First I'd like to say that we could use your engine size & specs. Stock or otherwise listed. This way it's a known. Then what your prepared to live with or whats to much in your opinion. Increasing the ratio is a great way for increasing performance. With that said........Read on. Sorry for the length. But I feel it's important. Examples listed below.
The higher the number, the higher the engine spins in RPMs to keep the same speed. This can be offset a little bit by a larger rear tire to a point. When choosing a higher ratrio to increase performance, you must keep this in mind.
Somewhere I have a formula that can break this all down and tell you what RPM and speed you'll travel at with a given tire size. It doesn't take into account converter slipage of automatics. Converter dependent, you can add a couple of hundred RPMs.
If you have a stock tire of (Lets just use round inch numbers) 25 inchs and 2.76 gears and make a jump to 3.55's, you'll probably feel there a bit much on the Hwy. An increase of an inch to a 26 inch tire will offset the cruise RPM a little without killing the off the line get up and go alot.
The ratio should also be a decent match to the engine. The engine parts that matter most is the cam and to a lesser extent, carb and intake.
If you make a move to a larger cam that requires a higher stall converter, then the converter also comes into play on how well it effects the performance of the car.
I'll list a few examples below on how things can go;
Ex1;
In my Cuda ( E-body/4spd/360 ) I run 4.10's and a 27 inch tire. This is a good street strip set up. The engine is ruffly a 11-1 comp ratio w/ a purple 292/.509 and a 750 cfm and super comp headers.
I can Hwy. drive this anywhere. You'll just need 2 fist fulls of dollors to do it. (LOL)
Ex2;
My '79 Magnum w/a 400 B/B is a stock HP set up. No big deal seeing the engine is a '78. But the ratio is 3.21 and a 26 inch tire. While no to great out of the hole, the next step up to 3.55's with a mild cam is a noticeable difference. Small changes and a few performance parts took this car from a high/mid 15er to a solid 14 second car. Still, it is a driver.
Ex3;
An old build I did was a 360 with a Crane cam. 272/284 and 3.23's. While not to bad off the line, it was real nice on the Hwy. The rear ratio made the car feel like it had plenty of up top energy. A swap to 4.10's and and 27 inch tires, it became a contender on the street. The previous smaller tire (25) was terrrrrrible. It became a sit and spin them on the street. However a great way to kill the tire for new ones. Even with the 4.10's, the mileage wasn't bad.
