Somebody needs to update these pics!
'Cause I just bought a fiberglass air-box for my DOHC-4 "CB900K0 Bol Bomber", and I'd like to make some copies of the thing at some point.
Even better than that however, would be to concoct a DOHC-4 appropriate version of the Sand-Cast "Lunch-Box" - after all this is the main reason why I got this new one in the first place. Well, that AND some twit P.O. or rather either the mechanic he paid to upgrade the bike or the mechanic who was the P.O.'s P.O. (I was too busy OGLING my new purchase to listen! Ha-ha) stuck PODS on my CV carbs! ARGH. Crazy thing, is having been distracted by all of the REAL upgrades to the bike, I hadn't even looked at it critically long enough to notice the things, I hadn't even formulated the word "PODS" in my mind, and yet when I rode it for the first time I felt this massive FLAT SPOT IN THE MIDRANGE! Argh. Yes - off topic I know, but one should never even mention POD filters on a DOHC-4 without clarifying how and why they are such a P.O.S.!
So yeah, I've either gotta figure out a way to stick a really good K&N OEM style filter (or more to the point, a proper paper filter element/cartridge with the same rated CFMs as the OEM style K&N filter from my old 750's OEM air-box - OR the CFMs rated on the individual filters, times 4 - for an appropriate flow rate or restriction to match my current jetting setting (Jet-set?) OR - have a Sand-Cast box made with a smooth flat forward face so that it can have the correct pattern of HOLES drilled in the front of it.
To tell the truth, my next DOHC-4 project is gonna be a low-tuned 750 ie the DOHC-4 motor from the 'C model or 'K model - at least, those are the frames I'm looking to work with, anyhow. But yeah - my point being, I'd really like to try and set one up with the SOHC carburetors. It's a cheaper mod than Keihin CR's yet they're still direct-pull carbs. AND they'd fit the SOHC air-box. Just gotta figure out whether there are BOOTS which will set the correct spacing for the SOHC carbs to match the DOHC head. Gotta look around the 'F-orums (
www.cb1100f.net) to see whether it's been tried. If anywhere probably on the
www.cb750c.com forums. Sure would be nice to see that somebody else has done all the hard work! Seems like it'd be a good mod though. Probably #$%*ty for the FUEL ECONOMY mind you, but for quick power on short jaunts? BAH - not what I wanna do with the bike anyhow. Yeah - a custom-made Sand-Cast style air-box would be the way to go.
Either way I'm sure there's gonna be plenty of demand for this same air-box IF I can make a copy of it. That is, once I've found some legit pics of it's use on classic racers, after sorting through all the pics of Keihin CR direct-pull carbs with POD filters on 'em ha-ha.
I've done plenty of work with moulds, and plastics & the like. A little bit with fiberglass - I'd love the challenge of a project like this. What's more, I'd love to have a little more freedom with body-work design. Rather than just tossing together a mix of random parts, I'd prefer to take something from the drawing on a napkin phase through to a real physical object.
Well, I've certainly done that with SMALLER parts, or less vital parts. But an air-box would be much more substantial.
I've heard it said before, that if you want a smooth running engine and straight across the line fuel economy, but with more power - then you need a bigger air-box. Maybe that's just a bunch of hot air? Well I accept it on faith.
With that in mind, and this idea of giving my DOHC-4 more of a Sand-Cast/Retro-Fried aesthetic, I've tinkered in the past with a DIY air-box made from thin ABS sheet. But what always appealed to me more would be an air-box more analogous to the OEM unit, but filling out more space under the seat. With a smaller gel battery, relocated tool-box, relocated electrics etc - the battery up in the fairing for instance, more like the Duck Pantah racers etc - well there can be a whole lot more room under the seat - As a lot of these newfangled Starbucks-Racers with the empty sub-frame section so "clearly" show!
Well, I'd love to try something like filling out that entire space underneath, right out to the bulbous surface of some decent side-covers etc, with one voluminous air-box with one enormous air-filter perhaps with successive stages or maybe just a very large air-box with a very clean filtrate due to smaller absolute particulate sizes? The idea being, to tune the engine for all available/feasible power, and yet maintain the smooth idle and low fuel consumption at lower RPMs etc, of the OEM configuration. Hard to imagine how you'd seal that entire space relatively air-tight and yet the parts be removeable and quickly replaceable - but perhaps instead of a tuned "snorkel" one could simply account for the air getting through the cracks?
What I'd REALLY like, is if the box could connect to the front of my bubble-fairing, not so much for a "Ram-Injection" type of thing, like was so amazing to us all when the ZX7 came out ha-ha. No I'm thinking more about the air TEMPERATURE more so than the pressure - Rather than collecting the inlet charge from BEHIND the cooling fins of the head & barrels, oil-cooler, HEADERS or even the space directly under MY ASS for that matter - I'd rather collect the inlet air from out in front, suitably screened for insect ingestion of course. Like you'd wanna have a bumble-bee sized filter then a honey-bee sized filter, all the way down through the gnats & "No-See-Ums" - but the inlet air would be as cool and as dense as possible.
That stuff makes a huge difference. The first ride I ever took on my newly purchased/rescued first-specimen '82 CB750F, I had to cross 250km of rapidly freezing ICE FOG, in Southern ALBERTA at the end of NOVEMBER - had to stop at every town along the way to buy more and more pairs of full-body long underwear, socks, gloves, etc - in increasingly larger sizes. Wrapped up in a good 10 or 12 layers of fabric plus newspapers and a big winter over-coat on top of it all, ski gloves over 3pairs of thinner gloves with fingerless gloves sandwiched in between, and clear packing tape all around the seam of the visor on my new full-faced helmet - I made the last 50kms of the trip with the needle wrapped at an indicated 275kph with a tail-wind of 100kph and brooding black clouds all around, snow beginning to sprinkle, and my first-"wife" trailing behind in the car so I could jump indoors with the heat cranked every 15-minutes or so the whole way home, so many cups of hot cocoa I was pissing like a race-horse, and a couple of rubber hot-water-bottles pressed against my chest. Forgot about that part but yeah I even bought the little tiny baby-sized one that was the last on the shelf. Kept it for years 'cause there wasn't much other use for it - they had little woolen booties around 'em too, in creamy yellow & orange plaid. Suffice to say I looked like an over-stuffed garbage bag and it was really hard to tuck into a proper crouch with all that bulk around my crotch and my gut - Probably only equivalent to the weight I've gained since then ha-ha. ANYWAY yeah - revving well up past the red-line, the needle wrapped tight against the pin a good 15-30-degrees of rotation past the 240kph last increment on the dial, I found ample resources of power in that engine.
Which NEVER came back again! I think it's pretty safe to say the bike was newly rebuilt - It came from a police Impound auction, was registered in Ontario, had new squiggles of RTV silicone squished from out of perfectly clean cases, fresh paint - and oil so clean it looked like nobody had even cooked any french-fries in it yet - Could very well be that I was "breaking it in" - and before you disparage how I burned some poor schmuck who'd been nabbed for tickets, let me point out that I paid all of $375 and that's Canucks, for it - albeit in Y2K dollars so not nearly as de-valued by inflation as today's money. But even so - If anybody else there had valued the bike they might have bid against me more than twice ha-ha. I'm pretty sure that was some old Farmer who wanted to use the engine to light the bulbs in his chicken-coop. I RESCUED that bike. If it's owner was in the clink I'd guess they got nabbed for more than speeding. Maybe they were a free-lance 'pharmaceuticals' courier or something. Maybe they had some teenaged abductee strapped to the back seat, headed out to one of our famous under-aged Bigamist "religious exemption" weddings - or some such.
I've always went on the premise that the bike scared 'em into a heart attack whereupon their grip went slack and their foot went off the rear-set peg and flipped the side-stand down as it dropped. The P.O. would've been found dead with a huge grin on their face while the engine still purred on a bike standing waiting for it's next rider - like the legend of "the dead man's gun" ha-ha.
Either way, that's not the point where I blew the damn engine out by revving it too hard, fact is I rode it just like the first time over the next two or three seasons until the oil-pump sucked bubbles into the crank bearings on a ride home from dropping my then-GF off at work, outside the city, some five minutes after we woke up in a panic. A screeching black streak of rubber all the way there, then the way back had the typical Southern Alberta Westerly 100kph tail-wind exchanged for a head-wind. They really ought to make half of the roads meander back and forth in a sail-boat's "Tack" so as to use that wind on carefully constructed aerodynamics, it would probably save millions in fuel costs every year.... But yeah - it died from being strangled around the twisted neck of it's throttle grip.
But that power NEVER returned. I mean, it had some piss & vinegar for a bike of it's age & displacement, but that initial first impression completely ruined it forever more, 'cause I'd always be itching for that little bit of extra juice.
And I believe that power loss was due to the air temperature being something like 60-degrees Celcius different and there being far less free Humidity in the air let alone half formulated aerosol particles of SLEET in the air, a palpable ice-fog that dropped the visibility down to some number of vehicle lengths. Tough to say just how MANY vehicle lengths, but at times I was following the road by looking at the painted strips alongside me more so than looking at the horizon ahead. Notorious stretch of highway for that time of year. The "Granum Road" was where I set my "all time personal best" etc.
So, being that refrigeration equipment would add even more weight than a Super-Charger and water-injection set-up, well for all intents and purposes the same damn thing - I'm thinking the tunnel from the front of the fairing to the air-box would be one heck of a fix.
Thing is, while a narrow inlet might be only so restrictive in and of itself, but when you stretch it out in to a PIPE, there's additional back-pressure with every inch that it's extended. Plus if the pipe's gotta be pinched here & there, bend this way & that, it's gonna cause further back-pressure.
This would actually make for a really nice use of an EGLI style back-bone frame. Especially when the engine isn't dry-sump lubed and you don't need the back-bone for an oil-tank. Just leave it hollow and channel the air from front to back. The Yamaha Virago did something similar, but it still ran in the opposite direction. So much the pity.
So I guess the trick would be to put it through the "tunnel" under the tank, and to have adequate heat-shielding across the bottom surface of everything. Just for a start. And then you'd have to figure out how to route the thing past the oil-cooler hoses, past the FORK, past the headlight, etc. Heck of a big & complicated project.
And my project's ALREADY complicated enough! Ha-ha.
But there's serious potential for it. Yanno what I'd use, would be some thin-wall thermo-plastic tubing, something you could heat up in the oven, thread through the tunnel of your bike up to the front, then hook up two plugs on either end and pump compressed air into the one end, bleed out from the other through a slow restrictor just enough for flow enough to cool it yet restricted enough to expand the tubing as much as possible - Maybe run two of 'em along either side of the main frame back-bone, maybe even do it with the tank on so as to make best use of the tank-tunnel space - then hook 'em up to rubber booties at either end of it. Maybe that's something else which could be constructed at home? Not vulcanized rubber per se, but silicone? Just a brain-fart. Probably better to go with a hard-line all the way from one end to the other, screw 'em to the air-box with a gasket etc.
But it's still a really good IDEA! Ha-ha.
Okay for the time-being, I'm gonna settle for a DIY air-box, or in the interim, adapting a copy of this old original Egli/Rau DOHC-4 "four-in-one velocity-stack" into an enclosed air-box with a FILTER inside. And hopefully it'll suck air from the TOP at least, or the sides - anywhere but right off the damn barrel fins!
Yeah, it's the BOTTOM half of this air-box which I need to be concerned with.....
-S.
