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Discussion Starter · #1 ·
Considering gear swap out when I have my R/E O/H for the True- Trac
Setup as follows:
1995 9C1
137k
3.08 rear with True-Trac soon to be installed
275/50/17 on OE Impala rims
Rammit, (CIA Tri-Y headers soon to be installed likely), Dynomax Ultra-Flo 2.5 catback breathing parts . . .

Figure me a daily driver on flat, straight Eastern NC roads
Probably no racing. Lots of driving 1 hour stretches-mostly highway.

Want to keep good gas mileage, and I realize there will be some difference.
I've read the sticky under drivetrain section, but the opionion seems inconclusive.
Stay with the 3.08 or go to 3.42 or 3.73?
I do like to go fast . . . . Don't mind losing some, but don't want to lose a lot of MPG.

Just trying to get back up to speed on all the tech and mods after 10 years absence, and interested in the comments from those that have been there and done that.
Thanks.
-back in the NTRSSPTR . . . .
 

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3:73's will be just fine but I've learned that my gas last much longer when I keep my foot out of the floor but I also rarely let my tank fall below the half mark....
 

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On my 100 mile daily commute (all highway), I get 4 days out of a tank with my 3.08s & only 3 days with my 3.42s. That's cruising at 80 and occasional speeding up to pass and avoid congestion. I fill up before the fuel gauge dips below 1/4 tank. Around town driving, the 3.08s & 3.42s get about the same mileage.

Fuel mileage aside, I like the 3.42s better around town & the 3.08s better on the highway.
 

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Stay with 3.08s. GM didn't pick those gears for no reason. The one-hour highway driving stretches is the key factor. 3.08s puts your car's sweet spot at the 30-80mph range, IMHO. Engine rpm, exhaust noise, occupant comfort, and gas mileage are all factors. Plus, you'll be spinning the accessories 20% faster on the highway with 3.73s which will lower their lifespan.
 

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My $02 is 3:42

I went 3:08 to 3:42 then 3:73....I did a T56 swap but would have put the 3:43's back in if I kept the 4L60E

I would think the lower the gear ratio the more rpm = less gas milage

there are RPM calculators online. tire size/rear gear ratios showing RPM
 

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2nd the 3:42's

Judging from your intro, anyway, the 3.42's seem like a good choice.

I love my 3.73's and feel that they would have made an *excellent* option to a 3.42 standard rear. IMHO the 3.08's are too high a ratio for an automobile this hefty unless it's going to be driven at 80+ MPH for looooong periods of time. The 3.42's are great (if less leggy, for all around use). The 3.73's are perfect if you want extra snap, drive in-town most of the time or tow frequently. 4.10's are great if you take it to the track more than once or twice a year. I'm surely a bit off in my numbers, but my general feeling is that each jump in ratio sheds about 400 lbs of weight from the car in seat-of-the-pants feel (the weight of two adults in the rear seats), about 2 MPG and 7 MPH in the cruising speed on the freeway. My 3.73's feel "right" at just under 75. I had trouble keeping it under 80 with the 3.08's when I was in O/D.

But that's just me.
 

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Discussion Starter · #7 ·
Thanking you all for the replies . . .

Right now the car will get 20-21 mpg combined, but weighted a little more to the HWY . . .and thats with me with a heavy right foot . . .
I've seen right at 25mpg from my home to Charlotte with all highway at 70mph.

Congested city about 18mpg..

Did not want to get too far off 20-21 combined with weight toward HWY.

My thinking was that with the intake/exhaust and perhaps a 3.42 ratio would make up any "loss" in being able to move the car more easily from stops.
That all things considered, everything might equal out in the mpg area and the car might have a little more "snap".
 

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Fuel mileage aside, I like the 3.42s better around town & the 3.08s better on the highway.
The gears are not the problem. The 4 speed transmission is the problem. You need 3.73 gears and a 5 speed tranny. Then you would be geared just right for city and moderate speeds but shift into 5th at 80+ if the RPMs get too high for your taste and get the best of both worlds.
 

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Stay with 3.08s. GM didn't pick those gears for no reason. The one-hour highway driving stretches is the key factor. 3.08s puts your car's sweet spot at the 30-80mph range, IMHO. Engine rpm, exhaust noise, occupant comfort, and gas mileage are all factors. Plus, you'll be spinning the accessories 20% faster on the highway with 3.73s which will lower their lifespan.
That's true, 3.08 shines at 80mph and up but doesn't do so good at 60 and even worse at 50mph, where it's kind of sluggish. The RPMs are just too low at these critical speeds. I spend much more time at 50 than at 80. Given OP is on the East coast, in NC, it's obviously different from a more flat terrain than say Arizona. I would factor that in the equation and go with a lower gear.

I spent a while trying to figure the best compromise, despite my skepticism, I came to realize that 3.42 is the best for sedan and 3.73 is the best for station wagons. These are big, heavy vehicles and they could use all the torque you can get. Especially in hilly terrain and loaded. If in doubt, go with 3.73. You can always put a large tire to change the ratio numerically down.

http://www.miata.net/cgi-bin/tirescgi

Now the OP has almost 28" tires which are 3% bigger than stock 27" tires. So if you put 3.42 in, you are not going to get 3.42 but more like 3.32.

I have 3.73 gears in this wagon but I can control the gear ratio with tires. I have a winter and summer tire. If I want more of a highway gear, I can put in a 28" or a 29" tire which will really bring it down numerically into the 3.50 range. Right now I have a 26" tire, which aside from looking stupid on the wagon raises my ratio to at least 3.80. Believe me, that beast needs it.

In most daily driving, the MPG difference is less than you think. Unless you do 100% highway driving on a flat, straight surface at 80+mph. 80% of the time, IME, 3.73 is more useful than 3.08.
 

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In my ERE 383 with 3.73 with cruise set at 75, I was getting 21mpg avg traveling the interstates here on the east coast.

I concur with dogma about using tire size to control gear ratio and resisting the ever present urge to smash the go pedal will help with gas mileage.:D

Dialing in the tune and converter lock up were also key points in achieving that mpg.

Curtis
 

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Thanking you all for the replies . . .

Right now the car will get 20-21 mpg combined, but weighted a little more to the HWY . . .and thats with me with a heavy right foot . . .
I've seen right at 25mpg from my home to Charlotte with all highway at 70mph.

Congested city about 18mpg..

Did not want to get too far off 20-21 combined with weight toward HWY.

My thinking was that with the intake/exhaust and perhaps a 3.42 ratio would make up any "loss" in being able to move the car more easily from stops.
That all things considered, everything might equal out in the mpg area and the car might have a little more "snap".
well from my experience with the 3.42 and the 3.73, 3.42 were perfect for the highway on a bone stock car. it gave more off the line that the 3.08 and still only gave up about 2-3 mpg if that. now the intake and exhaust is going to give you a loss in low end torque (or should i say move the torque to a higher rpm for the politically correct) so the gears will defintely help out with it. if all you ever plan to do to the car is intake and exhaust, then stick with the 3.42 with your factory tires. if you plan on doing a cam, heads, or bigger wheels in the future then the 3.73 is definitely the way to go. on another note, if u do decide on cam or heads in the future, then the cam can be tailored to your specific setup. but if u are gonna do big wheels, definitely the 3.73.
 

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daily driver on flat, straight Eastern NC roads
Probably no racing
Lots of driving 1 hour stretches - mostly highway
Want to keep good gas mileage
I do like to go fast ... but don't want to lose a lot of MPG
1) Based on
a) these statements
b) there is no way to predict if 3.73 will cause your driveshaft to impersonate a guitar string on the highway
c) gas will NEVER EVER AGAIN go below $2 a gallon

3.73 is definitely NOT recommended.

If you raced competitively, or you towed or hauled a lot, or you lived in the mountains, and MpG was less important to you, you'd be more willing to risk the extra $400 for a more precisely made and balanced driveshaft.
Since you're not, no 3.73.

2) One way to narrow down your answer depends on what speed you prefer to set your 'cruise control'.

Unless you want several custom PCM tuning sessions instead of one, you want your typical cruising speeds to equate to 1900 RpM or less for optimal MpGs.

Then select your rear gear and your tire size - two related but mathematically separate and distinct entities - to achieve this.

With 3.73 & 26.6" tires, 1900 RpM = 58 MpH
With 3.73 & 29.0" tires, 1900 RpM = 63 MpH

With 3.42 & 26.6" tires, 1900 RpM = 63 MpH
With 3.42 & 29.0" tires, 1900 RpM = 68 MpH

With 3.23 & 26.6" tires, 1900 RpM = 66 MpH
With 3.23 & 29.0" tires, 1900 RpM = 72 MpH

With 3.08 & 26.6" tires, 1900 RpM = 70 MpH
With 3.08 & 29.0" tires, 1900 RpM = 76 MpH

3) The more stop&go driving you do, or the more you enjoy gratuitous bursts of acceleration for their own sake, or the harder your engine has to work or play, the more 3.42 is recommended.
 

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3.42

2 years ago I struggled with this same dilemma... Though it was "which ratio to replace 2.56."

Seat of the pants with my lead foot, I wanted the 3.73s, and most everyone recommended that ratio. I ended up with 3.42. I too think it's the best compromise between the ever fun stop light racing and highway cruising.

I have 27" tires, and between 65 - 80mph the 3.42s give just enough acceleration on part throttle to squirt through traffic when there's an opening... Great fun! And the speeds I deal with here in the hilly, semi-mountainous, suburban SoCal area are generally higher than most city streets. So, predominantly 45+ in town, and 65+ on the Interstate (though you'll get run over if you go that slow around here!).

I can't keep my foot out of it, and get between 15 and 17 mpg. I also think there is something wrong, but don't know what yet. My last wagon, bone stock (and 2.56) was consistently getting 24-26 highway, and 17-19 in town. My current wagon dropped 4 mpg from the get-go, and another 4 after the gears and "tune."

I added an "H" style cross-over pipe half a year after the gears. I was disappointed in the loss of torque from a stop (and the change in pitch). But it paid off at highway speeds, where I do most of my driving.

I doubt you'll notice a lot of difference between 3.08 and 3.42. As someone said, GM picked the 3.08 for a reason - best compromise. That said, the fun quotient goes up with the 3.42s, and that's my recommendation!
 

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Gear Ratios -- Always a good subject.

Fifteen years of daily driving.

95 Impala SS since 9/95 with 3:42 gears.
95 9c1 Lt1 since 9/98 with 3:73 gears.
96 9c1 Lt1 since 4/05 with 3:08 gears.

I also found out with the different gear ratios,
you loose about 2 MPG with combined City/Highway driving between ratios.

If Gas mileage is important and you do alot of highway driving.
Stay with the 3:08 gears.

The 3:42 ratio is a nice combination for highway and city driving.

Personally,
My Sons and I enjoy driving the 3:73 car the best.

Wutz
 

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.... if all you ever plan to do to the car is intake and exhaust, then stick with the 3.42 with your factory tires. if you plan on doing a cam, heads, or bigger wheels in the future then the 3.73 is definitely the way to go. on another note, if u do decide on cam or heads in the future, then the cam can be tailored to your specific setup. but if u are gonna do big wheels, definitely the 3.73.
I bought two wagons this summer. Both LT1 with towing packages.

First one was stock with 2.93 gears. Second one had 3.73.
In the mountains, the both got the same MPG.
 
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