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3.9 Final Drive


IanS16

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http://www.z-store.co.uk/index.cfm?fuse ... rentCat=24

 

Just looking through the Z store and came across the avove. Does anybody know which OEM parts are needed extra?

 

Has anyone had this done as a 10%(ish) power increase is pretty damn good - better than £200 for a plenum and £150 for an air filter for a 1% increase.

 

Does anybody know what the top speed will be brought down to? I assume if it would be approx 160mph?

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Kev would be the best person to ask!

 

Not sure what the top speed would come down to. I'm sure it wouldn't really effect any of us normal drivers! :teeth:

 

I suppose it's like changing the sprockets on motorbikes.

 

 

 

Could be something I'd consider when changing the clutch and flywheel assembly...

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This "upgrade " only gives you a claimed 10% power increase in every gear and not to be confused with 10% bhp power increase overall.

 

Like Stew says best to talk to Kev regarding the other issues but it looks like the kit comprises of only a crown wheel and pinion and you will require seals, gaskets, bearings. shims and oil.

 

If you propose to go ahead with this then I have all the specialist equipment and experience required to set the diff up for you.

 

It is not a big job once the diff is out the car and would cost £150.00 labour for the diff overhaul. This price does not include any parts or the removal and refitting of the diff.

 

Hope this helps,

 

Alex.

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Cheers Alex I'm just looking at the moment to be honest.

 

What would the be the drawbacks to this? Shorter gears?

 

Oh, and what has the diff got to do with this? Is this not a sort of gear change in the gearbox?

 

Yeah mate I realise that you are only contemplating at the moment and I was only making you aware that the technical side of the final drive replacement would not be an issue. ;)

 

There would be no drawbacks if this is what you want or require.

 

But, fuel consumption fiqures will suffer slightly as you will be hitting the red line sooner on every gear as the gear ratios from the final drive will now be 3.9 - 1

 

Your speedometer will also be slightly out.

 

Your car will be slightly faster through the gears but your top end speed will be reduced.

 

Talk to Kev, he should be able to keep you right but not really a cost affective upgrade for you IMVHO. :)

 

Cheers,

 

Alex

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I'm only getting 14 MPG (5.8kml) as it is! :lol:

 

Cheers mate, appreciate the advice!

 

Some more for you mate retrieved from my archives.

 

What is a Final Drive?

The final drive is the final gearing before the rear wheels. The input from the transmission goes into the final drive receiving a final reduction before entering the drive axles. The final drive is made up of a ring and pinion gear and is mounted on the rear differential.

 

What is the OEM final drive ratio?

The 5spd automatic has a 3.357 final drive ratio.

The 6spd manual has a 3.538 final drive ratio.

 

Are there aftermarket final drives?

Yes. Currently only a 3.917 ratio gearing is available and is offered by several companies.

 

How can changing it help?

There are two options here based on need.

Going up in ratio gearing improves acceleration. (i.e. 3.3 ---> 3.5 ---> 3.9) This is generall NOT recommended for forced induction vehicles. Those who have done this in conjunction with FI have noted that first gear becomes worthless in 6spd tranny cars.

Going down in ratio gearing can improve traction and widen the gears for high power applications (i.e. 3.5 ---> 3.3) This is generally NOT recommended for naturally aspirated or lightly modded vehicles. It can severaly slow down the accelleration.

 

Can I put one in my 5spd automatic?

It is not recommended to install the 3.9 gears into an automatic. However, many owners have had success installing the 3.5 gears, improving acceleration.

 

Why is the 5spd automatic final drive different?

Because the transmission has few gears and each is gear has a different ratio than the 6spd manual counterpart. In short: the 3.3 gear is the appropriate OEM gearing for the 5spd, just as the 3.5 is the appropriate OEM gearing for the 6spd.

 

WIll it work with the XXXX LSD?

Is this a good modifcation for FI'd cars?

For lightly boosted setups, the gears can add additional performance while keeping your engine safe. Instead of risking a fatal engine failure, you could achieve the greater acceleration with a gear change. However, as you increase boost levels there comes a point where lower gearing would be more beneficial allowing you greater range in each gear to fully reap the benefits of a high horsepower engine.

 

Is this a good mod for the drag strip?

What is the top speed with the final drive changed?

 

What final drive ratios are available?

3.3: This is the standard final drive gearing that comes with the 5spd automatic transmission.

3.5: This is the standard final drive gearing that comes with the 6spd manual transmission.

3.9: This is the popular after market gearing for the 6spd manual.

 

INSTALLATION

 

How much does it cost to install?

Installation prices range from 300 to 600 depending on who you ask. Keep in mind you may need additional parts. See the Final Drive Wiki Page for more information on this.

 

What extra parts are needed?

need info....

 

Can I install this myself?

Only you can answer that. If you are asking this question then probably no. This installation requires some special tools. You have to drop the entire pumpkin assembly down from the chassis and I have heard that requires some of the rear suspension to be removed as well.

 

Is there an installation tutorial?

Not yet.

 

How long does the installation take?

It would be possible to do in a single day for someone who has all the right tools and is experienced. However expect at least 2 days and even longer if extra parts are required once the pumpkin is open.

MAINTENANCE ETC..

 

I hear funny noises after the install.

It may be ok to hear some noise, but too much noise means something could be wrong. The most likely cause is an incorrectly shimmed gear set.

 

Will this affect my gas mileage?

It has the potential to affect it, but not by too much.

 

Will this affect the TCS/VDC?

No.

 

Drivetrain Definitions

 

Axle

An axle is a central shaft for a rotating wheel or gear. In some cases the axle may be fixed in position with a bearing or bushing sitting inside the hole in the wheel or gear to allow the wheel or gear to rotate around the axle. In other cases the wheel or gear may be fixed to the axle, with bearings or bushings provided at the mounting points where the axle is supported.

 

Clutch

A clutch is a subcomponent of an engine's transmission designed to allow engagement or disengagement of the engine to the gearbox or whatever apparatus is being driven.

The coupling mechanism used on a mechanical power press to couple the flywheel to the crankshaft, either directly or through a gear train.

 

Differential

A set of mechanical gears that eqaulises the power between the left and right drive wheels, particularly when cornering, when the outside wheel travels further than the inside wheel.

A device - usually made of gears - that divides the torque between the driving wheels and permits the wheels to turn at different speeds. This is especially important when negotiating a corner, as the inside wheels turn more slowly than the outside wheels.

A unit that takes the power of the rotating driveshaft at right angles to the rear axle and passes it to the axle. It will not only drive both rear axles at the same time, but will also allow them to turn at different speeds when negotiating turns. In this way the tires do not scuff or skid.

 

Driveshaft

A driveshaft or driving shaft is a mechanical device for transferring power from the engine or motor to the point where useful work is applied. The 350Z incorporates a one-piece driveshaft which is actually carbon fiber reinforced plastic.

 

Final Drive

 

Flywheel

A relatively large and heavy metal wheel that is attached to the back of the crankshaft to smooth out the firing impulses. It provides inertia to keep the crankshaft turning smoothly during the periods when no power is being applied. It also forms a base for the starter ring gear and, in manual transmission, for the clutch assembly. Also see engine flywheel and fluid flywheel.

This is a large gear mounted to the back of the crankshaft which turns the engine when the starter is cranking.

A flywheel is a heavy rotating disk used as a repository for angular momentum. Flywheels resist changes in their rotation speed, which helps steady the rotation of the shaft when an uneven torque is exerted on it by its power source such as a piston-based, (reciprocating) engine, or when the load placed on it is intermittent (such as a piston-based pump).

 

Gearbox

A casing for gear sets that transmit power from one rotating shaft to another. A gear box has a number of functions: it is precisely bored to control gear and shaft alignment, it contains the gear oil, and it protects the gears and lubricant from water, dust, and other environmental contaminants. Gear boxes are used in a wide range of industrial, automotive, and home machinery.

The shell (metal casing) in which a train of gears is sealed.

 

Gear Ratio

The number of revolutions a driving (pinion) gear requires to turn a driven (ring) gear through one complete revolution. For a pair of gears, the ratio is found by dividing the number of teeth on the driven gear by the number of teeth on the driving pinion gear.

A gearbox contains several toothed wheels that are connected and disconnected to each other in order to switch into the intended gear. The gear ratio is the ratio between the number of teeth of the two wheels that are connected at a given time. If one wheel has 25 teeth and the attached one has 50, there is a 2:1 ratio.

 

Limited Slip Differential

A Limited Slip Differential (LSD) is a modified or derived type of differential gear arrangement that allows for some difference in rotational velocity of the output shafts, but does not allow the difference in speed to increase beyond a preset amount. In a car or automobile, such limited slip differentials are sometimes used in place of a standard differential, where they convey certain dynamic advantages, at the expense of greater complexity.

 

Pumpkin

The rear pumpkin, or carrier, houses the final drive gears and differential.

 

Short Shifter

 

Toe

 

Toe relates to the difference in the distance between the front of the tires and the rear of the tires on the same axle, or to the vehicle centerline. Toe-in, or positive toe, is defined as the front of the tires being closer together than the rear of the tires. Toe-out, or negative toe, is when the rear of the tires are closer together than the front of the tires. Zero toe is when the tires are parallel to each other.

 

Effects of Toe: Excessive toe increases tire scuffing and results in tire wear and drag on the vehicle. Excessive toe-in, or positive toe, increases scuffing on the outside of the tire. Excessive toe-out, or negative toe, increases scuffing on the inside of the tire, and in some cases can cause a darting or wandering problem. Bias or bias-belted tires will commonly show a featheredge or saw-tooth toe wear pattern across the entire tire tread area. Any tire wear pattern caused by a toe condition can be further affected by an excess camber condition and may result in irregular wear patterns.

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I've had this in my own car now for about 4 years

 

Speedometer is unaffected - the speedo is not indexed off the ring and pinion, it's done off the abs sensors, which contain wheel speed sensors

 

gas mileage wise, my car gets the same 320 miles to tank as it always did. Even with my built engine, I still get the same miles to tank, within 5-10 miles. I've taken the car on very long trips (longest was 14 hours) - gas mileage was the same as it was when I first got the car in 2003.

 

As far as extra parts, we have the details listed on our site:

 

http://www.z1auto.com/prodmore.asp?mode ... rodid=1726

 

ring and pinions do not add any HP, real or imagined. They are torque multipliers.

 

A more cost effective solution IMHO is the 4.08 - slightly higher, and particularly well suited to the 2005 + revup engines and the 2007 + HR's, but works well on the DE's as well. More cost effective though:

 

http://www.z1auto.com/prodmore.asp?mode ... rodid=2833

 

the top speed is reduced per gear by the % difference per gear vs stock. So, a 3.9 for example is ~11% shorter than the stock 3.54, thus top speed per gear is reduced ~10%, but acceleration is improved ~11% per gear. It's not quite a linear relationship, but it's very, very close.

 

It makes a very immediate and noticeable difference. Particularly if you've increased the rev limiter. On my own car, the 3.9 has been fantastic, but I'm going for an even higher ratio now, to better suit my NA engine (4.3)

 

Install wise...with the right tools, about a 5-6 hour job from start to finish. It's not a DIY unless you have some very specialist Nissan tools

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Hmn.. sounds like a good option again now :lol:

 

So am I correct in thinking all that is needed is the main 4.08 drive set and the install kit 1?

 

IMHO it is always good engineering practise to replace the bearings irrespective of the mileage. when replacing the crown wheel and pinion.

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Hmn.. sounds like a good option again now :lol:

 

So am I correct in thinking all that is needed is the main 4.08 drive set and the install kit 1?

 

depends on mileage and the skill/luck of the installer

 

Under 25k and your existing bearings can certainly be reused. However in doing so, you need to press them off the old pinion and onto the new one. This can go smoothly or it can be a bit of a pain. If the bearing is damaged or scuffed in any way, then it can't be reused and a new one will be required. That being said, it's about a 50/50 mix of people who buy the install 1, vs install 1 and 2.

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When I was considering it, I was told that it makes the car a bit more like a Honda where you have to keep revving high. Suppose it's down to personal preference.

 

Also depending on the driving you are planning on doing, in a stright line it could be a bit slower with extra gear changes ie 0 - 60 would require the 3rd gear if you have a 276 Zed.

 

Check here for more info

 

http://www.350z-tech.com/zwiki/Part:Fin ... _Gear_Sets

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When I was considering it, I was told that it makes the car a bit more like a Honda where you have to keep revving high. Suppose it's down to personal preference.

 

Also depending on the driving you are planning on doing, in a stright line it could be a bit slower with extra gear changes ie 0 - 60 would require the 3rd gear if you have a 276 Zed.

 

Check here for more info

 

http://www.350z-tech.com/zwiki/Part:Fin ... _Gear_Sets

 

gears are a linear change, the same change at any point in the rpm range

 

with the VQ35DE engine, we suggest upping the rev limiter, though it's certainly not a requirement

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When I was considering it, I was told that it makes the car a bit more like a Honda where you have to keep revving high. Suppose it's down to personal preference.

 

Also depending on the driving you are planning on doing, in a stright line it could be a bit slower with extra gear changes ie 0 - 60 would require the 3rd gear if you have a 276 Zed.

 

Check here for more info

 

http://www.350z-tech.com/zwiki/Part:Fin ... _Gear_Sets

 

gears are a linear change, the same change at any point in the rpm range

 

with the VQ35DE engine, we suggest upping the rev limiter, though it's certainly not a requirement

 

Can you just change the rev limit on the stock ecu via reflash or do you need the Haltech ECU or similar?

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depends on the year of the car as I recall. My own car is an 04, with 03 build date - I reflashed the ecu back in ~ December 2003 and upped it to 7200 at that time. When the utec was released, I left the rev limiter at that level, and then when my new engine went in, I upped to 8k and then 8400, where it currently sits. I think the 05 and up cars have specific requirements to them. Companies like UpRev, Cobb, Technosquare, etc can better fill you in on the nuances

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