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Engine, Exhaust, Transmission Discuss the FR-S | 86 | BRZ engine, exhaust and drivetrain. |
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11-30-2022, 03:58 AM | #1 |
vroooooooom
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Final drive higher or lower for auto turbo?
Hi everyone. I'm thinking of swapping my final drive to acheive a higher top speed in my 86. I am boosted 300whp in my auto 86 but 5th gear is still useless. My question is will going for a higher final drive (4.556) be more beneficial than a 3.9 fd if the only goal is to make 5th gear usable.
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11-30-2022, 04:25 AM | #2 |
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what you mean with useless.? you find it too short now? with 4.56 will become even shorter, with 3.9 longer
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11-30-2022, 05:02 AM | #3 |
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4.56 fd will be slower top speed. If you want more top speed you need to go a lower number than 3.9 fd. ie 2.9 direction.
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11-30-2022, 11:10 AM | #4 | |
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https://www.blocklayer.com/rpm-gear On a stock car, here's following top speeds on 5th gear based on your FD. 4.6 FD: 118 4.3 FD: 126 4.1 FD: 132 3.9 FD: 139 3.7 FD: 146 Technically, your 5th gear should be the least of your worry. How often are you in the 100-146 mph range that your 5th gear will mean that much to you? Usually people complain more about the lower gears, as with more power, you are going through the gears quicker, making 1st and 2nd gears more "useless" as you say. So lowering your FD to something like 3.7 will give you more time in each gear and help reduce tire spin as well. |
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11-30-2022, 06:53 PM | #5 | |
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11-30-2022, 09:43 PM | #6 |
vroooooooom
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The automatic gear ratios make 5th gear useless because it is almost like 6th gear in the manual. My question was if the short final drive can make 5th gear useable or should I just go with 3.9 final drive so my 4th will reach a better speed.
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11-30-2022, 09:45 PM | #7 |
vroooooooom
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for reference this is what i'm talking about. 5th Gear in automatic is practically useless at 4.1 fd |
11-30-2022, 10:04 PM | #8 | |
vroooooooom
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11-30-2022, 11:24 PM | #9 | |
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Example: I find 1st and 6th useless on track though the gear spacing is fine for all the other gears. All gears I find useful on the street.
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12-01-2022, 10:45 AM | #10 | |
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So if I understand your question correctly, a higher FD like I mentioned in your AT will make 5th gear more "useable" as it will have more torque. EDIT: Disregard my conclusion. You want a higher top speed in 5th based on your OP, then you want a lower FD. Last edited by Dzmitry; 12-01-2022 at 10:58 AM. |
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12-02-2022, 04:11 AM | #11 | |
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I know most people here don't really care about top speed but I was just genuinely curious if you could adjust that as I live in an area where such speeds are achievable legally (for the most part) Hope my post doesn't confuse others sorry. |
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12-02-2022, 04:15 AM | #12 | |
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12-02-2022, 04:26 AM | #13 |
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then would be stupid to put like 3.9 finaldrive in your car. You 'd want 4.56 or sth higher in number, as you wouldn t have the torque necessary for enjoying the car
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12-02-2022, 04:42 AM | #14 |
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I think 300 hp is nice Regardless of FDR
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