CBX Racing

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

Post by Syscrush »

Getting the CBX down to GSX-R weight is quite an accomplishment!

Thanks for the update.
Phil in Toronto
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Re: CBX Racing

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Too much of everything. 2 lots of dohcams, 2 lots of 2 piston calipers, 2 banks of 3 carbies, 2 three into one exhausts and now, 2 crankcase breathers.

More puff so, let it breathe.

The tank is the biggest issue weight-wise in that I have to carry extra fuel so an up coming mod is a second pingel on the rhs so I can carry less fuel for typical short races. Longer term an alloy tank as previously mentioned. Another item that could be put on a diet is the barrels. The iron liners are probably contributing to that extra weight because the barrels are surprisingly heavy and if I were to take it out to the class limit of 1300 cc I would investigate alternatives to those liners.
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Re: CBX Racing

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To be painfully honest about the weight comparison Phil, I have not measured it for over a year and I'm estimating based upon a multitude of changes in that time. I'm also comparing half wet weight of the CBX (oil but no fuel) with the published weight of the GSXR road bike. My track bike by contrast is lighter with all road gear removed and race glass.

Power wise the de-catted, re-flashed and dyno tuned GSXR probably has a few horsepower more than the CBX but there is not much in it really and that could be reversed by the time I get the carbs percolating properly with the new motor. Today I pulled the needles out to rectify the hesitation off a closed throttle but the circlips were already at the bottom notch of the 9 positions. That means I have to go back up at least one size on the mains as it is running too lean. The carbs came with 120 mains but we ended up going to to 100's with the old motor.

Clearly the new motor is sucking harder and can handle a set of bigger mains. Or, I could be wrong. Doing it by trial and error without a sensor or gas analyser is a pain.

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Re: CBX Racing

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20220624_145948.jpg
Roly reckons I'm wrong and the main jet size is correct and I should focus on the needles and perhaps go up a size in the slow jets.

I took the Lump out to the track yesterday to test a few things. I was not planning on doing too many laps which was just as well because every time the track started to dry out with a sunny break another heavy shower of rain would come thru'. I eventually got out for half a dozen laps but the track was still wet enuf' to throw spray and with slicks and open bell mouths not ideal test conditions.

The Brembo brake MC seemed to work OK altho' I was not using it as I would in a race. I've also been advised to try Castrol SPF brake fluid. Expensive but said to give superior performance and feel at race temperatures when the brakes get very hot indeed.

My new breather fixed the misting problem with the old breather but created it's own problems with oil escaping from it's bottle. I need to rationalise the 2 catch bottles and am planning to place a single larger catch tank higher up in the ducktail where I can vent it properly and where the oil can drain back into the engine without making an almighty mess.

The poor carburation off a closed throttle was also not good in the damp conditions because I would open the throttle thru' a turn only to have it hesitate, cough and then all 6 cylinders chime in with a bang causing the back end to step out. Disconcerting when over 100 hp are unleashed with no way to ride around it either other than be prepared.

Here is a pic I took of the trailer all loaded up and ready to go. I can usually hitch the trailer, load the bike and all my gear by myself in under 15 minutes and unload in similar time except at the track where I take a wee bit longer because I have to use ramps instead of my loading dock.
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Warwick Biggs
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Re: CBX Racing

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Why does this site put my pics on their ear sometimes. They are not that weird.

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Syscrush
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Re: CBX Racing

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Warwick Biggs wrote:
Sun Jun 26, 2022 2:36 am
Why does this site put my pics on their ear sometimes. They are not that weird.
It's an issue with the forum software. It's not just your photos that have these issues when posted here.
Phil in Toronto
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Re: CBX Racing

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Hmm. Is there a programming fix in the works?

Stupid mistake of the w/e was attempting to start the Lump with the bell mouth covers still fitted. There I am thinking it wont start because it is a Honda and it is cold and wet and lean to boot when it was me rushing and not focusing on what I was doing. The result was that I flooded it and had to pull off the tank and seat to extract the plugs to dry them. Worse still is the difficulty quickly removing plugs #2 and #5 where the engine hangar plates have to be removed first to get them out. I just left them in and luckily managed to start it on the 4 dry plugs.

Just as well because I did not have any ether, the conventional solution to hard starting. My old mate Dennis who helped me with converting the Lump in the early days always decried the use of ether, also known as aero-start or Start'yabastard. He reckoned it stripped the oil off the bore and caused premature piston failure.

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Re: CBX Racing

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Returning to the power and weight comparisons, a more accurate comparison would not be the GSXR with its linear fuel injected power delivery but rather the Quantel Norton. What is that I hear you ask? Well, it was a design that started during the last gasp of Norton's existence after the rotaries.

Norton asked Cosworth boss Duckworth to design and build components for a modern twin but kept changing his task. He ended up with a DOHC twin that used the engine as a stressed member with gearbox mounted cantilever swingarm and the head stem bolted to the head. It crashed in it's first race and died with Norton. However, a few decades later Quantel boss Graves who was sponsoring Oz racer Paul 'Angry Ant' Lewis came upon the engines stashed under a bench in the factory at Wolverhampton and grabbed them. He asked Paul and his Oz mechanic Bert Flood to see what could be done with them. What was done was the creation of a bike ultimately ridden by Roger Marshal that decades after it's inception won Daytona Twins a bit like the Britten. This was the bike Norton should have built.

That bike made 120 hp, weighed 190 kgs half wet (the motor weighed about the same as the CBX), handled and stopped really well but had light switch power delivery in the higher rpm, had no flywheel, was incredibly smooth (balance shafts contributing a lot to the weight) and that was fine for the Daytona banking but not much good on most tracks. EFI would have solved that problem.

This is about where the Lump is. Virtually identical power, weight and carburation problems. Roly is sending some jets to try but there is an almost endless combination of possible jets, needles and slides that make tuning CR Special smoothbore carbs a bit of a black art. What sustains me is the knowledge that I can see how competitive and great to ride it will be once the carburation and other annoying minor issues are sorted.

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Re: CBX Racing

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Warwick Biggs wrote:
Wed Jun 29, 2022 2:58 am
Quantel Norton.
Pretty rad!
ImageQUANTEL COSWORTH by msrphotographic, on Flickr
This is about where the Lump is. Virtually identical power, weight and carburation problems. Roly is sending some jets to try but there is an almost endless combination of possible jets, needles and slides that make tuning CR Special smoothbore carbs a bit of a black art. What sustains me is the knowledge that I can see how competitive and great to ride it will be once the carburation and other annoying minor issues are sorted.
IMO there's some crazy crap going on with airflow in the CBX head that introduces multiple challenges with carburetion for non-stock configurations. I have no hard evidence and no relevant expertise, but I suspect that they're prone to reversion - and that the unequal length intake ports spread out that reversion across a wider RPM range than you'd have otherwise.

If my conjecture is true, than IMO trying to mitigate such issues with jetting is like sweeping a dirt floor - you can make it better, but there's a limit.

Getting the bike set up for the best possible high RPM power and drivability is probably easier than dialing in good street manners, and as you've noted there are many, many options and combinations possible for your setup. The work you've done to get this far is admirable, I really hope that you get the payoff you want in terms of the bike and the experience riding it!

Keep up the great work!
Phil in Toronto
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Re: CBX Racing

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For a no-holds-barred race setup, I would love to see a CBX with a custom head using the combustion chamber and port designs from a more modern and less compromised setup. I think that the air/oil-cooled GSX-R750 head with its TSCC design would be a great candidate, as it's not (quite) liquid cooled, still uses side-draft carbs, and there's such an incredible amount of information out there about porting and cam profiles for different applications.

IMO there's no reason that this adaptation of the incredible Honda K20 head design to the venerable Nissan I6 couldn't be used as a guide on how to do the same kind of hybrid head for the CBX. Well, actually, there are 4 reasons I can think of...
  1. Packaging of the much-wider carb bank
  2. Racing class regulations
  3. Time
  4. Money
Obviously I'll never do it, but I do dream of seeing something like this done some day.
Phil in Toronto
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Re: CBX Racing

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Reversion is normally associated with back pressure from the exhaust and with double 3 into one systems and 120 degree firing order I can't immediately see a connection Phil.

I know the carbs fueled well prior to increasing the compression and it is not revving dramatically higher so I am expecting to be able to sort out the poor carburation with time and patience.

However, the CBX head design is definitely compromised by the unequal length angled inlet tracts. Interestingly, the Jyo Bito CR Special carbs have extra long intakes (see pic) compared with most CR specials or the CV carbs and I'm guessing that this is with the intention of evening out inlet gas flow. I would like to have my head properly analysed for flow but there is nobody within cooee with the kit to do this so I can only speculate as well. I have opined before that the weight and mass of 4 cams and 24 valves is the most obvious limitation of increasing engine speed.
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Re: CBX Racing

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Here is a pic of Herman's CBX with the CB1100R polished aluminium tank. I will post technical details elsewhere on the site but it is a simple mod to mount on a Prolink altho' being longer and larger than stock it is no good for a racer because it moves weight to the rear when you want to go the other way. The front is XJR1300 and the spoked alloy wheels are bespoke and a lot of time put in to make the alloy Z1 duck tail and detailed mods everywhere.

One of my problems with the Lump is the difficulty selecting neutral once the oil is hot. This makes gridding up difficult because if I can't find neutral while still rolling it means I have to overheat the clutch holding it waiting for the lights. This inevitably prevents a clean get away and puts me at the back of the pack going into the first corner. In short racers it is a disaster.

I asked if anybody had a fix without any responses and I know it is a common CBX trait. Well, I think I may have the answer. It is a slightly different clutch called a Rekluse. If you Google it you will see it is basically a centrifugal clutch like a scooter. You can leave it in first gear without engaging the clutch or neutral and only once the revs go over a pre-determined and programmed rate that the plates engage and you have a smooth take off. Paul Lewis of Quantel Norton fame and also involved in the hydrogen powered V8 m/c engine featured earlier has used it on his range of injected 2 stroke cafe racers under the brand name Salt. Further enquiries are underway.
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Re: CBX Racing

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Now the pic is pointing down so the site software bug appears to be inconsistent and random.

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Re: CBX Racing

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If holding in the regular clutch overheats it, then what makes you think the Rekluse won't have the same issue?
Phil in Toronto
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Re: CBX Racing

Post by Warwick Biggs »

Good question Phil and one I'm interested in following up. I'm assuming that it won't because it is specifically designed to work this way and is marketed as a defacto launch control system. I haven't found a detailed technical description yet but they do say the degree of slip is also tunable so I'm wondering if it has some sort of ramp like a slipper clutch and whether it works the same way on down changes.

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