NA 1.6 to 1.8 Transmission Differences

NA 1.6 to 1.8 Transmission Differences

There is something we want to address to the Miata crowd. It appears that there is a massive misunderstanding of the differences between a 1.6 and a 1.8 trans. The internet claims there is no difference or only subtle differences that Mazda claimed. A couple synchro differences, some shift linkage differences, reverse block out, and or something else minor that really doesn’t effect strength.

We DO NOT intend to start any drama, debates, arguments, smiting, or whatever else people do when there is conflicting information. This is just a quick post to say that the idea that the strength between the 1.6 trans and 1.8 trans is the same, is NOT correct. Maybe Mazda released power capacity between the two and it was the same? We don’t know, but what we do know is that the common knowledge on this box is wrong in quite a few ways. Again, we are not going to debate anything, but just provide obvious differences and let the readers decide what they want, and maybe just to wait for more information on choosing between a 1.6 trans or 1.8 trans as we release it until they see enough facts to make their decision.

We will do a full teardown and write up soon of EVERYTHING different between all four generations of the five speed Miata box. That is right. Four generations. Not many people know that the NC five speed is the “same” trans, but different case. Guess what is another little known fact. The ND 6 speed is this “same” trans with an obvious 6th gear and ratio differences and more to go along with those differences, so you can say there are five generations of this transmission for Mazda, but will only do the 5 speeds as the 6 speed is itself it’s own world of problems that we are developing fixes for.

We grabbed what we had of 1.6 parts left, since we tossed the rest, and set them side by side with the NA 1.8 bits. We know that some of the oiling differences and “thrust” in a transmission isn’t a well explained topic, let alone the calculus and statics that go into this piece of engineering, but we will shed some light on that on our website tech section as we can.

We just want this preliminary info out there as when we tell clients of the lesser core refund for a 1.6 transmission because we deem to have less power capacity and reliability, they understand why from us, the builders, and not the internet.

These pictures show thrust surfaces, the flat parts on the side of the gears with grooves, have oiling differences, reverse has many changes in design and oiling which is right next to your mid bearings which heat from reverse effects those bearings, thrust washer differences that don’t have oil grooves versus the 1.8, and of course the most noticeable in these pictures of the hard parts, the wider gear!

Now 1mm doesn’t sound like much, but between 18.5mm and 19.5mm, that is over 5% of a difference. Also being on the input gear, it effects ALL gears since everything goes through the input. These few items we post may not seem like much to effect anything, but every little bit helps.

The hard parts are only a portion of the power capacity. Build techniques, upgraded bearings, oiling modifications, thrust control, case studs, which is another topic we will shed light on, and a few other tricks that we do based on how we see and understand the actual dynamics of the internals and how to control them with the build process. The NC MX5 Cup cars couldn’t keep a factory built 5 speed together at 170hp. Our building process alone is allowing many racers to run 210-220hp, with zero issues, without any expensive tricks or parts. Completely stock, just built properly, and handles 50 more hp with complete reliability.

Again, this was only a teaser, if you will, of the differences and want to get information out sooner versus later as we have a ever growing waiting list on transmission builds because of how we do things, not to mention engine building, car building, race prep, tuning, and everything else that only the two of us here do.

That’s the difference in reverse. Straight cut gears versus helical. Bearing retainer differences as well.


No oiling grooves in the 1.6.

 Some NAs don t have snap rings for retaining the counter shaft bearing.

1.8 Gears are wider.

1mm might not look like much, but that's over 5% of a differences on these gears.

Shift rails are different.

Reverse Idler oil passages are bigger on the 1.8.

More oiling differences.

5th thrust washer.  1.6 has no oiling grooves.

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