Trapster, I think your odbox may have issues. Mine all shifted just fine; up or down. And why you would lug od down to 40 mph @1300rpm, with a built 340, I cannot understand. And powershifting into 1.67 second gear, and getting wheelspin,is actually a testament to the torque of your engine. IMO none of these are a poor reflection on the odbox.
However, the splits are pretty wide, and if your engine rpm fails to drop rapidly enough, then yes, you can have shifting issues. The slow synchronization may be due to the synchro rings being tired, or the cone-brakes might be highly polished from many miles of useage. There are easy fixes for those.
But as I said these odboxes are not built for high-rpm engines. When I started shifting at 7000/7200 my odbox had trouble synchronizing too.My rpm would not drop fast enough, no fault of the box,but of the design. So I took steps. Steps to make the rpm drop faster, and steps to help the box.
The split is worst on the 1-2, being 54% . So outshifting first at 7000, the rpm has to drop to 3783, or a drop of 3217rpm. That's an awful lot. The standard 2.66 box only drops to 5050, an amount of 1947rpm. But you have to rev it to 7000, to find power at 3783, after the shift. If you shift at 6000, more typical with a streetcam, then the Rs drop to 3240, and a big-cammed engine just has no power down there.
So what I did was street slick-shift my second gear. This allowed me to shift it normally, yet when I'm banging it, I can overpower the brass, and just slam it in there, no more waiting. Second gear with 3.55s is good to 95 mph, and the 2-3 split is tighter at 60%, so this is naturally a slightly faster shift, and I wasn't planning on going any faster.. However, without the slickshifting, I doubt you can powershift one of these; I didn't even try. Besides,my clutch leg was pretty fast in those days.
My 360 with the lightweight KB107s, and 11/1 compression, loses rpm pretty quickly when the throttles slam shut, so after the trans mod worked so well, I didn't get into flywheel swapping. Oh yeah, I dumped the gear oil and started playing with ATF. I ended at 2/1 ratio two parts ATF to 1 part 80/90. This also helped speed up the shifts.
But it only took about one summer for me to see the problem with this design/combo. The next summer I had the GVOD on it, being used as a splitter,Shazzam! Seven gears;
3.09-2.41-1.67-1.30-1.00-.78od-.54od.GVOD in red. and .73 used at the very last. The GV is power-shifted.
I have seen several combos that shouldn't have been using this box. The 1-2 split is just too far apart for high rpm shifting, with a pipey powerband.
