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Greetings all! Aki here, a 40+ year old noobie from the Bay Area (Sunnyvale, CA) going through an early mid-life crisis. I "needed" to have a 3rd non-family fun car to take up valuable garage space and feel that never ending urge to continuously search and purchase parts which stack up in boxes next to the car and not have enough time to work on it or drive it but yet have an excuse to go wrench on something to get out of an some "event".
I previously had a 1994 Miata M-edition that I sold during the pandemic for a ridiculous price but have been regretted it every day since. To fill the empty void and knowingly making a 100% unpractical choice in life, I purchased (after much negotiations with the wife of how the Miata will be a good financial investment because it tripled in price due to the pandemic) a 1990 Miata with 89k miles, mariner blue, no A/C or power steering, one owner, overall good shape. The Miata came with a 6 speed, where the previous owner installed it just for the enjoyment of driving. The diff was stock so it was a really fun but slow 500+ mile drive home when I picked it up from Oregon. This will be the car I will be keeping and teaching my daughter the lost art of turning a **** to open a window and driving a car with a 3rd petal (that's not the parking brake) when she comes of age.
The reason I got to this forum was due to the combination of 6 speed / 4.3 diff setup when I got the car registered. The smog guy had to do some tweaking to make it pass. Apparently for the smog test (CA emissions), the transmission gear you're in, the revolutions, and speed have to be within a specific range. The 2nd gear at 25mph, has to be at a specific rev range. Since I have a 6 speed, the revs were way out of range because it had to be in 3rd gear to reach 25mph. The smog guy passed the test only because it was an out of state car but told me when I have to smog in another 2 years (with a CA plate), I probably won't pass due to the car being "modified". The joys of ridiculous emission rules and the land of really bad Tesla and Prius drivers.
I recently joined the forum because my search for different differential options kept leading me you guys. After learning a little bit about the different differential setups, I got my hands on a 1.8 Torsen2 LSD - diff / axel / drive shaft from a local CL purchase and 3.6 ring / pinion from this forum. My first project will be swapping the diff from a 1.6 / 4.3 gear ratio to a 1.8 / 3.6 w/ LSD. Completion date, TBD depending on how many events there are with the extended in-laws.
Thanks for all the great information and help this forum brings and looking forward to being part of this community!
1990 Miata (current) taken at Shasta on my way back from picking it up in Oregon.
1994 M-edition right before I sold it...
Last edited by aki; 12-09-2022 at 12:20 AM.
Reason: added pictures
Welcome to the forum!
NA Miata prices are only headed up, glad you got one now.
I'm wanting to do that exact same diff swap on my miata now that it makes turbo power. The LSD would be nice to get the power to the ground coming out of corners. It's proving very difficult to find the parts locally though.
Please post details/pictures when you do the swap!
Welcome to the forum. It sounds like you are a realist regarding what you can versus wil do.
I really enjoyed the 6 speed with 3.63 gears but I'm not sure how sweet that would be with an elderly naturally aspirated 1.6. Let us know how it goes.
A little update on the Miata.
I found a good deal on Craigslist for a used Koni Yellow suspension kit with sways (equivalent to a Flyin' Miata 2.0 kit). It took me weeks to get everything installed, trying to find time here and there. The front suspension was a horrible horrible experience to work on solo. I nearly took out my back getting the darn thing out. I ended up doing the removal of the bottom control arm method, and had to ask for my wife's help to stand on the axles while I wiggle the newer suspension in. There was no shame here... Around the same time I got a flat tire. Tires were too old to fix so I jumped the gun and purchased a set of wheels and tires during black Friday.
1.6 to 1.8 diff swap has been a continuous long project. I was able to find a local shop to install the 3.63 ring and pinion into the 1.8 Torsen LSD. I spent a bunch of short spans here and there and finally got the diff installed tonight. Tranny and diff fluids filled. Just need to get the brakes back on (I lost the clips for the pads so waiting for new ones to be delivered) and I'll be able to go on the first test ride. Excited to see how the new gearing feels.
Since I did a LOT of research and ran into tons of questions and issues along the way during the diff swap, I decided to document as much as I could along the way. I thought I could share my experience (or lack of) with anybody who's thinking of doing a diff swap. I attached a word file to this post.
Will update with pictures once it's back on it's feet.
Last edited by aki; 01-05-2023 at 01:54 AM.
Reason: updated file
Missed your post the first time around. I bought my first Miata (a bone stock '92) at 44, and haven't looked back. That one has become a full-on track car, and we were up to 4 Miatas at one point, now down to 3... hopefully 2 after tomorrow. One secret is to get your wife driving the car... especially on track. Makes justifying things much easier.
Make sure you keep all the 4.3 stuff. As sixshooter noted, a 1.6 with 3.63 will be painfully slow, even with a 6 speed. If you can't just convince the smog guy to run it in 3rd for the test, I'd be swapping the diff every two years.
Make sure you keep all the 4.3 stuff. As sixshooter noted, a 1.6 with 3.63 will be painfully slow, even with a 6 speed. If you can't just convince the smog guy to run it in 3rd for the test, I'd be swapping the diff every two years.
6-speed with 3.63 works out to be pretty much the same ratios as a 5-speed with a 4.3 for gears 1-3, and 4th is actually shorter so it's going to be faster.
I decided to document as much as I could along the way. I thought I could share my experience (or lack of) with anybody who's thinking of doing a diff swap. I attached a word file to this post.
That is amazing! Thank you.
Have saved the file for future use.
I love a good DIY writeup.
When I go into a big job I'll print out a writeup or put together my own after some research.
Sure beats using a computer or phone with greasy hands.
That file should really be posted in it's own DIY thread for anyone searching.
12-06-2022, 06:07 PM
Early Mid-life Crisis
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