CBX Racing

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

Post by Warwick Biggs »

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Warwick Biggs
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Re: CBX Racing

Post by Warwick Biggs »

Note the straight inlets.
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EMS
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Re: CBX Racing

Post by EMS »

So are the "inlets" on the stock carbs. The problem is not at the carbs, the uneven length and angled inlets are in the head, Warwick.
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Re: CBX Racing

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Yes EMS, I realise this. Which is why I asked if you had any further info on the machining of the inlet stubs that you described as "more or less successful". That might give me the confidence to explore this option.

In the absence of information on how one might approach machining the head I was pointing at another problem related solely to the straight bank of CRS carbs made by Keihin USA. Fitting a straight bank to an angled head is just compounding the problem and creating an even more convoluted gas flow. This is the current unsatisfactory situation I have with my race bike and one that I would like to rectify.

The internals of the outer connecting rubbers for the straight bank have large 'steps' that will detrimentally affect gas flow and the rubbers are of unequal length. If the head could be machined to accept a straight bank of carbs with short equal length rubbers, then the straight bank would have greater utility but in the absence of any info on machining the head or capacity to do so then the next best option is to adopt a 'V' shaped carb bank consistent with Honda's original design.

As a stroke survivor I can assure you that I have a particular interest with rectifying 'in head' problems.

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Re: CBX Racing

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I have personally seen only one head that had this done. They milled the inlet on the head down and then bolted steel stubs on the head that accepted a straight set of carbs. I seem to remember in order to do this right, they took an old head and cut it apart to see exactly how the inlets would route to the combustion chamber. Quite an effort and back then, I thought a bit too much for a street bike. You are talking racing and that may justify going the extra distance.
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Warwick Biggs
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Re: CBX Racing

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In the absence of any new cases for a while, planning for the National Historic Championship has re-commenced with early November 2021 looking likely. Questions remain over the International Challenge at the Island Classic in January. Its' hard to see how it can proceed due to the worsening crisis in the US and the UK. With the latter a short sharp lockdown should stabilise numbers but in the absence of a coherent community wide response things can only worsen in the US and those countries lacking unified leadership. As I have observed b4 federations don't work too well in the absence of a unified sense of purpose.

It is possible to crush second and third waves of the disease but it requires a strong and unified response based on the best scientific advice and a focus on the public interest, not sectoral, financial, political or religious interests. Meanwhile, conspiracy theorists and libertarians indulge in cynical self aggrandisement that endangers us all. IMO.

Practice at the track went as well as could be expected with dry conditions, lots of sessions and only one pick up - a fellow who had to find out the hard way that VRods are not ideal track bikes. I did some minor ploughing of the track myself on the gixxer despite having dropped the front forks and pushed the rear preload up as far as prudence allowed. I have to conclude the rear spring is probably a stocker (9) and in need of replacement (11 or 12). Suzuki seem to focus more on capturing the widest market, including those of shortened stature at the expense of taller, heavier riders. I have also discovered, not surprisingly, that it can be hard to keep the kilos down during a pandemic.

The motor was strong and linear after removing the cat and re-flashing the ecu with Woolich software but the heavier steering was hard on my hand and we will need some spacers in the rear shock to fix that. Four sessions was all I could manage b4 I started to lose feeling in my fingers and the hand completely seized up. Very stiff this morning but 'use it or lose it' seems an apt observation to conclude with. Certainly no way I could manage the much heavier CBX clutch, yet.

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Re: CBX Racing

Post by Syscrush »

Thanks for the update. It sounds like you're having steady progress with your left hand - is that a fair summary?
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Warwick Biggs
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Re: CBX Racing

Post by Warwick Biggs »

Not really Phil. I seem to have hit the wall on that and its a problem. I'm seeking alternative advice from an expert in Adelaide.

It looks like the border controls will be coming down soon as new cases are confined to travelers in quarantine. Community transmission has been eradicated in Oz & NZ but we are still having many people arriving from overseas carrying the disease. Most are from the sub continent closely followed by the US. There are calls to ban travelers from the US which is now classified as a super spreader State. In the middle of an election too. Crikey! Time for the Yanks to pull up their socks and confront the situation b4 their health system and economy collapses IMO.

Anyhow if the border restrictions between SA and Victoria are loosened I'll be able to get another opinion on what to do with my hand. Maybe its just age catching up but that just means I have to go faster!!!

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Re: CBX Racing

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Incredible dissolving BMW fuel lines is a first for me. It seems that some BMW fuel lines are only shielded on the inner surface and if used inside the tank, simply dissolve. Not an unusual occurrence according to one dealer and something else to bear in mind if your BM just quits on you. Shades of Mission Impossible self destruction - the ultimate in consumerism. The only time anybody outside Spandau touched those lines was for a fuel pump recall. Thanks BMW!

I've pulled the rear shock out of the GSXR and am awaiting a more appropriate 11-12 kg/mm spring and then will fit a spacer to lift the back end to get the belly off the deck and improve turn in. The little NC30 is awaiting a new set of iridium plugs. They are tiny with an 8 mm thread and 13 mm hex making them very unusual and expensive and hard to come by. Many US suppliers do not appear to be shipping and the Europeans and Japanese are also experiencing shipping problems due to the pandemic.

Altho' the second wave and community transmission have been completely crushed in Oz and most restrictions lifted it seems the rest of the world is not so fortunate and our global village is as crook as a chook, to mix a metaphor. Meanwhile our next track test at the end of the month (for the hand) will determine whether we enter the SA Historic Championship in early January, urgings of old adversaries notwithstanding. If we do it will probably be on the NC30 while the CBX sits anonymously under a sheet.

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Re: CBX Racing

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Incredible dissolving BMW fuel lines is a first for me. It seems that some BMW fuel lines are only shielded on the inner surface and if used inside the tank, simply dissolve. Not an unusual occurrence according to one dealer and something else to bear in mind if your BM just quits on you. Shades of Mission Impossible self destruction - the ultimate in consumerism. The only time anybody outside Spandau touched those lines was for a fuel pump recall. Thanks BMW!

I've pulled the rear shock out of the GSXR and am awaiting a more appropriate 11-12 kg/mm spring and then will fit a spacer to lift the back end to get the belly off the deck and improve turn in. The little NC30 is awaiting a new set of iridium plugs. They are tiny with an 8 mm thread and 13 mm hex making them very unusual and expensive and hard to come by. Many US suppliers do not appear to be shipping and the Europeans and Japanese are also experiencing shipping problems due to the pandemic.

Altho' the second wave and community transmission have been completely crushed in Oz and most restrictions lifted it seems the rest of the world is not so fortunate and our global village is as crook as a chook, to mix a metaphor. Meanwhile our next track test at the end of the month (for the hand) will determine whether we enter the SA Historic Championship in early January, urgings of old adversaries notwithstanding. If we do it will probably be on the NC30 while the CBX sits anonymously under a sheet.

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Jeff Bennetts
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Re: CBX Racing

Post by Jeff Bennetts »

Warwick, here is an example of a CBX head that has been machined, welded, re-bored and fitted with flatslides. The HP numbers didn't increase that much from the standard head configuration but along with the other motor modifications allowed the motor to rev up to redline very quickly!
IMG_1139.JPG
IMG_1140.JPG
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Warwick Biggs
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Re: CBX Racing

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Can you tell us any more about this motor Jeff? Lighter crank/rods/valve gear and higher compression might be expected to make for a faster revving engine (the flywheel effect alone) but the inference from your example is that better, more direct gas flow had little effect on outright power. That suggests to me that there was some other impediment.

All things being equal, higher revs normally means higher power. The CBX is not a particularly high revving engine despite it's relatively sophisticated specifications compared with a tuned 2 valve GS motor, for example. The latter consistently out performs the 4 valve CBX in revs and power output and that has often been blamed on the head design (poor gas flow) as a result of CBX packaging compromises (squeezing the carbs in at less than optimal angles).

Your post suggests otherwise so it would be interesting if you could expand a bit more on the subject. I also have in mind that 18,0000 rpm Blanquard CBX.

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Re: CBX Racing

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Just looking at those rather crude looking inlet manifolds makes me wonder about the machining and then how the welding was done. Whether it created an effective venturi.

Also, we know that very small differences in carb bell mouth lengths can have significant effects on performance so we really need to know what is happening with gas flow and this can be monitored and measured.

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Jeff Bennetts
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Re: CBX Racing

Post by Jeff Bennetts »

It's been 15 yrs but here's what I remember, no guarantees. Some of the basics of the motor!
1163 Aries piston kit, 11:1
Falicon crank and Falicon knife edge rods
CB1100F valves
KW titanium under bucket kit
Mild head porting
36mm Mikuni flatslides
Kerker custom exhaust
Full loss electrical system, hand held starting

IIRC he was getting about 139 hp with this setup (using the standard inleted head) After the head inlet modifications he gained about 7 additional hp, up to 146 hp. After all the bench flow and dyno time, money and effort to make the head work, if you ask me it was only a marginal success!
Last edited by Jeff Bennetts on Fri Nov 13, 2020 12:28 am, edited 2 times in total.

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Re: CBX Racing

Post by Warwick Biggs »

I can't help wondering about that inlet manifold. Here is a pic of the Blancquart CBX that looks like it has a pretty stock head fitted with a V shaped bank of flat sides.

If the stories are correct it was revving to 20,000 rpm and making over 200 hp. It certainly sounds like it revs much higher than any CBX's that I've come across altho' I note your past skepticism Jeff.
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