Wrist pin offset or Cylinder bore offset
Wrist pin offset or Cylinder bore offset
(OP)
Anyone here has dyno experience or has studied the effects
of wrist pin offset ???
And what about cylinder bore offset in either
with crank rotation or against crank rotation ???
Know the net effects ???
I've offset bored blocks along the crank axis to unshroud
larger intake valves, but never tried the other ways...
its one of those things i often wondered about or thought by know i would have tried !!
I did switch the pin offset (reverse pistons in bores)
on an Olds 455 cid Stocker engine in the late 1970s
..relatively small intake port cross-sectional area
for that size engine (455 cid W30 Olds) ...from that point on the car was faster in MPH trap speeds and a little faster in ET ...but does anyone here have better evidence ??? or data ?
of wrist pin offset ???
And what about cylinder bore offset in either
with crank rotation or against crank rotation ???
Know the net effects ???
I've offset bored blocks along the crank axis to unshroud
larger intake valves, but never tried the other ways...
its one of those things i often wondered about or thought by know i would have tried !!
I did switch the pin offset (reverse pistons in bores)
on an Olds 455 cid Stocker engine in the late 1970s
..relatively small intake port cross-sectional area
for that size engine (455 cid W30 Olds) ...from that point on the car was faster in MPH trap speeds and a little faster in ET ...but does anyone here have better evidence ??? or data ?
Larry Meaux (meauxrace2@aol.com)
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers





RE: Wrist pin offset or Cylinder bore offset
Never looked at crank offset either, except for a few brief calcs to answer a question here (did you know it changes the # of crank degs between TDC and BDC?).
RE: Wrist pin offset or Cylinder bore offset
RE: Wrist pin offset or Cylinder bore offset
Cheers
Greg Locock
RE: Wrist pin offset or Cylinder bore offset
It seems that offsetting the wrist pin would increase the tendency of the piston to rock in the cylinder bore.
RE: Wrist pin offset or Cylinder bore offset
Yes, you can alter the rocking behavior of the piston by offsetting the wristpin. Picking a good offset allows you to better control the piston rocking motion (to reduce "slap"). This is what I was alluding to in my prev. post about piston secondary motion. There are programs out there that allow you to simulate piston secondary motion, given sufficient information about the engine geometry. A search on yahoo for "piston secondary dynamics" should turn up such products (ADAMS, PisDyn, etc). I've had good experiences with the PisDyn - in the few times I've used it, I've found that the predictions match real-world evidence (measurements, skirt/liner wear patterns, etc) pretty well.
RE: Wrist pin offset or Cylinder bore offset
Rod