Push a broom when the handle is nearly vertical and it's pretty hard because there is a lot of friction between the broom head and the floor. Push a broom when the handle is nearly parallel with the ground and it's much easier. Same principle - short rods mean the pistons endure more friction with the bore. Long rods therefore are conducive to revability. It is possible to have rods that are too long though!
Daniel is spot on the mark - except a L20b is 85x86, making it slightly undersquare. Many people comment on the legendary FJ20's stratospheric redline, with it's 89x80mm bore/stroke. Another very oversquare engine is the 86x73.7 RB26. Coincidentally, note that neither of these engines are regarded as any good under 3000-4000rpm, which indicates the downside of motors designed to rev: poor low rpm torque. This is one of the reason why Holden and Ford make their engines so undersquare: torquey easy-to-drive motors make for good family cars. Wear also increases exponentially with revs, so to avoid having to actually make reasonable quality parts (witness the Holden V6 - cast internals when Datsun were forging everything but pistons 30 years earlier) they make engines which don't like to rev.... - Tom Ben C wrote: > umm, he was asking about the rod lengths, not stroke length > > yes the longer the rods the better it is up high int he revs, > basically because the maximum angle of the rod to piston gets less, > the longer the rod is....if that makes sense...probly not, its hard to > explain....someone else got a better explaination??? > > ----- Original Message ----- > *From:* Daniel Kroehn <mailto:[EMAIL PROTECTED]> > *To:* [EMAIL PROTECTED] > <mailto:[EMAIL PROTECTED]> > *Sent:* Monday, September 23, 2002 5:14 PM > *Subject:* Re: stroker motors > > Basically you have a ratio of bore size to stroke size. A typical > L20B is a "square" engine, i.e. 1:1 bore to stroke ratio. As the > engine becomes more and more "undersquare" (bigger stroke than > bore diameter), the piston has to travel a greater distance down > the bore for a given engine rpm than a shorter stroke engine. > This means that the piston speed for the undersquare engine is > greater even though the engine rpm is the same as a shorter stroke > engine. Basically engine materials dictate maximum rpm that can > be achieved from a particular bore to stroke combination. The > reason for the high revving formula one engines is about a 2.5:1 > bore to stroke ratio, i.e big bore diameters and really short > stroke, this cuts down the piston speed to a level where the > engine materials can handle it. But anyway enough of my rambling, > to answer your question, a shorter stroke engine will have a > tendancy to rev more than a longer stroke engine simple as that. > > Cheers > > Daniel Kroehn > > > ----- Original Message ----- > *From:* David Costello <mailto:[EMAIL PROTECTED]> > *To:* [EMAIL PROTECTED] > <mailto:[EMAIL PROTECTED]> > *Sent:* Saturday, September 21, 2002 11:05 PM > *Subject:* stroker motors > > guys, when building a motor using a stroker crank, which is > better....longer rods and shorter pistons? or shorter rods and > taller pistons? > > I assume because increasing the stroke is going to slightly > reduce the engines ability to rev then longer rods and shorter > pistons would give back a little of the revability? or is it > the other way round? > > Internal engine physics was never my thing, any help would be > greatly appretiated guys...I don't want the engine to shake > itself to death at high revs, and it will be seeing quite a > bit of boost too. > > Dave > > --membersozdat------------------------------------------------------- > > OZDAT Mailing List Please Note:- > Send (un)subscribe requests to [EMAIL PROTECTED] > Send submissions to [EMAIL PROTECTED] > No unauthorised redistribution of this email > http://www.ozdat.com/ozdatonline/index.htm > http://www.ozdat.com/ozdatonline/listindex.html > http://www.mail-archive.com/[email protected]/ > --------------------------------------------------------------------- > > > --membersozdat------------------------------------------------------- > OZDAT Mailing List Please Note:- > Send (un)subscribe requests to [EMAIL PROTECTED] > Send submissions to [EMAIL PROTECTED] > No unauthorised redistribution of this email > http://www.ozdat.com/ozdatonline/index.htm > http://www.ozdat.com/ozdatonline/listindex.html > http://www.mail-archive.com/[email protected]/ > --------------------------------------------------------------------- > > > --membersozdat------------------------------------------------------- > OZDAT Mailing List Please Note:- > Send (un)subscribe requests to [EMAIL PROTECTED] > Send submissions to [EMAIL PROTECTED] > No unauthorised redistribution of this email > http://www.ozdat.com/ozdatonline/index.htm > http://www.ozdat.com/ozdatonline/listindex.html > http://www.mail-archive.com/[email protected]/ > --------------------------------------------------------------------- --membersozdat------------------------------------------------------- OZDAT Mailing List Please Note:- Send (un)subscribe requests to [EMAIL PROTECTED] Send submissions to [EMAIL PROTECTED] No unauthorised redistribution of this email http://www.ozdat.com/ozdatonline/index.htm http://www.ozdat.com/ozdatonline/listindex.html http://www.mail-archive.com/[email protected]/ ---------------------------------------------------------------------
