MFactory B Series Final Drive Gear Set for EM1 Civic/Integra

MFactory Final Drive Gear Set - B-Series (B16, B17 & B18)

A final drive change multiplies the power you already have through every gear in the box. On a B-series, where the engine is willing but displacement is limited, gearing is often the cheapest real performance available. Six ratios spanning from a tall 3.47 to an aggressive 5.167, so you can gear the car for whatever it actually does.

Measure Your Ring Gear Hole First

This is the check that determines which version you need, and it's the one thing to get right.

B-series transmissions use two different ring gear hole diameters, and they aren't interchangeable:

109mm (small) covers the B16A, B17A, and B18B transmissions.
116.8mm (large) covers the B18C1 and B18C5, meaning GS-R and Type R.

Go by the actual measurement rather than by what your car is, especially on a swapped or rebuilt gearbox. On B-series cars that are now twenty-five to thirty-five years old, transmissions have moved around considerably.

Know Your Starting Point

Worth checking, because it determines whether a given ratio is a step up or a step down for you.

Hydro transmissions (B16A, B17A, B18A, B18B, B18C1, B18C5) came with a 4.400 final drive.

JDM B16A cable transmissions (A1, J1, Y1, Y2, S1) came with a 4.785.

So on a hydro car, anything above 4.400 shortens your gearing and anything below lengthens it. Coming from 4.785 on a cable car, the 4.92 available to you is a modest step rather than a dramatic one.

Find Your Ratio

Small 109mm ring gear, hydro transmissions
Fits 1992-1993 Integra GS-R (YS1), 1992-2001 Integra LS (YS1, Y80, S80), 1994-1997 Del Sol B16 (Y21, S21), 1999-2000 Civic B16 (S4C)

Large 116.8mm ring gear, hydro transmissions
Fits 1994-2001 Integra GS-R and 1996-2001 Integra Type R

Small 109mm ring gear, cable transmissions
Fits 1988-1991 B-series cable transmissions (Y1, S1, Y2, A1, J1)

Two things worth noting. The 4.26 is only offered in the large ring gear version, and the cable transmissions only get the 4.92.

What A Final Drive Actually Changes

Worth explaining, because it's easy to confuse with a gearset.

Your final drive is the last gear reduction between the transmission and your wheels. Every gear passes through it, which means changing it affects all of them at once. A gearset changes individual ratios. A final drive shifts the whole transmission.

Go numerically higher and you get more torque multiplication at the wheels in every gear. The car accelerates harder and pulls out of corners more willingly. The trade is speed per gear, so you shift sooner, your rpm at a given road speed goes up, and top speed comes down.

Go numerically lower and everything reverses. Longer gearing, lower cruising rpm, and higher top speed per gear.

This Range Goes Both Directions

Important to understand before picking, because coming from 4.400 these ratios split into two very different intentions.

5.167 and 4.92 are the aggressive short ratios. Serious torque multiplication in every gear, built for autocross, drag racing, and tight technical tracks where you're living in the low gears. Highway driving means high rpm.

4.71 is the moderate step shorter. A real improvement in acceleration while staying usable on the road, which suits a car that sees track days and still gets driven there.

4.26, 4.00, and 3.47 go the other way. All three are taller than the factory 4.400, which means longer gearing rather than shorter. That's the right choice for high speed circuits, standing mile events, or a boosted build making enough torque that stock gearing has the car running out of gear too quickly.

Be clear on which problem you're solving before you order. Most people shopping a final drive want shorter, but the tall options exist for a reason and they're the correct answer for a specific kind of car.

Pair It With A Limited Slip

Worth thinking about seriously, because it's where a lot of the gain gets realized.

More torque multiplication means more torque at the wheels, and on a front-drive car with an open differential that often just means more wheelspin from the unloaded side. A shorter final drive can genuinely make an open-diff car worse out of a corner, since you're feeding more torque into a system with no way to manage it.

A limited slip sends that torque to the wheel with grip instead. Both parts require splitting the transmission case, so doing them together means one job rather than two on a gearbox that has to come out either way.

What Else To Sort While You're In There

Your speedometer will read wrong. Changing the final drive changes output speed relative to your wheels, so the speedo and odometer will be off. Plan on a correction.

Inspect bearings and seals. Anything you remove to reach the ring gear should go back in fresh if it has real miles on it. They cost almost nothing next to the labor of getting to them.

Look at your synchros. These transmissions are old enough that if it's started grinding, this is the moment rather than pulling the box again next year.

Fitment

1988-2001 Honda and Acura B-series transmissions, both cable and hydro. See the tables above for the correct part number.

Select by ring gear hole diameter, not by vehicle.

Who Should Run One

This is for the B-series owner who wants the car to accelerate harder without chasing power, or who needs taller gearing for a high speed application. It's the cheapest meaningful performance change available on these cars, and the range here covers everything from a drag setup to a top speed build. Measure your ring gear hole, check what you're starting from, pick your direction, and sort your speedo.

Fits: Honda and Acura B16, B17, and B18 transmissions, cable and hydro. Ratios: 3.47, 4.00, 4.26, 4.71, 4.92, and 5.167 depending on application. Stock final drive: 4.400 on hydro transmissions, 4.785 on JDM cable transmissions. Important: select by ring gear hole diameter, 109mm or 116.8mm. Note: speedometer correction required after installation. Pairs well with a limited slip differential.