tomard

Today, I have the stock 3.07 gears with stock Th350C lockup tranny in my 80 - those are the only things still stock on this car!

I would like to hear from the guys that HAD similar tranny & gears, that changed to either 3.55 or 3.73 and their opinions on performance gains.
If you went to .55 and then to .73, even better .....

There may be a tranny conversion in my future, but for right now, it is what it is .....

Just can't make up my mind right now, and the calculators don't show enough difference to make up my mind for me! So I really would like to hear from guys that have already lived it!

TWINRAY

FWIW, if you're going to be doing much 60+ mph cruising, I wouldn't go lower than the 3.55's with that 3 speed auto.

RagTop69

This isn't Corvette experience, but we swapped out the 2.79 8" gears in my 302 powered 69 Mustang for a set of 3.55s. The car has a 3 speed C4 automatic. The car tachs about 3500 at 70 mph now and it really isn't a practical freeway cruiser anymore. It did provide me with about 0.5 seconds at the drag strip, however. We also swapped my son's stock 2.75 9" gears in his 351W powered 69 Mustang for a set of 3.73 TracLocs. This is also a 3 speed automatic car (FMX) and it now howls on the freeway at 3700 rpm at 70 mph. You can completely waste a pair of rear tires coming out of the hole at full throttle. Both cars sound like they want to shift up one more gear. Given the cams and other speed equipment we have on both my convertible and his fastback, gas mileage has never been a realistic issue for either car. My vert dropped from around 15 mpg to about 10 mpg. On long trips it will knock down 13 mpg. If I had it to do over, I wouldn't have done the 3.73 in the fastback without a tranny swap and should probably do the same with the vert. With the high rpms you will also be wearing out your engine.

stinger12

I was sort of in the same situation as you when I was deciding which gear set I wanted to go with. My car originally came with 3.08 gears, but I wanted kick in the butt acceleration (I still wanted to be able to drive the car on the highway every now and then...not too much though).I decided to go with 3.73 gear ratio in the rear. It will create high RPMs, so too help with that, I am going to install an overdrive tranny. You mentioned that you wanted to stay with your stock tranny right now which is fine - I think the 3.55 gear would be a good choice for you since it won't kill your engine like 3.73 gear will without the overdrive. I haven't driven my car yet, so I still don't know what it is going to feel like - but I would think the 3.55 gears would be what you want.

painterman52

I went from 3.08 to 3.70 with a th400. It really helps acceleration. I really don`t go very far, have never been on the freeway in that car, so I`m good with no overdrive. If I have to ever replace the rear I`d go with 3.55. That seems like a good compromise.

stinger12

Yeah, the 3.55 gear seams to be the gear to use between extreme acceleration and actual driveability. If you want seat of your pants acceleration, go with the 3.73's. If you want acceleration but still good driveability, go with the 3.55 and no overdrive trans

redwingvette

I changed from the 3.08 to the 3.55 and liked it but it did suck on the highway a little. Plan on seeing 3400rpm's @ 70mph.
I later added the OD trans and now I really like it.

Les

That pretty much sums it up. On the whole, for overall use the 3.55s would be your best bet. The difference in acceleration between the two isn't significant enough to make that much difference. However, going from 3.08s to 3.55s will pull RPMs noticably quicker & the gap between gears will be tightened up too.

Belgian1979vette

The gearing should match the rpm band of your engine.

GTR1999

If you're planning on an OD tranny in the future you may want to go to 373's.

stinger12

Also take this into consideration. When you switch to an overdrive trans, your RPMs will drop, and then you may ask yourself why you didn't go with the 3.73 ratio instead. When are you planning on upgrading to an overdrive trans? That should play a good role in your decision making process.

stinger12

Check out this thread I started a while back when I didn't know what gear ratio to go with. I have decided on going with an overdrive trans instead of the stock TH350, so I also went with the 3.73 gears. I also decided to flare out my vette and put 12" wide tires on the rear lol.

http://forums.corvetteforum.com/show...highlight=gear

7T1vette

If the THM350 is not an O/D tranny and you don't plan on getting one, I'd suggest that you go with 3.36 ratio. The torque multiplication you get from the tranny converter along with the 3.36 ratio should give you a nice acceleration boost...but it will still get decent mileage at highway speed. If you go with an O/D auto tranny, 3.55 or 3.73 is OK....whatever "floats your boat".

76 VETTE

I put 3:70s in my 76 with a 350th tranny.For just around town it was nice. But on the highway seemed like it was working too hard and engine seemed to run hotter.I went with the 3:55s and am happy with it.Good all around gear.

Binnie77

I just swapped out my 3.08 yesterday for 3.55 I will put it back in the car tomorrow. The picture is our heavy duty equipment instructor at my college helping me with the swap. Nice to have all the gear to work with

BKbroiler

To give you some actual performance data to think about, I changed from 3.08 to 3.73 gears in my 77 and lowered my quarter mile ET by 5 tenths.
I have a TH350 trans. If you don't do a lot of high speed cruising you can live with 3.73s.

Fast81

I went from 3.08 stock gears to 3.54, BUT i also swapped from a th350c to a TCI 700R4 at the same time. My present setup is good but i've always wondered what the 3.73's would be like behind the 700r4 1st gear. Another element you forgot to mention is your rim/tire plans. if you're staying original or stock dimensions, the 3.55 should be all you'd need. BUT if you're thinking about going 17"or 18" in the future, 3.73 would be my choice.
One more thing, what hp is your motor and what do want the car to be??? if your setup will be a torque monster, 3.73s will just magnify your existing traction problem while costing you top end speed.
My ~400hp 355 with 700r4 and 3.54 rearend pulls hard up thru 135 where my faith in the "still stock" suspension, steering, and brakes got the better of my judgement.

"Speed costs $, how fast do you want to go?"

tomard

Isn't that the truth, about speed=$, I think Einstein came up with that one too

Anyway, I was again thinking, and if I am going to change trannys on this car, I WANT MANUAL .... and don't have deep pocketbook for TKO!

So, I am left with Muncie or Borg 4 speed.... What would my gear choice be now to get max low end pull? I have lots of high end juice from my AFR heads, and the intake/carb has provided some low end, but mostly over 4k rpms, now I want the "throw my a$$ back into the seat when I put foot to the floor" kind of reaction

bozzman3

Really 5 tenths??? Wow I cant wait to go to the track this year!! My vote is 373s thats what I did in my 80 with the turbo 350c

1981Z06Vette

Why not do one of the Ford T5 swaps? They hold up pretty well, are available used for cheap, and you could probably sell (if you have the 4 speed now) either a BW Super T10 or a munice for enough to do the whole T5 swap. Would make it very easy to go to a Ford style Tremec later as budget permits. With that, I'd go 3.73.