Buzzin

iTrader: (1)

Need good used or new 4:88 or 5:12 LSD or Torsen.

Call Charlie at 805-466-3015 days 805-462-2524 eves California

Thanks

Charlie Buzzetti

Spank

iTrader: (1)

Charlie you will be very hard pressed to buy what you are looking for. There are very few people using the setup you are asking for. Those that are using them, keep them.

Sorry

Spank

yelwoci

I run a 4.89 plate diff from Racing Beat and am think of getting the 5.1 C&P

IanC

Jims5543

iTrader: (2)

I am looking for a better ratio too. I do not see this on RB's website is this a call in item?

its66

iTrader: (2)

Call Mike at ISC. He can get you one, and make it fit in your diff(some machining is required). I think he is a few weeks backed up though...1-863-324-4539.

tims

for the 5:12 you will need the first gen ring and pinion, available from Mazda. the pinion is then cut and grafted to the pinion from the second gen. some machining is done and the setup is installed. this setup has been used quite a bit but it is a little fragile. seems that once you have the torsen and the big r&p installed there is not much room for gear lube. this then requires a cooler and a pump to keep it alive. some who don't use the torsen have found they can go without the cooler, but it would be cheap insurance and the conversion is not cheap. good luck finding one used.

SPiN Racing

http://cfrscca.org/Checker.pdf

Check in the Classifieds, and look under parts on the right side.
4.88 and 5.12 for 950.00. Appears to be two complete rearends.

Not mine nor do I have anything to do with the person..

Jims5543

iTrader: (2)

Does any one have an opinion as to wether running 4.30's and 22" tall slicks will provide a good final drive ratio. I am mathmatically challanged.

I am currently running a 4.10 rear and my mechanic friend said I might want to try a less drastic change like a 4.30 first and go from there.

This is for an optimum Autocross setup.

RexRyder

iTrader: (10)

yea it'll work

tims

5:12 is still the hot setup to get the car to pull off the corners. not sure if it's the best autox setup, but for the road racers it is.

its66

iTrader: (2)

The 5.12 is gone, but Larry might still have the 4.88

Jims5543

iTrader: (2)

Excuse me if I am beating this into the ground.

My slicks are 22" tall. My streets are 24.7" tall. The Miata tire calculator says that at 60 MPH on my streets my slicks will be at 53.7 MPH or a 10.6% differance.


As I understand it. You can buy the 4.88's from Mazdaspeed. They are made for FB's and need to be modified, actually they need to have a lot of work done, to fit an FC rear. They are intended for 100HP cars and a 180HP IT car will be taxing it. A 460HP BP Autocross car like mine will probably destroy it like it was a bad joke.

Am I understanding this correctly??

If it is indeed a FB rear made to fit an FC I think I will go with the 4.30's and see how they feel, at least they will hold together.

SPiN Racing

Well.. How many badass FCs have you seen that autocross? There have been quite a few over the years since they came out. They all had to run a rearend in thier cars... They also had to have a gear..

The ONLY people I have ever heard of breaking a rearend gear.. which is the spline.. is Drag racers. And they (that I knew of that broke the pinion) have solid everything.. and launch at 6K with drag slicks. Front wheels light etc.. They will break some rearend parts... and everything else for that matter.

Far as the 1st gen rear gear.. the only thing I have ever seen happen to it with a lot of power being put down in a FB or pre-RX-7 is the axles breaking first.
In the Scca 2nd gens.. I havent heard of people breaking them.. but Have heard of people buying extra rear axles.


Ehh... Maybe. If you are going to break a rearend.. it will be a 3.9, 4.1, 4.3 etc. If you are gonna.. you are gonna..
I myself.. I would go 5.12 for a autocross car. MUCH more usable gear ratios in the tranny at that point. Sure.. topend goes down.. but shoot.. unless you do Solo Trials/Solo1 No worries.

Keep redline shockproof in it.. and keep it cool... make sure a professional sets it up properly(lash etc).. and you should be fine.

If you are going to do anything OTHER than autocross with it.. then the 4:30 may be more functional.

Jims5543

iTrader: (2)

I this what I need to buy?

I have a friend/mechanic that is an awesome custom fabricator and knows how to set up a rear end. So modding is not an issue. Getting the right parts is.

From the Mazdaspeed Website:

Eagle7

That's the 4.88 parts. There are also 5.12 parts for about $300 more.
I would NOT have your friend lengthen the pinion. There are a couple places in the country that do this well - use them. It'll cost you another $300.

Jims5543

iTrader: (2)

You underestimate my friend. Trust me he can handle it. He has been building tranny's, rears, and making his own parts since before I could drive.

I am afraid the 5.12 is going to be too much. I would like to be able to somewhat street drive this car if only for around town. Its too pretty to just be an Autocross car.

SPiN Racing

Thats all well and good... And I am sure he is really good and all. I know a couple of the best Rotary pioneers in the country/world personally. People that were doing things in the 70s/80s that 99 percent of the forum has never even heard of...... And they are INCREDIBLE fabricators. I mean things that would truly amaze you. Both of them also design thier own chassis, and re-design existing ones etc etc etc..
In essence, we call them Gods.

Now all that crap spewed... and I have to say. They both would most likely give the RP to ISC/Mike VanSteenburg, becauseof two things.
1. He HAS a person he sends them to who does the work for him and has for at least 10-15 years. And has done countless lengthen jobs.. and knows what works.. and what doesnt.
2. It is much easier to pay the cash to have it done, than take a risk and maybe not have it perfect. They CAN do it.. and I am certain they are capable of doing it correctly.. but some things are better done by someone who does it all the time.

Personally... If you cant afford to pay the 300 bucks to have it lengthened by ISC etc... then you SHOULDNT take the risk of blowing your entire rear carrier/pumpkin and associated parts on a hunch that your friend is capable of welding that pinion.

Thats like saying I cant afford to buy race gas at $4 a gallon.. so I will brew my own... I can mix some stuff up and it will be good. Cause I know someone who has done it....... Is saving a buck or two worth the risk of blowing the engine up?


Anyhow... Yes that is the 4.88 you "need"
But for me... I would cough up the $295 and have it done "right".... then you dont need to think about it.
http://www.iscracing.net/axle.htm

Or do what I did... buy a pre built 4.88 with Torsen.. in the housing.. with (IIRC) 6 races on it for 1000. Used. /shrug

But honestly you should do what you can actually afford. Many people will rattle-can thier car for 40 bucks instead of paying 150 for a cheap econo-bake job. If you cant afford 150... you cant afford it.. its that simple. (Course how can you race then)

Jims5543

iTrader: (2)

I agree 100% with you there are a LOT of Rotary guys out there doing things that would blow all these internet experts minds. Just because they are not on the internet does not mean they have a diminished ability.

Its not a matter of money to me but moreso quality. I trust this mechanic/fabricator more than anyone else in the business. I am not taking away from ISC at all they are good people but in thses parts of Florida the insiders go past ISC and to this guy.

I am just concerned these N/A or FB gears are not up to the task. I will chat with my friend on Tuesday when we corner weigh my car.

tims

this unfortunately is the only option. unless you wish to commission someone to build a custom ring and pinion for you. This is a very common setup and has been used by alot of racers for many years now. the only issues I have seen are cooling the fluid on road race cars. for autox it should not be a problem. as far as who does the work, this is your call, but it is not terribly difficult for a qualified machinist. A Mazda specialist may make other mods to the diff that maybe worth having them do the work.