eyolf
Addicted to ArboristSite
Somewhere in the dim recesses of my memory stands a tidbit of data suggesting that at higher rpms the oil in an engine becomes a sort of mass around the rotating crank, staying with it unless pulled off by oils scrapers...some engines experience oil starvation because not enough oil was able to be picked up by the oil pump. This was but one reason for dry-sumping.
Another reason was that it takes power to pull that mass of oil around. Even if you can make power to spare with nitromethane, why "tip the can" any more than you must?
Forgive me if I'm missing something, but does that apply to two-stoke engines, esp in chain saws? The link talks about long-rod engines with high decks and tall pistons. Chrysler hemi's fit this description, as do such engines as Ford's FE series, the old AMC 287/327, the GMC truck V6, Buick and Olds V8's and the IHC binder V8. Long rod engines are more forgiving and torquey, but more important, are cheaper to manufacture because tolerances for such things as bearing clearance, piston-pin offset and con-rod "twist" are more forgiving. Ignition timing is often a bit "later", as the piston effectively "dwells" longer near TDC, but the pounding effect of preignition and/or lugging on bearings is slightly reduced because the crank has had the opportunity to swing a little farther around, softening the blow. All good things for a mass-produced truck engine.
Chain saws are designed to be as compact as possible, reducing the likelihood that somebody would succumb to the urge to stretch them out, long-rod engines usually have flatter torque peaks and at somewhat lower rpms, but in two-stroke engines the long-rod engines have fallen from favor because making space for that rod entails reducing crankcase compression ratios (and power, efficiency) too.
Plus, there better not be enough liquid anything rolling around that crancase.
Another reason was that it takes power to pull that mass of oil around. Even if you can make power to spare with nitromethane, why "tip the can" any more than you must?
Forgive me if I'm missing something, but does that apply to two-stoke engines, esp in chain saws? The link talks about long-rod engines with high decks and tall pistons. Chrysler hemi's fit this description, as do such engines as Ford's FE series, the old AMC 287/327, the GMC truck V6, Buick and Olds V8's and the IHC binder V8. Long rod engines are more forgiving and torquey, but more important, are cheaper to manufacture because tolerances for such things as bearing clearance, piston-pin offset and con-rod "twist" are more forgiving. Ignition timing is often a bit "later", as the piston effectively "dwells" longer near TDC, but the pounding effect of preignition and/or lugging on bearings is slightly reduced because the crank has had the opportunity to swing a little farther around, softening the blow. All good things for a mass-produced truck engine.
Chain saws are designed to be as compact as possible, reducing the likelihood that somebody would succumb to the urge to stretch them out, long-rod engines usually have flatter torque peaks and at somewhat lower rpms, but in two-stroke engines the long-rod engines have fallen from favor because making space for that rod entails reducing crankcase compression ratios (and power, efficiency) too.
Plus, there better not be enough liquid anything rolling around that crancase.
