cbrian

It's totally finished now and tested. Banshee power makes it a real beast! http://www.apriliaforum.com/forums/showthread.php?303741-Gulf-Coast-Hybrid

It's been quite a journey with this bike, but the end is in sight. Just a little jetting and I'm off to the races. Thank you all for your posts, I get quite a lot out of them. This build can be seen on the Aprilia forum. http://www.apriliaforum.com/forums/showthread.php?303741-Gulf-Coast-Hybrid

The company making the cradle kit is Fast from the Past (www.fastfromthepast.com) and it is only to mount a Yamaha RZ350 engine into the Aprilia RS250 chassis. The builder I selected was F.A.S.T. (www.farmandsandtoys.com) . I talked to several of them listed on this forum and I felt most comfortable with them and they had excellent communication. He echoed what was said previously, that staying with the 68mm bore and 4mm stroked crankshaft was the best to go with. The oversquare 72mm bore wasn't going to give me much more perceptible power and with vibration being such a concern, it wasn't worth it. Thanks to all of you that posted constructive comments for me to read, you are a great resource.

I have quite a bit more information now than when I first posted. I am told by others that have done the Banshee/Aprilia hybrid that the stiffness of the Aprilia frame translates a lot engine vibration to the rider and anything over 7 mm extra stroke results in unacceptable discomfort. With that in mind, and the extra cost involved, I'll stick with the 4mm stroked crankshaft. The 68mm bore (421cc) serval engine is the minimum engine size I'll use but I am curious of increasing the bore to 72mm. This would make it a rather oversquare engine and I would like to hear from you forum members on your opinions of the pluses and minuses. I have selected a builder and have discussed my build with him but before going any further, I would like to have your opinions on this (72mm bore) alternate.

The chassis it will be put into is an Aprilia RS250. There have been many RS/RZ conversions out there and the Two Stroke Shop sells the cradle and mounts. Nova Racing in England is set to have a close ratio transmission in production for the RZ350 engine ready later in the year. My tranny concern is that the RZ and Banshee have different shifting drums and the RZ part is no longer in production. I'm trying to source one used right now. I would appreciate an education on the shift pattern and particulars on the Banshee shifting mechanism. I think that 95 HP would be acceptable with this bike since that is what my 2002 Honda CBR600f4i makes right now, but what I am really after is as smooth a torque curve as I can get. I love the two stroke hit, but don't want it when I'm cranked over really deep into a turn. Thanks for all of the replies, this helps.

Hello All, I have started the process of getting a new engine for motorcycling purposes. The bike will be used not for racing but for track days (see http://www.nolamotor.com/) which is riding as fast as you can stand for 20 minute sessions, one session per hour, six sessions per day total. I do three to four track days per year. As an old two stroke guy, I want my new engine based upon the yamaha rz350/yfz350 banshee and the research for information on this engine has led me to this forum. I had no knowledge of the banshee world and what you guys are getting out of what is essentially a 30 year old design is really impressive. My goal is to have an engine that can at the very least keep up with the current 600cc four stroke bikes which have about 50 lbs/ft of torque, 115 crankshaft horsepower and weigh 400 lbs. The machine I use weighs about 330 lbs, so power to weight would be 42 lbs/ft and 108HP. I wouldn't mind power a bit in excess of these targets. What I am asking for is recommendations and please be as specific as you can as to what components, manufacturers and suppliers I will need. Crankcase - stock or ? Crankshaft/bearings/rods Transmission modifications (need close ratio 6 speed) Clutch & drive ratio Cylinders - bore & stroke Power valve or not Cylinder Heads & dome size Pistons Intake Carburetion - filtration Power generation Ignition Lubrication Cooling Exhaust - silencers and anything else you see that I've missed Main criteria for me is: Reliability - (rebuilds too often makes for an unhappy wife) Parts availability - especially pistons Broad spread of power throughout the rev range - peaky power delivery upsets chassis too much Serviceability Fuel used will be non ethanol pump gas 93 octane Bike run at sea level Any recommendations for engine builders would also be appreciated. Thanks