74 Duster 408 Daily Drivability with 3.73 Gears Vs Stock 3.21 Question.

[TimS]

I'm working on getting my Duster back to the original drivetrain and was thinking of changing the 3.73SG gears back to the stock 3.21SG first. Anyone see any issues with having the higher gears in the rear for better highway driving connected to that 408? Tranny is the original 4 speed.

Thanks !!

 

[toolmanmike]

The 408 has a lot of torque. It can pull that 3.23 with ease and probably still be able to smoke the hides.

 

[Super-Cuda]

I'm working on getting my Duster back to the original drivetrain and was thinking of changing the 3.73SG gears back to the stock 3.21SG first. Anyone see any issues with having the higher gears in the rear for better highway driving connected to that 408? Tranny is the original 4 speed.

Thanks !!

No issues but, I have had 3:23, 3:91 and now 3:55 with a similar 408 setup with a 4-speed.

I find the 3:55 a great all round gear for highway/performance.

 

[go-fish]

I'm running the original 3.21 SG and a pretty mild 340 (Cam and intake). 3 tanks a week, true Daily Driver here. I think, for me, the Holy Grail would be a 3.55 with a GV. I live in the country so about half my drive is cruising 45-65.
The car is great in city traffic as well, but 1st is geared a little too high when paired with 3.21. I have to pedal the throttle while letting the clutch out to get rolling. More rear gear would help but a change to the 3.07(?) 1st gear would be ideal with a 3.21 (or 3.23 and below, FWIW)). It's not like parking lots are unnavigable now; 1st gear just isn't a parade gear with the stock '73 A833.

 

[Ant]

As someone who used to daily drive a car with no overdrive and a 3.58:1 rear gear, I'm going to say it depends. Lower RPM on the highway would be nice, if your 408 has plenty of lower end grunt, go for the 3.23 gears. Another option would looking into different gearing options for your transmission and maybe have an overdrive 4th gear.

 

[Murray]

I love my 3:55s but tachs a little high on the freeway.

 

[TF360]

I have 3:21's with my 360 4-speed and it runs real good. With a 408 in a light A-body it should function really great unless you have a huge Cam in there.

 

[TimS]

Guy that installed the 3.73's lives in a good sized town with the main drag minutes away. I live in a very small town a highway runs thru so I'm a good 15 minutes from a good sized town. With the 3.73's I'm really turning the R's down the highway. I've had 3.55's in other cars and they also seem to tach a bit high. I was really worrying about take off also, clutch chatter possibilities etc... going back to the 3.21's. I don't plan to drag race it so trying to tame it down some with the stroker still in the car. I will need to take a look at cam size.

 

[TF360]

You won't have any Problems unless your motor is set up for high rpm racing. I will be just right.

 

[273]

I find it funny, almost everyone is all about Torque this Torque that but see no problem throwing away about the equivalent of 75 lbs-ft at the crank going from 3.73 to 3.21's

 

[aaronk785]

I like 3.55s the best. 28 inch tires on the street and 26 for the track. You can definitely feel the difference between the two.

 

[TimS]

I find it funny, almost everyone is all about Torque this Torque that but see no problem throwing away about the equivalent of 75 lbs-ft at the crank going from 3.73 to 3.21's

My focus is general drivability. Not torque, not et, not burning the tires bald. I’m working to put the Duster back to its original state which makes it more driver friendly on the highway and not have to invest in a gas station to drive the car.

 

[273]

My focus is general drivability. Not torque, not et, not burning the tires bald. I’m working to put the Duster back to its original state which makes it more driver friendly on the highway and not have to invest in a gas station to drive the car.

I was just saying in general, one of the main reasons generally people build a 408 cause of torque, it's your car gear it how you want it. Less gear just makes it harder to get into the powerband , if that's a lesser concern to you, it all should workout.

 

[TimS]

I was just saying in general, one of the main reasons generally people build a 408 cause of torque, it's your car gear it how you want it. Less gear just makes it harder to get into the powerband , if that's a lesser concern to you, it all should work out.

Yes the main concern is getting closer to a stock situation. Buddy I sold the car too back in 2013 began setting the car up for better performance. The way it is now though it’s just not a highway driver at all. I see what you are saying though.

 

[mbaird]

I just finished installing a 408 and a 46rh and 3.55s . Only driven it about 8 miles but I gave it a quick 1/4 throttle from a stoplight and it boiled the rears . My tires right now are just 205/70-14s Michelins but it had plenty to turn a bigger tire .
55 mph @ 2000 rpms !
My plan is to go to a 225/60-15.

Engine is a mild build with a 221/229 - .550 (1.7 harlan Sharpes ) on a 112 .

 

[1MeanA]

I find 3.55s to be max gear for freeway or highway on short trips. For anything longer i would go 3.23.

 

[65 Cuda 340]

You realize that even 3.21 rear gears will give you a lot of cruising rpms at interstate speed by today's standards. With 26 inch tall tires, no overdrive, 70 mph is around 3,000 rpms, 80 is roughly 3500 rpms, etc.

Of course, back in the day, when I was young and impatient, I used to cruise at 80-90 mph on two lane roads with 3.23 gears. Now I don't even drive that fast on interstates. It's all what you're used to.

 

[mbaird]

You realize that even 3.21 rear gears will give you a lot of cruising rpms at interstate speed by today's standards. With 26 inch tall tires, no overdrive, 70 mph is around 3,000 rpms, 80 is roughly 3500 rpms, etc.

Of course, back in the day, when I was young and impatient, I used to cruise at 80-90 mph on two lane roads with 3.23 gears. Now I don't even drive that fast on interstates. It's all what you're used to.

If you don’t go 80+ on the interstate here some asshat will be 12” off your bumper in a monster truck . Even on my motorcycle! I prefer 65 unless I am traveling 100s of miles .

 

[65 Cuda 340]

If you don’t go 80+ on the interstate here some asshat will be 12” off your bumper in a monster truck . Even on my motorcycle! I prefer 65 unless I am traveling 100s of miles .

Yeah, I don't get on the interstates often anymore, but when I do I usually cruise at 75 or so. More cars than not zip by me at 85-90. Big change from the days of 55 mph speed limits.

 

[Mean416]

Why not consider overdrive setup?

 

[Super-Cuda]

Why not consider overdrive setup?

I considered it.

A lot more involved and its an expensive venture.

GV only offers one option for A-Body's and requires mods.

Buy Now - Gearvendors

 

[go-fish]

OP is in the same situation as myself. Numbers matching. I am willing to go the GV route because it'll still retain everything the car was born with. One of the few advantages it has is that it's an add-on and not a substitute. If my car didn't have the original VIN stamped 4 speed I would get a TKX.

@Super-Cuda , while you have your druthers on the level of modification you want to accept I personally can attest to that even the slightest overdrive is a world of difference. The truck OD is an excellent option, especially if you nail the cam profile and rear gear ratio.

 

[Newbomb Turk]

One of the things that can make a car with deeper gearing miserable to drive is not getting the engine in an rpm range where it is the most efficient.

Crane used to give a cruise rpm range where that specific cam would be the “happiest”. It’s too bad no other cam grinder offered at least a suggestion.

And it goes both ways. In other words, you can run the engine at a cruise rpm that is too high (the gearing is to low) or the cruise rpm is too low (the gearing is too high).

In the former the engine is running with its tongue out and the rpm is higher than it should be so the engine almost hunts for a taller gear. The engine is struggling because the rpm range is higher than enough that the length of the manifold runners and the header primarily tube length is out of tune far enough to cause the engine to struggle.

In the latter the is lumbering along with the rpm too low and it’s almost hunting for a lower gear and the manifold runner length and header primary tube length is out of tune far enough to cause the engine to struggle.

99% of the time we are stuck with manifold runner length and header primary tube lengths. Very few are building custom intake manifolds and headers.

The other factor is cam timing. It is the easiest to change.

To me, there is nothing more miserable to drive than an engine with gearing that is too tall and the cruise rpm is low and the engine is lumbering along. I detest that.

I can live with an engine that is hooked to gearing that is low and the cruise rpm is too high. That is far less miserable to me than the other way.

The other thing that affects what an engine is like under low load, high vacuum driving is the tune up.

Suffice it to say it it at least equal in importance than cam timing and the rest of it.

Probably even more so.

 

[Backally]

70 Duster with a 408. Had 3.23’s when I had the 340 in it, switched to 3.73’s when the 408 went in. 245/60-15 tires. 3.73’s are a LOT of fun in town, but I was going into 2nd before I could out of an intersection. And interstate I was not comfortable going very far. Put the 3.23’s back in. Way better for daily driving, (3000ish rpm @ 70 mph), and still can light them up if I want to

 

[TimS]

70 Duster with a 408. Had 3.23’s when I had the 340 in it, switched to 3.73’s when the 408 went in. 245/60-15 tires. 3.73’s are a LOT of fun in town, but I was going into 2nd before I could out of an intersection. And interstate I was not comfortable going very far. Put the 3.23’s back in. Way better for daily driving, (3000ish rpm @ 70 mph), and still can light them up if I want to

Exactly what I’m looking for with my 74 until I get the #s engine back in. Same setup that you have. Tires and all.