Hmmm, things are looking pretty good: the 749R is +1kg lighter after losing the Humvee seat, the 851/926 is timed a little more appropriately, both bikes have had a hit out, what more could you ask for?
How about something a lil' more out of the comfort zone...how about a race? (the crowd goes "Oooooooh...!")
Unclench those arse cheeks, it's nothing that serious. The Racing Club were introducing a "Golden Era" class, but for whatever reason they're seems to be a bit of a disconnect between the Modern and Historic racing clubs so it was almost a toe in the water type exercise judging the interest. I thought it was a great initiative, but only a half dozen or so Golden Era bikes turned up.
That half dozen were soon reduced to 5. It seems the 851 also has some of those Sophia Loren genes more evident in the 916 and she obviously felt slighted by the lack of interest: she took a bit to get going, eventually warmed up ok, but refused to come out of her dressing room come (disappointing) show time. Bloody flat battery.
So she never even turned a wheel. But how could that be after running ok once she got going?
The answer was pretty easy to find, with something like this waiting for me when my first move was to unplug the alternator to check the output to the rectifier:
A bit of online chat later and the consensus was "they all do it", be it an early single phase system like the 851's or the later 3 phase systems, if you have a charging system issue go here first. It's not a peculiarity to Ducati's either, jump online and you'll see all sorts of similar photo's related to CBR's, VFR's etc. Consider this a public service announcement from Sophia Loren....
The older prima donna was obviously feeling slighted that I'd lavished some attention on the "new and improved" 749R, so it suited both of us for me to have a look at some of those issues I thought might be limiting hp, focussing on the air intake side of things.
I had nothing to prove it but just looking at it I had a gut feeling about that all encompassing foam sock/loaf type air filter. Remembering here that there is a trade off: you can have max flow and you can have great filtration but it's very difficult to have both. On a road bike great filtration is more important than a few cfm flow, on a race bike the emphasis is flipped with the odd small bird inside the airbox acceptable if it makes more hp.
Just to recap, here's how the serious racers would have run my bike back in the day:
Air comes in the front air "conveyor" as they called it, around the steering head, into the airbox, and pretty much straight out the back and sides: not only was it completely unfiltered it was completely unsealed.
This was my original filtration solution:
To be fair, it has a huge surface area which is good, but the sheer thickness of the foam, and small pockets for the intake trumpets had me suspicious. I mean, intake trumpets are also called velocity stacks, and it was the velocity side of it that I thought might be suffering.
Initially I was stumped for an alternative...until I spotted these lil' fella's in the throat of the airbox. I can't even remember what the mounts were for, maybe the voltage regulator(?) but it's a bit of a beer-fuelled blur:
You'll have to excuse that green injector plug, it wasn't quite long enough to route in front of the frame brace with the rest of the harness. I've inserted the wellnuts in what were just a couple of bare brackets, and gone on to make a carbon fibre frame to sit across that opening:
Applied some adhesive velcro:
Now for the filter material (no not even I would hack it up with a craft knife, it's just for size reference):
I cut the filter material just a smidge larger than the frame to fill the inevitable gaps. And there you have it, with a couple of M6 Ti bolts to screw into the well nuts:
I had to machine a couple of small nylon standoffs to space the filter the thickness of the frame tubes:
How does it fit up? Hang on a sec', I've still got to do something about those 50's style velocity stacks, with their half-hearted "made on a Monday" intake radius. Here's a comparison against some carbon Corsa stacks of the day:
The problem with no inlet radius, or a poor inlet radius, is air entering the throat gets all discombobulated at the sharp opening, causing an artificial narrowing at the entry:
Ducati seemed to agree as the next gen 916 and many models thereafter had these instead:
Unfortunately for me when they upgraded the shape they completely changed the mounting arrangement and the way the throat fits into the throttle body, so even though they are the same 50mm bore they aren't interchangeable. Bugger.
The carbon Corsa units aren't impossible to find although they do have a few variations in shape. One thing they all seemed to have in common other than the scary pricing, was length, all looking roughly similar. But I'm not revving the thing to 13000rpm, and have completely different cams, what length would suit my mongrel machine?
There are so many variables to consider: the intake valve opening and closing sends pulses back up the trumpet, basically high/low pressure waves, those waves then reach the end of the trumpet and, at the point they expand into open air, send a reverse wave back down the trumpet. If you make the intake tract the right length for the right revs (frequency of pulses) you can ride that reflected high pressure wave and stuff a bit more air/fuel into the combustion chamber and make more power. So what length do I need? I didn't have a fukn clue....
But do you remember those sexy 999RS-copy Jetprime velocity stacks I fitted to the 1098 TB's...the ones I couldn't make fit my airbox? (GRRRR!) Bloody short eh? I posted a pic online and a well respected tuner in Europe said he had tried them on a 1098 and they made less power than OEM, surmising they were designed to work at much higher revs than a stock setup would allow. Another renowned Aussie tuner in the Eastern State's also suggested I make the stacks a bit longer, which should increase torque. Okey dokey, I was happy to have some expert guidance, and I was living in the real world not Corsa-land.
So I found some of these adjustable stacks:
Available from these guys, delivered fast and quite reasonable pricing:
You simply slide the bellmouth inside the base to the desired length, and clamp with the silicon hose. Shown here against the OEM 851 stacks:
As you can see the OEM stacks actually insert inside the throttle body up to the flange, which would have eaten into a fair bit of the extra length I was hoping for. Worse, without that portion it would leave a flow reducing step inside the throttle body. So I parted off the OEM stack inserted section in the lathe, put those inserts in the beer fridge before heating up the alloy throat portions and shrunk them onto the inserts. Nothing else required, they weren't going anywhere!
Size does matter:
A better shot showing the air filter in place; after the 999RS engine inhalation debacle there was no way I was not lock-wiring the Ti bolts, even if a half dozen 1mm drill bits did die in the process:
Hmmm, it's actually starting to look like a proper airbox now....apart from the fact the air would still be ripping straight across the top of the bellmouths and out the back/sides: air moving across an orifice creates a vacuum (insert sound of game show "wrong answer" buzzer here).
Enter Grandma's "door snake" draft stopper: some adhesive foam strip to fill the void you could poke your fingers through:
Ease up on the sock-puppet face, I'm only sizing it up here planning the way forward. The tank base actually has the perfect flat edge, just begging for some sort of seal to be attached and I didn't need to be asked twice. Yes, it looks bloody awful above but it's reasonably unobtrusive with everything in place below:
So hopefully that would give the engine a filtered, pressurised, relatively stable volume of air to draw from, versus trying to suck from the previous cyclonic wind tunnel. On top of resetting the cam timing there really wasn't a helluva lot more I could do without tearing it all apart again. In my gut these feel and look like improvements, and will hopefully add up to something significant, but there's only one way to really know: "bring-bring....Mr Dyno-man? A table for 2 please..."
Oooh oooh, I nearly forgot! Some good did come from that aborted race meeting mentioned above. I'd had the ol' girl approved for Historic competition, log book issued (Period 6 New Era - Solo machines dated 1/1/1983 to 31/12/1990), I'd sorted my competition licence...but I didn't have a race number. So I was a lil' cheeky in making an enquiry about number availability, and absolutely stoked to put these on the bike:
Thanks must go to Nathalie, the Administrator Officer at Motorcycling Western Australia, for humouring my request, I'm sure she's busy enough without me being a pain in the arse.
This seemed like a good opportunity to take a few snaps...juuuuust in case:
