<VV> Cracked Pistons

[James Cuneo]

Dan, I would be glad to share one with you, I have three to choose from. Send me your address.Thanks, Jim



--Forwarded Message Attachment--From: djtcz at comcast.netTo: virtualvairs at corvair.orgDate: Thu, 23 Jan 2014 18:21:47 +0000Subject: Re: <VV> VirtualVairs Digest, Vol 108, Issue 57Hi James, 

Would you be willing to loan me one of those cracked pistons for a little modeling and analysis? 

Some tuning aberration likely exists that should be identified and corrected. 
But Corvair pistons with slotted oil ring grooves have a pretty bad rep around here in high boost engines. 

Slotted oil ring grooves do a nice job decoupling the piston skirt from the dome and allow running tighter skirt clearances than designs with drilled oil holes and thus quieter running. 
As a result slotted oil ring grooves were pretty common in factory forged pistons in the early days to permit street use. But in real severe service that lovely advanced dark gray TRW aluminum alloy was no match for the stress concentration that a crude slotted oil return causes. 

When Jim Hall's Chaparrals were using aluminum block 327 engines they were using factory HP pistons and experiencing some piston cracking. In typical, practical, Jim Hall fashion they simply modified the otherwise acceptable piston with a clever detail right out of standard machine design text books. According to a couple of sources Hall later said something like "The pistons are stock but for a stress-relieving hole drilled at each end of the slot in the oil-ring groove to stop cracks." 
http://www.sportscars.tv/Newfiles/Chaparral2.html 

Hot rodders and race car builders lavish all kinds of attention on all kinds of //other// parts. 
It seems like incorporating "Jim Hall" piston modifications in Corvair pistons would be appropriate and actually carry some bragging rights all by itself. 

(Geometry can trump exquisite material every time) 

Dan T - 01886