With good driving, meaning baby throttle from dead stop and keeping the RPMs nice and low, I maintain about a 19mpg in the city which I think is very good for my car.

I have the stock 2.73s in the back, I was online last night and I found that Thunderacing has some excellent deals on their rearends. Complete 3.73 with a 3 series carrier all brand new for about 190 dollars, plus another 40 or 50 for the install kit which should be around 240 dollars.

I like my gas mileage, but I am aware that the 2.73s aren't really performance oriented gears, more on the economic side of things.

How badly would 3.73s hurt my gas mileage? Its either those or 3.42s

 

well we have to assume that you have overdrive transmission and not a th350 or 400 or any other three speed, or a 3 or 4 speed manual either

3.42 and 3.73 is extremely commonly factory installed in overdrive vehicles

great mileage on the freeway and good in town also since it would take less pedal to get going with the deeper ratio than it does with a higher one such as the 2.73 junk

in stock from with stock fuel system and so forth anyways


an open drum 3.42 or 3.73 axle should be easy to find good used for around 150, extremely common axle under these cars





good luck

 

I would say not much. 1-2 MPG AT MOST. I GET 16.5mpg mixed city/ highway with a 383ci with a 750 double pumper holley and a 3.73 rear. 92mph up the freeway appears to be turning around 3000rpm though.

 

I think you are mis-reading....

That would be, 3.73 gears FOR a 3 series carrier.

A suitable carrier, i.e. a "posi", would be about another $400.

The install kit will be about $100.

Yeah it would be a wonderful world where we could get a gear AND a carrier AND an install kit for $240; don't bet on it happening in this world though.

3.73 is too much gear for a mostly stock TBI motor. It doesn't produce power to speak of at RPMs above 4000; you'll end up with one of those cars you see that has this HUGE grunt off the line, but won't be able to pass a minivan at 55 mph in a 70 mph zone.

Now if yours is NOT mostly stock, i.e. you have some other heads besides the swirlies, you've changed out EVERY SINGLE PIECE of the exhaust system from the heads to the back bumper with something MUCH LARGER, and you have a cam with 20° more .050" duration in it than stock, then it's a different matter. All 3 of those things must be true, otherwise your car is not ready for that much gear.

3.42 is absolutely as high as I'd go on a stock TBI car. 3.23 might even be better. That will all depend on your "slight" mods.

Unless you DO buy a carrier, then any gears you buy that are 3.23 or higher, either you'll have to buy the "special" 3 series gears to fit on your existing 2 series carrier; or you'll have to buy a ring gear spacer. I personally wouldn't do either one, I'd buy a 3 series posi; but of the other 2 options, IMO the spacer is better, because then you can put a 3 series carrier in it later (much easier to find 3 series posi units than 2 series), and still use the same gears by just leaving out the spacer.

 

I totally disagree that a 3.73 gear is too much for a stock tbi or tpi. I have a 4.10 richmond set up in a 1986 tpi IROC (2.73 was stock) (rest of car is stock) and it totally woke the car up! As far as the comment about going out of the hole hard but not getting any passing power from 55 to 70 mph is completely wrong. In overdrive at 70 mph I am only turning 2300 rpm. When I hit the gas at 70mph the car takes off and pulls super strong.

The stock 2.73 gear took FOREVER to get up into the peak torque range. My 1987 Monte Carlo SS (stock with a 3.73 gear) would beat the Camaro with the 2.73's easily.

Changing your gear will give you more noticible change than any other mod you could do for that same small amount of money.

I say drop the 3.73's in they will be a big improvement and a lot more fun!

 

My car lost 3 mpg when I installed the 3:73's

 

I think you would be better off with a 3.42 rear. Ill bet you could find a whole rear end for your $240 dollars. If you were interested in 4th gen rims, you could find a 3.42 rear AND posi AND maybe rear disc brakes for much cheaper than a gear swap. Or you could try and find one from a 3rd gen and keep your axle lengths the same. With a 4th gen rear you would not need rear spacers.

I agree with sofakingdom, I think it may make the car feel faster but you'll run out of gear fast trying to pull past someone. Try and think about this as a system, with everything working together. For example TPIS told me not to get a 3.73 rear with a TPI beacuse a TPI already has plenty of low end torque, so the need for 3.73's or 4.10's is not needed. (when I had a TPI with a 700R4) Not to mention you only get to rev to 4500 RPM before she runs out of breath. And I know a stock TBI intake is not going to be any better, proably worse! And with low gears like that thoes rpm's come up fast!! Hope that helps.

 

Around town, I could see an increase in mileage with 3.73s, I know my 5,500 lbs tank came up with 3.73s. My 1994 with a 305 TBI came stock with 3.73s out back. Going from 3.08s to 3.73s really woke things up. The 3.73s work especially well with a mild stall and a cam. I would recomeend going to 3.73s, swapping to a 2,600-3,000 rpm stall torque converter, and going with a cam (retune you ECM). Eliminate the inadequacies of the TBI engine and you will get more power than you think.

I run the same combo on my 1983 G20 (5,500# brick). 3.73s with a 2,800 rpm Yank converter. In front sits you mild bolt-on 350 TBI with was until recently the stock heads and cam. It was a good match for me. I never had any trouble with the the gearing and the converter, even pulling 4,000+ lbs behind me.

Here happens to be a log of my passing power, pulling a 4,000# boat behind me, like I do nearly every weekend.



I actually get over 20 MPG with the cruise set at 70-75, I would not doubt that I got 16+ pulling the boat, it rolls along pretty easily behind me.

 

some guy on the boards is selling his complete rear end out of a 2000 T/A for about 200 dollars...I think it comes with everything, it has the 3.42s gears.

I thought Thunder Racing included the 3 series carrier as well?

I could be wrong.

But if thats the case I am gonna go ahead and buy it from White GTP I believe his name is, I haven't fully decided yet.

I just need to know the condition of the rear end as well, I don't expect mine to last very long, its been making alot of noises lately.

 

Indeed you could.

The $190 is the gears ONLY. As stated, a carrier (which would typically be a posi) is in the $400-500ish range. This page is carriers; this page is gears, plus a kit, some oil, and a "girdle" cover. The cover plus the oil is about $125-150 of that $400 price tag. You do the math.

Read BigWhiteGTP's posts REAL CAREFULLY - ALL OF THEM - before you buy a rear end from him. I'm not saying, don't buy it; only, it would be wise to be informed about what you might be getting into, beforehand.