Transmission dilemma
think it will pass the wife imposed "financial austerity" rules....
Oh-oh,lol.
All the best to you
BTW
As a point of interest; If I had it to do over, I would not put a GVod on a Mopar 4 speed again, for any other reason that to use as an overdrive.
What I would do is use a 700R4 with a hi-stall of about 2800, and a lock-up. This makes it a 5.5 gear combo, namely; 4 in the trans, a hi/lo in the TC, and a half-gear in the lock-up.
This GM trans boasts slightly wider splits than the A500,
bolts right in to the 67 up floor pans,and
adapters and rear mounts are available.
The ratios are 3.06-1.63-1.00-.70 overdrive; splits of .53-.62-.70
How does it make 5.5 gears? Glad you asked.
First, you have to understand that the TC is more than just a fluid coupling. It is also a Torque Multiplier. It takes whatever torque is coming into it,and multiplies it to a higher number going out. This is expressed as a ratio. The ratio is highest at zero mph, and it diminishes as the speed goes up.
The highest starting ratio I have heard of is 2.0, but more typically it is about 1.8. At the lower end, at around a hundred miles per hour, it may have diminished to 1.1 or a bit less. So that makes a range of 1.8 to 1.1. expressed as a gear it would be 1.1/1.8=.61, which is a very fine split, about the same as is in the automatic; 1.45/2.45=.592, in the case of the A904/A727
So right there you have an automatic 2-speed in the TC, continuously and automatically variable, between 1.8 and 1.1.
Then the 4 in the main box including overdrive. and finally the lock up which is usually good for a 10% rpm reduction. So 2 plus 4 plus 1/2=5.5 gears.
Let me show you what the rear tires will be seeing. And I'll gear it for ~2400@70 with 25" tires, in loc-up; so, that would take a 3.64 rear which I will round down to 3.55s.
Ok.
So how this works is TC ratio, times trans ratio, times rear ratio equals a number that you can multiply your engine torque by, to get what I call "road torque" And you do it with each gear. Remember this is with the 700R4
So in first gear @zero mph;
1.8x 3.06x3.55=19.55 out the back.This number will automatically diminish by the shift rpm to something like
1.2x3.06x3.55=13.04 at shift rpm.Then into Second
1.2 x1.625x3.55=6.92 ; and into third
1.1x1.00x3.55=3.91, and into overdrive
1.1x.70x3.55=2.73 and finally into lock up
1.0x.70x3.55=2.485
Lets line them all up;
19.55-13.04-6.92-3.91-2.73-2.485 count them; I get 6 ratios.... from a 4 speed.
The splits are .67-.53-.56-.70-.91
Ok so;
70=2340, very nice
starter gear is 10.86, very nice!
KD @28mph is 4100 ,OOps a lil high, but not for a 268/276/114 cam, it will go to 5500/38mph.
2 out of 3 is pretty good!
This trans could be run with a 3.23, but then the cruise rpm will be excessively low at 60=1825, for that 340 cam. Low because that cam is dirtying up the intake because of the 64* Ica advertised , which, seat to seat ,is probably another 15 degrees later, or more. In other words the intake valves will be closed, finally, just about the time the pistons are half way up the bores. And we haven't even talked about the overlap period of 44*, which actually ain't that bad,lol.
Dirtying up means, reversion; the the pistons are pushing a portion of the just ingested fuel/air charge, back up into the intake plenum. This makes the low-speed circuit hard to tune, and it invariably runs rich. The slower the rpm the worse it is. It usually takes 2200 to maybe 2400, and lots and lots of ignition cruise-timing, to clean it up. This all means that there is not much point to lower the cruise rpm of a 340 with a 340 cam, in an attempt to find fuel economy. With just 104* advertised power duration, a lot of energy is going straight into the tailpipe, sent there by the early opening exhaust valves. There are not a lot of street cams that get below 100*, But again seat to seat, the 340 cam will be waaay down there. For this reason, I see no point in cruising any slower than 2400 with that factory 340 cam.
I got off track again, didn't I,lol.
Oh yeah, I remember;
count them; I get 6 ratios.... from a 4 speed.
I call it a 5.5 cuz lock up is only gonna be about 250 rpm.
The A904 with a GVod could be used with 3.55s for 70=2740@5% slip,
and a starter of 2.45x3.55=8.70x1.8 in the TC=15.65 at zero mph,
and 30 @ KD into first is ~4120, shazzam!
That would be 3 for 3!
But I think you would have to cut the floor open just a little, to make a space for the GV unit.
This combo would have ratios of
2.45-1.45-1.00-.78od and splits of .59-.69-.78 nice but no lock-up, so just 5.0 gears. Geared for 70= 2740 slipping 5% requires a rear gear of no more than 3.55s . So
1.80x2.45x3.55=15.65; and
1.20x2.45x3.55=10.44, and
1.20x1.45x3.55=6.18, and
1.10x1.45x3.55x.78=4.42, and
1.06x1.00x3.55x.78=2.94, and
no lock-up, and
15.65-10.44-6.18-4.42-2.94
with splits of .67-.59-.72-.665, pretty sweet!
and now you have unlimited A904 TC selection.
With 3.23s it would be
70=2490,
a starter of 14.24>9.50, and
KD into first at 32=3750
Oh yes I'm liking those numbers.
Fun with math
