mayo

Norm, what's it all mean Man!!!lol
I'm stickin with the 3.73 with my auto, while im sure the 4.10's would be fun they may prove to be a nuisance at times with everyday driving.
Anything would have to be better than the 3.31's I currently have, for sure.

GhostStrykre

see here's my question, i want to go with 3.73's, but since my 2012 v6 manual is my DD, i gotta worry about snow. ohio just got its first snow storm 2 days ago and i barely made it up my driveway to the garage (big hill). i had to shovel it first. does the 3.73 gears made mustangs even worse in the snow? if so, i bet the 4.10's are even worse than that. hmm.

Norm Peterson

Don't bother comparing 1st gear (most of the time you can't use 100% WOT in it anyway)

2nd gear with the 5R55S and 3.73's is a total gear reduction of 8.54:1
2nd gear with the TR3650 and 4.10's is only a total gear reduction of 8.20:1
Gearing advantage - 5R55S by about 4%

3rd gear with the 5R55S and 3.73's is a total gear reduction of 5.74:1
3rd gear with the TR3650 and 4.10's is only a total gear reduction of 5.41:1
Gearing advantage - 5R55S by about 6%

It's only after the 5R55S-equipped car has to shift up to 4th that the gearing advantage goes over to the TR3650-equipped car.

Even accounting for somewhat greater losses through the automatic having to pump its fluid in order to work at all, you don't need 4.10's with the 5R55S to match a car with the TR3650 and 4.10's, at least for speeds up to the top of 3rd (about 80 - 90 mph in most cases). 4.10's and the 5R55S compares to a TR3650 with axle gears somewhere between 4.56 and 4.88, which only a very few people would run.


Norm

JIM5.0

Good point about considering the other gears below 1:1 tranny gear ratio.

I must clarify since I left out a bit in my previous post of considering total first gear ratio:
The reason why I focused only on 1st gear is typically, the reason why someone would want such a deep rear gear like 4.10:1 gears is to improve off-the-line launch. Thus my discussion was only focused on that and not what happens when you shift into 2nd & 3rd or 4th (if one has a tranny with the 5th gear being 1:1).
As often said, the 1st 100ft in a drag race determines if you can get the max potential out of your car.

Other assumptions I was operating under: The tires and traction are good to exploit the torque at the pavement. The tire height is the same as stock tires.
An automatic has a torque converter such that it revs at the line to launch at near-lock-out condition (i.e. the pressures inside the converter are so great that the fluid forces are such that it is as if launching with a rigid solid coupling).

Now, in DD, since that was part of my discussion, very true the torque converter adds virtually an infinitely variable gear ratio on top of the actual gear, and of course, very very rarely in DD does one ever have to take off from a dead stop in WOT conditions.
I am no expert in automatic transmissions, but I assume the torque converter also does its variable ratio thing when shifting to 2nd and subsequent gears also to prevent hard jolts. At least before to prevent the jolts so that when lock-out engages, it is smooth and not a hard jerk.
Now, under hard acceleration, given a powerful enough engine is turning the torque converter hard, the pressures inside the converter can become great enough that even under hydrodynamic coupling conditions, it is as if someone in a manual dumps the clutch even when shifting up to the next gear.

This leads me on to my next thought which is somewhat off the discussion: The concept of mating a torque converter to manual transmission to relieve clutch wear.
Several car makers make manuals with torque converters mated to them so you just simply dump the clutch and you don't have to worry about jerking the car and jolting the drivetrain. Well, not too badly depending on how hard you are accelerating and how powerful your engine is.
I am surprised that this is not modern automotive industry standard. I assume that cost and overall weight of the vehicle is a concern. Plus the troque converter must have its on fluid supply independent of the transmission since a manual is not hydraulically actuated (we all know manual transmissions are actuated in an ancient but proven analog method: Elbow Grease!).

Norm Peterson

A torque converter also briefly develops a torque multiplier (aka "stall ratio") that can be made to exceed 2.0. The 5R55S tranny's stock converter was rated at 1.92:1 maximum stall ratio, so it isn't just the slippage enabling the engine to run up closer to the fat part of its torque curve that's helping you out. Briefly, that 3.22 low gear really does transmit torque into the driveshaft as if 1st gear was around 6:1 and mechanically connected without any slip.

A dedicated dragstrip car or a serious street/strip car on slicks or possibly DR's may be able to hook 4.10's on a prepared track, but for the street tires and street driving that this and most similar threads are about, hooking 4.10's is wishful thinking.


In order to use a torque converter to avoid the use of a mechanical clutch once rolling, you'd have to get the ECU to do all of the rev-matching for any combination of possible gear changes, which would probably limit you to up- and down shifting just one gear at a time, every time. The need to get the revs matched at least somewhere close (within the capabilities of the synchro friction surfaces to finish the rev matching in the available time) is why you have the clutch in the first place. Though once you're rolling it is entirely possible to shift any conventional manual transmission without ever touching the clutch pedal if you know what you're doing (a useful skill to have, actually).


Norm