I've got a 4.3 rear end gearset.

In the stock RX-7, it's 3.909 with a 3.622:1 first gear. That equates out to 14.1584 final drive ratio.

If I switch to a Miata tranny. That's 3.136 first gear, wiht my 4.3 rear end, it'll be 13.4848...

Will that 0.6 ratio difference hurt my launch? That's assuming that the car launched well stock, which it probably didn't.

 

your final drive is taller, so you'll have less torque, slightly higher top speed in 1st.

 

he he guess what i have in my diff.... he he


4.88 gears man is my accel is QUICK!!! i litterally have no first gear... lol but damn she is quick... lost alot of top speed... i went from 250km/p to 190km/p , but that doesnt matter to me cuz i need the torque and accel for my drifting and 1/4 mile so ...
flame on boyos!

Cory

 

So I'll be able to spin it out in 1st longer befroe upshifting... But will 0.6 difference really make that MUCH of a difference?

 

So what exactly are you trying to acheive?? u want better speed or quicker acceleration??

if you want acceleration put the 4.1 with the rx7 gearbox.

if u want speed then put the miata gbox with the std diff

the way you drive will adapt to the car so u will launch the same if not better after a few trys

-James

 

I have the Miata diff with 4.30:1 ring and pinion...

I'm debating on whether to use the stock 12A 5 speed or a Miata tranny.

 

I thought that that only Miata Diff with a 4.3 ratio was the 90-93 which is a 6" diff and not compatible with an FB. I thought 94-up was 4.10 and interchangable with an FB. I could be mistaken.

 

Also, if you are using a stock flywheel a shorter first gear will hurt your acceleration or at best not affect it because the flywheel is so heavy. A light flywheel will REALLY improve the acceleration with a shorter gear ratio.

 

Now hold on a minute here, I am trying to get my gearing figured out. I want more top end speed and less acceleration ie running through the gears sooooooooooo quickly. I have 4.1 rear end. Do I wan a higher number diff or a lower number diff? I thought the number represented the number of times that a tire would rotate per one revolution of the driveshaft which would mean I want a higher number...

Please clear up.

Brian

 

4.10:1 = 4.10 turns of driveshaft to 1 turn of the wheels.
Higher top end/less acceleration means you are looking for taller gearing, or a lower number. Lower gears (higher number) will give faster acceleration, lower top end.
Hope that helps.

 

3.909 will give a higher top speed then 4.3

 

I guess I should have stopped and thought about it...one rotation of the driveshaft equals 4.1 revolutions of the tire...duh. That would give some crappy acceleration, but hey, 100 mph in first gear after about a 10 mile downhill start would be fun. And don't get me started on 5th gear.

Thanks for the help.

Brian

 

Hey were did you get your setup from, it's sounds like you have a sweet setup.

 

1999+ 5 speeds had 4.30:1... Touring or Type M or some such options package had a Type II Torsen diff as well. This is what I scored.

Scrap yard. It's not built yet, but it is indeed a boltup. My rear axle needs sandblasted and repainted... As soon as I figure out how I'm gonna sandblast it, I'll post pics.

I'm not assembling a rust covered axle.