Very short stroke 250cc single! Advise appreciated.
Very short stroke 250cc single! Advise appreciated.
(OP)
I am currently building a 250cc 4 stroke single which employs an extreme b/s ration of 1.6...b=80, s=50. Does anyone know of any practical probs im going to have in reality? im especially concerned with the cam timings, i have used a 165mm long con rod, it is 4 valve and on Methanol although due to the c/r prob may have to use petrol or a mix.
Also to make my life easier i would like to build the other with a 85mm bore but this would mean 45mm stroke!!! surely this is too extreme! Is this beyond the limit of possibilities?
Any help much appreciated.
Also to make my life easier i would like to build the other with a 85mm bore but this would mean 45mm stroke!!! surely this is too extreme! Is this beyond the limit of possibilities?
Any help much appreciated.
RE: Very short stroke 250cc single! Advise appreciated.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Very short stroke 250cc single! Advise appreciated.
I was a bit worried with it only being a single cylinder, the only thing i have a few variables and doubts on are flywheel weights? You got any ideas from experience save me alot of R&D and hassle...although supposidly thats half the fun!...
If i can stick with the Meth than knock will definately be out of the equation so one less problem to worry about. I have several valve sizes in mind, im lucky enough to have a few heads that ive started on different combos, just have to try it all and see....thanks mate.
RE: Very short stroke 250cc single! Advise appreciated.
Why a single cylinder 4 stroke? This is a heavily traveled area and for the most part the factories dumped that type of setup nearly 50 years ago. Multiple cylinders proved to be waaay more powerful.
RE: Very short stroke 250cc single! Advise appreciated.
Was hoping someone had some hands on experience with these type of b/s ratios on a single, i know they are quite common on multis...cbr 6 being a good example, but i dont have the luxury of 3 other cylinders to help keep things moving...
RE: Very short stroke 250cc single! Advise appreciated.
Do the rules alow adding some ports and making it fire every revolution?
If not maybe you can run a hundred PSI, or so, in the crankcase and lighten up the crankshaft
RE: Very short stroke 250cc single! Advise appreciated.
As far as i can make out there is no restriction on ports?? I can only use 1 carb and 1 exhaust (not that this would matter?)but it does say the engine has to be N.A with no forced induction?...now i know that rule is in place to make sure turbos and s/chargers are not used, would using crankcase pressure be `normally aspirated`?...bit of a grey area, i`d have to get written confirmation i could do it if i were to?......still worth looking into though..if you have any info it would be much appreciated.
Many thanks.
RE: Very short stroke 250cc single! Advise appreciated.
It was two different "ideas". The first one, if you did not get it, was to run a 2-stroke. They don't suffer much from sticking to a single cylinder and they can put out tremendous power.
The other was just a 5 second frivolous whim thinking about making a 4-stroke single rev higher, no ports on that one. F1 uses air for valve springs, why not air for a piston spring? I'm sure there is no rule against it, nor would I mention it to them.
RE: Very short stroke 250cc single! Advise appreciated.
Need valve sizes, head config. port sizes and lengths, air/water cooled etc. What is the basic engine your starting with and what are the class restrictions. See if we can build you a world beater!
RE: Very short stroke 250cc single! Advise appreciated.
Never liked 2 strokes, never will but i do respect the huge power they can achieve from relative small cc.
the phantom, going to be playing around with it a bit his weekend, will sort out some facts for your `number cruncher` and see what comes out. Its all a bit `vague` at the moment with regards to ports, head cc etc..
Thanks for the tips everyone.
RE: Very short stroke 250cc single! Advise appreciated.
RE: Very short stroke 250cc single! Advise appreciated.
RE: Very short stroke 250cc single! Advise appreciated.
All a bit experimental but...4 valve, OHC, single cam, air cooled, methanol fuel, inlets: either 29, 30, 34 or 35. Exh: same sizes, prob go with 30 (mm) but depends on what choice of bore i use...either the 80 or the 85.
port size and length unsure on, unmanifold length is in the region of 75-80mm inlet and 70mm exhaust!...shared/siamesed ports for each valve.
As for rules!..basics are 32-36mm single carb, unlimited single exhaust although diameter has to be uniform onlong its length, capacity: 250cc.
No electronic aids permitted.
Running either motoplat, selettra, PVL or interspan.