After a lot of research on the subject,
The search for longer gears for the FD Differantial carrier, has finally come to an end.
We have a direct replacement solution for those who are looking for taller gears for their FD's without having to resort ot the Cobra 8.8 IRS carrier and subframe option.

Bellow are pictures of 3.73 Ring and Pinion gear that will dirrectly interchange into the differential of the FD Rx7

The 3.73 is on the left, the OEM 4.10 is on the right
This gear came out of an '89 MPV Sport (5 speed version)
We have located the OEM P/n and are in process of acquiring global availability info.




The ONLY difference between the 2 gears is the main bearing collar (The machined surface for the big Pinion bearing) on the 3.73 gear shaft is 5mm smaller on the OD.

Due to the increased mechanical loads of the Turbo engine on the FD.
The main Pinion bearing is bustantially larger, but the shaft that transmits the power is exactly the same in all other dimentions on both gears.

I found a solution to accomodate the larger OEM Pinion bearing of the FD to the narrower collar found on the 3.73 shaft.

We were able to source and acquire some hardened sleeves to take up the difference between the OD's and ID's or each.

Below, I will post some pics illustrating differences and the applied solution.

GT1-20b

 

This pic illustrates the massive diffefence between both pinion bearings
MPV on the left, FD on the right

 

This pic shows the difference between the FD bearing ID, and the 3.73 collar OD

 

This pic. illustrates the increased OD of the 3.73 pinion when the hardened collar is pressed over the shaft

 

This last pic., illustrates the Large FD pinion bearing, seated over the hardened collar ready to be pressed over and onto the shaft permanently.



Obiously, a NEW crush collar " Distance piece" as Mazda calls, needs to be installed in order to maintain correct spacing
The crush collars are a one time use only part, as the name implies, it crushes and compresses to a specific distance and presure, maintaining both pinion bearings firmly agaist their respective races.
The the driveshaft's drive plate and the Pinion nut are then slipped over the splines and torqued to OEM specs.

We are activelly working w/ the manufacturer to see about finding sone new gears for resale.
We are keeping hardened collars in stock for anyone interested in doing this conversion.
Also, If You find a used gear, we can set it up for you for a nominal cost in addition to installing all the new bearings, shims and seals.

Carlos
CLR Motorsports Inc.
GT1-20b

PS.

Especial thanks to "Ray" from the V8's Rx7 Forum.
Who's help and collaboration helped bring this project to fruition.

'c

 

Nice find Carlos. I see you're been buisy with R&D.
I have a RX-8 that is in need of that gear.

 

Great find!

And please keep us udated on any new findings on your R&D on this project.

Thank you.

 

Good info here! I am definitely interested in this setup. What kind of price point are we looking at here? Please let me know. You can PM me if you would like.

Thanks...

 

I also would like a set of gears, good find!!

 

Awesome. I'm definitely interested in this. Where can we buy the stuff and how much?

What sort of power levels have you tested this at? It seems like it wouldn't be as strong as the FD rear. Although it has a hardened collar pressed over it, that doesn't seem like it would help the twisting motion?

 

Carlos,
What would this do to improve things over the 4.10 or 4.30?
Ernie

 

Just got in from 7 Stock X.
Glad to see all the einterest !

We'll have info on this later in the week.

GT1-20b

 

Im very interested in this as well, but for an FC turbo. Do you know if the input pinion from the FC turbo diff and the FD diff are the same (or close enough to make this work)? Good find!

 

Any update here?

 

Yea, any new news on this? Thanks

 

The lenght of the Pinion Shaft on the FC is much longer that the FD.
Unfortunetly, this will not work for the 2 gen.

 

I've successefully set up the 3.73 Ring & Pinion gear inside my FD's diff.
I opted to use an LSD. from an FC rather than the FD's Torsen unit.
The Torsen is not as compliant when driven on un-even pavement specially when putting down big power.

Pic's will follow early next week.

 

Ernie,

The more power You make,
The longer the gear You can pull or stretch.

Shortening the gear like going fron a 4.10 to a 4.30 gains mechanical advantage, or leverage for the engine to do the work easier.
Certainly, a great way to increase rate of acceleration, but at the expence of top speed.

Increasing engine's power output reduces the need for shorter gears.
The engine is capable of doing more work (accelerate) without sacrificing speed or fuel consumption.

Combine a good 6 speed gearbox: One having a good low 1st gear, proper gear drops, a decent OD, somewhere in the 20% range (.80). Along with a longer rear end gear, and ...
You get the best of all worlds: Hard acceleration, great top end, and better milage !

 

bump!

 

T T T.............

 

^

 

Bump...

 

^^^

 

Do you have any updates for us?

 

6 months and counting.....