https://forum.miata.net/vb/showthread.php?t=160969

Not much assumption going on there. The person working with quafie straight up said they would be stronger...

MFMike, can you make the helical teeth have more 'meat' behind each tooth or does that cause issues with the way helical gearing works? By doubling the thickness of the teeth (and so halving the number) you'd be adding more resistance to the sort of destruction bbundy is talking about. But normally a helical engages on two teeth so by widing the teeth you'd be dropping that additional contact and halving the contact area right?

Also my understanding of surface hardening is that the outer 1 or so mm of the teeth surface is hardened to prevent wear, which makes it brittle and basically non-structural. Most of the actual load goes through to the inner core that remains soft. The 1mm hardened layer on all sides means a small gear tooth has far less structure holding it to the gear than a larger tooth. So a doubling of width will actually increase strength 3 - 4 fold.

Yes, we can increase the thickness of the teeth. Normally, we don't use as high of an angle on the teeth (what we call semi-helical)

I bought parts for it rather recently. Its still available.

I can confirm from experience stronger than a stock 5 speed but not much if any stronger than the stock six speed.

The 5 speed Quaife gear set manages to get about the same strength as the 6 speed despite having much narrower gears and lighter shafts. About 12 lbs less rotating mass of shafts and gears and I believe this is the reason it feels like it shifts so much snappier than the 6 speed. The shafts are better supported by the case in the 5 speed but there is not enough room to make the gears wider face or even near as wide as the stock six speed. seems like you could make the shafts bigger maybe put some bigger bearings in but that's allot of engineering and would likely require machine work on the case. maybe you could add a spacer to the case and make it a little longer to gain some room for gear width.

The six speed probably has quite a bit of strength to gain by doing some of the tricks quaife did with the 5 speed gearset (reduced helix, lower tooth counts for bigger teeth etc) this makes it have allot more gear noise. I think it would be hard to improve on what Quaife did with for the 5 speed without digging much deeper in the bag of tricks than they did like getting bigger better bearings to fit and lengthen the box to fit wider faced gears.

If you remove those pesky synchros you can fit in much wider gears. I haven't run this yet but I'm looking forward to the whine.

https://cimg6.ibsrv.net/gimg/www.mia...5098b9583b.jpg

I am all for a dog box with Semi Helicut gears. Given the proposed cost the Quaife sequential looks like a far better value though. I am not sure I could go any other direction after getting a ride in Emilio's car anyway.

We would only be willing to make synchro engagement gearsets, not dog engagement gears.

There is far too much hassle with dog engagement, as shift ever so slightly wrong (usually not shifting fast enough) and you've broken a dog tooth, which requires either machining down the dog tooth (if there is enough of it left) or buying a whole new gear. The same actually applies to sequential transmissions as those are essentially the same but with a different shifter mechanism, although it's not as easy to shift wrong with these.

Ill try and dig up some pictures tonight of torn apart 5 and 6 speeds side by side. One thing to note however is the 5 speed has that bearing plate in the middle making for three sets of shaft bearings to the case keeping the shaft flex controlled and only 4 gears on the shaft between bearings supporting the shaft. the 6 speed has only two sets of shaft bearings and the only gear not between the bearings is 6th so including reverse there are six pars of gears on the shafts between the supporting bearings and 4th gear is right in the middle of that unsupported length of mainshaft. Shaft flex might be an issue with the six speed and probably the reason why the shafts are massively heavier in the 6 speed than they are in the 5 speed.

You know, all this makes me think I should pull open my old Leeson crashbox and take pictures - hugely beefy gears in a 5-speed case. And good ratios, and a dogleg first. Who did the gearbox you posted?

One point about helical vs straight cut gears that always seems to get left out is that straight cut gears let you move to tooth pitches and designs you can't make with helical gears - F-1 style gears take this to extremes. Saw this pointed out in an interview with an XTrac engineer somewhere - so yeah, you don't have as many teeth in engagement, but the root is hugely thicker, and that's where performance stuff fails things. Also, it's a line contact rather than basically a point contact with helical gears.

Build for the AZ-6.
Straight cut
Ratios:
2.8
2
1.52
1.22
1
.87

Isn't that just the Nismo S15 gear ratios, essentially?

I'm not 100% sure but I think it is PAR set.
MX5DS-SET ? MX5 Roadster Close Ratio Dog Engagement Gearset ? PAR ? Precision Automation Robotics

They do helical synchro sets in 5 and 6 speeds too. Might be worth finding out what power they think each box can handle.

I contacted them a few years back. By the time you get their gearset here and installed, your not too far shy of the Quaife Sequential which is rated for 375bhp. Thus why we run a Quaife sequential.
I think any higher capacity PnP Miata trans solution needs to be less than 5k installed, not including a donor Miata transmission.

I still want to see something done with Hewland FT gears, honestly, but probably have to do it myself. The annoying thing from where I sit is that all the newer options are sequential, which SCCA penalizes in most classes.

A few years ago the aussie dollar was over $1US. Now its down around 75c so there would be a 30% saving now. PAR don't have the fastest turn around time for manufacturing though.

Feb 2015 email to PAR Engineering (Precision Automation Robotics) PAR ? Precision Automation Robotics ? Precision Automation Robotics

********
1. Do you still offer the AZ-6 dog box conversion for the MX5?
We still offer the set.
2. Do you have a torque capacity rating for it? If not, could you estimate torque capacity improvement over OEM?
850N.m
3. How close can you get to the following ratios: 2.8 ,2 ,1.52, 1.22, 1, .87
Current ratio I have in stock 2.88, 1.94, 1.43, 1.15, 1.0, 0.64 (you can use you standard 6th and you will get close to 0.87 with our input shaft)
4. Total cost, FOB for such a box with your billet shift forks?
You can have this set for $7,500 Australian (USD5750 at Feb 24, 2017 exchange rate)
5. Have you produced any of the AZ-6 dog boxes for MX5 customers?
Many

Ratios are a bit wide. They no longer list any AZ-6 options on their site but I'm guessing they could still build a set to order.

That is over 600ft lbs! I wonder what my dog 5 speed is rated to. Probably 500?

If you are spending nearly $6k on a H pattern dogbox then the quaife isn't that much of a step up in price and a far better end solution given the sequential shifter.

There is a market for something in the 3.5 - 4k range. If Mfactory can produce a synchro gearset for a 6 speed for around that price that could handle 450ftlbs it would be an attractive option.

As mentioned, if we do not need to make a 1st/2nd (and thus mainshaft), the cost of a 3rd/4th/5th gear set is cost effective. Based on our previous offerings on other platforms, at the power levels you require, it would probably be around the $1500 range.