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Tracking / Autocross / HPDE / Drifting What these cars were built for! |
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05-08-2023, 10:25 AM | #1 |
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Gearing issues /solutions
So I'm guessing my home track was built around making BRZ transmission builder's profits, trying to get them to sell custom gears.
I originally had a bunch of "bad spots" where I'd bounce off the rev limiter in 3 tgurns. I *was* able to solve the problem, before the gear change, by going to a 45 series tire, which got me just enough mph (and slower to get there) to solve the problem. However, the difference in lap times was noticeable. Taller gears, more rotating mass further from center and I'm fairly confident the higher CG/less Aero played a role too. I stepped up with the steeper differential and solved those problems. Now I have them in 3 different turns. Delightful. I really don't want to go to 45 series sidewall. I also think it may cause a problem in 2 other turns where I just barely justify shifting. Middle ground is new wheels are running a 255 or 265 tire, but I have a feeling it won't be enough to solve the problem (and maybe cause problems on other turns). My only other solution was bumping up the rev limiter about 250-350rpm, by my rough math. What's the consensus on doing that for engine life and durability? Big deal? NBD? Unknown?
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05-08-2023, 10:41 AM | #2 |
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I'd be careful, do you have a way of monitoring oil pressure?? The primary issue with increased rev limit is that we're already fighting rapid pressure dropoff at stock rev limit. I don't know the limit for stock valve springs but hopefully someone has input. Honestly, it's not something I'd be terribly worried about if your oil pressure is stable
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05-08-2023, 11:14 AM | #3 |
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I'd recommended looking at the gearing chart from Jacks and seeing if there is a ratio that will suit you. I know reading 949racings build they went clear down to a 4.67, i'd imagine this gets them up into higher gears with a wider spread to help this issue. If you ask the 949 guys they would probably give you more insight.
https://www.jackstransmissions.com/b...ar-ratio-chart https://www.ft86club.com/forums/showthread.php?t=131052
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05-08-2023, 12:16 PM | #4 | |
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Quote:
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2014 BRZ: Full track car. Gutted, caged, coilovers, AP enduro, OMP, bolt ons, aero, etc,
2013 Viper GTS : Tractive Coilovers, ACR sway bars, aero, carbon, exhaust, etc. 1992 NA Spec Miata: 1.6 + 1999 NB Spec Miata: 1.8 w/ all the goodies. 2018 GLE 63 AMG: +800hp whistling AWD TT V8 grocery getter 2016 GX460: IDK. Too reliable to sell. Too boring to use. |
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05-08-2023, 12:39 PM | #5 |
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I was running a 7,800 rpm redline on my 2017 for years, zero issues.
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05-08-2023, 01:13 PM | #6 | |
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I ask because I do see people that continually blow up the stock trans switch to another gearbox all together over doing a custom built one like the one from jacks..
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05-08-2023, 01:33 PM | #7 | |
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05-08-2023, 01:42 PM | #8 | |
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I was too, then went back down to 7600, now going back to 7800.
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05-08-2023, 02:02 PM | #9 |
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Blub had the MFactory 6th that fixed the big gap between 5-6. Normally it probably wouldn't make sense to do, but with their rear diff ratio they were in 6th at around 120mph or so.
They've still got that transmission for sale
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05-08-2023, 04:28 PM | #10 |
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Just to double check you broke a jackstransmission making 205whp ? So what is the point of it then ? lol
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05-08-2023, 04:35 PM | #11 | |
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The collar that replaces the the weak snap ring seems to have come loose, collar wore against the other gear, and let the gear walk... which is what it was meant to prevent in the first place
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05-08-2023, 05:08 PM | #12 |
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Where is the factory rev limiter? I could have sworn mine came on before 7600. But if Factory is 7600, I think 7800 would get me darn close. At worst, it's a half second before I brake.
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2014 BRZ: Full track car. Gutted, caged, coilovers, AP enduro, OMP, bolt ons, aero, etc,
2013 Viper GTS : Tractive Coilovers, ACR sway bars, aero, carbon, exhaust, etc. 1992 NA Spec Miata: 1.6 + 1999 NB Spec Miata: 1.8 w/ all the goodies. 2018 GLE 63 AMG: +800hp whistling AWD TT V8 grocery getter 2016 GX460: IDK. Too reliable to sell. Too boring to use. |
05-08-2023, 06:36 PM | #13 |
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7450-ish is factory redline.
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05-08-2023, 06:39 PM | #14 |
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Gearing is always a tradeoff. No car is geared perfectly for every track every corner; every time you change gearing, you gain somewhere to lose elsewhere.
I recommend you short shift to get the gearing you need, or have a soft rev limiter installed that you can ride. |
The Following User Says Thank You to CSG Mike For This Useful Post: | NoHaveMSG (05-08-2023) |
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