I have figured out a way to do 4.44, 4.77 and 5.38's for the FC both turbo and non turbo.. How I go about making them will depend if there is any interest in a quantity, if there is I will employ a CNC Lathe and mill to do the parts, if its low, I will just turn my own on my manual machining equipment and have done with it.

 

What sort of price range are you looking at? In my opinion, thats the reason noone else has made them. There are factory options available, albeit requiring some work.



Theres a huge range of gears available for the miata and 1st gen rx7, with many different ratios available from junkyard cars in the US. You can use a miata 3rd member in the n/a rear diff housing(the part with the mounts), and just need a longer driveshaft and custom front diff mount. For the TII diff, a 4.44 is available from the rx8 which Im pretty sure will go into an fd 3rd member.



I really like the idea, and Id love to see it become a reality. But I am a little skeptical about how many people will actually come through with the money. I plan on using a ford 8.8 IRS for my next project. Parts are so cheap and readily available that its only going to cost marginally more to go with a custom rear end than gears for the stock rear end. And Ill save tons of weight and have full adjustability.

 

The price really depends on how many are interested. I will use the FC rears, I looked at remounting 8 and FD housings, in the end it wasn't that feasible. I have seen a remounted SA centre section tried, the webing gave away when used as an anchor point. I looked at the cobra 8.8 as well, its an option but thats alot of ring gear to turn on something like a 250 hp p-port, the rotary is a pretty low torque motor, 7" of ring gear is enough for just about all n/a applications. It's always a battle between weight and strength on some cars.

 

yeah the rear end is something we never broke roadracing.....



for our tracks around here, and the classing we all run in, its a 15x7 wheel, and 4.7 or 4.8 i think put is right at the top of 4th at the end of the main straight at t-hill....



imo, you should prolly plan on doing about 4-5 of these, we called it "production prototype"

 

If it weren't for dumb class rules requiring people to use more expensive and probably more failure prone options (welding the pinion shaft of the Miata gears to fit the FC case), then I'd say that making a kit comprising a custom front mount solution for the Miata front section and a longer driveshaft would be the way to go. I think something along the lines of a Y shaped mount that attaches to the rear mounts for support, mounts to the diff nose in the middle, then goes forward and uses the stock mount location would be best. However your potential market for this would likely be small, just a few hardcore NA track addicts who don't have class rules to comply with or who run in open classes.



Whatever you do, make sure it'll be cheaper than modifying the Miata gears, otherwise no one will be interested.

 

Wow, interesting this shows up!



I've just been looking at what to use for a new rear end ratio in my FC.. I was going to swap a solid axle and 4 link in the rear but, I don't think I can hammer that out before next season with the list of other stuff I need to do.



So I was going to pick up the 4.778 (7") ring and pinion from Mazda (MM057-27-110)





Unless of course you already cut a 5.38 that you want to sell me...

 

Heres an idea. The 7" ring gear in the fc and miata is also the same one in the S2000, which has a rather wide range of gears readily available, and I know the 4.77's are very popular. You should get the info on the company making those, and see if you can source the ring gears from them, and then just make an FC specific pinion shaft matched to the ring gears.



Or just make them straight cut. The price difference will probably matter much more to the target market than the extra gear whine.



I think to be realistic from a business perspective, the price point needs to be around, preferably below $500.

 

Hi! I could be interested in a 4.77 ring and pinion or lower (its for a race car). Please let me know if you finally will go with the project. A lot of people from rx7 club can also be interested. Cheers



Regards



javi174@gmail.com

 

Its for a FC NA 7" ring, isnīt it? Cheers

 

Yes, FC NA's use a 7" gear, the TII and FD use an 8" gear. 1.8L Miatas (1994-2005) use 7" gears, the 1.6's use a 6" gear. I believe the SA/FB's use a 7" gear as well, same short pinion as the 1.8 Maitas.