RX7/8 LSD into NA MX5

[Donovan]

My Trekk continues with the build of my car, ok, well no building is going on, just amasing a whole pile of parts all over the place ready to be slapped in.

Have just got myself an 04 HSV V8 and maybe a transmission. Now I just have to sort out the rear end, and then it's all ready to go.

In the US they have been using either the Cadillac or Ford 8.8, these items might be common over there, but not so much here. So the other item for consideration is either the Batmobile Rx7 diff or Rx8 diff.

So, does anyone have an opinion out there as to whether one of these would fit into the NZ MX-5 without to much hassle, and secondly whether anyone thinks it will handle to Torque of the HSV motor if I ever get the traction sorted out. This car is destined to spend most of it's time on the track, so it will be driven in anger 80% of the time.

[Gravelben]

Could be worth seeing what the guys who drift RX7s use, they put a fair bit of power through and abuse the crap out of them so should have an idea what can handle it.

[Keith Jones]

Neither the Batmobile or RX8 diffs will fit an MX5 easily as they are a completely different shape without the wings.
For your power the turbo RX7 series 4/5 might be an option.
With an 8" ring gear and large dia axle shafts it will certain take a lot more torque than any other Mazda diff, although I don't know the max rating.
To fit this needs modifications to the PPF and new axle shafts and drive shaft made.

[Donovan]

I had a chat to a guy after I put this post on with a Lexus v8 in his which is "only" running the stock 200kw, and he has used a series 4 turbo diff. He said part of it butts up against part of the subframe in the rear so needs to modify it. He seems to think that these diffs were built pretty strong, but not sure how it would handle the V8's fury.

[MX4000]

The ratio is also waay too low - 4.1:1. With the Lexus you feel like you need another gear or two. Nose of the diff also hits the fuel tank - needs a fair amount of hammer surgery. I'm running a Holden diff - easy enough to fit to the subframe with a few brackets. 3.08 ratio is a bit lazy - a 3.5 or 3.7 would be about right but with the LS power you could pull a higher ratio. The axles are where the money is - maybe $1500 for a pair.

[Donovan]

Yeah, someone else has mentioned the Holden diff to me, I just didn't know easily it would go in, but I guess if you have been there and done it before then it ain't impossible.

The other one that has been mentioned is out of a Nissan Silvia or Skyline, they stand up to a lot of punishment from the drifters, and the HP that some of those guys are pushing out.

I suppose you made up your axles yourself?

[Donovan]

Hmmm, according to my friend Wiki, diff out of the Cadillac is the same model as out of the Commodore, and flynin Miata have the axles for the Getrag diff from the Caddy in various different setups for taking the HP, as well as driveshafts.

http://www.flyinmiata.com/V8/configurator.php

I have also just found a LSD Commodore V8 diff for sale.

I am normally sit in the blue oval corner for the V8 racing as does the rest of the family, so I imagine I am going straight to hell for this build since it is looking likely to be using all Holden running gear.

[Stevo]

When you are into the build, how about starting a new thread and adding some photos, Im keen to follow your progress. Cheers Stevo

[Donovan]

Yep, Stevo, no probs.

But be warned, there maybe lots of swearing and cursing in it when I realise that things don't fit or work, and have to get different parts.

[MX5.9]

Hi all,
Ive gone with the Ford 7.5" IRS and axles mainly due to the fact that there is a wide range of ratios readily available, and the axles should be good to around 600nm.... with this diff setup in a nice light car should never blow Just my opinion

Cheers
John

[Donovan]

Hi all,
Ive gone with the Ford 7.5" IRS and axles mainly due to the fact that there is a wide range of ratios readily available, and the axles should be good to around 600nm.... with this diff setup in a nice light car should never blow Just my opinion

Cheers
John

Is this diff out of the Falcon, I thought they were 8"? Was there too much of a problem getting it to fit in the rear and where did you get the axles made up?

[MX5.9]

Nope the diff is out of a Mustang and the axles are from a Couger... I got the set up from the us.... the 8.8 diffand axles are too big for our application, as they hit the shocks

[MX5.9]

And fitted in without too much hassle

[Donovan]

Well the time is almost upon me to start putting all the bits in the car that I have been stashing away for the last 6 months or more. I got a Holden HSV LSD and axles and will look at shoving that in the back. Turns out they are different from a Caddie diffs that they use in the US, so the axles they have over there won't work.

Apart from MX4000 (I won't bother him, as I am assuming he is busy with other things down there) is anyone else running a Holden diff? And if so, where did they get the axles made up. Would like to get these done by someone who has done them before rather than re-inventing the wheel.

[Growler]

I know you have the diff already but the Hilux LSD diff could be an option. There is a wide range of ratios availabe too.

[2low2c]

I had some custom half shafts for a subaru made by ADL.
you could try heat treatments .
you will have to know the lenghts and spilne sizes .