if i were to get a gtus 4.33 LSD rearend, how much would it improve my acceleration? anyone think it could drop a second off my quartermile time?

i have never been sure how much they really help your acceleration. i've always assumed it didnt help much, but it never hurts to ask. anyone have any before/after experience with the 4.33 gtus rearend?

 

I put one in my convertible to help offset the weight. IT will change your rpm gearing by about 500rpm in 5th (I used to stay at 3000 at 80, now it is closer to 3600). As far as acceleration improvement, well I was sort of disappointed to be honest, considering that I went from a 3.9 all the way to a 4.3. If I had to guess, it might drop a tenth or 2 off your time.

Even now that I have the hi-comp turbo motor installed, it doesnt seem much quicker with the gears than a regular t2. Course, there is a bit more weight there, but not a lot more than say, a 10th anny or s5 t2.

Bottom line, if you've got one, put it in. Don't go out and get one just to be doing it though, unless you get it really cheap.

 

It's only a 5% change in ratio compared to a 4.1:1 diff. That ain't much...

 

Nope. A 4.3 isn't a big difference. Making the switch to a 4.8 gear however is a 17% difference. A 4.8 gear would make 5th gear seem like 4th!

 

Where can i find a 4.80 rear or higher setup for the 2nd gen? Would a b2000 or a b2600 gear etup work?

Jon

 

Yea, I will join that question...where can you find a 4.8 gear set minus hi-po, hi-price race difffs?

 

You wouldn't want that on a street car...

 

IF you want short *** gear ratios, get a 1gen trans. All you have to do to make it work in a 2gen is swap the tailhousing so the crossmember works. Your 5th gear is now about like your 4th used to be. I have a couple of GSLSE trannies if you need.

 

I have a 4.38 in my car, with a 12A tranny, but series 5 fifth gear for cruising.

110 mph at 7200 rpm in 4th.

65 mph at 3300 rpm in 5th.

 

Yeah it's not that big a difference, if it's the last ounce of acceleration that you're trying to squeeze out, then go for it. But if money is an issue and you have to pay for that. then spend it somewhere else for now. i've thought about it, but it would make my 1st really short, and as soon as i launch i would have to shift again.

 

Another option is 15" or even 14" wheels just for drag runs.

 

Nope, and I wouldn't want to pay for the gas either!

 

The GTUs rear is 4.30, not 4.33. I also swappin in a torsen LSD into the GTUs rear, because I feel that the viscous unit is not up to my standards. As far as helping acceleration, I havent been able to test it much, but I did not feel a HUGE difference, maybe a little quicker pull in the upper gears, but nothing major...

 

Good insight guys.

I was going to pose this question sooner or later.

Is there no other diff ratio that is interchangeable? The choices are strictly 3.9, 4.1, and 4.3?

Kevin - Driving the FB, (12A 5 speed), I noticed it seems alot like my 5 speed mated to the 4.10 in my GXL, except 5th is shorter, rather than taller.. I didn't realize the entire tranny was geared shorter..

 

Stock, yes.

YEah, in my experimentation, I think that the FB 5th gear is almost the same as the FC 4th gear. IT is actually useable for throwing down on people!

The only thing that kept me from putting it in my convertible a few weeks ago during the engine swap is that I like to get out on the interstate and run 100 or so consistently, which would really be pushing the engine at about 5krpm or more. Right now it's around 4200 IIRC.

FWIW< to my limited FB knowledge, they all have 3.9 rearends, so mating a 1gen trans to a 2gen 4.1 or 4.3 will push the revs up even higher than in a 1gen.

 

If you guys are talking about tranny ratio's, don't forget about swapping in the 5 speed Miata Gears.

 

Thanks for the info, Kevin.

I'll look into the diff ratio on the FBs.. As for the tranny itself, is the GSL SE tranny the only one that will work? Or are they all the same in the FB? etc..

 

There is no escaping the reality that porting or forced induction is the only way to get a lot more power. Exhaust is good, too, but loud.

You can even combine porting with forced induction . . .

 

IM told from a local 1gen buff that the 5th gear ratios changed along the way several times (even between the 84-85 SE) but that all 1gen trannies are basically teh same and will all bolt up, including 12A ones. Note that FB trannies are slightly weaker than 2gen NA trannies, from what Im told. I think mazdaspeed7 said he ran one a while on his car until it broke, but he is making pretty good power with a modified ported engine.