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      09-09-2014, 10:42 AM   #23
Stvee
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Quote:
Originally Posted by ASAP View Post
Everyone here is aware that 3.46 is the stock auto final drive right? lol

It works perfect...
Completely irrelevant to the discussion of using a 3.46 final drive on a manual since the gear ratios are different.
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      09-09-2014, 10:52 AM   #24
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Quote:
Originally Posted by Stvee View Post
Completely irrelevant to the discussion of using a 3.46 final drive on a manual since the gear ratios are different.
I guess I am not sure that I see the concern... you have your choice of final drives... choose the one that works best for you. Somewhat pointless to discuss since people will have different needs / concerns.
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      09-09-2014, 11:05 AM   #25
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There are both positives and negatives, of which I've listed both, as well as addressed some common concerns and "myths"

At the end of the day, you should choose what is right for your setup, and also the capabilities of your tuner.

I (we) are here to help with anything gear related, so please don't hesitate to ask or pm any questions
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      09-09-2014, 05:22 PM   #26
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Quote:
Originally Posted by MFactory View Post
Boost goes by rpm, which does not change. Longer gears = stay in boost longer, is a myth. If that was the case, why even change gear?!?

Acceleration goes by speed, not distance. A shorter geared car will always accelerate faster to 100mph than a longer geared car, regardless of how many times you need to change gears (which isn't any different anyway. It's only 200-300 rpm difference). Do you want to be quicker to 100mph than everyone else (i.e acceleration), or quicker to cover a mile (i.e top speed)?

What people need to realise is, a shorter geared car is NOT about the rpm difference (and therefore when you need to shift), unless you are deliberately fine tuning you gear ratios for a track car. For 90% of you, a shorter geared car is about Torque Multiplication. Say you had 400lbft:

3rd Gear is 1.58 ratio. Torque to the ground is 400 x 1.58 x 3.08 = 1946lbft

If changed to the 3.46: 400 x 1.58 x 3.46 = 2186lbft

That's a 12% increase in torque throughout the entire rev range. It has nothing to do with shifting gears quicker or slower, nothing to do with what modifications you've done to your engine. It is a 12% increase no matter what you do to your car.

The only disadvantages to a shorter gear ratio are:

1) Traction. If you can sort out the traction (better tires, better chassis setup etc), then this isn't an issue
2) Top Speed. This is why you should use a gear calculator, to see if what you end up with is sufficient

Obviously there is more to this, but this is it explained very basically.
It doesn't just go by RPM, it goes by load.. more load = more fuel burnt = more boost, sooner.

take a log in 2nd gear vs 3rd with the same load tables/no boost by gear.. 3rd will hit a higher peak boost.

you're right, the 3.46 car will hit 100km/h even on a kill tune stock frame RB/stock.. because in 1st/2nd already, the torque multiplication is such that shifting at redline is optimum

however, highway, road course, drag strip.. because you shift at ~6000 with the power band peaky and narrow, 3.46 gets less acceleration above 80-100mph..

yes you get more torque through the higher rev range still, but you have to shift to the next gear that provides less torque, sooner, due to the torque dropping off too rapidly.. you're increasing how much torque you get for a shorter period of time.. and again, the time spent shifting (even .1 second per shift) has to be taken into account.

i'm having trouble finding the good calculators to show this though haha (one that does full 1/4 mile and time spent accelerating count)

for cars with a midrange power band... longer gears = better high speed acceleration, 1/4 miles etc.

for a car where you shift at redline for peak acceleration (ST N54's etc.)... shorter gearing is better.

I remember another thread that had it all properly calculated, and a 2.56fd with all factors considered (launch/60ft/shift time) 2.56 came out a fair bit quicker in the 1/4.

Last edited by flinchy; 09-09-2014 at 05:28 PM..
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      09-09-2014, 07:59 PM   #27
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Again, you've based your assumptions on distance (i.e 400m), not net acceleration.

If you have to do calculations on distance, then yes, you need to calculate which ratios are most suitable, as well as have the correct tune/setup.

But for acceleration on a general road car, or even one which does road course/auto-x, where distance is not a set factor like it is in the 1/4 mile, shorter gears (with the correct tune/setup)would prevail.

Torque is torque, and it is increased throughout the entire rev range, not just at high rpm
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      09-10-2014, 02:13 PM   #28
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Quote:
Originally Posted by MFactory View Post
Again, you've based your assumptions on distance (i.e 400m), not net acceleration.

If you have to do calculations on distance, then yes, you need to calculate which ratios are most suitable, as well as have the correct tune/setup.

But for acceleration on a general road car, or even one which does road course/auto-x, where distance is not a set factor like it is in the 1/4 mile, shorter gears (with the correct tune/setup)would prevail.

Torque is torque, and it is increased throughout the entire rev range, not just at high rpm
Have you been to the Texas mile?

Any Toyota supra MK4 with 400rwhp or so just spins tires in gears 1/2/3
its Getrag V160/161 is very close in ratios to the ZF 37GZ family units in the 135/335; you need to fit DRAG SLICKS to put down the power; a 135/335 does not have Supra size rubber in the rear stock (17x9.5JJ and 275mm rubber)

changing ratios may be more "exciting" for the street; but in reality there will be TRACTION issues.

I do support a local 1,200rwhp drag BMW (9.0@159mph) ~ 1.4 sec 60 foot.

- just real world data........ when the ratio is TOO SHORT; the car cannot hook up.

when the final drive ratio is TOO LONG; the car will bog on launch
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      09-10-2014, 03:36 PM   #29
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Hence why setup (i.e traction/chassis/tune) plays a very important role. If a 400whp Supra is spinning in 1/2/3, they need to find a better tuner.

You also need to remember, those who have installed the 3.46 so far have also installed our LSD which helps with traction immensely.
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      08-05-2016, 06:30 AM   #30
berne
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have u notis any more sounds, after u the swap? more noice inside the car?
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      08-31-2016, 06:35 PM   #31
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Hi, I no longer have the 135i anymore but the unit worked great while I owned it. No issues at all.
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      04-20-2017, 03:39 PM   #32
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Anyone else have this in a 2011-2013 car?

I have a stock 2013 135i Msport 6MT with a Dinan Stage 2 flash as the only mod.

Is there any ECU trickery that needs to happen to get the cars speedo to play nice with the 3.46 ratio diff?
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      05-01-2017, 01:21 PM   #33
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2009 BMW 135i  [4.25]
Quote:
Originally Posted by Wegz View Post
Anyone else have this in a 2011-2013 car?

I have a stock 2013 135i Msport 6MT with a Dinan Stage 2 flash as the only mod.

Is there any ECU trickery that needs to happen to get the cars speedo to play nice with the 3.46 ratio diff?
Thread necroed, but with my 09, I didn't touch the computer. Speed is measured by your wheel sensors for ABS/TC iirc.
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      08-21-2019, 02:35 PM   #34
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Hi. I've been debating on whether to go 3.08 or 3.46, so I ran some rough numbers for those interested (estimated tire size.)

First off, we have the 135i with a 3.46 final drive vs. the M2, which also happens to have a 3.46 final drive.

Second, we have the 135i at 3.08, 3.46 and the m2 at 3.46 to compare (only speeds listed.)

Third, we have a 2015 Suburu WRX, which I thought was an interesting comparison, because my friend has one, and it has the same wheelbase as a 135i. The Suburu redlines at 6600, so I showed both at 6600 and at a virtual 7000. The Suburu has the shortest gearing of the cars in this comparison.

Finally, we have a 2019 Porsche 718 Cayman S, which redlines at a higher 7500.

I'm leaning towards 3.46, because the majority of my driving is fun mountain road driving, I like to shift, and it shouldn't hurt too much at my local track.
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Last edited by duder13; 08-21-2019 at 03:01 PM..
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