Daffy's SE

[bruce]

I used the oven but then realised I might poison myself with any residue. Wrinkle coated roast duck anyone?

[Daffy]

Are you sure the diff itself has failed cause it looks like the diff arm failed which may have cause it to kill a shaft.

Thats the factory failure point too.

I’ll have to wait until we get it up on the hoist at the end of the month and see the full extent of it all and if there was damage to the diff itself- I’m not hopeful though the diff may be salvageable as there was a loud “mechanical” sound and jutter from the back end just before the bang when the mounting arm snapped.

[Daffy]

Getrag diff upgrade homework has started..... bit more research and emails to Kmiata RE stage 3 kit to be done before kickoff at the end of the month, as well as sourcing a GM CTS (or Aussie equivalent) diff- more to come

[speed]

After all this you will literally have the strongest driveline in the land!

If only you could engineer a LS whatever...

Apologies to your better half for putting ideas in your head.

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[The American]

Let us know if you are able to find a local diff that works with the KMiata bits.

[mr bender]

If you are looking at different diffs other than the CTS-V , then there is really no reason to buy the kit.

The axles that come with the kit will only work with the CTS diff ( spline count ,size etc)
The axles are the biggest expense , other than that there is only about $50 dollars worth of steel in the mounts.

if you where looking at using a diff from something that is available in Australia you might aswell price up some custom axles too.
after you find a Cts lsd diff, , the right ratio, front bushing , buy the swap kit and pay for shipping and GST , it might be cheaper to get it all made in Australia.

another option is RX7 rear end , a friend of mine has one in his mx5 and it works really well and was a hell of alot cheaper a CTS upgrade.

just my 2 cents.

[speed]

another option is RX7 rear end , a friend of mine has one in his mx5 and it works really well and was a hell of alot cheaper a CTS upgrade.

just my 2 cents.

Hope I'm not talking out of turn here.. Daffy is researching diffs capable of 600hp and ratios of 3.2, 3.4, 3.7 or 3.9

With the BMW box he may be looking at 3.4 or 3.7 but is waiting on more info so he can make an educated decision.

Just out of curiosity what sort of power and ratios are available with the FD diff?

Cheers!

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[mr bender]

I think most of the Rx7 ratios are all around high 3.9 to 4.1 but I'm not to sure.( so no good for for Daffy)

also look at the ford 8.8, as there are so many ratios to choose from for the 8.8.

[speed]

I think most of the Rx7 ratios are all around high 3.9 to 4.1 but I'm not to sure.( so no good for for Daffy)

also look at the ford 8.8, as there are so many ratios to choose from for the 8.8.

Thank you! I'm sure he will now you've mentioned it. Thanks again

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[ManiacLachy]

I took Daffy's meaning as: we don't get the CTS here, but GM/Holden might have used the same diff in other cars that we did get locally and that's what he's looking for.

[Daffy]

I think most of the Rx7 ratios are all around high 3.9 to 4.1 but I'm not to sure.( so no good for for Daffy)

also look at the ford 8.8, as there are so many ratios to choose from for the 8.8.

I took Daffy's meaning as: we don't get the CTS here, but GM/Holden might have used the same diff in other cars that we did get locally and that's what he's looking for.

I’ve heard great things about the Ford 8.8 and if I was to look at a custom set up it would be a serious consideration.
As Lachy says, I am looking to verify if the GM CTS is the same as what’s being used in the later model Commodore V8’s (Google searches are just sending me in circles, so when I get some days off next week I can face to face with a couple of contacts to try and confirm if they are one in the same and I can source one locally. Previous experiences with custom made gear always seems to end up costing more than planned, added to this a lot of fabricators can be a bit vague on warranty matters. The Kmiata/V8 roadster kit for the getrag diff has been well tested and are provided with warranty, added to this it was developed to pair up with the BMW box transplant. I will have a more accurate final cost to work with, and if required I would be able to hit them up to source a quality used diff in the desired ratios from the US for a reasonable price (around $400 USD) that can be included in the conversation kit delivery. Going Locally made custom set up or The Kmiata kit, it won’t be cheap either way, but it (should) be a final fix in the very last weak point of the problem child that hopefully I won’t have to revisit for a long time, with no niggling thoughts of what if’s going by way of a full untested custom setup. I’ll be posting asap after I have the facts RE total cost and availability etc.

[Lokiel]

Love these updates Daffy since I'll be looking into doing {some|most|all} of them at some time and it's good to know ahead of time what may be required.

Regarding the diff query:

Can you find a "Parts List" breakdown or "Collision Guide" of the GM CTS and "CommonDoors" on "the Google machine"?

You can usually find them for older cars because someone has found them and posted them but newer ones tend to be harder to find.

If so, that's your definitive answer and you're not left wondering if your answer is "just what someone reckons".

eg. https://www.miata.net/garage/90-99Parts/NB_collision_guidepdf.pdf

[mr bender]

The later model commodore diffs are a very different style to the Getrag CTS ones, they only made the CTS style diffs for CTS-V ,STS ,SRX ,Solstice and Saturn (the first 3 are pretty much the same car) Non of them where available in Australia so they would not of used the diffs in anything here.

They only made that style for 4 years before they changed the style again on those cars as they had problems with pinon bearing seal , Whine at different speeds and snapping the housing in half, when they axle hop or launch hard in the heavy CTS which shouldn't be a problem in a mx5.
saying that im sure that most of the V8 mx5s in the world use the CTS diff without problem, although i have seen a few diff swaps that have pulled/torn/ripped out the stock mounting bolt from the subframe so thats something to keep in mind.

From 2004 to 2008 should all be the right style(with the wings) but you have to make sure it has the 3 bolt front flange ( same style flange as the commodore) as some of the later ones came out with the round flanges.

interestingly there is two different 3 bolt flange between the early CTS diffs to the late CTS diffs should be able to tell by the case casting on the top off the diff and the pinon seal. The tail shafts that V8 roadster sell have holes for both type of flanges.


also there is a swap kit for the ford 8.8 already available from V8 roadster
: https://v8roadsters.com/product/ford-8- ... ft-061818/
you can get the ford 8.8 diffs in a aluminum casings too if you are worried about the weight but i'm unsure if something needs to be changed on the aluminum housing to use it with the kit.

another interesting fact is that the 8.8 diff is used to upgrade the CTS-V diff if people who race them keep on breaking the stock diffs.
https://creative-steel.com/shop/04-07-c ... -upgrades/

[Daffy]

Thanks for the quality feedback with the research assistance- thats what I love about this forum, It’s giving me a lot to ponder with the best direction to take- I’m working night shifts next week, so I’ll be able to call up the US guys direct for a bit more deep and meaningfuls before committing to a final decision. Either way, there is some good options ready and available. Just got to stick with the mindset “do it once, do it right”
Apart from sourcing a quality used, there is also the option of genuine new available (just bloody pricey, but perhaps the peace of mind my be worth the extra outlay)

[Daffy]

Differential update;
ZF 6 speed in and sorted with 0 issues now, (previous posts refer). However, as some have read before, with mine, increased power gain not lost through a more sold drive line has well and truly killed the Problem Child’s SE torsen rear end (a true hero’s death it suffered- I’m thinking of fliationg it out on a wooden boat and striking it with a flaminging arrow in true Viking sea burial style .)

This is the plan of action to replace the SE torsen with the GM Getrag.

The new stage 2 kit V8 Roadster purchased via Kmiata includes; (copy and paste from their web page)
Getrag mount with polyurethane bushings and grade 8 or better hardware
32 spline axles with high output inner and outer CVs rated at 550 lb. feet of torque
New billet high horsepower hubs
ARP extended wheel studs.

There was no need for upgrading the driveshaft, I got one of those with the BMW ZF 6 speed adapter kit, we just need to send it off for some slight fitting mods.

The diff purchased is a 3.73 ratio (GM part number 2587349, again, copy and paste from website)
RWD manual 2006-2007 CTS-V 6.0 ltr

A Cadillac 04-07 CTS Rear Differential bushing will be utilised in the install as well on recommendation, as the standard one sucks balls.

The reason of choice of the 3.73 ratio (factoring in the beemer box ratios) is that I aim to maximise the quickest possible 0-250kph acceleration range (given that I can keep some unbroken traction down - I’ll be hunting some slicks soon just dir rhat atraight line soeed curiosity). With a few extra E85 inspired PSI of turbo boost thrown in-
This added expense Beemer box, CTS diff and all is a big hip pocket hurting outlay (again), but to give some confidence that the driveline will now not break..... ever........ seems worth it (fingers crossed)

In recent times over the past 3 odd years, so many of us punters out there have been able to take the MX5 power levels so much further than when I 1st started building on mine. With new advances in engineering, performance product availability, there does seem to now be a growing amount of research needed into how to keep that power in check from the flywheel to the axles. I’m fortunate enough to be able to test the waters with this in mind with the road I’m taking, here’s hoping that what I’m trying to achieve will help out others with far more superior mechanical minds than mine, to be able to rework some of this info into more cost effective locally made solutions and variations to what I dread to see as an eventual lead to a massive shortage of broken. and depleted numbers of NA/NB 5 and 6 speed boxes and diffs dwindling in availability for replacement. I want us to be able to carry on having happy street/track days in these incredible cars beyond the availability of replaceable parts that are now disappearing in numbers.

Install posts to come.....