Its in. The 3.5 DS arrived Friday. I set up a dyno and R&R appointment at a local shop with a Dynojet 630 and good reputation with the speed shop crowd. I went in on Saturday at 1:00 PM to do a baseline dyno, remove the old stock DS on a lift, replace with new 3.5 aluminum, then immediately roll it back on the dyno for a comparison run. Same car, same day, same dyno, same driver, same tune, 3.31 stock open diff. For those who will ask, I ran on both runs with Brenspeed's 91 tune with stock settings. Both were 3rd gear pulls, as the goal was not "my Hp is higher than yours" but to compare apples to apples with a DS change. (of course I did not want my stock DS blowing out on me at 6300 RPM on a 1 to1 gear either...)
First objective = to asses the build quality, install, fit and clearance of the new DS vs Stock. My car is lowered by 1.0 inches front and 1.25 in back with Roush springs. I have installed the new MGW shifter set at 6 out of 10 full turns out.
The fit was perfect. It is same or smaller diameter than stock and I had avsolutely no clearance problems with stock placement of parking brake bracket or MGW shifter (see pics). At ride height I can easily put a couple of fingers between all close objects and the DS.
Second objective = To asses any actual un-biased HP or toque differences on just the DS change out.
The numbers are dissapointing ( we were all hoping for more) for those who are looking at another guaranteed HP mod. My dyno results (see pic) are
190 rwhp / 220 rwtq on the baseline pull, and
191 rwhp / 218 rwtq on the second pull with new DS. Almost identical runs. within the + or - error factor on the physical limitaion of the dyno.
As to why the torque actually dropped, I happen to think that since my measured pinion angle before the swap with stock DS was -1.5 degrees (pushing the edge of reason) and the articulation of the center spline joint in the stock shaft kept it on safer ground and compensated for the low pinion angle somewhat. the swap to the one piece actually lowered the angle to near 0 and at WOT actually drove it past 0 degrees into positive numbers. needless to say I am in the hunt for an adj. UCA next to match my fixed J&M LCA's.
Overall driving inpressions = I saved the best news for last!
The car is tons more driveable now. The rolling take off is twice as manageable. The acceleration feel is smooth and top end rpm's seem stronger, My peg-leg burnout test was more impressive. As for high speed that is still on the test list, but I am confident now that I can easily (on a track with a helmet), exceed 125 with no problems.
I highly reccomend the 3.5" Shaftmasters DS for many reasons, but the best and brightest is that Robert will use his 25 years experience building driveshafts to make yours personally. And he actually cares how it turned out like it was his own. If you have a lowered 4.0, and want the best powertrain you can get this is the real deal.
http://s170.photobucket.com/albums/u253/billybix76/th_HPIM0181.jpg http://s170.photobucket.com/albums/u253/billybix76/th_HPIM0179.jpg http://s170.photobucket.com/albums/u253/billybix76/th_HPIM0172.jpg http://s170.photobucket.com/albums/u253/billybix76/th_HPIM0168.jpg http://s170.photobucket.com/albums/u253/billybix76/th_HPIM0174.jpg http://s170.photobucket.com/albums/u253/billybix76/th_HPIM0188.jpg http://s170.photobucket.com/albums/u253/billybix76/th_HPIM0187.jpg http://s170.photobucket.com/albums/u253/billybix76/th_HPIM0175.jpg http://s170.photobucket.com/albums/u253/billybix76/th_HPIM0189.jpg
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06 4.0 Vista blue 5spd
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C&L CAI, Xcal2, Brenspeed, VMP, BAMA, tunes
Flowmaster AT, JBA Powercables, MGW shifter, Royal Purple fluids, Hellwig rear sway, CHE K-brace & limiters, 4 way Roush springs, tinted glass, J&M UCA/LCA's, 17" Gt take off bullits, 1/4 louvers, shaftmaster aluminum 3.5, T-lok, 3.73's, SS Shorty headers
2006 Mustang... Results of Shaftmasters 3.5 driveshaft install & dyno 
