Looks like Speedtek is taking preorders for their dog engagement gearsets. They're quoting power handling of 600 FWHP. At (preorder pricing) of $3k a set it seems pretty comparable to the ZF swap. Ran some numbers with the Speedtek Ratios and the 3.6 and 3.9 diffs, which are below (I used KPower's calculator ironically KPower Gearing Calculator ).

https://speedtekautoracing.com/colle...gearset-dogbox


Speedtek ratios with the 3.9

Speedtek ratios with the 3.63

 

Dang that 6th is a god bit taller than stock. That’s probably a good thing for most people though as most tracks won’t necessitate 6th gear. I vaguely remember going through the KP hearing calculator and finding that a stock 6sp/3.6 combo netted a top speed of 153mph? Same as the 3.9 would with this gearset.

Interested in hearing the feedback once someone actually gets and installs a set. Dog gears on the street might be a little rough, but so is doing a whole transmission swap…

 

Assuming I'm reading this correctly, they actually maintained the 5th and 6th gear ratios from the 6 speed.




Imo the target market for this is still fairly small though. This would make the torsen the weakest link, and I figure if you're replacing the torsen you're probably deleting the PPF. At that point a custom transmission mounting option is going to come into play, and then it seems like the ZF swap makes more sense?

These seem like they'd be a great option for someone looking for 3-400 WHP with great reliability, but over that I think most people would want the ZF and Caddy diff.

IDK though, I don't have much first hand experience in the drivetrain swap world.

 

Ahh, I'm a dunce. I was assuming top speed figures with a 7k rpm redline, not the 7.5k listed.

For road racing applications, the torsen seems to be able to handle 400whp reliably assuming the housing is reinforced. Thought I remembered reading about maybe one guy on the high HP Miata FB group that actually shredded a tooth launching his torsen at the drag strip but not much else.

I mean sh*t, my 6 speed died on me tracking the car at 270whp. If I could have had a semi-guaranteed bulletproof drivetrain good for 400whp without doing the trans/diff swap, I'd have gone the dog gear route for sure. $3k for the gears plus labor to install em still puts you under half what a ZF/G80 conversion will run you...

 

Stop talking me into buying these I've already dumped too much money into the car this winter... but they are on sale

And yeah, it would only get you to a reliable ~400 WHP, which is obviously not going to be enough (read: way too much) for most people.

 

What's a little more?

 

A "Stage 3" 5spd from Walter is over $3000 and they are reusing stock gears. If this is all new gear sets, eliminates the aluminum shift forks, and holds up to what they say it will, it's not that bad of deal.

 

Their website says the Stage 3 uses a Mazda Motorsports gear set. I appears to only replace 2nd, 3rd, and 5th, though?

 

I think the Speedtek set is a pretty reasonable deal, I'm just not in a place to throw that much money at my car right now.

IIRC, Donut rebuilt one of their Subaru transmissions and only used an upgraded dog gear for 4th. I'm curious if that would be an option given how often the AZ6's seem to fail by stripping the teeth off 4th gear specifically. No idea if Speedtek would go for it, but it might be worth asking about.

No idea how sensible of an idea that is.

 

I missed that detail on quick glance, so that does add some cost. Stage 2 is still getting close to $3k depending on options selected. IIRC 4th gear is cast into the input (or output?) shaft, so you can't change it without a new shaft.

It's been a few years since I've had a Miata AZ6 apart, but IIRC 3rd and 4th are cast into the output shaft. That means changing out the most problematic gears on the AZ6 requires a new output shaft which is costly.