Gearing issues /solutions - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

GrandSport · 05-08-2023, 11:25 AM

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?

DarkPira7e · 05-08-2023, 11:41 AM

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

NoHaveMSG · 05-08-2023, 12:14 PM

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

GrandSport · 05-08-2023, 01:16 PM

Quote:

Originally Posted by NoHaveMSG

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

Yeah, I'm trying to avoid the cost of a custom transmission. At that point, I'd just go sequential.

Code Monkey · 05-08-2023, 01:39 PM

I was running a 7,800 rpm redline on my 2017 for years, zero issues.

autoracer86 · 05-08-2023, 02:13 PM

Quote:

Originally Posted by NoHaveMSG

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

first I am seeing about jackstransmissions would this make the gt86 transmission "bullet proof" at stock power levels up to say 250-300 from FI ?

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..

RedReplicant · 05-08-2023, 02:33 PM

Quote:

Originally Posted by autoracer86

first I am seeing about jackstransmissions would this make the gt86 transmission "bullet proof" at stock power levels up to say 250-300 from FI ?

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..

Probably not. I broke mine making 205whp.

NoHaveMSG · 05-08-2023, 02:42 PM

Quote:

Originally Posted by GrandSport

Yeah, I'm trying to avoid the cost of a custom transmission. At that point, I'd just go sequential.

That is not exactly what I meant. You need to look at the speed RPM chart and see what may work for you as far as FD gears. I don't recall Blub running custom transmission gears but I could be run.

Quote:

Originally Posted by Code Monkey

I was running a 7,800 rpm redline on my 2017 for years, zero issues.

I was too, then went back down to 7600, now going back to 7800.

RedReplicant · 05-08-2023, 03:02 PM

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

autoracer86 · 05-08-2023, 05:28 PM

Quote:

Originally Posted by RedReplicant

Probably not. I broke mine making 205whp.

Just to double check you broke a jackstransmission making 205whp ? So what is the point of it then ? lol

RedReplicant · 05-08-2023, 05:35 PM

Quote:

Originally Posted by autoracer86

Just to double check you broke a jackstransmission making 205whp ? So what is the point of it then ? lol

Yeah, lol, just a little salty about that.

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

GrandSport · 05-08-2023, 06:08 PM

Quote:

Originally Posted by NoHaveMSG

That is not exactly what I meant. You need to look at the speed RPM chart and see what may work for you as far as FD gears. I don't recall Blub running custom transmission gears but I could be run.

I was too, then went back down to 7600, now going back to 7800.

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.

strat61caster · 05-08-2023, 07:36 PM

Quote:

Originally Posted by GrandSport

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.

7450-ish is factory redline.

CSG Mike · 05-08-2023, 07:39 PM

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.

05-08-2023, 11:25 AM	#1
GrandSport Senior Member Join Date: Sep 2018 Drives: 13 Viper; 14 BRZ; 90 Miata; 18 AMG Location: TX Posts: 382 Thanks: 82 Thanked 230 Times in 128 Posts Mentioned: 5 Post(s) Tagged: 0 Thread(s)	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? __________________ 2014 BRZ: WRL Build (GP2) Gutted, caged, coilovers, AP enduro, etc- 2014 FRS: Similar WRL Build. Back up / parts / practice race car. 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. 2022 CT5 Blackwing: Stock.

05-08-2023, 11:41 AM	#2
DarkPira7e Rust bucket enthusiast Join Date: Feb 2017 Drives: 2013 Turbo Firestorm FRS Location: Vermont Posts: 4,024 Thanks: 3,289 Thanked 4,177 Times in 2,098 Posts Mentioned: 33 Post(s) Tagged: 0 Thread(s)	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 __________________ Turbo FR-S Build - Build Thread JDL EL Recirc manifold, Boostlab BL58x Turbo w/ T51R, 17x9 ARC-8, IAG block

05-08-2023, 03:02 PM	#9
RedReplicant Senior Member Join Date: Aug 2015 Drives: None Location: Arizona Posts: 960 Thanks: 1,533 Thanked 1,324 Times in 557 Posts Mentioned: 11 Post(s) Tagged: 0 Thread(s)	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 __________________ 2015 Subaru BRZ - K24 Swap - NASA TT5 2005 Lotus Elise - K24 Swap - NASA TT3

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05-08-2023, 01:39 PM	#5
Code Monkey Senior Member Join Date: Jul 2016 Drives: Subaru BRZ Location: Atlanta, GA Posts: 864 Thanks: 960 Thanked 585 Times in 352 Posts Mentioned: 4 Post(s) Tagged: 0 Thread(s)	I was running a 7,800 rpm redline on my 2017 for years, zero issues.

05-08-2023, 07:39 PM	#14
CSG Mike Join Date: Jul 2012 Drives: S2000 CR Location: Orange County Posts: 14,561 Thanks: 8,941 Thanked 14,211 Times in 6,854 Posts Mentioned: 970 Post(s) Tagged: 14 Thread(s)	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.

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