[PDUB]

This discussion may have shed some light on a question I have been pondering for a couple of months now. I've been talking with Brent about building a stroked 289 motor with a casting date in the '64 range. As most of you know, Ford transitioned from a 5-bolt to a 6-bolt block/bell housing design that year for the 289. But why? What was the real reason to change?

This was during a time when they were seeing rapid increases in power from the little V8 family, as they punched it out to 289 and went racing with the little bugger. This, in turn, would have stressed the flywheels of the time significantly, no doubt with some explosive results. It occurs to me that this may have been the primary motivation to affect that change in design, in order to help contain the fireworks (though it may have had minimal effect). Look at the two setups and you'll see that the 6-bolt is much stouter than the 5-bolt stuff.

There would not have been any fanfare about this, as Ford would not have wanted any bad press about failures and such, so the 5-bolt design might have gone quietly into the night with some other reason taking center stage as to why. Of course this is only speculation, and could be way off base, but it seems to fit very well with this discussion, the timeline, and the resultant parts used on the 289. I'd like to hear from anyone knowledgeable on this subject. The only thing I've been able to dig up so far on it was that the change was made to reduce some vibration, which doesn't seem very plausible.

Interesting stuff, as I was thinking of using a QT bell if I ended up with a 5-bolt block. QT is the only game in town to be able to mate that with a toploader...