2mm over bore - Pointy?

[yorkie_chris]

Originally Posted by andrewsmith

Doesn't it mean the top RPM is elevated

No.
Maybe if you reduced stroke too, but still depends what is limiting factor, valve bounce or other valvegear issues, breathing etc. Then maybe you would use shorter rods as part of an overall strategy, which would include a new ECU. But still, no.

[andrewsmith]

Originally Posted by yorkie_chris

No.
Maybe if you reduced stroke too, but still depends what is limiting factor, valve bounce or other valvegear issues, breathing etc. Then maybe you would use shorter rods as part of an overall strategy, which would include a new ECU. But still, no.

and if your spending that kind of money go buy a TL, SV Thou or RSV as its still cheaper

Maybe they are a racer looking for an advantage

[yorkie_chris]

Originally Posted by andrewsmith

and if your spending that kind of money go buy a TL, SV Thou or RSV as its still cheaper

What are you doing in this thread Andrew? It doesn't seem like you understand the subject and that isn't too helpful to the man's question really is it.

[andrewsmith]

Fine I'll shut up.

Was wanting the Q I put in answered.

[Sid Squid]

Originally Posted by andrewsmith

Was wanting the Q I put in answered.

Rod length is decided very carefully when the motor is designed, primarily it will be a function of some practical considerations such as physical size of crank, and stroke length, but an important factor is crank/rod angle at various points in the cycle. Essentially if you were to change nothing else but rod length, (you almost certainly can't, but just entertain it for a moment), at midstroke for example a shorter rod would make a greater angle between cylinder axis and rod axis. The angle between the line of crankpin axis/main bearing journal axis, and rod axis is important in deciding the torque loading of the bearing and as far as is possible you'd like the maximum cylinder pressure to act on the piston when that angle is as close to 90 degrees as is possible, (of course the whole thing is dynamic thus constantly altering as the engine runs, so cannot be exactly 90), but you'd like to centre the best cylinder pressure around the 90 time as that gives the best mechanical advantage.

HTH

In short changing rod length is not something that would likely be contemplated in tuning unless lots of other things changed too.
Piston travel and swept cylinder capacity would not alter - those are functions of crank dimensions, (distance from main bearing centre axis to crankpin axis), Very generally speaking most engines pistons run very close to the crank at BDC, so in the case of a modern motor fitting a shorter rod means is that the skirts will get funky with the crank webs. And not in a good way .

the question was after info on a 2mm overbore not shall i have 2mm overbore or buy a tl 1000. very helpfull

Prilpot what pistons are you putting into this that require a 2mm overbore as I only know of the Hayabusa and the Wiseco 700cc (and beyond) ones.

its just something twf sells.asked him about getting more hp and he said easiest way would be do a 2mm overbore bored throttle bodies and cam swap.he says should make over 80 hp he normally gets 85.was just wondering if any one had done it to see on reliability.he did also say would hav to use stronger rods

[andrewsmith]

Well we've all got the wrong end of the question.