Hello all, since everyone knows how hard it is to get your hands on a GTU'S diff, I was wondering if anyone has purchased the 4:30 ring and pinion gear set and has had it installed into their stock diff? I have a 87T2 and I was thinking of doing this in the future. I heard that it was a improvement from the 4:10 that come stock. It is around $450.00 for the gears but I do not know how much labor would be? any comments would be appreciated, thanks

 

I always thought the TII's came with a 4.3, and the GTUs was the only N/A that came with a 4.3

I could be just flat out wrong though. Any one else know for sure?

 

Stock ratio for NA's and TII's [excluding 'verts] is 4.10

4.30's for TII's are available from Mazdatrix

Bring the beefy checkbook: NA =441.50
TII=413.40

 

Mazdaspeed sells 4.33 ring and pinion sets for the NA and TII differential. Make sure that you order the correct set, as the NA and TII differential use different gear sets. The performance "improvement" depends on your point of view.

The TII came with 4.1, and the GTUs came with 4.3. The other FC coupes had 4.1 in MT cars, and 3.9 in AT cars.

The reason why a lot of people think that the TII came with a 4.3 is because of the misnomer of the GTUs being the "TII without the turbo". While this may be a good way to explain the GTUs concept to the nubies, it is not at all correct mechanically speaking.

 

the only mechanical difference on the gtu's is that it has the diff, everything else is the same on a s5 car

mike

 

How much would this improve acceleration? Probably increase obtainable top speed for all of those who enjoy such high speeds.

 

Actually top speed is decreased when going to a higher final drive gear, but you will gain some acceleration from it.

Do ALL verts have a 3.9? That really sucks, what the hell am I going to do with like a 150mph top speed?

 

You will have to buy the 4.3 gearset because the GTUs has the same diameter ring gear as the other N/As.The TII has a larger ring gear so the GTUs diff and gearset won't work.

 

What about the 88 GTU? I hear conflicting info sometimes. Also wondering if trannys are the same? What does it mean when people say the t2s are more "beefy"? Sorry bout barging in on this thread, it kind of pertains to this.

 

What about the 88 GTU rear end gearing? I hear conflicting info sometimes. Also wondering if trannys are the same? What does it mean when people say the t2s tranny/rear end are more "beefy"? Could that be the larger ring gear and others like that in the tranny? Sorry bout barging in on this thread, it kind of pertains to this.

 

Sorry nout double post, my computer or network was F$*Ked UP.

 

5th gea ratio is different also, lighter weight carpet etc.

 

IM looking to buy a GTUs rear diff, so if anyone has one for sale shoot me a PM

 

top obtainable speed will go up, top theoretical speed will go down

 

Really confused @ above post. If one were to go to a lower gear, higher number, top speed, obtainable and theo, would go down. 7000 rpms would naturally be the same, but top speed would be reduced by @ 5.5% with the lower gear.

 

Yes but top speed gearing wise for a N/A with the 4.1 rear diff is around 190MPH. But, we have nowhere near enough power to go that fast with those gears, we are drag limited to about 137MPH. With a shorted gear (higher number) our theoretical top speed goes down (about 170-something I think) but we will be able to reach a higher top speed than with the 4.1 because we will be higher up in the rpm range, and more into the power band.

 

Disagree. If that's the case, put a 5.13 in there and get a really high top speed!

 

Im not saying top speed will go up drastically, maybe 1-3MPH. Truthfully Ive never done it, so Im just kinda speculating. The main reason for installing lower gears is for acceleration purposes, but I could see how if those gears put you into a more potent powerband at higher speeds where it could increase it by a few MPH.

 

OK I see what you're thinking, but if you do put the lower gears in, you'll see a decrease in the top speed in every gear. You just can't go lower and experience an increase in speed at the same RPM's, unless you change the ratio in the trans, if at all possible, which would then defeat the purpose of installing the lower gear. You could change 5th gear ratio, again if it were available, then have better pick up and top speed.
Just my thoughts.

 

I think that there is MISUNDERSTANDING here. my hole purpose is to go to the 4.30 gears as opposed to the stock 4.10 is for faster qtr mile times. I know that my top speeed lets say 110mph and up will be slower, but I will be quicker off the line and my power band will be quicker.
I'm not trying to go 170 mph. IF any one has done this swap in a T2 please let me know results and if it was worth it. thanks

 

With a 4.3 rear end your gonna tach out before you run out of hp.
With a 4.1 rear end you tach out but more then likely run out of hp first...(7700rpms 5th gear 162mph downhill)
-oh yeah dont ask Gabe

 

The basic idea is here (nillahcaz), but for more information see my post about "How to get speed 101". That'll give you guys a better idea of how the power, gearing, and aero (don't forget that) all work together to determine the top speed of an object/vehicle.

 

No, the top speed will actually be higher due to mechanical advantage. No NA RX-7 (stock) can reach it's gear limited top speed, including the GTUs.

Quote:

Do ALL verts have a 3.9? That really sucks, what the hell am I going to do with like a 150mph top speed?

All 1988 'verts have the 3.909 differential. The 89 and up depends on auto (3.909) or manual (4.10) to determine the differential gearing. And you aren't going to hit 150 mph in a vert without serious mods... although the gear limited speed with the 3.909 diff approaches 200 mph, there is no way you'll get there with an NA 13B.

 

Someone told me that with the right gearing, a stock T2 could run a 13, they were saying something like 2.78 gearing, is this even close to being true?

 

The 88 GTU only came with a manual transmission, so they all had 4.10 gearing.

Beefier TII transmission narrative:
http://www.mazdatrix.com/g1.htm

Differentials:
http://www.mazdatrix.com/g5.htm

The TII also has a thicker driveshaft and halfshafts than the NA MT models.