From what GV told me; more power, or no power, has to be going in than is going out during the shift; either upshifting or down-shifting. And the driveshaft always has to be turning in the "Forward"direction when the GV is engaged.
So when downshifting, the wheels are powering the driveshaft which is powering the pump inside the unit, and the planetary. With no power going into the front, the GV is happy. With more power in, the GV-clutch has to also brake the engine. If there is a fluid coupling in between there then you may get away with it. But with a Hi-Po clutch, and 11/1 Scr and 185psi cranking pressure , the GV has a nasty time backshifting cuz the direction of the torque is the same as when in reverse.... which I can tell you from personal experience, kills the GV unit almost instantly. That cost me 50% of retail to rebuild plus shipping,both ways I think, back in about 2005. And, I was without the GV for most of the summer.
But in the forward direction, under full power, the shift from second to 2-od always breaks the tires loose. With 3.55s that can be as high as 80 mph.
For you guys with clutches, and having bypassed the GV-computer for split shifting; there can be a shift lag from the moment you press the button to the moment it shifts. The slower your driveshaft speed, the more pronounced the lag.When I spoke to GV about what I was wanting to do, they said I would need ~4.56s to get the pump pressure up fast enough to not slip the GV clutch to death, at low engine rpm, in first gear. By the time the 2-od shift comes there is plenty of pressure.
At the time I was running a 2.66low gear and with 4.56s that makes a minimum starter gear of 12.13. I did the math to get the driveshaft rpm per 1000 engine rpm, and then did the testing with the 3.55s that I had in it, to find the driveshaft rpm where the GVclutch lagged seriously.
Next I got me an ODbox with the 3.09 low, for a starter gear of 3.09x3.55=10.97, and did the testing with that; and found that after about 3000engine rpm, it was a non issue; 3000 in 10.97 starter gear is 22mph so it's not a big deal. That's how I solved the shift lag.
Further more, when the unit is new, it will hold it's pressure for at least a minute. So if you roll to a stoplite with the unit still engaged, chances are very good that it will remain engaged, and you can motor away. I exploited this one summer by installing 4.88s, and starting in 1-od, after having charged the pump. This gave me a starter gear of 4.88x3.09x.78=11.76 around town, and a starter of 3.09x4.88=15.08 for; 550rpm=2.9 mph for idling around, and parading.
But I gotta tell you guys, getting your engine to idle at 550 with a 230/235 cam, and make enough torque to pull itself... is a bit of a trick. And to do it in a parade for a couple of hours is a different trick,lol. You shoulda had a automatic,lol.
The following summer I tried it with 4.30s, but by the end of the summer, that od box was proving to be a pita. The gears were just too far apart for city driving. And timing the backshifts was getting to be real aggravating.
So by next summer I had a Commando 3.09 box in it, and that has been working very well for me ever since....... with 3.55s, which make a starter gear of 10.97, and a parade speed of 4mph@550rpm. I later sold the 4.30s.
Now I can splitshift the first two ceares ... If I want yo.... but no longer have to. The splits in the main box are sufficient.
For you guys with 5speeds
Your gear splits are progressively shorter having splits as large as .5 or .55 on the bottom, and as close as .80 up top. The GV has a split of .78, about the same as from 4th to 5th, and only a little closer than from 3rd to 4th. The GVod works best with splits in your trans of .78x.78=.60. Like what is usually found between first and second.or occasionally between second and third. Like the Mopar 4spdod. It has ratios of 3.09-1.67-1.00-.73od so the splits are .54/.60/.73
But the AX15 5speed for instance,has ratios of 3.83-2.33-1.44-1.00-.79od so the splits are .61/.62/.69/.79 and splitting these produces ratios of 2.99-1.82-1.12-.78. Combining these gets you
3.83-2.99-2.33-1.82-1.44-1.12-1.00-.78-.79;yes 9 usable ratios, and splits of
.78-.78-.78-.79-.89-.78-1.01; notice how nicely things work out in the first three gear, but going into 1.00/Fourth from the 1.12/3-od split, the split is down to .89.... which at 3500shift is just 385 rpm. And .79fifth is the same as .78-4th-od.
But ask yourself; what is the likely hood that you will be able to split first and second... because the driveshaft speed will be so slow. and what is the likelihood you will need to split second and third. The split from third-od to fourth produces an rpm drop of just 385rpm so means about nothing. and double od puts your rpm at 65~1900 with 4.11s and 30s; can your engine pull that? and to what end?
So what would the GV actually get you?
Well if you had a diesel with similar ratios, you'd get a nice 2-2od-3-od run and then the 315 rpm-drop into fourth from 3500rpm in 3od. Is that worth the approximate $4000 buy-in? only you can decide.
But I have no idea what your diesel ratios actually are; the above is only a study.
