I fixed the failed primary tensioner and my "expensive noise" has not returned.

The whole job went pretty smoothly, and only took about 3 hours to take it apart and another 4 to put everything back together. Certainly not a small job, but easy enough. The crank pulley was very cooperative in being removed. Not so with the stock one.

I thought I would try with the stock lower pulley back on vs the larger lower I had on there. There is the expected loss of power in the downward direction from the reduction of 4 lbs of boost.

However, I'm still getting 13-14 psi with the STOCK upper and lower pulleys, whereas I was getting 18-19 psi with the lower +4 pulley, so this proves my designs of reducing intake vacuum and injecting the water before the blower has given me 3.5 to 4.5 psi more than it read stock as I was reading 9.5 to 10 psi when all stock on the same gauge that is now reading 13 to 14 psi with stock pulleys and with my mods. If it were a bit colder out, the gauge would probably read +1 lb more. When I first took this for a spin with the stock pulleys back on, it was raining and I was seeing 15 psi.

So even at the slower blower rpm with the stock upper and lower pulleys, my mods have gained me +3.5 to 4.5 psi. Pretty good I think...

As an experiment, I'm going to see if I can live with "only" 13-14 psi. My thoughts are I can always swap the pulley back on, but I know I get used to whatever power I have, then it starts to feel not so fast anymore. Alas, this is the route with adding performance upgrades. I think the car right now is probably borderline 12.9xish-13.1ish 1/4 mile, whereas with the +4 lower it was probably faster than a 12.7. It is still surprisingly fast for a XJ8

I'm hopeful that the car will be completely reliable without any surprise repairs needed over the next few years.