Bore X Stroke

[rice_me_up]

hi all.

as the title states, why does haveing the bore and stroke the same (or similar) size make it capable of reving high? if im wrong dont flame me cos this is just what I have been told. by a very knowledgeable bloke, so i believe him.

cheers guys.

james.

[govich]

It doesn't. Short stroke motors generally rev harder. A shorter stroke means a lower piston speed for the same engine speed so basically you can spin it faster without breaking stuff.

[VB-]

yeah, i dont know if square (same bore as stroke) motors are rev happy, motors with less stroke than bore tend to be more like that. take RB26 VS 2JZ, the 2JZ being square, this is one of the reasons they hold together so much longer than the RB26, coz they dont really have to rev to make the power.

[Bl4cK32]

rb30 is a square motor (almost same borexstroke as 2JZ)

[Busky2k]

Of course the bore x stroke is not a be all end all of how hard a motor can rev. (Note; the valvetrain design is also very important!) For example, the Honda B18C was actually undersquare, despite the fact that it revs easy to 8000rpm+.

[andylaurel]

motors with a very short stroke are capable of revving significantly harder than motors with equal bore/stroke, or longer stroke.

A motor with a long stroke, however is capable of producing more torque at a lower RPM.

This is why the SR20 makes MORE torque than the RB20 whilst having the same capacity.

[rice_me_up]

ahhhhh! i get it now. thanks for your help every one.

cheers. james.

[T.F.S.]

on a long stroke engine the piston has to travel a further distance than in a short stroke version, that means travelling faster and causes more stretch on the rod which means tougher materials or a lower rpm limit

[Mandingo]

Is there a rule of thumb for a certain amount of stroke can only go to X RPM?

[mad082]

i don't think there is a rule for stroke vs rpm. it partly comes down to the design of the rest of the motor. the cams and timing and valve ports, etc would play a role in it too.

but it is also a case of what the motor is being used for. if you have an engine that revs itself into next week, and want to use it for towing, it isn't going to be very good, but if you have an engine with a nice long stroke, then it is going to have bucket loads of torque so it will just chug along.

[R33S14]

Yeah i know this is a stupid question but what is the stock bore on a series 2 RB25DET.

[Piggaz]

Yeah i know this is a stupid question but what is the stock bore on a series 2 RB25DET.

86 mm