Steve, Doug,
The main message for you, Doug, is that Ford was very conservative about how
much overboring their thinwall casting Windsor blocks could take. Their
recommended 0.040" or 0.060" overbore limit is set to ensure that there is
always sufficient wall thickness and is much less than the allowable
overbore for non-thinwall blocks. I know of some smallblock Ford "experts"
that are loath to overbore at all, and certainly not without first
confirming the wall thickness by ultrasonic testing. The ultrasonic testers
cost about $1,500 and have a resolution of +/- 0.001", although their
accuracy is only about +/- 0.005", the error due primarily to the roughness
of the casting surface. The question of how much thickness is needed is
difficult to answer and depends on how hard the engine will be stressed. If
you want 300+ HP output, then it will need thicker walls. The minimum
required thickness will be in the ball park of 0.090" to 0.125", depending
on how highly stressed it will be.
Steve writes:
"Actually, Bob, if you drew the conclusion that I was claiming the 260's
(and I DO mean the 3 freeze plug models ONLY as on the Tiger, not the
earlier 221 over sized 2 freeze plug), then I misstated my intent."
Huh?? Typing too fast again?
"The REAL intent is to state that the 260, 3 freeze plug model had a thicker
wall than the 289, but not the same OD to the outside of the wall."
What is your basis for asserting that 260's have thicker walls? Is it the
0.040" versus 0.060" maximum overbore numbers? Doesn't it make engineering
sense that even with the same nominal starting wall thickness, that the
larger bore 289 will need more wall thickness for a given maximum strain
than a 260?
"And Doug should NOT listen to his "expert mechanic's" incorrect data."
I don't think Doug has told us what his "expert mechanic" thinks, just the
"old" mechanic, and we all know they can't be trusted. ;-)
Bob
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