Is anyone actually tracking a turbo Miata without heat shielding the exhaust the full length of the transmission? Mazda thought it was necessary at stock power levels. How could it be unnecessary at twice the power or more? Shielding is much cheaper and less failure prone than external coolers, if you haven't done that first. My trans temp went from ~270 to ~200 with just shielding (according to Harbor Freight thermo gun), and I'm not pushing nearly the power of some on here. The diff had a similar drop when I shielded back there.

 

The OEM shielding is to stop burning your feet/trans tunnel, no?
Having said that, I've got some thermo stuff around that area, but mainly aimed to stop heating from getting in the cabin.

 

Which would by proxy stop heat from getting into the transmission considering the heat does not seek out the cabin, it just radiates in all directions.

 

Instead of a vertical adapter fitting, replace the drain plug with a banjo bolt/fitting and route the hose towards the back.

http://www.ebay.com/itm/Banjo-Bolt-K...345#vi-content

 

Increased wear would show up in a UOA, but it doesn't. Amsoil is very, very good at not allowing accelerated wear, even when fluid temps are very high.

https://www.miataturbo.net/race-prep...u-thems-56841/

 

I stand corrected

 

What about metal fatigue? I thought things get weaker with increasing temps. It's strange the way these trans fail. Once they give up they chew right through an entire gear. That to me seems odd. Most other trans failures I have seen (other cars) start by loosing a tooth or 2. Never before have I seen a gear stripped all the way around like I have seem on Miata's.

Thoughts?

 

300*F is nothing for a steel alloy gear. I would tend to expect overloaded gears that arent failing from case flex to break off the weakest tooth and then cascade fail from impact loading the other teeth.

I would expect gears failing from impact loading, IE super hard shifts, to just break 1 or two teeth.

 

Mainshafts are steel, which doesn't fatigue significantly at only 300*F. Aluminum, OTOH, does, and case flex is something that a lot of applications struggle with. If we can keep the case cooler, the trans might last longer.

Wrapping the exhaust isn't going to help with longevity of the exhaust, but it should drop tranny temps. It's a good idea for track cars that don't get used in the rain a lot.

 

as far as i can gather case flex is not the main issue. this is from this thread Syncromesh gear kit for racing/FI applications - Page 2 - MX-5 Miata Forum from when the quaife gearset was first in development.

Based on my and Quaifes findings the "flexing case" syndrome which has been touted as the main cause of the OE 5 speed transmission failure simply isn't true. Does the case flex, yes. But, with the Quaife gear set or any other gear set w/o the OE gear set short comings, case flex will not be the cause of transmission failure. The bottom line is if case flex was the culprit for transmission failure, this gear kit WOULD NOT HAVE HAPPENED, PERIOD. Quaife has no intension of putting together a gear set that would wind up getting destroyed every time it's subjected to hard use.

The main cause of failure has to do with the shallow OE gear teeth and the extreme helical pitch they are cut at. A helical gear has much more torsional load than a straight cut gear. During the initial meshing, this load is concentrated in a small contact point on the teeth of the input and counter gears because of the pitch and depth of the gear teeth. When a excessive amount of torque is applied to the teeth over a short period of time (like during a speed shift) it will eventually lead to shorn gear teeth and ultimately transmission failure. The case flex only compounds the problem by putting an already small tooth to tooth contact point in jeopardy of misalignment.

The Quaife gear kit will be cut at a semi helical cut for a much larger contact patch between gear teeth, plus the gears themselves will be larger which will allow the teeth of each gear to be cut deeper for even more contact between the gear teeth.

By having a semi helical cut, Quaife is reducing the amount of torsional load on each gear which will maintain them in alignment and minimize parasitic driveline losses. Further, by minimizing torsional load across the gear teeth, less will be transferred to the case, hence less case flex. How much less is currently unknown as the gears are still be manufactured.


AS far as i am aware quaife are the only ones to do any real testing on the box and release any findings. Keeping the box cool though cant do it any harm and may go some way to reduce any case flex however insignificant it may be.

As has been said here and i am sure elsewhere the problem is excessive torque overload on the oem gears. i would love to know the real world limitations of the Quaife gearset. has anyone actually had one fail?

 

Aluminum gets weak rather quickly above 5/600F.

But I was not aware that the modulos of elasticity is reduced with temperature. Until it melts, that is.

corky

 

 

This is in fact the opposite of what we see at work in Evo 8/9 and DSM transmissions. I'd say 9 out of 10 gear failures involve both gears (fixed and floating) being stripped all the way around. The Supras, Evo 10s, 3S's, GTRs all have heavy enough gearsets that we rarely see any gear damage from torque. Running without fluid is another story...

When we see the rare single broken tooth, it's in random enough places (1st gear, center diff, front diff), that we assume it is from general fatigue or a defect, though to my knowledge we've never spent the money to have it analyzed post-mortem, so to speak. Safe enough to guess that a single tooth broken off 1st could be from shock loading given the driving habits of most of our customers (drag racing not road racing). When a gear strips all the way around it is usually 2/3/4, and will let go at peak torque whether it's been shocked or not.

 

We have some data on trans fluid temps but what about the actual gear teeth temps? Does everything equalize and the fluid temps reflect gear face temps? Looking at that chart for carbon steel it takes a nose dive at 600.

Is the trans like a motor where the pistons etc (or gears in this case) run hotter than the oil?

 

If the gear face temps were 600*F the fluid would most likely flash, it would almost certainly flash if you were using non-synthetic.

 

I totally missed this, so let me contribute:
Please, get that tampon changed. Other e-mails where exchanged, such as:
Let me repeat:

Not necessarily to strengthen the box. I would advise that the torque limit would be the same as the limit on the original gearbox.

 

Laurens, how many days on your Quaife box at ~300whp?

 

Only 9 so far, 10th this weekend.

 

I'd love to hear more from folks who've used a Jerico or other dog box. There's a couple of multiple time National champ AutoX guys in the SFR that use them in their Mod cars. Dog boxes seem to be the answer for quicker shifting, and the straight cut gears must reduce friction/heat/wear/LOSSES.

Anyone know what the losses are relative to a Miata box? Speculation over beers with guys a lot smarter than me have suggested there's another 2-3% to the wheels to be had. That's got to be running much cooler too.

 

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