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Kawasaki 350 F discussion forum:RE: 165MPH ´71 Kawi F-9 |
| RE: 165MPH ´71 Kawi F-9 |
| Charles said 2004-12-15 09:15 |
| J. Kuss; I wrote a lengthly reply a couple of nights ago, but when I sent it something "choked" and my server never would connect to send it.. I cannot duplicate the message, but I will try to hit the "highlights" of it.. Back in the late ´60´s (I believe) an engineer had a theory about extracting large amounts of horsepower from small, underpowered engines. Eventually, to prove his theory, he took a Kawasaki F-9 engine, as it was undoubtedly the poorest "horsepower to cubic inch" ration around, and worked his magic. This engineer´s name was Kevin Cameron and he wrote an SAE White Paper to detail out his theory and findings. Around 1970 I wrote to Kevin Cameron (I got his mailing address from Kawasaki), requested and received two typed written pages of modifications to transform the 350cc F-9 engine into a Fire-Breathing Dragon. After I finished my engine, mounted it into a Bridgestone 350GTR frame, I had it Dyno Tested.. it put Fifty Horsepower "On the ground".. that was a lot for a 350cc engine at the time. If I still have those two pages of specs, there are packed away and buried somewhere in "my stuff"... you might try contacting a Kawasaki Distributorship to see if they might still have a copy, of maybe do an Internet Search for published SAE White Papers.. I can tell you that "just" modifying the F-9´s engine will NOT produce a 160+MPH bike.. the internal Primary Ratio is too "low".. the F-9 is, after all, a trail bike.. I did a little "modifications" of my own on the Primary Ratio and the F-9´s gearbox.. First, I obtained a gearset from the 250cc F-81M Motorcrosser.. it is a "Close Ratio" gearset then I exchanged the F-9´s Clutch Hub for one from the H-1 500cc triple.. The clutch disks are the same size, but I installed a set of Barnett Racing plates. The "ring gear" on the H-1´s hub is smaller so it didn´t contact the crankshaft pinion gear.. I took an H-2 750cc triple pinion gear.. it mated with the teeth on the H-1 Hub, but the mounting hole was too large for the F-9 crank.. I had to have a special "double tapered spacer" machined in order to fit the H-2 pinion gear to the F-9 crankshaft.. This gave me a very tall Primary Gear Ratio. Coupled with a Fifteen Tooth Countershaft Sprocket running a 530 chain to a Thirty Tooth Rear Wheel Sprocket, I transformed an engine that would "cruise" at 55 MPH in top gear to one that "peaked" First Gear at 55 MPH! The bike I built tipped the scales at 255lbs "wet" (filled with gas & oil). I fitted a Honda CB750-4 Front Hub to the Boranni front wheel so I could have a Front Disk Brake.. The speed the F-9 reached needed a good "anchor" to get it stopped! Additionally, I fitted a Fiberglas gas tank, seat and "Dolphin" Fairing for aerodynamics... which were the best at the time, but crude by today´s equipment. The modifications to the F-9´s engine aren´t anything "radical", just the "usual" porting of the cylinder & piston, CCing the head & machining a 10mm "Squish Band", shaving the rotary valve and fitting a 38mm Mikuni Carb (I´m pretty certain it was a 38mm.. might have been a 40mm). The "serious" modification was in the design of the expansion chamber.. it was huge!! So big, in fact, that I had to build it in such a manner that it ran under the centerline of the RoadRacer, otherwise it would drag the ground in the corners.. not a good thing to do.. I know, I laid over a twin cylinder, the pipes drug the ground, lifted the rear wheel and down I went at over 100 miles per hour!! Fun ride, but them damn stops are what hurts!! We ran "low-to-the-ground" frames "back in the day"-- modern RoadRacer frames are much higher than ours were, this might be a better option for you to think about. The specs for the expansion chamber were included in the Kevin Cameron Specs for the F-9 engine. The important thing this expansion chamber did for the engine was to give it gobs of torque from 3000RPM to 9000RPM.. It had so much torque, in fact, that the simple act of "speed-shifting" into third gear produced a 45 degree "wheelie".. I was running right at 100 miles per hour when this happened and looking "down" thru the fairing, beside my front forks, just to see where I was going!! Even when I shifted into fourth (after "landing" the bike like a 747), it got "light" in the front-end. I cannot address your comment about building a Monocoque Frame, as I know nothing about the design. I can say with authority, that I would not want to build a frame that was "too light" and power it with a modified F-9.. not unless you had the "balance" slighted towards the front.. and that would take some serious knowledge of chassis engineering. Not something I possess... I don´t know if you ever rode a Kawasaki 750cc Two Stroke triple or not.. it was a heavy bike (500lbs or so) but it was so light in the front it was all one could do to keep the front wheel on the ground.. this bike was deadly! It was dropped from production in favor of the (then) new KZ-650 (which evolved into the KZ-750 then the KX-1000).. As far as building a Cafe-Racer using the F-9 engine, that was my intention after I "retired" from Professional Racing.. My F-9 as it is geared (both Primary and Secondary) is basically "unstreetable".. low gear is "too tall" for stop&go traffic and one could never use fourth and fifth gears with the Seventy Mile Per Hour speed limits on the freeways.. if one did, he´d be "lugging" the engine. A "simple" solution would be to change the Secondary ratio (drive sprockets).. the downside to that is, if you use a thirteen tooth countershaft sprocket, as an example,the power transfered to the rear wheel would be so quick that one would have to be damned careful to not flip the bike completely over or incur unexpected "high-speed wheelies" when shifting gears. In short, an all out modifided "GP RoadRacer Engine" would not be a wise first choice for a street bike.. but that´s just my opinion.. The upside is, due to the wide powerband the modified F-9 produces, one could easily "cruise" the freeways in the 3000/3500 RPM range and probably be passing everything on the road ;-} Sorry I could not supply the specific modifications.. that was, after all, thirty-four years ago. I wish you well in your search for these specs and success in building your Monocoque framed Cafe Racer.. Keep me posted as to your progress and zap a pic of the bike when you get it finished. Charles. (Former AMA Pro #185N) |
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