mikeric

iTrader: (20)

As with any project/race car mine has had its share of problems including my last track even where an oil starvation issue an a long right turn warped my apex seals. Car is back at Speed 1 (formerly KDR) getting new apex seals, springs, and bearings as well a a 3 quart Accusump system.

Car is currently dynoing at 330 horses. Pretty much every upgrade has been done to it and my weakest link is the rear differential. There is currently about 1-2 inches of play on the rear. Imagine accelerating out of a corner, you put your foot down and as soon as power hits, you have a clunk as it hooks up. Repeat whenever you take your foot off the gas to shift or brake before a corner. It is only a matter of time before the thing blows up and leaves me stranded at a race event after paying the expensive track fees.

I would like to upgrade/fix this issue while the car is down awaiting the apex seals which are on order. My mechanic (Dave at KDR) said that the ring and pinion are worn and would need to be replaced if I was to rebuild. It with new ring and pinion, bearings, and plates will run about $800. A Kaaz will add another $1k to that.

I'm not sure about the Ford options etc. From what I have read, rebuilding a stock rear at over 300whp will just be pretty useless.

Anyone have any suggestions or comments?

mikeric

iTrader: (20)

Also, FC and Miata differentials may be an option.

Turbo or road race guys, please speak up!

mikeric

iTrader: (20)

Ok, at the risk of hoging my own thread here...

I have decided that I will be going with a Torsen unit. I would prefer a T-2, but if I find a inexpensive T-1 unit from a Miata, I will go with that as I'm not made of money. I have contacted Fuji Racing about a month ago, but they did not get back to me. In addition, they are not answering their phone...

I have a few questions about that. Will any Miata Torsen work? I'm assuming the FD Torsen will not work as I have not seen anyone try it. Also, is there any difference between the regular Miata Torsen differential and the Mazdaspeed Miata differential?

In addition, where can I buy 3.8 or 3.9 ring and pinions from. I find myself toping out 3rd but not having enough space to go to forth and back down. Anyone with experience with that rear?

peejay

I dunno, man. I'm at 200hp and I go through a bunch of rearends. I've been twisting them until the driveshaft/pinion angle goes inverted. Adjustable links will only help so much with that.

I do set up the gears on the tight side (~.003-.004" backlash) so that when under load and everything spreads apart, the gear mesh is correct. Howls under deceleration though. Not concerned with that.

Next up will be a Toyota 8" or Ford 8.8" Explorer rear.

Jeezus

iTrader: (4)

Just throwing this out there, but I have always wanted to do a 10th gen thunderbird/cougar rear end.
Depending on which engine size, you can get an 8.8 or 9" and IRS for dirt cheap.

j9fd3s

iTrader: (3)

the FB/ non turbo FC/ 94-2005 miata/ s2000? all use the same 7" ring gear.

the FD/turbo FC/ v6 mpv/rx8/ 2006+ miata all use an 8" ring gear.


the early gsl-se's have a 4.076 vs the 12a 3.933, basically its the same difference as going from 185/70/13's to 205/60/14's, in other words its not much, and they just put the 3.9 in everything mid 84... the 3.9 is just stock so you'd just order it from the dealer...

traditionally the rotary people put something like a 4.4 to 4.88 instead of using 2-3-4 in the trans it puts you in 3-4-5 which are geared closer.

but since you have a turbo, maybe the 3.7 the miata people have found would work for you better?

mikeric

iTrader: (20)

Thanks good info. I thought the SE had 4.111 ratio. I definately do not want to go lower as this is not a drag car and I want my mid range and a useable third gear.

Also, the FC does not have a Torsen differential and I'm looking for a Torsen and some Miatas have Viscous differentials.

Anyone know if the Mazdaspeed Miata had different splines on the axles?

Hyper4mance2k

iTrader: (40)

You cannot use a torsen 7" rearend. I make 190whp and blew one in 2 weeks. The Miata guys throw them in the trash once they make over 200whp. Stick with a clutch type LSD.

j9fd3s

iTrader: (3)

the only miata's that are viscous are the 89-93, and those have a 6" ring gear which won't fit anything else except the 323gtx.

all the other diffs interchange within their series.

mikeric

iTrader: (20)

Really? There are people on here that swear by them. Are you sure yours was not worn when you put it in? Would you recommend a N/A FC one instead or are you talking about going full Kaaz?

mikeric

iTrader: (20)

Anyone here try the OS Giken units?

http://grassrootsmotorsports.com/articles/whats-diff/

http://949racing.com/osgikenlimitedslip.aspx

DriveFast7

iTrader: (1)

I've seen 8" Torsens behind a 13b PP last for years in road racing. But those Miatas usually turbo the 4banger which creates more torque.

mikeric

iTrader: (20)

Well, I have brand new Axles, control arms, FC brakes, rotors, and pads so I do not want to throw all that away to go with a Ford. So, I will have to keep it 7".

From feading the S2000 site, their stock Torsen unit is crap and is always failing. I will be wise and stay away.

23Racer

I have the original Mazda RX7 Competition Preperation and Service Manual and they used to use the stock 1st Gen rear end with some changes. They added 3 brathers to the top of the case and blocked 1 off if it was a predominantly left or right hand drive course. They also had a lot of information on rear end break-in (400 kms less than 100 kmh and varying light to moderate load). They also discussed the required pre-load (with a new bearing 9-14 kg-cm, used bearing 2.3 - 3.5 kg-cm). They were also very concerned with pinion angles and wanted the diff to angle upwards by 2 degrees only and the length of the lower control arm as being 495 mm. This leads me to believe that they wanted to remove all potential loading from the case to minimum stress induced wear and heat build up.

They ran a stock diff behind a peri port GT2 car in 24 hour races and got it to live over 20 years ago. They also were using standard 90 wt hypoid gear lube. One thing that they did do was run coolers to the diff and I have measured the housing temps of my dif after a 1 hour race (2nd Gen. approx 220 rwhp) and have seen temps over 300 degrees. Diff coolers may be something to look at as well.

One thing that I do know is that the multi championship winning Kendall 1st Gen IMSA car ran a narrowed Ford 9" and never, ever, ever had any problems. Since that time companies have also developed 9" Ford pods now in aluminum so there wouldn't be a huge weight penalty.

Regards,

Eric

mikeric

iTrader: (20)

Well, since I know I need a new ring and pinion and new bearings and seals, I went ahead and ordered those from Racing Beat, ca-ching $. I went with the 4.111 as it is the closest to stock that they have (if anyone knows where I can get a 3.8 new for under $500, let me know). Once those arrive, Dave will drop the differential and see what the damage is.

He has plenty of new clutch plates, so I may just swap in some new plates for now and see how it holds up. I have about $3.5 k set aside to finish the widebody and paint, so I do not wnat to blow half of that on a OS Giken right now.

If I blow out this unit, at least my bearings and ring and pinion are new and then maybe I'll cosider the $1,600 OS unit.

DriveFast7

iTrader: (1)

Mazda and RB do sell thicker than stock clutch plates for the diff that make it tighter and put more to the ground. Usually only need one of those. Something to look at.

mikeric

iTrader: (20)

I am really tempted to get the OS Giken unit. Any one have any experience with those?

mikeric

iTrader: (20)

Any one with any opinions on the Quaife vs. the OS Giken differentials?

CoffinRX2

get a toyota hilux rear modified to suit. costs over here in Australia about $1800AUD to get it done, huge range of ratios too. ... there is one currently going on www.ausrotary.com for $1150AUD (nfi on shipping costs to USA tho)

I just put one in mine, .... had an S3 rear in it with 320rwhp and all was fine, but upgraded to a hilux rear now that im 400+rwhp

Attila the Fun

iTrader: (1)

FC: I have an '87 T-II rearend behind a 20B at 368 rwhp/ 425 lb./ft. rw torque. No problem

FB: I have a stock GSL-SE rearend behind an '87 T-II 13B at 390 rwhp/ 301 lb./ft. rw torque. No problem - except the stock LSD is toast. I have another differential with a late-model Miata Torsen LSD that I haven't installed, yet. David Lane's turbo-GSL-SE has been running that set-up with about 300 rwhp for about ten years with no problem.

The FC has been taken to the track with no probem. The FB is still getting sorted out. No drag racing on either one. David Lane's car has been autocrossed a lot for 25 years.

mikeric

iTrader: (20)

Thanks!

I ended up going with the OS Giken unit so that I will never have to worry about it again.

It should be going in this weekend and I will update when I know.

Hyper4mance2k

iTrader: (40)

Miata Type 1 Torsen... 355 HP uncorr. at 19 psi

mikeric

iTrader: (20)

This is why I went with the OS Giken unit.

I did research on both the Miata and the S2000 Torsen units on their forums. Everyone who had about 300-350 whp complained and had trouble. The S2000 guys absolutely hated and complained about it (probably due to having more power out of the box).

From my research, the OS Giken is indestructable and is used in 700hp cars without the terrible feel and noise of the KAAZ unit. Yes it costs almost twice as much, but you tend to get what you pay for and OS Giken makes extremely good products.

In addition, I do not know of any first gen guys running one, so I think I will be the first.

UPS just told me it has been delivered, so it should be waiting for me when I get home.

tasty danish

iTrader: (5)

Dang I thought I'd be the first...

But here's the problem more so than the diff. What about the ring and pinion gears? I shredded mine behind 250whp...

Jeezus

iTrader: (4)

Mmm beef up your diff