisk ride day pace. Of course, that is not race pace but I can certainly crank it over at respectable speeds without it threatening to lever up the front wheel and high side me into the bushes. Yesterday was sunny and hot but today much cooler with some big floods over in the east and a bit of rain finally reaching us this arvo'.

The air caps worked fine, steering was good with easy turn in and mid corner line changes. The increased swing arm angle gave excellent drive out of the corners and enabled me to tighten my lines thru' the apex which encourages an aggressive approach.

The 0.5 mm spacers under the needles seemed to work too with the bike revving out cleanly past 9,000 rpm. The hole around 4,000 rpm is still there but I just have to be careful rolling the throttle on in the really slow corners. Everywhere else I can just bang it wide open and it responds instantly.

Still a bit down on power tho'. It is fairly certain the the mid range hole is caused by the Delkevic 6 into 1 so my next step is to have a better exhaust fabricated by an expert. Then another session on the dyno to see if we can round up the missing ponies.

I had successively removed the baffles and then the muffler when I first started looking for ground clearance and it was very loud with a crackling backfire on the over run braking into corners. So loud that I was warned I would fail a noise test if they brought out the meter and I had a succession of curious people passing thru' the pits coming to inspect the howling curiosity - what is now an unusual and fairly rare race bike circulating at full noise.

One guy had never seen an air cooled six cylinder motorcycle and was absolutely astonished that a 39 year old relic of the past could keep up with his cross plane R1. I hasten to add that is not unusual to observe occasional track day riders who are dismayed to discover that their latest you beaut' modern mega $ superbike can be dusted off by a good rider on a 125 trail bike on a race track. And that rider will easily clean up a fossil on a CBX too!

Some other smaller ergonomic things need attention, mainly narrowing the front of the seat so I can reach the ground (& I'm over 6 ' tall) after lifting it up quite a lot and additionally so I can move around better. Also fitting grabbier foot rests to stop my feet sliding on the pegs. And I had a digital tyre warmer go crazy on me - probably the thermostat. Luckily I could drive home and get another one and only miss one session. The advantage of having my own track close at hand.

Also for some reason the neutral light ceased turning off when in gear and it was an annoying distraction so I disconnected it but I will have to trace the wiring and see what is going on there, but overall the CBX should be pretty well ready for the Seniors in May. Our combined age will be 108 years so I will easily qualify for the 100 Plus Cup.

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Re: CBX Racing

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I neglected to mention that I finally managed to get under my best CBX lap time set back in 2017/18 when it was still on 18" wheels. Only by a second but still 4 seconds better than during the races a few weeks ago.

The improvement was noticed and it was nice to receive some congratulations instead of the usual commiserations. I'm sure many in the road racing community consider the CBX to be an unlikely race bike because of it's sheer size and bulk and there are definitely easier bikes to get going fast. But they don't have the raw appeal of the big 6.

The improved lap times are nearly all down to increased corner speed as a result of improved ground clearance. However, I'm not at the limit and know there is more to come. I won't be satisfied until I can knock off another 4 or more seconds and get it into what is generally considered to be the fast category (by modern standards). A little more power just from tuning and some minor mods should help.

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Re: CBX Racing

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Warwick Biggs wrote:
Sun Mar 21, 2021 11:33 pm
I'm sure many in the road racing community consider the CBX to be an unlikely race bike because of it's sheer size and bulk and there are definitely easier bikes to get going fast. .
Sure one of the reasons Honda did not consider the CBX to be competitive. Not even in endurance racing.

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Re: CBX Racing

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This is a wonderful update, Rick - very glad to hear that you were able to take a second out of your best 18" wheel time. That sounds like a really significant milestone.

Any thoughts of going back to an OEM-like 6-into-2 to cure that 4k flat spot?
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Re: CBX Racing

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Yes, I've discussed it with a number of people including Ken Onus of Megacycle Exhausts who does many of the race bikes and has some experience with the CBX salt bike.

The consensus is two 3 into ones rather like the original road bike. I can probably retain my existing headers and the first part of the collector so not too hard to modify. James Fisher runs a 6 into 2 into 1 on his racer but his fabricator is charging over 1,600 pounds sterling. The trouble is going into Melbourne, an 8 hour trip because of that city's horrendous traffic.

I have to take my BMW road bike over there as well because the ABS module has packed up. A new one from BMW is $3,800 but I know somebody who can repair mine for less than half that.

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Re: CBX Racing

Post by EMS »

I just sold a Supertrapp. That would be a great exhaust. It is tuneable for all kinds of different set-ups and lighter. Just a little hard to find now.

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