My car is up on jackstands right now, as I'm taking out the 700r4 for a T56 this week. According to what several people have told me (I did the math also, but I don't trust myself) , 4th gear with the 700r4 and 2.73s would be the same rpm/mph as 6th gear with the T56 and 4.10 gears. My problem is that I keep hearing that you should match your gearing with the cam's powerband. The car has a 305 TBI right now which is pathetically weak (very small cam duration and lift). Im definitely dropping a 350 later on (roughly 375 hp), but I don't know if I should wait to do the gear swap after the 350, or if I can do it now and be able to benefit from it.

 

You'll benefit in the 0-60 and stop light racing department, but in the 1/4 you're going to suffer till you get some higher rpm breathing.

 

Yeah, it'll accelerate great up until it quits breathing (about 3500)
4.11's are a lot of fun with a motor that pulls to 7000, but with a stock 305 TBI, you're gonna be shifting a lot.I'm running 3.73's with a T5 trans (soon to be replaced with a Tremec TKO), but my motor pulls to about 5500.If the motor upgrades are coming soon, go for it.Otherwise, I'd stay in the 3.23-3.42-3.73 area.
My high School car had 4.88's with a small block that spun to 7000!Couldn't do much freeway driving, but I could take anybody in town, stoplight to stoplight!Not a very practical car.
-Rich-

 

The car is gonna be 95% for the street and 5% for 1/4 mile. Its my daily driver. I know it'll run awesome with more power, but I don't know if going with that short a gear ratio right now will hurt performance too much.
Heres what I'm thinking-
With the .76 4th gear and the 2.73s-

.76 * 2.73 = 2.0748

With the .50 6th gear and 4.10s-

.50 * 4.10 = 2.05

I think this is the right way to determine the final drive ratio, right?

From what I understand, I would still get the same rpm/mph on the highway as I did when the car was stock.

 

I am doing the exact same thing in about a week. I am swapping to a T56 with the .5 overdrive ratio and I chose the 4.10 gears. My 305 will be far from stock though and should pull to ~5200. Most people with a relatively stock 305 tend to go with 3.73 gears. As RICH92RS350 said if motor upgrades are in the future go with the 4.10s.

I you are correct with your math though.

 

Ok, assuming a 26 inch wheel, the car would be running 95 mph at 2500 rpm in 6th. In reality it would be slower, cause of air resistance and crap, but it doesn't sound that bad. Maybe I could go with 3.73s and it would be a better compromise for now and after the motor swap.

 

Sounds like 3:73s would better suit you, going with 4:10s is going to run you past 5200 rpms.

 

If your car can handle 373s it'll handle 410s. I just made the switch, and only turns a few hundred more rpms. I turn 2600 rpm @ 70mph, with stock tires and wheels. I also run a 700r4. Rember the deeper gear you go, the larger tire WILL be needed. I can't use wot, untill I get it moving. Just goes up in smoke. Was needing new rear rubber anyways.

 

I've run both 4.10s and 4.56s on the street. Both are fun to drive with around town. One big advantage of bigger gears is that it will allow you to put a taller tire on it. When I street drove my 87 I used a 275/60r15 tire which is real close to the 10.5x28x15 slicks I use now.

 

Ok, I've thought this over and this is what I've come up with. I definitely want to put in 4.10s to go along with my 6 speed and the 350, but the car isn't going to get a 350 for a while (low funding). Would the 305 and 4.10s make a really horrible combiantion? Cause I was thinking I'll drop them in while I have the 305 and the 6 speed. Worse case scenario is that the car is going to be annoying to drive until the motor swap.

 

Unless you have a cam that produces power to around 5800 rpms or higher, you're going to hurt your perfomance 1/4 mile speaking. Though you're 0-60 time will be a lot better. Of course when you get the 350 in with high rpm breathing you'll be set.

 

As long as it's temporary it will be alot better in the 1/8th...

Another thing that will slow you down is all the shifting... Remember, you should be running the 1/4 mile at 1:1 @ redline in the tranny, not overdrive.

My car runs great N/A and I run 4:10's. Works perfect 1/4 mi at a hair over 6,000. Now with NOS it runs too quick and I have to hit OD to finish, so technically 3:73's would be a better choice now.

You say 95% street. I drive mine alot on the street and 4:10's suck on the highway or any fast 2 lane road. 35-45mph cruise is perfect though.... Of course I have only 30% OD with the 700r4 so you'd be better off in that department... So go for it!!!

 

Here's a good formula for you guys...

RPM x tire diameter
---------------------------------------- = MPH
336.13 x trans ratio x gear ratio

 

heres what i can contribute, on my last vette i had 3.43 rears and a zf6 with a 0.5 6th Cruising on the highway tach barely registered 1600, and it got between 33-35mpg if i left the cruise on.

My current car with a 3.07 rear runs about 2000rpm on the highway and gets about 27-29mpg

Something to consider if mileage is important to you, another thing to consider, 4.10's could render 1st gear useless. It was pretty hard to maintan traction in first with 3.43's

Personally i would go with 3.73's

 

Anything you can put in will help. I think the T56 will be practically undriveable with the 2.73's you've got. Remember 1st gear in the T56 is about 2.66, and you've got no torque converter to help you get going...

 

Ok, I was set on putting in 4.10s, but now I'm not sure if I should go with those or 3.73s. What would you guys go with? I'm thinking how difficult its going to be to get traction in first, and that I could probably get a set of 3.73s at a junkyard pretty cheap. Thats another point- Is it worth the effort to pull a set of gears off a junkyard car, or am I just being stupid? I know the four cylinder camaros all came with 3.73s, and from what I understand, I wouldn't have to shim them. If I buy new gears on the other hand, its close to 200 plus another 200 to get them shimmed. If I go with some used gears, I could get an slp posi unit for $100 and still have about 200 bucks left over.