Converting Diff in ITA Miata

[the1jbh]

I am not a mechanic and at the risk of sounding stupid, I'm going to go ahead and ask this question anyway. Is there any way to convert my open differential to a the limited-slip without having to buy a completely new diff? I have a 96 Miata which will hopefully be complete for the 2012 season and I intend on running 4.77 gears. ALSO, if I am able to convert from open to LSD, will I have to change anything with my gears? All advice is appreciated.

[ner88]

A 96' Miata has a 4.1 diff.
The most common one used is a 4.3, I don't know how or where you can get a 4.7 gear set?
You can drop in a Torsen into the open unit, if you can find one probably paying $400+.
A 4.3 ring and pinion will cost you about $450 from Mazda.
or buy the complete torsen 4.3 for around $1000 used.

[red986s]

I am not a mechanic and at the risk of sounding stupid, I'm going to go ahead and ask this question anyway. Is there any way to convert my open differential to a the limited-slip without having to buy a completely new diff? I have a 96 Miata which will hopefully be complete for the 2012 season and I intend on running 4.77 gears. ALSO, if I am able to convert from open to LSD, will I have to change anything with my gears? All advice is appreciated.

Not sure if the drive shaft and half shafts are the same between an open and LSD. Hopefully someone smarter will chime in. 4.77 is great for short technical tracks. 4.30 or 4.44 might be better for longer/faster tracks. Tranny Gear ratios have to be stock per the GCR.

I don't know how or where you can get a 4.7 gear set?

I got my 4.77 from the front axle of a Kia Sportage 4x4. It's actually a Mazda part, drops right in.

[pitbull113]

axles are the same. forget the torsen and have someone install an rx-7 lsd unit in your carrier with the 4.77 or which ever gear you decide on.

[Andy Bettencourt]

Best bet is to get a 4.3 torsen from a 99. Same carrier etc so legal. Call Marc at Planet Miata or Jim at East Street. One will have a whole unit in stock.

Keep your unit as a spare in case you crack the carrier.

[the1jbh]

Any advice on what gears I should run for Summit Point and VIR? I plan on buying a 4.30 also. I'm also thinking of trying out NJMP, eventually. Thanks

[the1jbh]

Is the RX-7 LSD a direct bolt in to the 96 Miata diff casing? Which year RX-7s?

[Andy Bettencourt]

I don't know about Summit, but I have run SM's and my ITA Miata at VIR. The best top speeds in the SM's were with a 4.3. Could hold 4th up the hill on the back side. Going to 5th hurts it.

My car has a 4.44.It was fine there with the extra IT power. Seems right on the front.

[zchris]

The 86 RX7 GXL posi unit is a direct bolt in for the miata diff. Have built 6 of them and they work fantastic.

[Dano77]

The 83-85 LSD is also a direct fit,as well as the gear ratios.

[Chris Humphrey]

The 83-85 LSD is also a direct fit,as well as the gear ratios.

I don't think the 83-85 rx7 LSD will work it does not have provisions for the clips on the axle that hold the axle in on the Miata.

[tyler raatz]

I agree with Andy, 4.44 is the gear for VIR, also works very well at Road Atlanta. I have a few torsen diffs, one RX7 lsd and one Eckrich lsd, the car feels way better on the lsd than the torsen.
For those who were wondering, 4.77 gear is from the front of a Kia Sportage SUV, can be had VERY cheap at a pull-a-part.

[Dano77]

When I purchased my Cheater Miata,that was one of the things that were wrong with it. Had a first gen plate type LSD and 4.44 gears. Eventually took them out and used them in my IT7 car and got the correct diff from a yard. So you may be right,they may have modified it and I wasent aware of that.

I do know that it works the other way with no issues.

[the1jbh]

So you are saying, I should look for the 86 and NOT the 83-85 RX7 diff? That is the one that is the clutxh type LSD?

[seckerich]

86 and newer RX7 LS is a bolt in for the 1800 rear. Earlier will work but requires some modifications to make it last. Diameter for stub axle is not always the same and wears out the case.

[Andy Bettencourt]

So I can't stress enough that the easy-button here is a complete torsen 4.3 out of a 99 Miata. This accomplishes a variety things:

1. It is a complete package that is less costly than any other option
2. You can resell it should you need to to fund your 'V.2' effort
3. It will provide you a spare carrier if you ever break
4. It is an upgrade to the 4.1 you have and will allow you to have 'enough' gear if you haven't raised the rev limit on your motor and/or tuned for a new powerband
5. It will also get you up and running quickly while you make notes on what tracks you run to determine if a 4.3, 4.44, 4.77, 4.88 or whatever, is best - then you can sink the real money into a custom geared, clutch-pack if you want.

[pitbull113]

So I can't stress enough that the easy-button here is a complete torsen 4.3 out of a 99 Miata. This accomplishes a variety things:

1. It is a complete package that is less costly than any other option
2. You can resell it should you need to to fund your 'V.2' effort
3. It will provide you a spare carrier if you ever break
4. It is an upgrade to the 4.1 you have and will allow you to have 'enough' gear if you haven't raised the rev limit on your motor and/or tuned for a new powerband
5. It will also get you up and running quickly while you make notes on what tracks you run to determine if a 4.3, 4.44, 4.77, 4.88 or whatever, is best - then you can sink the real money into a custom geared, clutch-pack if you want.

agreed.

[red986s]

So I can't stress enough that the easy-button here is a complete torsen 4.3 out of a 99 Miata. This accomplishes a variety things:

1. It is a complete package that is less costly than any other option
2. You can resell it should you need to to fund your 'V.2' effort
3. It will provide you a spare carrier if you ever break
4. It is an upgrade to the 4.1 you have and will allow you to have 'enough' gear if you haven't raised the rev limit on your motor and/or tuned for a new powerband
5. It will also get you up and running quickly while you make notes on what tracks you run to determine if a 4.3, 4.44, 4.77, 4.88 or whatever, is best - then you can sink the real money into a custom geared, clutch-pack if you want.

+1

[mazdagt3]

4:44 was perfect in our ITA car for njmp, wgi and road Atlanta.

The less expensive option is the 4:30 setup from a 99 like andy has stated.

When you're serious get the 4:44's.

Forget about anything steeper than that unless you're going to run a 1.6 up around 8000 rpms!

Call me at 570 262 1013 email [email protected] with questions.