Midnight Express

im sold on 3:73's.

Alopez0630

I agree with allt he feedback and "constructive criticism " but can anyone really explain to me the pros and cons of either 3.73/4.1 . If my car is stick and i want to do things the right wway without messing anything up in the long run what should i do?

almach

I went from 3.31 to 4:10 when I was NA. I was concerned when I went FI but I find it's still usable and I go to the track four or five times a year and I have a lot of fun. This car is my DD, but I like a little excitement. I think 4:10 is the best choice for your mods and I agree don't fear the gear!!

jobeonnet

Im going with 3.73 on my auto to keep the RPM in range at cruising speed, A motive or richmond gear will whine more than a ford probably not right off but as they age they generally do because they are softer (racing gear) ffrp gears or a much harder gear that will wear better but under extreme loads will break not bend.

Margarita Girl

I switched out the 3.55 gears on my manual for 4.10's

Cusp

I tried 2 sets of Richmonds and they both whined. 3rd time was ford OEM gears. They were perfect. Quite and smooth.

Norm Peterson

If it's launch performance of any sort that you're seeking, that's an operational issue, not a mechanical one. You don't have to be at the strip to load the converter up a little, and if it matters that much to anybody on the street then I'd guess that's what they need to be doing there as well.

IOW, directly going to deeper gears instead is just band-aiding poor technique, so don't blame/patch the mechanicals when the driver is not using what's there to best advantage.


<sigh>
What you're describing sounds like a two-element fluid coupling as used in GM's ancient Hydramatics. I'm not the later Turbo-Hydramatics (TH350/400), but the 1950's AT. The 4 speed Hydramatic used a really deep 1st gear instead of a torque converter, not in addition to having one. I had a 1957 Pontiac that had this 4A tranny, and it was gutless off the line even with its 347/four barrel carb (that's a Pontiac 347 BTW, not the 347 that most folks here will probably think of first and wonder if I'm losing it second).

The third element in a three element torque converter changes the direction of fluid flow internally and generates additional torque from the reaction to the flow direction reversal. You need to have some 'slip' for this to occur, and stall speed and stall ratio are loosely related.


Norm

Norm Peterson

Better that I give you some questions to answer for yourself than push any of my preferences at you. What's right for me may not be for you and vice-versa.

1. What's in the axle now? (I haven't been keeping track since 2008) Like Nuke has said, new gears with only about 5% more ratio (3.73 ÷ 3.55) aren't worth doing except in a very few very narrowly defined situations (see Argonaut's post). Decide if any of them apply to you.


2. How will the car be used? If more than one use, which one will govern? (DD, weekends only, street/dragstrip, any autocross or road course track time) I won't get into street racing beyond guessing that it's like the dragstrip only without as much starting line grip.


3. It is possible to make an educated guess at the improvement in maximum performance, and swaps like 3.73 or 4.10 from 3.31 and 4.10 from 3.55 are more "worthwhile" to most people.

If you're at the same throttle opening in both cases, the difference between 3.73 and 4.10 is about 10%, as in about 10% less time to accelerate between two given speeds with the 4.10's. And about 5% less time to drive between two fixed points on the ground. That's enough to clearly notice, but isn't anywhere near any visions of "twice as fast".

What can't be guessed at is how often it will all get used, or subjective things like satisfaction with the improved throttle response - or tolerance for sustained running at slightly/somewhat higher rpms on a long highway trip.


4. Highway rpm may or may not be much concern. About 2000 rpm (3.31) vs 2150 (3.55) vs 2250 (3.73) vs 2500 (4.10) at 70 mph with the OE-diameter tires. Purely your call.


Norm

def67

Qiuck question for you guys, what is the best milage RPM for the 4.6L engine, so kinda what gears will give the beswt milage at 70 mph as I've heard some can get better milage in fourth not fith gears with 331's?

Cusp

Drove my 3.31s for a year and racked up 8000 miles. 4000 of them were open highway. I made several trips to Arizona. Last October I replaced the 3.31s with 3.73s but have only been on a couple short trips where I could run without traffic jams. (did not go to LA ;-))

For the AZ runs I was seeing 27.5 - 28 ish @ 75 to 80 MPH. So far the best I have seen in the shorter 70 Mile runs has been 25 MPG @ 65 - 70 which included going over a 2000 foot mountain. Around town where my speeds tend to be in the 25 to 40 MPH range, I have seen no change in gas consumption if I baby it like I did with the 3.31s. I just use 3rd and 4th more and 2nd and 3rd less. Even 5th can be used now as low as 35 MPH on level ground. So the engine RPMs remained low because I use higher gears.

That all changes if I get into spirited driving mode. The 3.73s allow higher RPMs faster allowing the engine to produce more power sooner hence higher acceleration. Doing so will cost 4MPG in the city my 18 becomes 14. You have to pay to play. Driving like that with the 3.31 cost me 3 MPG.

I have another AZ run in the works for Memorial weekend. And a run to the Pacific N.W. for early summer. Will know more how the 3.73s effect the MPG and thus the range between fill ups then.

If you can go 70, the 3.31 can pull any highway grade in 5th. The trouble was if traffic slowed me to 60. Any less and I had to get into 4th to feel right about being kind to the engine. At 60 there was just no power to accelerate on those 6% grades. Had to get into 4th or even 3rd. The 3.73s give you a 300 RPM leg up on those situations.