Those Running 3.73 And a TF w/ LockUp.. What's your highway Driving Like?

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Dantra

Dantra

69 Dart.. AKA Butters
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Doing a rear-end swap.. The one going in is a 3.73 and I'm just not sure if I'm going to like that gear. It'll see a little bit of highway time but not alot.. car shows, occasional drive to work etc. Possibly Power Tour..

69 Dart with a 6.4 Hemi and a 904 lockup.. Just a driver and not a track car. I know a 904 LU isn't ideal, but it is what it is for this year. I did have it beefed up with new bands/reds/steels/4.2 etc. Tires are (will be) approx 25-26 tall. Looking at about 500hp when it's all said and done. I'll go 8 speed or 46RH next winter.. maybe.

I know there are all kinds of calculators and guys that can dazzle me with math but I'd really like to hear some real world stories before I go throwing money at 3.27s

Thanks Guys!
 
Do the math, what rpm are you comfortable with at 55, 65, or 70? My Dart, 3:55's, 26" tall tire is 2500 at 55. My Road Runner, 3:73's, 31" tall tire should be at 2200 at 55. I don't go out on the interstate.
 
Those Gen 3 Hemis are happy at pretty much any rpm. No need to cruise at more than 3000 I don't think. Their 6 and 8 speed transmissions knock the highway rpm down to 2000 or less where the bet mileage is. Your call.
 
toolmanmike said:
Those Gen 3 Hemis are happy at pretty much any rpm. No need to cruise at more than 3000 I don't think. Their 6 and 8 speed transmissions knock the highway rpm down to 2000 or less where the bet mileage is. Your call.
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I've an 8 speed in my other swap (64 A100 Truck) with 3.55s...cruises nice at around 1900. Just trying to decide if 3000 rpm is gonna drive me insane
 
Dantra said:
I've an 8 speed in my other swap (64 A100 Truck) with 3.55s...cruises nice at around 1900. Just trying to decide if 3000 rpm is gonna drive me insane
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It's interesting how we get used to our new vehicles and things seem strange when we drive our old ones. I keep waiting for another shift or convertor lock up in my Swinger. I had a free lock up 904 at one time and junked it out with the car. :BangHead: :BangHead: What was I thinking. They are good for a MPG or two.
 
Dantra said:
I've an 8 speed in my other swap (64 A100 Truck) with 3.55s...cruises nice at around 1900. Just trying to decide if 3000 rpm is gonna drive me insane
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I've had 3.55s in my Duster with a non-lockup 904 for the past year and a half, acceleration is excellent but the cruising RPMs got on my nerves enough that I'm swapping the 2.94 3rd-member back in. Freeway speed limit here is 70 mph between cities and most traffic cruises at 75-80, 3200+ RPM at those speeds gets old pretty quickly. It would be tolerable at 60 mph but then I'd be getting passed by every semi-truck and minivan on the road. Gas mileage sucks too, iirc it's around 13 MPG with the 3.55s. I've gotten 17-18 with the 2.94s cruising on the freeway.
 
Dantra said:
I've an 8 speed in my other swap (64 A100 Truck) with 3.55s...cruises nice at around 1900. Just trying to decide if 3000 rpm is gonna drive me insane
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Something doesn't sound right there.
 
toolmanmike said:
It's interesting how we get used to our new vehicles and things seem strange when we drive our old ones. I keep waiting for another shift or convertor lock up in my Swinger. I had a free lock up 904 at one time and junked it out with the car. :BangHead: :BangHead: What was I thinking. They are good for a MPG or two.
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IKR.. There was a time that 3 grand was normal in a mild street car. I knew that if I was taching 31-3200 with my 3.55s and a 4 speed, I was doing 70 or so... Didn't bother me a bit. Now that I'm much older, not sure how I'm gonna feel about it. Just wondering if the lockup is gonna make it tolerable. I've read anywhere from 200-500 rpm drop...
 
Dantra said:
How so?
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I guess that's about right. Here's a single O/D with lock up.

1710955736494.png
 
L/U will help about 200 rpms, who drives 55mph? I've done it in the past with 3.91s city and 30–40-mile trips at freeway speeds, if you want to take a long trip (Power Tour) have a 2.76 3rd member ready to swap in, will take 45-60 min. The car I'm working on now will have more noise/heat insulation, so I have an opportunity to hear my wife talking.
 
moparlvr166 said:
L/U will help about 200 rpms, who drives 55mph? I've done it in the past with 3.91s city and 30–40-mile trips at freeway speeds, if you want to take a long trip (Power Tour) have a 2.76 3rd member ready to swap in, will take 45-60 min. The car I'm working on now will have more noise/heat insulation, so I have an opportunity to hear my wife talking.
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I went 8.8. A Body 8-3/4 pricing is outta control
 
MopaR&D said:
I've had 3.55s in my Duster with a non-lockup 904 for the past year and a half, acceleration is excellent but the cruising RPMs got on my nerves enough that I'm swapping the 2.94 3rd-member back in. Freeway speed limit here is 70 mph between cities and most traffic cruises at 75-80, 3200+ RPM at those speeds gets old pretty quickly. It would be tolerable at 60 mph but then I'd be getting passed by every semi-truck and minivan on the road. Gas mileage sucks too, iirc it's around 13 MPG with the 3.55s. I've gotten 17-18 with the 2.94s cruising on the freeway.
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Right on.. Nothing like real world advice!
 
Dantra said:
I went 8.8. A Body 8-3/4 pricing is outta control
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That changes that idea. I thought of doing the 8.8 also but with my gear set options I already have I spent more now for another A body housing. Now it time to pick your poison and enjoy your ride.
 
moparlvr166 said:
That changes that idea. I thought of doing the 8.8 also but with my gear set options I already have I spent more now for another A body housing. Now it time to pick your poison and enjoy your ride.
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Leaning towards a 3.27 but wanted to hear if others were hating their 3.73s on the highway or if it was tolerable, before spending the money on a gear set
 
This is like asking what the best engine oil is, or best mufflers. You are the only one that will know what is tolerable and what isn't. So many things in this equation, rpm, mufflers, headers, engine , interior, sound deadening etc. One person's quiet is another person's noisey.
 
My '68 Dart has a 383/727 and I went from 3:23 to 3:91 because I hit the track last October. 27" (255/60-15) radial.

With the 3:23's, I drove the thing everywhere. If I wanted to keep up with feisty L A traffic I could cruise at 80 and the tach would read 3500 or so rpm. Now that I have the 3:91's on it and the track day is long over, I think about my freeway drives now--70mph and 3600 rpm! In L A, you need to move aside! Or if I'm inclined to pass cars "for a second", I'll hammer it and it will read 4200-4500 rpm for a bit and I am able to keep up! I feel like if I want to keep the gears on, I should probably consider a Gear Vendors OD.

Or, give up the noticeable off-the-line torque increase and reinstall the 3:23's! It turns into a quandary!

You may be a prime candidate for a set of 3:55's if you want 1 gear set.

David
 
CRUZE 418 said:
This is like asking what the best engine oil is, or best mufflers. You are the only one that will know what is tolerable and what isn't. So many things in this equation, rpm, mufflers, headers, engine , interior, sound deadening etc. One person's quiet is another person's noisey.
Click to expand...

Very true. In my specific case it's not really the noise, more the feel of having to use more throttle to keep the car at a steady speed and how much engine braking there is when I let off the gas. For me it's more the knowledge that my engine is spinning way faster than it needs to and I'm basically just wasting gas and wearing the engine faster. I know these engines (360/5.9L SBM in my case) were designed to run at 3k RPM all day but I'm sure the Magnums in the '90s trucks were able to last 200k+ miles due to having overdrive and much lower cruising RPMs, in addition to port EFI. Just my $2.00 ($.02 adjusted for inflation lol).
 
6-david-5 said:
My '68 Dart has a 383/727 and I went from 3:23 to 3:91 because I hit the track last October. 27" (255/60-15) radial.

With the 3:23's, I drove the thing everywhere. If I wanted to keep up with feisty L A traffic I could cruise at 80 and the tach would read 3500 or so rpm. Now that I have the 3:91's on it and the track day is long over, I think about my freeway drives now--70mph and 3600 rpm! In L A, you need to move aside! Or if I'm inclined to pass cars "for a second", I'll hammer it and it will read 4200-4500 rpm for a bit and I am able to keep up! I feel like if I want to keep the gears on, I should probably consider a Gear Vendors OD.

Or, give up the noticeable off-the-line torque increase and reinstall the 3:23's! It turns into a quandary!

You may be a prime candidate for a set of 3:55's if you want 1 gear set.

David
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A quandary indeed!

I looked at the 3.55s originally. The RPM difference is only a few hundred below the 3.73. I may occasionally hit a track but it's mostly just a fun driver..PS,PB, Factory AC, Bench a Column Shift.. Something for the wife and I to have fun in.

Screenshot_20231103-093314_Gallery.jpg
 
CRUZE 418 said:
This is like asking what the best engine oil is, or best mufflers. You are the only one that will know what is tolerable and what isn't. So many things in this equation, rpm, mufflers, headers, engine , interior, sound deadening etc. One person's quiet is another person's noisey.
Click to expand...
Expected this reply

BTW what IS the best oil :lol:
 
MopaR&D said:
Very true. In my specific case it's not really the noise, more the feel of having to use more throttle to keep the car at a steady speed and how much engine braking there is when I let off the gas. For me it's more the knowledge that my engine is spinning way faster than it needs to and I'm basically just wasting gas and wearing the engine faster. I know these engines (360/5.9L SBM in my case) were designed to run at 3k RPM all day but I'm sure the Magnums in the '90s trucks were able to last 200k+ miles due to having overdrive and much lower cruising RPMs, in addition to port EFI. Just my $2.00 ($.02 adjusted for inflation lol).
Click to expand...
Ya know, that's kinda it.. I've not run a 3.73 in the Dart, so I guess I'm not sure what to expect.. Is it gonna just feel wrong? If it feels wrong to most, then I'm sure it wont feel right to me either.
 
here's the calculator:
spicerparts.com

Spicer Transmission Ratio RPM Calculator

Use the Spicer Transmission Ratio RPM Calculator to determine your engine’s RPM based on the transmission gear ratio, tire height, MPH, and ring and pinion gear ratio.
spicerparts.com spicerparts.com

from my own experience, 3.23 is the best all around compromise. i've driven my car 727/3.23/26" tire coast to coast several times, up and down the pacific coast from the tip of bajaj to alaska and all points in between.

with the 904 you've got a better, lower gear set so you're not going to lose all that much coming out of the hole, and it's not a racer either.

that G3 will happily lope along at 3K all day long too.

if i had your set up and was building a car right now for what you're trying to do, i'd go even lower with like a 3.10 knowing that i have the power to push it, the low gear set for the jump and that i'd be cruising it.
 
junkyardhero said:
here's the calculator:
[/URL]

from my own experience, 3.23 is the best all around compromise. i've driven my car 727/3.23/26" tire coast to coast several times, up and down the pacific coast from the tip of bajaj to alaska and all points in between.

with the 904 you've got a better, lower gear set so you're not going to lose all that much coming out of the hole, and it's not a racer either.

that G3 will happily lope along at 3K all day long too.

if i had your set up and was building a car right now for what you're trying to do, i'd go even lower with like a 3.10 knowing that i have the power to push it, the low gear set for the jump and that i'd be cruising it.
Click to expand...
I like the idea that you did so much highway time with the 3:23. I'll have to think on the 3.08 and do some reading.. As I mentioned, I'll eventually put something an OD in. So, I'm not sure what final drive etc is with something like a 46rh

Thanks for the input!
 
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