3.73:1 with a TH350?

[80VetteL82]

I have a 1980 L82 Vette and Im about to do a new rear end. I have the stock, freshly rebuilt, TH350 tranny and I was planning on doing a new Dana 44 with 3.73s. Do you guys think 3.73s is too much for a 3 spd auto with no overdrive? Anybody have a similar setup? If so what do you think? As for what I use the car for, just town driving (the longest trip would be a few towns over for car shows.) I really never go on the highway. The motor is a mostly stock L82.

Thanks for any input,
80VetteL82

 

[BLACKDOG]

Here are some #'s for you to look at : running 255/60/15's with 3.73's ... 55mph=2550rpm's 65mph=3013rpm's 75mph=3477rpm's and if you want to get to 85, you'll be turning 3941rpm's.

 

[TJay]

80VetteL82, 3.73 is not a bad gear for around town, but as BlackDog stated. You will be running a bit higher RPM which in turn comsumes more fuel, it's only highway driving were you will notice gas mileage decline. Good gear set up though overall.

 

[Tom Bryant]

I agree with Dog and Tjay. I think you will enjoy the 3.73s around town and even on 55-60 mph out of town excursions. There should be a definate improvement in off idle response.

Tom

 

[80VetteL82]

thanks... i appreciate all the input.

 

[AKRAY4PLAY]

i'm running 3.70:1 with my TH400 and love it! pretty much the same as what you have with a TH350 except for 1st and 2nd gear ratios are a little different.

 

[Evolution1980]

You should still have a working lock-up torque converter, so...that'll help somewhat. Have you considered a swap to something else like a 700R4? That effectively gives you a 3.73 first gear, plus AWESOME highway cruising RPM's...

 

[80VetteL82]

You should still have a working lock-up torque converter, so...that'll help somewhat. Have you considered a swap to something else like a 700R4? That effectively gives you a 3.73 first gear, plus AWESOME highway cruising RPM's...

I was thinking about that...so the 700r4's 1st gear is just like having a 3.73 rear? So what would happen if you had a 3.73 rear w/ a 700r4, too much? I had been leaning towards a 200-4R because its supposed to be a better swap for the TH350. Thats got a less agressive 1st so 3.73s would be good with that right?:W

 

[Evolution1980]

I was thinking about that...so the 700r4's 1st gear is just like having a 3.73 rear? So what would happen if you had a 3.73 rear w/ a 700r4, too much? I had been leaning towards a 200-4R because its supposed to be a better swap for the TH350. Thats got a less agressive 1st so 3.73s would be good with that right?:W

Correct about the 200R4 and gearing. Also, the 200R4 is a direct fit, where as the 700R4 requires some customizing (new crossmember, shortened drive shaft, etc).
However, the 700R4 with an actual 3.73 rear would give you somewhere in the 4.xx range for a first gear, but your cruising rpms would still be much more tolerable.

You can go out to Bowtie Overdrive's site 700R4.com and somewhere in there they have a chart of the combinations. Also, somewhere in this C3 section, I posted pics of my speed-vs-RPM's with the stock 3.08 rear and the 700R4.

On a side note, some people register complaints about the 700R4 because the 1st & 2nd gear are so far apart, that unless you are really running at WOT from the start, it's not the best transmission for racing or whatever. I'm not exactly how the argument is phrased, but it has something to do with the difference in gearing between 1st and 2nd...


Here's the link to my post with the RPM -vs- Speed pics... Clicky!

 

[AKRAY4PLAY]

go ahead and swap the rear end to 3.70 and put the 200R4 in later. the 200R4 is a much more friendly tranny than the 700R4. as mentioned install is direct fit, they are stronger, and the gear ratios are more suited to cars. the 700R4 was designed for light trucks. it has a deeper first gear to get rolling, but second is a big jump. this is not a big deal with trucks since they run shallow gears compared to cars. most cars have 3.08's and most trucks run 3.73's. of course swapping your car to 3.70's will negate most of the 1-2 shift with a 700R4, but the 200R4 will still perform better with more consistent gear changes.

 

[Evolution1980]

updated my post above with the link to my speedo/tach pics.

 

[Glensgages]

I was thinking about that...so the 700r4's 1st gear is just like having a 3.73 rear? So what would happen if you had a 3.73 rear w/ a 700r4, too much? I had been leaning towards a 200-4R because its supposed to be a better swap for the TH350. Thats got a less agressive 1st so 3.73s would be good with that right?:W

'assuming' your 1980 L-82 is equipped with 3.08 gears, combined with the THM350 you currently have, your 'effective gear-ratio' in Low is now 7.76:1 (2.52:1 1st gear in the THM350 x 3.08 rear-gears ):
a swap to 3.73 gears, with no change in transmission gearing, will increase the TQ-multiplication over 25% (3.73 div/by 3.08 = 1.211, or a 21% increase ), resulting in an 'effective' 1st gear ratio of 9.40:1.

If you go with either A/OD transmission and the 3.73s, the 'effective' ratios are even deeper, to 10.26:1 with a 200-4r (2.75:1 First Gear ratio ), and to 11.41 with a 700-r4 (3.06:1 Low Gear ratio ):
a possible problem arises when you shift out of 1st gear, because the ratios in either A/OD are so wide-apart, the RPMs may fall out of the power-band, causing the motor to momentarily 'lug', or bog-down, losing any advantage off the line you gained.

I have 3.73s behind the 700-r4 in my '82, and the car shifts-out of Low Gear soon after I pull-away from a redlight/stop-sign, and then falls on it's face:
in the rolling country-side of S.W. Pa., the 3.73s are better-suited to keeping the motor wound-up in it's power-band for pulling hills once the car is moving-along, but the ratios are too-far apart for my tastes, and at speeds under 45 MPH (approx 1400 RPM ), I'd prefer keeping the car OUT of over-drive, and in 3rd Gear (approx 2000 ) {1:1, which is High Gear in your THM350 } so I'd have so power under-foot if I'd need to accelerate suddenly.....

Since the car isn't used much, if-at-all, for long-distance, highway driving, I'd think it would take you forever to save-enough in fuel to pay-for the added expense of making the swap to the A/OD transmission:
as-stated above, to run 85 MPH, you'll need to turn almost 4000 RPM, but how-often do you plan-on running 85+ MPH when you are traveling "just-a-few-towns-over-for-Car-Shows" .....
:confused

Just my thoughts on the subject.....

 

[80VetteL82]

great info. I appreciate your input.

 

[Evolution1980]

...at speeds under 45 MPH (approx 1400 RPM ), I'd prefer keeping the car OUT of over-drive, and in 3rd Gear (approx 2000 ) {1:1, which is High Gear in your THM350 } so I'd have so power under-foot if I'd need to accelerate suddenly.....

Just for the sake of conversation...
I would think it shouldn't matter what gear you're in because if you need to "accelerate suddenly", the transmission will automatically downshift when you get on the gas, thus putting you back in the higher rpms where you were trying to keep it prior to the acceleration request. No???

...That aside, everything else you've said sounded good.

 

[MoeJr]

Also remember that most 700R4 trans except those in 85 and up Vettes have a WOT lock out in 4th gear. I bought the sleeve to fix that silly thing in my 84.

The 200R4 does not have that lock out and has a 2.74 first gear as compared to the 700's 3..06.

I would definitely swap the 3.73's in with the 200R4 if ya have the means to do it. If not I would not want 3.73's with your stock tranny.

Just my .02

 

[GerryLP]

80Vette,

Go to Chevyhighperformance and search on articles such as this one http://www.chevyhiperformance.com/techarticles/68560/index1.html

They have pretty good info as well.

I am running a 3.31:1 along with my stock TH350C in my L81. It provided me the best ratio to take advantage of my XE268H cam. I don't have to make my car switch to higher gear or won't bog-down, for it cruises at approximately 65% of the powerband range.

I did noticed the higher RPM's sound at first, but I quickly got used to it and the higher revs made for a super sound effect (running stock-like mufflers).

GerryLP:cool

 

[Glensgages]

Just for the sake of conversation...
I would think it shouldn't matter what gear you're in because if you need to "accelerate suddenly", the transmission will automatically downshift when you get on the gas, thus putting you back in the higher rpms where you were trying to keep it prior to the acceleration request. No???

It probably would/might, but matting-the-skinny, waiting for the transmission to un-lock the converter, down-shift into 3rd WITH lock-up re-applied, then wait for the converter to un-lock AGAIN, is a joke:
until I get onto a 4-lane, open-road, I usually leave it in 3rd Gear, especially in my neighborhood, in-town driving, and even in parking-lots.....

With the .7:1 OD, even 3.73 gears result in an effective ratio of 2.61:1, a gear ratio usually reserved for the diesels of the early-'80s, so rather-than 'putt-around' in OD, I pull it into 3rd, and the car has more 'omphh' on-tap, and feels more-like my Z28 that has 4.11s.....


It's probably just a 'preference'-thing, but I like a car with gear.....

 

[Evolution1980]

It probably would/might, but matting-the-skinny, waiting for the transmission to un-lock the converter, down-shift into 3rd WITH lock-up re-applied, then wait for the converter to un-lock AGAIN, is a joke:...

Mine doesn't even get into OD until around 50-55 mph. So mine is normally doing in [D] what yours does in 3. It's just the way my TV cable is adjusted right now. I'd prefer to cruise along at 1400rpm myself. Hehehe... ta each 'is own!

 

[Glensgages]

Mine doesn't even get into OD until around 50-55 mph. So mine is normally doing in [D] what yours does in 3. It's just the way my TV cable is adjusted right now. I'd prefer to cruise along at 1400rpm myself. Hehehe... ta each 'is own!

My friends think I'm nuts, planning to install the earlier iron IRS housing onto the aluminum 'batwing', adding many HD parts (4.10:1 gears) and slicks, then changing the motor from a stock Cross-Fire to a carbed 450 HP 355" SBC, and replacing the 700R4 with a THM400 and 8" converter to do some drag-racing with a 26,100-mile 1982 Corvette when we move to Florida, where we'll take the car off the streets entirely:
my friends just don't 'understand' racing.....
:crazy

 

[80VetteL82]

I didnt realize how cheap these transmissions are compared to what I expected. They range from $895-$1,325. I cant decide between a Level 1 or 2 yet, because Im not quite sure how crazy Im going to go with the motor. I think Im going to go ahead and put the 3.73s in for now. Then sometime during the summer I should have decided on where to go with the motor, and Ill just get the 2004r tranny to match the HP.