4.7 Final Drive Vs 5.1 Final Drive

If you’re modifying your car or choosing gear ratios for a build, you’ve likely asked: 4.7 Final Drive vs 5.1 Final Drive – Does It Make a Big Difference in Acceleration? The short answer is yes, it can make a very noticeable difference, but the impact depends entirely on your vehicle and goals.

This choice is a classic tuning decision. It involves swapping the ring and pinion gears in your differential to change how many times the driveshaft spins to turn the wheels once.

A higher numerical final drive ratio, like a 5.1, will generally make you car accelerate quicker off the line. But there’s trade-offs to consider, such as top speed and fuel economy.

Let’s break down exactly what changes, why it matters, and how to decide which is right for your project.

This comparison is common in many rear-wheel-drive and four-wheel-drive platforms, from drift cars to off-road trucks. The 4.7 and 5.1 represent the final drive ratio.

Simply put, with a 4.7:1 ratio, the driveshaft spins 4.7 times for every single rotation of your wheels. With a 5.1:1 ratio, it spins 5.1 times.

That extra 0.4 of a rotation is the key. It means your engine is doing more work per wheel turn, multiplying torque more effectively.

Understanding Final Drive Ratio

The final drive is the last gear reduction in your drivetrain. It works together with your transmission gears.

Think of it like the gears on a bicycle. Your transmission is the front set of chainrings, and the final drive is the rear cassette. Changing the rear cog size has a huge effect on how easy it is to pedal (accelerate) versus how fast you can go (top speed).

Higher Number (e.g., 5.1): More mechanical advantage. Better acceleration, quicker off the line, feels “snappier.” Often called a “shorter” or “lower” gear.
Lower Number (e.g., 4.7): Less mechanical advantage. Higher potential top speed, less engine RPM at cruising speed. Often called a “taller” or “higher” gear.

The Math Behind the Acceleration Difference

Let’s put some simple math to it. The difference from 4.7 to 5.1 is roughly an 8.5% increase in ratio.

This means, all else being equal, you’ll get about 8.5% more torque multiplication to the wheels in every gear. This directly translates to a perceived 8.5% improvement in acceleration force.

In a typical car, that can mean a couple tenths of a second shaved off 0-60 mph times. For a dedicated drag car, that’s massive. For a daily driver, it’s a very feelable change in seat-of-the-pants response.

Real-World Driving Impressions

Swapping from a 4.7 to a 5.1 final drive will make you car feel more lively. Throttle response feels sharper.

You’ll likely find you don’t need to downshift as often when passing, because the engine is already in a higher RPM range for any given speed. This can be a big advantage on a twisty road or track.

However, the trade-off is immediatly apparent on the highway. Your engine RPM will be significantly higher while cruising.

Example: At 70 mph with a 4.7, you might be at 2800 RPM. With the 5.1, that could jump to over 3000 RPM or more, depending on your tire size and transmission.
This leads to increased engine noise, higher fuel consumption, and potentially more wear over long distances.

Impact on Top Speed and Each Gear

A 5.1 final drive doesn’t just make first gear shorter; it makes every gear shorter. Your top speed in each gear is reduced.

Your car might hit its rev limiter sooner in each gear. While acceleration to a given speed is faster, the maximum speed the car can achieve in that gear is lower.

For most street cars, top speed in 5th or 6th gear is still far beyond legal limits, so this isn’t a major concern. But for track use, you must ensure you won’t hit the limiter at the end of a long straight.

Gear Speed Comparison Example

Assume a car with a 5-speed manual and 24.5″ tall tires:

With 4.7 FD: 3rd gear tops out at ~85 mph at 7000 RPM.
With 5.1 FD: 3rd gear tops out at ~78 mph at 7000 RPM.

You gain acceleration to 78 mph, but lose the ability to reach 85 in third.

When to Choose a 4.7 Final Drive

The 4.7 ratio is often the better choice for certain applications. It favors efficiency and high-speed stability.

Consider a 4.7 if:

Your car is a daily driver with significant highway miles.
Fuel economy and reduced cabin noise are priorities.
You have a high-revving engine with plenty of power, so you don’t need the extra multiplication.
You’re running larger diameter tires (which effectively make the final drive “taller”).
Your car is used for high-speed events where maintaining lower RPMs is beneficial.

When to Choose a 5.1 Final Drive

The 5.1 ratio is the performance favorite for good reason. It maximizes acceleration and responsiveness.

Choose a 5.1 if:

Your primary goal is quicker acceleration (drag racing, autocross, drifting).
You have a torquey engine that can handle the shorter gearing comfortably.
You do mostly city or backroad driving with little extended highway use.
Your car is underpowered and needs more “leverage” to get moving.
You’re running smaller diameter tires (common on some track setups).

Installation and Cost Considerations

Swapping a final drive ratio is not a simple bolt-on job. It requires setting up differential gears, which is precise work.

We recomend having a professional mechanic or specialist perform the installation. Improper gear setup leads to whining, premature wear, and catastrophic failure.

Typical costs include:

The ring and pinion gear set (4.7 or 5.1).
Installation kit (shims, bearings, crush sleeve).
New differential fluid.
6-10 hours of skilled labor.

It’s a significant investment, so it’s crucial to be sure of your choice.

How Tire Size Changes the Equation

Your tire diameter is part of the overall “final” gearing. A larger tire acts like a taller (lower number) final drive. A smaller tire acts like a shorter (higher number) final drive.

If you switch to a 5.1 but also put on much larger tires, you might cancel out the effect. Always calculate your “effective” ratio.

Use this simple check: If you go to a taller tire and want to maintain the same feel, you may need a higher numerical final drive (like going from 4.7 to 5.1) to compensate.

Making Your Decision: A Step-by-Step Guide

Follow these steps to choose between a 4.7 and a 5.1 final drive.

Identify Your Primary Use: Percentage of track vs. highway vs. city driving.
Check Your Current Setup: Note your current ratio, tire size, and transmission type.
Use a Gear Calculator: Input your data. See what RPM you’ll run at 70 mph with each ratio and your tire size.
Consider Your Engine’s Power Band: Does it make power down low or up high? A 5.1 can help keep a peaky engine in its power band.
Budget Realistically: Include parts and expert labor. Don’t cut corners here.
Talk to Owners: Find forums for your specific car model. See what others with similar setups experience.

FAQ: Final Drive Ratio Questions

Will a 5.1 final drive always make my car faster?

It will make it accelerate faster from a stop or out of corners, but it can reduce your top-speed in each gear. Overall lap times may improve, but it depends on the track.

Is the fuel economy hit with a 5.1 ratio severe?

On the highway, yes, you could see a 1-3 MPG drop or more due to higher cruising RPM. In city driving, the impact may be less noticeable, or it could even improve if you’re less heavy on the throttle.

Can I just change my final drive myself?

Unless you have specific experience setting up differential gears, we do not advise it. The tolerances are extremely tight, and a mistake is very costly. The meshing pattern and backlash must be perfect.

Does a 4.7 vs 5.1 difference matter for an automatic transmission?

Yes, it matters a lot. The effect is similar, but modern automatics have many gears. A shorter final drive can affect shift points and how the transmission behaves. Sometimes a tune is recommended to optimize the change.

What if I have a 6-speed transmission? Does that change the choice?

A 6-speed, with its overdrive top gear, can make a 5.1 final drive more livable. The overdrive gear can bring highway RPMs back down closer to comfortable levels, giving you the best of both worlds: acceleration in the lower gears and reasonable cruising RPM in 6th.

Final Verdict: Is It Worth It?

The jump from a 4.7 to a 5.1 final drive absolutly makes a big difference in acceleration. You will feel it every time you press the throttle.

Whether that difference is right for you comes down to your driving environment and priorities. For a weekend toy or dedicated performance car, the 5.1 is often a transformative upgrade that maximizes fun. For a car that sees long commutes, the 4.7 might be the smarter, more comfortable choice.

Do your research, run the numbers with a gear calculator, and plan for a proper installation. When done correctly, changing your final drive ratio is one of the most effective ways to alter the character and performance of your car.