GEO4
The 855,IIRC, has ratios of 2.64-1.92-1.40-1.00-.69od.
The standard A833 has..... 2.66-1.92-1.40-1.00 (and .78od with the GVOD.)
Whadaya wanna gear it for? and how much engine are you running?
I'll tell you a secret, there's about a .8 split between running the 1/8th and running the qtr.That is to say, a car that goes 116 in the qtr optimally geared, will run about .8 x 116 =93 in the qtr. So.................... a trans with a 3-4 split of .8 will hit both bases. None exists with enough capacity for a 3400 pound raceweight, to go this fast.
But the GVOD comes pretty close with its .78 split. So to hit 116 optimally with a 360HO will require about 4.56s to hit it at 6400 with a stick, in direct. But 4.18s (rounds down to 4.10) to do it in 3rd-over.
So what that means is you can hit the 93 in third(1.40ratio) at 6410(with28s), and you can hit 116 at 6230 in third-OD (1.4 x .78). That's a 180 rpm difference, and,on paper, is about as tight as it's ever gonna be.
4.10s will get you 65=2500 in 4th-over, and the starter gear is 4.1 x 2.66=10.91, perfect for a high output SBM in a streeter. And only a small handicap on the start-line when racing.
Now lets work it out for the 855
To hit 116 in 4th,you will need 4.56s to hit it at 6350, (cruises at 65=2450)
To hit 93 in third. you will need 4.10s to hit it at 6410, (cruises at 65=2210)
This is about as insignificant an rpm difference as you can imagine,60rpm, but it did require a chunk change.
The starter gear is adequate for a streeter with either rear.
But suppose you have less or more power and neither rear gear is correct for your application. No problem, the split remains about one rear ratio.
So let's go back to the A833(3.09low)/GVOD.
The ratios are;3.09-2.41-1.91-1.50-1.40-1.09-1.00-.78od....GVOD in bold
Notice that 1.4 and 1.5 are pretty close together. In practice you would run one or the other, never back to back. Ok so what you say? Well if you gear the car to hit 93 in second over 1.40 ratio, you will have four ratios to get you there with very tight splits. The correct ratio to hit it at 6400, in 1.40 ratio is 4.10. So what about the 116. To hit that at 6400 requires an overall ratio of 4.598. So how to get it? Let's try it with 1.09 ratio. I get 4.22s So between the two, 4.10s looks like the winner. Lets do the math.
93 will be 6410 in 3rd (1.40 ratio), and 116 will be 6220 in 3rd-OD(1.09 ratio).
The starter is now 3.09 x 4.1=12.67, a little much for street, but great at the track. and 65 will be 2490.
The nice part about 4.10s is you can hit 65 at 6110, wound out in second, having used 3 ratios to get there!; the 12.67 to launch with, splitting it at about 35/40mph,then hitting second at 50/54mph and then powering thru to 65mph. I did this for quite a few years with 4.30s. But I shifted a lot earlier, and at part-throttle, cuz really it just spins all the way at WOT.
To be fair, the GVOD shifts like lightning...........when it shifts.
But you have to learn to anticipate the shift. It doesn't always shift the second you hit the button. At lower speeds,the lag is noticeable. The unit gets it's operating pressure from the spinning driveshaft. With 3.55s, driving normally,shifting 1-2 at say sub-3000 rpm it takes a while to build pressure. With 4.88s the pressure is right there. So I rarely split the 1-2 unless wound up. Again, with 4.10s this will not be a problem. What will be a problem is the carnage behind it. Using a CFII, I broke a lotta parts.
So what I'm saying is that the combo is dynomite on paper, but in real-life, it comes with a bit of a learning curve.
Oh and you have to wire it in such a way that it can never be engaged in reverse; that spells almost instant death for it. And you're not supposed to downshift with it. You can downshift into a gear that already has the OD selected, that's OK. Say you're slowing down entering town from cruising in 4od, and you forget to disengage od. So you're going from 4od to 3od to 2od; that's fine. Just clutch it before de-selecting od and it will all be fine. You have to disengage the OD when downshifting into it, that is to say;remove the power from the input side, then de-select. . On the upshift not so. You can pump full power into it not using the clutch at all. But is likes to break stuff behind and in front of it when you do this. My engine broke three A833od boxes, well really; just one input gear,and the others where blown up od gears. It also tore the straps off the rear yoke and blew up 3.91s. I upgraded as I went,lol. I then pulled the CFII disc and swapped in a dealer-supplied 340 disc, which it tore two of them up. I finally softened the hit by spacing the PP away from the flywheel about .080, and stopped driving like an animal. This was all street-driving with 295s on the back, I wasn't about to give them up! The 340 discs last quite a while now.
So again, that GVOD has a bit of a learning curve. For me,in the end, it was worth it. When that 367 hit 93 (1/8th)first time out, jamming 5 ratios, I was ecstatic and parked her right then. Yes, sometimes I wonder what she coulda done, not in street tune, but.............................naw, 93 was lots.
Update; I run 3.55s now on the street. With the 3.09 low gear,the
starter gear at 10.97 (base1)is just right. And it
cruises at 65=2236(base2). But the nice part is 3.55s get me
32mph at 2710 in second, and 4360 in first(base 3).And
60mph is 6380 in first-over (base 4)
93 is 6140(base 5) in second over, about perfect for my combo.
I haven't run the qtr but if she could hit 116 it would be 7160 in third and 5590 in 3-od, neither of which is optimum. If she hits 112 it would be 6900 in 3rd,and 5400 in 3-od. Still sux, so I don't go. I figure 5 bases out of 6 is close enough for me.
