|
: : : I have been following this thread with a great : : deal of interest. I am somewhat reluctant to add
: : a post due to the fact that some of you people : : evidently are very knowlegeable on this subject.
: : My question: When you stroke a MM engine, what do
: : you do about rods? Do you find a suitable replace-
: : ment off the shelf, or do you cut and weld an : : original? Sorry if this seems like a "stupid : : question", but I have no experience in this area
: : and am curious as to how you engine builders go : : about this. : : A new post to move this discussion to the top
: : : of the pile. : : : I have been following along and wish to add my : : : two cents.It has been said that these tractor
: : : engines have little in common with automotive
: : : engines, which is not true.They are both Otto
: : : four cycle engines.The principles to improve
: : : engine performance within a given RPM range are
: : : the same!
: : : That said, rod/stroke ratio is important to max-
: : : imizing power because of its' relationship to cam-
: : : shaft specifications.Translated, that means the
: : : valves need to be open and closed to seal maximum
: : : pressure in the cylinder.Valve movement needs to
: : : be timed just like ignition does.Piston acceleration
: : : with lower rod ratios happens sooner, in crankshaft
: : : degrees,than with higher ratios.Two engines, identical
: : : except for rod lenth, would need to have the camshaft
: : : "degreed" differently to make the most power.
: : : IHRA pro stock cars have 800 plus c.i. with rod
: : : ratios low as 1.25, the point being not to give the
: : : competition a cubic inch advantage for a better rod : : : ratio.Even though racing V-8s rev much higher than
: : : pulling engines, they still operate in a narrow rpm
: : : range,similar to pulling.
: : : Acceleration is crucial to pulling, even antiques
: : : because momentum will help you go farther, especially : : : in classes under 5500 lbs.Otherwise, why would we
: : : need taller gears and faster ring and pinions?
: : : To help compare engines of similar horsepower but
: : : different displacement, remember this formula.
: : : torque times rpm divided by 5252 equals horsepower. : Replacement rods for stroker applications are often from
: other engines. An engine is laid out on paper, a length is
: geusstimate is made, and you start looking for something close.
: Often when offset grinding a crank a small rod journal big end
: is welded to the little end of the original rod to : get the correct length. Farmall H big ends are a common donors
: when using this method. Custom rods, forged and billet, are
: now available from several manufacturers. While expensive,
: these do gaurantee the rod is not twisted or bent. Hope this : helps you, remember a "stupid" question is cheaper than a
: "stupid" mistake!
|
