Another 6 speed bites the dust. - Page 17 - Miata Turbo Forum - Boost cars, acquire cats.

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Suspension, Brakes, Drivetrain discuss the wondrous effects of boost and your miata...

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Old 12-16-2013, 12:46 AM   #321
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After looking at the 6 speed 3.3 combo on the gear calculator i wonder if this combo will hurt the 6 speed due to the added stress. i have blown the 5 speed when shifting to second and once in 3rd. I wonder since we have just turned the 6 speed ratios much the same as the 5 speed if there will be a reduction in the ability for the 6 speed to hold the power. any thoughts??? for those blowing 6 speeds did you have the 3.6 combo ?? i have personally seen a 6 speed get abused with flat shifting and the boost at 20 psi 300whp and it held up fines for many drag races. they had a 4.10 rear ratio tho. anyone here about the retainer spring upgrades that some spec miata builders use??
here a video on you tube.
I have also wondered if the taller rear end would produce higher stress in the box. I mean obviously to produce the same acceleration rate the amount of torque transmitted in the drive shaft is higher at specific operating points. As far as drag racing goes I don’t think it is a good comparison. Full power through the RPM range in a gear only happens once per pull on a drag strip where it happens multiple times per lap on a road course. The syncro issues must have something to do with technique none of my shifting parts or syncros have even looked very worn in any of the transmissions I have broken. I haven’t even considered it a weak point.
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Old 12-16-2013, 03:11 PM   #322
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Interesting thought. However, if this were true then slamming into 4th or 5th would more likely break things than slamming into 2nd or 3rd.
My experience "slamming" has little or nothing to do with it. It is more the amount of time spent at elevated torque levels.

The gear teeth donít chip off when you slam it in gear. They break when in gear and accelerating through the peak torque operating point of the engine.
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Old 12-16-2013, 04:01 PM   #323
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.... It is more the amount of time spent at elevated torque levels.
And the time spent in 5th would probably be vise to maximize in the tracks you use.
So 3.3 might be a poor choice (longer time in 4th)?
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Old 12-17-2013, 01:56 PM   #324
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And the time spent in 5th would probably be vise to maximize in the tracks you use.
So 3.3 might be a poor choice (longer time in 4th)?
Exactly. A 3.909 gives plenty of top end speed even up to 400 hp and better usability of 5th. 5th can't be broken it doesn't involve any gears so it has lower drivetrain loss as well. Anything taller than that is only necessary for better usage of first and second gear which are never gears used on a track anyway. Unfortunately I need a 3.636 to have a usable autocross gear with second.
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Old 12-17-2013, 09:01 PM   #325
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My experience "slamming" has little or nothing to do with it. It is more the amount of time spent at elevated torque levels.

The gear teeth donít chip off when you slam it in gear. They break when in gear and accelerating through the peak torque operating point of the engine.
My thinking re: slamming into gear was that the tires breaking traction limits the torque and torque shock transmitted through the tranny. A taller rear will increase the torque at the prop shaft during wheelspin. However if it is as you say then the rear ratio has no effect on the torque passing through the tranny.
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Old 12-18-2013, 05:55 PM   #326
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My thinking re: slamming into gear was that the tires breaking traction limits the torque and torque shock transmitted through the tranny. A taller rear will increase the torque at the prop shaft during wheelspin. However if it is as you say then the rear ratio has no effect on the torque passing through the tranny.
A taller rear end will increase the amount of torque in the drive shaft at the operating point of wheel spin. I have friends who have drag raced hopped up Diesl PU trucks. Tall tires made for twisted drive shafts. Small tires yielded no twisted drive shafts even with the same motor output. The gear supplying the torque to the output shaft in the transmission has to supply more torque to produce the same acceleration rate at a given vehicle speed. you have to select a lower transmission gear to get the transmission to output that higher torque it stresses the drive shaft, the output shaft and the gear driving the output shaft on the transmission more.
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Old 12-21-2013, 01:29 PM   #327
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...ALSO I think the strength issue of 4th gear is dramatically diminished if the car doesn’t see the track. Almost never do you get the opportunity to do a full power run through the rev range in 4th gear for any kind of sane street driving even if you typically drive like a jackass every day to work. Especially combined with super sticky DOT Slick tires whereas on a track you could do it 3 or 4 times per lap.
I am going to be installing the 3.3. My car is a street car, not a track car. The above raises the following question, especially for those with even higher TQ levels than mine (320wtq):

When dyno tuning, my pulls were in 4th gear. Obviously, dyno tuning requires several full power pulls through the rev range. I am guessing future dyno tuning should be done in 3rd or 5th gear once the 3.3 is installed? If so, is 3rd preferred over 5th or vice versa (from a failure perspective)? This may be even more important if I ever go the EFR 6758 etc. route.

Last edited by 05pearl; 12-21-2013 at 06:22 PM.
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Old 12-21-2013, 06:04 PM   #328
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Originally Posted by JasonC SBB View Post
My thinking re: slamming into gear was that the tires breaking traction limits the torque and torque shock transmitted through the tranny.
Slamming the shift lever into the next gear can potentially break synchro components, but the action of actually violently moving the shift lever will do little to harm gear drive teeth. Possibly the synchro engagement teeth and/or slider.

Shock loading the transmission and drivetrain by no-lift shifting and/or sidestepping the clutch definitely can break gear teeth.

Doing both can break a lot of things.
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Old 12-21-2013, 06:40 PM   #329
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Originally Posted by 05pearl View Post
I am going to be installing the 3.3. My car is a street car, not a track car. The above raises the following question, especially for those with even higher TQ levels than mine (320wtq):

When dyno tuning, my pulls were in 4th gear. Obviously, dyno tuning requires several full power pulls through the rev range. I am guessing future dyno tuning should be done in 3rd or 5th gear once the 3.3 is installed? If so, is 3rd preferred over 5th or vice versa (from a failure perspective)? This may be even more important if I ever go the EFR 6758 etc. route.
You should always dyno in the direct drive gear in the tranny.
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Old 12-21-2013, 06:54 PM   #330
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^ 5th gear then for me (and 150mph, lol)
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Old 12-21-2013, 08:52 PM   #331
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What transmission fluid & additives were you using when the 6 speed & other transmissions broke?
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Old 12-21-2013, 10:42 PM   #332
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I cannot recall if anyone has asked, but does anyone use a transmission cooler? Is it beyond worrying about at this power level?
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Old 02-11-2014, 06:02 PM   #333
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So, has anyone had any luck with alternative trannys?
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Old 02-11-2014, 07:26 PM   #334
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What transmission fluid & additives were you using when the 6 speed & other transmissions broke?
based on all the 5 speeds I broke with different stuff in them I don't think addatives make a bit of differance.
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Old 02-11-2014, 07:29 PM   #335
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So, has anyone had any luck with alternative trannys?
I got side tracked and it is still sitting in my shop. Going to be a little tougher than Id hoped. input shaft is too long and output shaft may be too short. both are splined differently than a miata.
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Old 03-18-2014, 07:35 AM   #336
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Has anyone tried reinforcing the tranny case to see if flex is causing it to break? Perhaps the case flexes under torque and adding some bracing would help?
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Old 03-18-2014, 07:57 AM   #337
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So, has anyone had any luck with alternative trannys?
Nah, not my thing!
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Old 03-18-2014, 09:00 AM   #338
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Nah, not my thing!

You prefer the conservative type?
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Old 06-13-2014, 07:54 AM   #339
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Just finishing up my build and found this post and the other 6 speed post. These two post have me worried and after some research I found this. Seams like a good high HP and T fix. I emailed them and I
Was informed this will fit in the Mazda box. They will even make custom hear ratios. It's a lot cheaper then the Nismo box as well.

http://www.par-engineering.com/Products/Catalog/ProdID/410/CatID/120/FS6R92A_1st5th_Synchromesh_Engagement_gearset.aspx

Sorry thought it better belonged here.
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Old 06-06-2016, 03:41 PM   #340
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Last edited by vtjballeng; 06-08-2016 at 01:01 PM.
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