We had another dyno session with Big White Ford Explorer and the XB-1a on November 30th. We did a few dyno pulls again with the 2.7" pulley and improved standoff pulley on the bottom side of the SC belt. You can see the last pull as runfile 2 in the sheet above. This time we were datalogging and we saw the MAF counts plateauing when it was expected to see them keep rising. We checked in the previous runs to see if there was any possible restrictions before the blower (airbox/filter) and there was nothing noted. What the MAF counts showed when put with the dyno data from runs 0-2 (only run 2 is shown above) is there was definately some belt slip happening - more so from 4500 rpm and above. On run two we saw a max boost level of 6.01 lbs at 5.64k rpm
The guys at Stage and I then decided to change the 2.7 (2.65 actual?) pulley to the 2.8 (2.86 actual) and try it again. Surprise (see runfile 3 above) - we saw a larger max HP number and boost number (almost 8 lbs) with the larger 2.8 pulley which means that there was alot less belt slip. So it seems pretty clear that belt slip is the main issue. If the 2.7 pulley had not been slipping, I suspect we would have seen probably mid 320's or higher on HP, perhaps 360's on torque and probably more than 9 or 10 lbs of boost. The maf counts in the datalog continued to rise this time as expected too. You can see that at 4700 RPM and above, with the 2.8 pulley, HP continued to rise and the 2.7 pulley, HP was dropping (belt slip)
Unfortunately after that last dyno run, I finally took the truck out on the road for a few miles (about 15 total) of actual driving - shifting at a max of 5400rpm (AWD 4R70W Transmission with stock 2nd Gen Explorer Torque Converter). The blower started making some bad noise and it appeared the the high speed bearing in the XB-1a decided to have some issues.
here is what the blower sounded like before this issue
The blower only had the previous dyno pulls on it and no driving. The blower had never been spun higher than the recommended 50k rpm. It was sent back to the builder and the builder confirmed
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The inside high speed bearing was damaged a little. Probably overheated or lacked enough lubrication for some reason...
Multiple Dyno runs are some of the harshest conditions any engine parts will see !
We will replace it this time for no charge, tho
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From my visual inspection prior to sending it back - the impeller and surround area seemed fine with no damage. Seems as if only the high speed bearing is what had a problem.
I spoke to the guys at Stage and we intend to check the oil pressure going into the blower after it comes back. I am asking the builder what the oil pressure spec for the XB-1A should be at if this is what caused the problem. Wondering if the oil pump in the Explorer 302 puts out different pressure from that in the SN95 or Fox Mustang 302?? As far as overheating, again the blower was never spun beyond 50K and not sure what else could have caused the issue. We are still having some discussions about it. I am waiting on photos of the bearing and hope to confirm what the specification of the high speed bearing is installed in this new production XB-1A blower.
Once the blower comes back, we will stay (for now) with the 2.8 pulley and work on increasing the crank pulley from 6.5 to hopefully 8 inches which would allow us to run the 2.8 pulley or larger to further eliminate the belt slip and hopefully see a better result with this blower.
