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Old 11-13-2017, 11:46 PM   #1
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2017 diff swap

Has anyone attempted to swap out their stock differential with the new 2017 rear diff? I've been thinking about doing this to mines due to the more aggressive gear ratio,but i'm not sure if the new diff has different dimensions that would cause some sort of issues. If you've tried this or have some insight, comment below. Thanks guys!
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Old 11-14-2017, 08:26 AM   #2
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You don't need to swap the whole diff. There are final gears available that you use with your current one.


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Old 11-14-2017, 08:44 AM   #3
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Originally Posted by JOE APO View Post
Has anyone attempted to swap out their stock differential with the new 2017 rear diff? I've been thinking about doing this to mines due to the more aggressive gear ratio,but i'm not sure if the new diff has different dimensions that would cause some sort of issues. If you've tried this or have some insight, comment below. Thanks guys!
Final drive replacement is a tradeoff, not really a power upgrade. Your engine will be working harder to do the same work. Acceleration will be quicker but sustained speeds will be at higher rpm. You might like it in the city since the car will feel quicker. But freeway driving will be worse; engine will be running at higher rpm on freeway, it will be noisier, and gas mileage will be lower. Even on track, you will be compromising your top speed for acceleration.

You want more power. So the right solution is getting more power. I recommend one of the followings.
- header + tune
- forced induction

If I had the 2017, I would go back to 2016 final drive and upgrade with FI again.
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Old 11-14-2017, 08:58 AM   #4
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Final drive is a great way to go. It's a great analogue upgrade that is simple and effective as is the trans gear upgrade they did in the 2017's. The combination should net noticeable results. The 2017's have 4.33 gears now I believe. Not everyone needs to go FI. What is your goal with the car?
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Old 11-14-2017, 10:03 AM   #5
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Final drive is a great way to go. It's a great analogue upgrade that is simple and effective as is the trans gear upgrade they did in the 2017's. The combination should net noticeable results. The 2017's have 4.33 gears now I believe. Not everyone needs to go FI. What is your goal with the car?
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Old 11-14-2017, 10:10 AM   #6
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What don't you understand?
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Old 11-14-2017, 10:40 AM   #7
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Quote:
Originally Posted by JOE APO View Post
Has anyone attempted to swap out their stock differential with the new 2017 rear diff? I've been thinking about doing this to mines due to the more aggressive gear ratio,but i'm not sure if the new diff has different dimensions that would cause some sort of issues. If you've tried this or have some insight, comment below. Thanks guys!
If you can get one out of a totaled car, great. Otherwise it can be much cheaper to change gears in your existing differential...

Note: the 2017 only went from 4.10 to 4.30, and only on the manual cars.

This small of a change is very, very subtle. I went all the way to 4.56 and I sometimes wish I had gone to 4.88 on my manual daily driven car. I personally would not think the change to 4.30 is worth the expense.

Gas milage takes a very small hit. With AC off, level freeway driving I still get 32 US MPG. Overall I average 26 mixed city/highway.

Engine turns faster, but benefits from mechanical advantage - e.g. it may actually be under less stress.
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Old 11-14-2017, 10:41 AM   #8
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What don't you understand?
You assert that final drive swap is "great: without giving any reason. Then ask "what is your goal?" as if you care. What is "great"? How is "great"? How does that greatness fit to the "goals" you asked?

We are discussing a technical topic, I would expect a little more logic and reason in the discussion.
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Old 11-14-2017, 10:44 AM   #9
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An extra ~165 rpm at 80mph in 6th is negligible. Top speed is drag limited, so the gears will actually help in that department.
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Old 11-14-2017, 11:05 AM   #10
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Watch "BRZ 4.1 to 4.88 Final Drive Thoughts" on YouTube


I'd really want to do the swap but on my opinion price keep me away
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Old 11-14-2017, 11:23 AM   #11
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Watch "BRZ 4.1 to 4.88 Final Drive Thoughts" on YouTube


I'd really want to do the swap but on my opinion price keep me away
Have no idea why his labor cost was so high and they needed 3 days...

If you can do the labor the parts and oil are $600. The only tricky part is gear setup - and that is about $300 at a reputable shop. If you need full service (e.g. can not swap the differential yourself) that is another $300. All in should be about $1200 and one day.
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Old 11-14-2017, 11:27 AM   #12
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Originally Posted by nextcar View Post
If you can get one out of a totaled car, great. Otherwise it can be much cheaper to change gears in your existing differential...

Note: the 2017 only went from 4.10 to 4.30, and only on the manual cars.

This small of a change is very, very subtle. I went all the way to 4.56 and I sometimes wish I had gone to 4.88 on my manual daily driven car. I personally would not think the change to 4.30 is worth the expense.

Gas milage takes a very small hit. With AC off, level freeway driving I still get 32 US MPG. Overall I average 26 mixed city/highway.

Engine turns faster, but benefits from mechanical advantage - e.g. it may actually be under less stress.
This is what i was thinking.. 4.10 --> 4.3 isn't that big of a change. I have 4.88 and wouldn't have it any other way for an NA car.

Best way to go is get a used diff carrier from an IS300, you can find some with an LSD already, or get a "fun" differential :p, by the gears and swap it at your own leisure taking your time with the shims. At least, this is what I did and it worked out great. I'm using the MFactory Mechanical LSD, had the innards WPC treated, fine tuned the preload and lock capacity and after the 3rd oil change I hardly have any chatter. That might be a little far from what you want to do, but DAMN is it fun!

Just my 2 cents.
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Old 11-14-2017, 11:40 AM   #13
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An extra ~165 rpm at 80mph in 6th is negligible. Top speed is drag limited, so the gears will actually help in that department.
Top speed is determined by the combination of power, drag, and gear ratio. Since drag is proportional to square of speed and power is a function of rpm, obviously, power will be balanced with drag force at a certain speed. If that limiting speed balancing power and drag is below the theoretical speed determined by the gear ratio and engine specs, the top speed will be limited by drag. Do you have the numbers and equations to back up your claim for our cars? It will not be as easy as saying 3000x4.1/4.33 -3000 ~ 165 rpm.
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Old 11-14-2017, 11:54 AM   #14
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Even with a 4.88 swap the difference is not that much. You have faster acceleration in same gear, but you have to shift sooner and the longer final drive ratio catch up..

Here is a comparison:

[ame="https://www.youtube.com/watch?v=9X_jYLtoCMg"]BRZ 4.1 vs 4.88 Final Drive Comparison - YouTube[/ame]
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