The higher the compression ratio, the greater the need for harmonic dampening which may be why many of the 239’s didn’t have a damper to begin with.  What’s probably misleading on the Y-Block damper is the dampening ring being behind the belt pulleys so it’s not overly obvious.  ATI does offer a Y-Block specific damper which is of the dual elastometer design and there are also some fluid filled dampers also available for the T-Bird engines (these are longer than the passenger car units).  The scrub damper can be fitted as the crankshaft snout on the Y is only ~0.004” larger in diameter than that of the scrub.  The scrub damper can be honed to size or the Y crankshaft snout can be turned down to fit; I have done it both ways and would rather hone the damper at this point in time.  Aftermarket scrub dampers are easier on the pocket book is the obvious reason for using them but a new timing pointer will need to be fabbed to get a correct timing reading on the retrofitted damper.

Is there a particular Scrub fluid damper that works? How about pulley attachment? Oh yeah and is it worth the money and effort? Chuck

Chuck.

When using a scrub damper, I’ll opt  the for the one that fits the LS1 as it has a longer snout.  This saves building a seal sleeve to go behind the shorter snout damper.  Unfortunately there is a problem using the ATI dampers on the Y if going in a passenger car and that is the thickness of the ATI damper ends up putting the pulleys further to the front.  This means relocating the generator or alternator and the water pump pulleys more forward in which to accommodate.  In your case this also could also play havoc with the blower belt pulleys.  If using a marine cover, then no problem as the ATI damper can be moved in closer to the engine which would solve the belt alignment issue.  The Y specific damper from ATI is not a problem on the T-Bird engines as the lower belt pulley can be spaced appropriately forward on the front of the ATI damper to keep the belt alignment as original.  The Y specific damper also has the timing marks aligning correctly with the stock timing pointer.

Worth the effort?  I’m required to use SFI certified dampers so yes.  For any high horsepower or high compression application I’d also say yes.  For a street car, doubtful due to the amount of work necessary to make everything align but if memory serves me correctly, Pat Fleischman had an aftermarket damper on his blown ’57.  Don't remember if it was an ATI or a fluid filled though.