I went into Ferracci's outside philly and the big man there said they used to make a cb350 race engine that put out 50hp. He could be talkin out his ass tho, he was pretty old. old people lie a lot, like my gramps who told me I was smart...
Aren't the full tilt Todd Henning 350's supposed to be 50+ hp? I mean + like in 57 hp. That's with the scary Todd pistons and the head completely reworked with new valve angles, giant valves, and I think dual plugs. Kinda hard to believe.
In general it's staring to appear to me that without really digging in and changing fundemental design, the most you are going to get out of a two valve, SOHC four stroke is about 120hp per litre. Which is only 42hp on a 350... so maybe I'm full of crap.
johns probably right. i dont know about 57....but i know chris' and franks are doing 50-52. chris' pistons are todd copies, then also modified to the chris standard. ive had the chance to get a nice look at franks and chris motors in the past few weeks and they have plenty of trick shit. 4mm valves, lightened cranks, big motor studs, etc etc etc...apparently todd used to get his cranks so lightened theyd explode on occasion. chris' motor had the boretech cylinder coating etc etc etc...he chewed the crap out of it last summer though. lost a pin clip and it trashed the entire motor. chris claimed he had 4000 into his top end alone when it was new. that almost borders on just stupid. (an i mean "stoopid", not dumb). 51 is pretty common. id like to know what buff's getting out of his.
Waisted valves do seem kind of like a freebi as far as breathing goes. I was all set to go to 4mm valve stems in my 175 until I talked to some experts. Vintage motors often have short valves guides that offer little support for the valve, along with rocker arms that side load the valve. Unlike modern engines with longer guids and cams that act directly down on the valves. Also heat disipation is a problem with vintage valves and smaller diameter stems transmit less heat to the guide.
So waisted valves are kind of the best of both worlds, you get your larger OD valve stem in the guide, and a smaller OD in port, plus some reduced mass. Not to mention that the valve is basically no stronger than the OD of the keeper notch at the top anyway, often a mm or so smaller than the large OD of the stem.
I'm having my head completely redone right now....forgot to ask for waisted valves though....maybe the guy will think of that one himself.
you should see these valves they use. they are so nice. i got a lecture on valve spring tension from chris the other night that was so mind numbing i wanted to kill him. actually, i shouldnt say that. what i should say is, i just dont get that interested in the performance index of my motor. man, guys like branson and chris m just have too much time to think about things like having the perfect valve spring tension. too much robs hp, not enough floats valves. im waiting for the day i can ride a 51 hp cb350 though. i guess it wont be this year. actually, i dont think chris's valves are waisted. they are just 4mm stems. really long and skinny. that was a misrepresentaion on my part. but who knows what the guides are made of in that motor. i dont. i guess if youre pulling it apart every season and rebuilding it, it really doesnt matter too much. i know his motors are built to the point of being on the line as far as reliability is concerned. like any more extreme, and it wouldnt hold together. are you sure todds 450 didnt put out 57?? it wouldnt surprise me if his 350s saw 57 on occasion. just before the cranks exploded. he used to say he replaced cams and followers almost after every weekend because of the oiling problems in the 450. im sure todd did tear downs after every weekend just to check things though. i really dont know anything though.
Yeah I kind of lean towards a little less power and more durability.... I'm not making, nor will I ever make, a living doing this stuff.
My heads are being redone with Ampco 45 guides and one piece SS valves. Mich Rich is doing the work and he pretty much talked me out of the 4mm valves. With the valve train problems that 350's are noted for I'm guessing Chris went with 4mm to reduce mass. That would then require less valve spring pressure and would help the rockers, cam and cam bearings last longer. Or I guess you could keep the same pressures and go to higher rpm before float. The 350 also has a larger valve, so more contact area with the seat to disapate heat, but that trade off gets complicated cause the larger valve soaks up more heat too.
The problem is you can only get so much air in and out of these old two valve engines. So when you are maxed out in breathing and compression you have to look for rpm. A little 175 like mine with a 41mm stroke is good to about 16,000 rpm before you hit piston speed problems. Yes the crank and rods would probably take the rpm...not likely the valve train would take more than 13,000. So that's the weak point, and one that's difficult...or rather..very expensive to solve. Ti valves would certainly help, then you are talking exotic stellite seats and such.
I'd be more inclined to build a freakin Ti frame, magnesium brakes etc to get the chassis as light weight as possible...see you don't often blow up your frame or brakes Spend the money once, use many times. Unlike exotic engines which often seem to be spend the money once, use the engine twice.