I'm pretty sure doing this mod would void the warranty on your tranny if it came down to it. But I guess as long as you still have the engine under warranty it's okay.

 

my guess is that it MIGHT void it. I mean there going to really have to look at it to figure out that some1 put a new FD RATIO correct?

 

Good point.

If the service department is already suspicious because of mods done or if they happen to test drive it which they will and happen to notice the difference in gear ratios then they might look at it.

The way it sounds it would make a considerable difference.

Not too sure about the Kia gears though.

 

The lower gear will multiply the hp and torque, mechanical advantage at the wheel with a trade for rpm. More hp and torque, faster car.

 

Will this mod greatly affect the lifespan of the transmission? More wear?

 

More wheel torque, same engine torque, same engine horsepower, lower RPM limit for each gear.

On the freeway, a little. Ditto for the engine. But most any mod will be that way to some extent. Actually, it's probably easier on the transmission when you're taking off from a dead stop, and aggressive launches won't take quite the gazillion-RPM clutch bomb they do now.

 

Because everyone drops from 4k anyways


it won't make a difference.

I do it every stop light

All kidding aside, starting from first gear won't need much gas if any.

 

That is definitely true - response in the low rpms have noticeably improved in all gears, even in 6th.

 

There is surprisingly hardly any change in sound/noise, especially inside the car.

 

Theres all this talk but has anyone actually had it done to their 8 yet?

 

It would be REALLY REALLY hard to void the warranty on the tranny from changing the final drive. That would be like trying to void someone's warrenty because they always drive 10mph over the speed limit.

I'm guessing that the most they could void would be LSD and Halfshafts. Anything other than that would be one heck of a stretch.

 

If I get into the diff one day, I'm going to change the LSD while I'm there. Any thoughts on this??

 

Definitly will NOT add any HP. Why do you think that the measured whp does not change (ignoring losses) with the different gears you dyno in?

 

No horsepower gained from the engine, the power is gained by the mechanical advantage in the rear differential as the torque and hp is multiplied. There will be more torque and horsepower available to the drive axles and tires.

 

Fab8 has done it

 

More research on the final drive. There are 3 different R&P gearsets available from Mazda with a 7" ring gear.

1) Short Pinion: S2000, Kia, 1st gen RX-7, pickup 4x4 M/T 87-88, Miata

2) Long Pinion: 2nd gen RX-7,

3) Turbo Pinion (8" ring, but smaller than Long Pinion, Medium Pinion???): 2nd gen TurboII RX-7, Twin Turbo RX-7 3rd gen

 

More pieces to the puzzle:

 

Last but not least, a possible 4.875 fitment:

Hmmmm, this makes me think about that extra part in the FEED 4.777 R&P set pic, the ring 10-bolt spacer. Will call MazdaMotorSport to verify.



AND even more compelling from the Miata Drivetrain Interchange Guide,

differential shaft diameters and splines:
7" small axle = 25mm x 24 spline (808, RX-3, 79-83 RX-7)
7" large axle = 27mm x 26 spline
7" S2000 = 29mm x 28 spline
7.5" small axle = 27mm x 26 spline '84-03 B2000/B2200 & early 95-97 Sportage
7.5" large axle = 29mm x 28 spline ('98-05 Sportage)
8" = 31mm x 30 spline. TT/TII/929

 

Nice work Detective Slick8

 

LOL... okay, I spoke with MazdaMotorSport and they said the short pinion can be installed in a long pinion pumpkin by doubling up the spacers. Seems easy enough.

The rep said that they only have one upgrade for the RX-8, the 5.125 for $1,116.00.

I hope this works out, I put some time into this, been a real fun waste of time.

 

Now here is a question, of all the diameters and splines which one does the 8 have in it stock? I may have overooked it in the thread. Thanks.

 

Nobody knows

 

Thanks for all this info Slick 8. I think there is already a spacer between the Ring Gear and Gear case or at least that what it looks like I've been staring at the pics in Need for Speeds thread. Also from looking at it, it appears that that is the standard diff and not the LSD. So maybe that spacer is just used if you dont have the LSD?
See the 2nd Pic.
https://www.rx8club.com/showpost.php...54&postcount=1

 

Good eyes, thanks QBallz.

 

My Kia 4.778 is coming in next week 12/12. I was thinking of ordering the FEED 4.778 also to do a comparison. If this doesn't work out, I'll sell the 4.778 to an S2000 guy at cost after I cryo treat the R&P.