Certainly the rod stroke ratio is improved by a stroker crank with longer rods to help match the original ratio. Conversely, using shorter rods with the longer stroke makes the ratio significantly wider.
Using a stroker crank along with factory length high quality rods, such as Carrillo rods, along with very lightweight pistons to reduce some of the strain on those rods, seems to be a reasonable compromise. No?
George
George, Are you reigniting the late great Smokey Yunick debate? I'm thinking the current ProStocks have been moving down from that magic 1.8 ratio of yesterday.
I’m not trying to reignite anyone’s debate(although I have great respect for old Smokey😉) RC Engineering’s method was to do a 6mm over weld up stroker crank using dark ages techniques, then combining that with 3mm shorter than stock Golden rods. It surely made a less than ideal situation.
I’ve read a number of articles from well respected engine builders on the rod/stroke subject. Most agree the longer rod offers less overall stress on the piston/walls with its slightly more vertical focused force on the pistons. But often there is assumed to be a point of diminishing returns.
As in, once you reach a rod/stroke ratio of X, there is little to nothing to gain from going longer on the rods as compromises in other things start to make up any added gain. Most of the reference material I have read on the subject were related to V8 auto engines, so it’s just a general situation. What that tip over point is for out sohc4s, no idea. Perhaps what is considered reasonable for an all out race motor is different from a big street gas compression registered road bike? The race motor will undoubtedly put more stress on the rotating assembly with the extra power used and situation(drag racing, road racing, land speed). All of these are a lot harder on an engine than driving on the street. Unless someone has a death wish anyway😳
If I were set out to race a big bore stroker engine in a very demanding situation (I can’t think of anything more severe than Bear’s heavy total all up weight sidecar road racer😳) then absolutely going with a set of 1100f rods(1.5mm over stock) makes total sense as it puts the rod/stroke ratio back to reasonably close to factory.
I have a motor that was drag raced for many years in the late 70s through the early 90s with an RC welded stroker crank and factory length rods with a stroker plate and standard compression height RC 73mm H/C Arias pistons. Lots and lots of 9.xx second passes on a D&K lay down frame(it was owned by David Morgan from St Louis at the time). That crank may very well have been an anomaly for lasting as long as it did. Reportedly it was retired from service because of fear of it being tired rather than because it failed.
I’m not convinced of anything on the subject, but I’m interested in hearing more opinions about it.
George
