I was thinking more of the 0.82 5th. Looking quick it looks like now there's even a .90 5th as an option that I never saw before.

 

My spreadsheet from a few years ago has the following for the 2.95 1st ratio T5:

(.63 stock)
.75 Gforce
.90 Gforce
.81 Medatronics $236
.78 Astro $279
.73 OEM discontinued ratio via Astro $192

These are helical gears because streetcar.

I haven't done the swap so take that for what it's worth, but 5th gear is outside the main housing and can be swapped relatively easily without complete disassembly. Unbolt the back portion, there's a sometimes PITA ring that holds a gear on, sometimes some clearance needed depending on which 5th you go with, something like that. "Minor".

 

The 0.90 on jegs says it requires machining on the housing because the bearing is larger. And of course there's also the .83 Gforce to add to that list. I think there's also a 2.42 1st gear ratio available.

 

Isn't the T-5 one of the transmission options for the Lakewood/Hays bellhousing for the BP engine available from Summit or Jegs?

 

If you are lucky you'll find it's a bearing coming apart and some minor smearing/pitting on some gear teeth. But a loud clickety clack like that is likely broken teeth.

That it's quiet in 4th gives me hope that it may be a countershaft bearing coming apart.

 

This is getting interesting. There's a gearset available from JEGS with some almost perfect ratios:



I switched the overdrive gear for a compromise ratio that will be livable on the highway. As you can see, it's a close-ratio gearset (approx. 20% drop in the middle gears) that closely approximates that of the wide-ratio Quaife. Second gear is even better and is close the the magical <6.0 total ratio that Savington deems desirable. If a road racer specs the 0.82 overdrive gear, the drop is 18% and speed at 7,200 rpm is 147 mph.

As a bonus, this gearset is rated for 500 lb-ft in a 3,300 lb vehicle. I don't think many turbo Miatas, even the extreme ones, will break these.

I'll probably end up doing a teardown at some point. I'll definitely update you with what I find. If (fingers crossed) it's only minor smearing/pitting, can the gears be saved?

 

Ehh, the pitting not really. Once the mating surfaces begin to fret then there's no reversing that, and it's a matter of time before the wear is bad enough to snap teeth off. If they are smeared then you've got some time left, but that sort of wear is a function of torque load and lubrication. Turn down the power or find a gear oil that takes the abuse a little better.

 

Have we talked about using a t101a with a 3.3r&p when it's available?
Launching from a stop will so suck, but a dog box that will never fail at 500+ might be something to look at.
Thinking 2.45/1.75/1.33/1 ratios - puts rev drop to ~6k at 8k shifts.
That first gear is still gonna suck - forget driving the car into the trailer



This is using 2.86/1.86/1.33/1 ratios 245/40-15



There's all sorts of options, of course will need bell, clutch and shaft.

http://www.texracing.com/pdfs/GF4A%20Ratio%20Chart.pdf


Edit to add: this was Sav's suggestion

 

Going with a 3.636 will make your 4th gear the same as 5th in a 1.6l car with a 4.3 pretty much, you would be cursing at 4k on the highway at like 75.

 

I've suggested it to a few people. For a dedicated, trailered track car, you won't beat the strength-to-cost ratio.

 

The quicktime + t101a isnt exactly light though. 26lbs for the bell housing and another 74 for the tranny + a few more for the shifter. And you could always step up to the jerico 5 speed that only weighs 6 lbs more. But just kind of crams 1 more gear in without giving an over drive.

Another new idea, The jerico 3 speed with a gear vendor over drive. Then you actual get over dive gearing (0.78), and 6 gears.

 

If it weren't for rules limitations and weight of the bell housing id have a t101a in my car. Abandoned the project for the Quaife. Throwing 6 speed shredding torque through it, it hasn't skipped a beat.

If you are gonna go Quaife...do it right. Send it to a reputable builder. I used Mike at Helios Motorsports and thus far couldn't be happier. I had him replace the entirety of the internals. Literally only reused the case and he did some magic coating / stress relieving process to the case.

Shifts are fast, positive (almost bolt action rifle like)



BUUUT. If you can make it fit within the rules of your class....the t101a is much cheaper (not including fab work to make it fit) and stronger

 

This +1

 

how much does a stock 6spd weigh, If you are making enough power to need a 4spd dog box then you can make the power to move the added weight.

I think i would be much happier having a bullet proof drivetrain and 450whp then having a car sitting in my garage with a broken 6spd and armchair engineering all the negatives of 30 extra lbs.

 

^ my rational exactly. Mine'll be a straight-up 450hp fun track car that, yeah, I wanna track... not have to replace transmissions every other weekend. I even contemplated a quaife sequential but thought the divorce would be more costly.

 

Your point is very well taken. However, what if you can source a gearbox that is within spitting weight of the stock unit and then find strong gears that will work well for street and track use? No-one's commented on the T5/custom gearing option I referenced above. It seems if I'm not missing something important, it's a decent solution that can probably be adapted to a Miata with reasonable effort.

 

I like the idea of the T5, I need a transmission to go into my K swap car, does the T5 use the same bolt pattern as 4spds? Right now I'm planning to use a MSM 6spd because of ease of use and i won't be pushing the power right off the bat.

 

My holdup is not being sure the t5 and the t10 use the same bellhousing bolt pattern.

 

http://www.jegs.com/webapp/wcs/store...&storeId=10001

 

Is the BW T5 the same pattern as the tremmec T5? Or do the GForce gears not care which case they get put in? We want the T5z for shifter placement which would be the tremmec one anyways.