Why would you want to Hipo a 260 (if that is even possible)? Why put stress on the rare original engine?
.... It is a very sweet running engine.
You asked so I guess you want an answer. Actually you already gave part of the answer - I think the 260 is a very sweet running engine.
Back in the late sixties, drag racers like Dempsey Wilson "buzzed" them up to 10K routinely.
As you well know, I've had a lot of practice with powerful 289 race motors that put out as much or more than your 347 street motor while being limited to cast iron Ford production heads, flat tappet cams and dual plain intakes. I know power but I'm thinking about something a bit different for an experimental street motor.
I just got back from the UK and I'm still suffering from the sticker shock from $14 per gallon gas. For some Tigers with hot rodded or poorly tuned engines that's about a dollar per mile! In Britain there's a lot of interest in 5-speeds. They are thinking a lot about efficiency over there.
A decade ago, Dr. Mayfield taught the list that a Tiger only needs 40 HP to cruise on the highway at 70 MPH. Your stroker probably exceeds that at idle. Any increase in RPM above that which is needed to produce this 40 HP is basically wasted. If you cruise at 3000 with a toploader or even 2000 with a 5 speed you're still throwing away a lot of gas. My thinking is that with all things being equal, a 260, being a smaller displacement, would waste less gas per extra RPM so it would more efficient at cruise. Compared to a 260, a 347 is a third larger. To me that translates in 1/3 more power, 1/3 more heat and 1/3 more gas.
I'm currently wondering about two projects for this winter: 1) I can get the race motor over 500 HP? and can build a 260 that, when combined with a 5-Speed, will get 30MPG, produce 300HP and cost less than $2000? I don't know the answers but hope to start this week by changing cams on the race motor. The 260 will have to wait until the race engine mods are completed. But I can think about it now.
As far as the stress goes, the weakest link in 260s are the rod bolts followed by the rods themselves. Most of the stress on these bolts is due to high RPMs, not the loads on the power stroke, since the rod is then in compression. The easiest way to lessen the load on the rod bolts and the rods is to reduce the weight of the piston. Back in the day, 260 pop-up pistons weighed 575 grams. Today they can be made a lot lighter. Spinning an old piston at 6K produces a similar load to revving a modern piston at over 7500. Now there's no way I'd expect to do that but I was just trying to illustrate how "hot rodding" an engine can actually reduce the stress.
On the other hand, the stress on the block is increased when the HP goes up. Balancing a V-8 is a compromise and certain harmonics are produced. In racing we've seen a lot of SBF blocks crack or even split in two with larger HP. I've never seen this in an engine producing "only" 300 HP. Using my "1/3" comparison, a 300 HP 260 when stoked to 347 would extrapolate to only 400HP. This is mild "hot rodding" compared to your 450HP stroker.
What percentage of time am I using WOT? Maybe 1%? I'm just thinking about trying to build an engine that is more suited to my likes for the other 99% of the time.
But you're absolutely right about the cheap cost of Chinese stroker kits and heads that have flooded the market. They are impossible to beat in a $ to HP comparison. Didn't Joe Stalin say that there's a certain quality to quantity? He could have been talking about stroker motors with their raw cubic inches advantage.
Right now I'll go back to "wondering",
Buck
