Chriz88DX

iTrader: (1)

Sup guys,

I am looking to purchase a new gear set for my car, to help support my bridge port engine running NA drivetrain, EFI, ITBS, and 18 inch wheels. I'am having a hard time finding options (due to the long pinon gear of the fc housing).

Does any one know of any other higher gear alternative of than the mazdatrix's gears which for the 5.12 I want are close to 1200?

thanks in advance,

Tanj!

iTrader: (5)

The 5.12 is the highest gearing available. It's a custom created pinion made by grafting the 5.12 pinion from a FB onto the long pinion shaft of the FC. There are a few shops who still do the service. $1200 is in the ballpark of what a used 5.12 R&P is worth. New they run in the 2.4k to 2.6k range. The highest OE gearing available for the FC is a 4.30 from the GTUs.

eage8

iTrader: (9)

The mazda part number for the FB 5.12 is 1480-27-110

you can buy one and have it modified locally... it might be cheaper.

Chriz88DX

iTrader: (1)

thanks for the quick responses, if 1200 is about right then I will go for it. Lately I have tired to locate a 4.30 out of a gtu but I have not had any luck. This gear is the last component i need for my na build. The car right now is a blast but the stock gearing is too long.

j9fd3s

iTrader: (3)

you could run shorter wheels and tires too...

eage8

iTrader: (9)

+1

you can run some nice 225/45/15s

better gearing + an inch of lowering with zero suspension geometry consequences.

replacing the stock 25" tires with 23" tires (miata, civic, corolla size) is the equivalent of replacing the stock 4.1 with a 4.46, a 4.3 becomes the equivalent to a 4.67

RotaryResurrection

iTrader: (8)

It would be far cheaper, and better in the long run, to use a turbo II drivetrain, and get an rx8 4.44 or 4.77 stock gearset for the LSD turbo II diff. It is a direct install and you could do this for $750 or so, and have a far stronger setup than your old NA drivetrain.

eage8

iTrader: (9)

RX8s use the same diameter gears as T2s, but the pinion is short like the FD's so you'd still have to lengthen the pinion and be in the same boat...

Chriz88DX

iTrader: (1)

true sir the long pinion ruins all hope I will just have to pay for the 5.12 gears from mazdatrix


smaller tires and wheels is not my first choice got to look good while going fast lol

I have always kept my overall circumference the same as stock with any wheel and tire combo I have run.


Iam currently looking to run 17x10 in the front and 18x11 in the rear

eage8

iTrader: (9)

It's very hard to find 25" tires for 17s... you're better off running 18s in the front.

most large 17s (anything above 255s) are 25.7" tires

Chriz88DX

iTrader: (1)

well thanks to this handy calculator I will be going with the 4.87 final drive gear. I can see why this is simulator to the mazda speed gear set it is a good multi purpose gear.

Whizbang

yea, screwing making things. Mazdatrix sells it.

note: that was news to me as learned about it about a month ago. I recall them having no non-oem options not that long ago. Would be great for my rally car. muahahahah

RotaryResurrection

iTrader: (8)

I think you could still get it done for a lot less than $1200-2500 that people are talking about here...

Chriz88DX

iTrader: (1)

oh almost forgot to include the gearing calculator I use.


MFactory™ Competition Products - Performance Driveline Components

Chriz88DX

iTrader: (1)

From alot of my research it seems that the oem gears in the fc where not setup for any kind of performance. It does a great job at keeping rpms low for highway cruising i guess lol. Out of all of my simulations i have run (mostly on forza 4 which is pretty close to real life). Have proven serious gains in the all around performance of the car. Also just about every ITS race car uses some kind of higher gear than stock.

Whizbang

well that is normal for any naturally aspirated car. Gearing is the key to power. Say you have 170hp, what good does a 4.10 do you? will you ever reach 150? unlikely. might as well get to 120 sooner.

RotaryEvolution

iTrader: (30)

i would probably run the RX8 6 speed instead of all the rest of this bs.

Whizbang

while it has improved (but not really good) gear ratios, the final drive has a much different effect in torque multifplication.

consider that the gearset is to modify when your shifting for peak power. The final drive however, changes the overall effect, regardless of the transmission's rations.

eage8

iTrader: (9)

the entire point of the 5.12 ratio is to get rid of the horrible 2nd -> 3rd shift in which the rpms drop way too much and you fall out of the power band.

You're probably much better off just swapping out the gear set or swapping in a 6 speed, you'll end up with a more usable car.

I think they use 5.12s in IT racing because they're not allowed to touch the trans (but I could be wrong)

Gravity Fed: if the transmissions ratios are bad, changing the final drive is just a band-aid for the actual problem...

Chriz88DX

iTrader: (1)

Transmission

going by the mazdatrix gearing page the rx8 gears are not much different. the miata gear box "swap" isn't much different either the end result in both of these swaps would be mild if even noticeable. most rx8 guys still you the "kia sportage" 4.77 final drive.

And for anyone brave enough to really top out FC on the street more props to you. The stock gearing I think tops out past 170mhp . so being limited to around 150 is ok with me lol

jjwalker

I got to about 145 at redline in 4th gear. 5th gear was too high and dropped to 140.

How this was possible and safe, before i get flamed...

There is a 2.5 mile span of bridge that crosses our local lake. The lake is owned by the city of Dallas, thus the bridge is technically IN the city of Dallas. Dallas is 20 miles to my east, so there is no police patrols of the bridge. Local police weill sit on either side of the bridge to catch people speeding as they come off the bridge into their jurisdiction, but not on the bridge itself. This was also done at 2am when there was no traffic on the bridge at all.

I did it once to find what the actual top speed of my car was, and I wouldn't ever do it again.

eage8

iTrader: (9)

your gearing:
3.475 2.002 1.366 1.00 .756

your virtual gearing with a 4.87
4.13 2.378 1.623 1.188 .898

RX-8 gears:
3.76 2.269 1.645 1.187 1.00 .843



looks pretty good to me.....

Whizbang

your mistaking the ability to bandaid a car, with actually building a proper transmission and final drive combination.

case in point, the mazda competition gearbox was coupled with 4.88 final drive. the competition box has a proper looonnnggg first gear, followed by well measured small drops between shifts through 5th.

mazda comp
1st: 2.350
2nd: 1.608
3rd: 1.240
4th: 1.00
5th: 0.881 or 0.839

79-83 12a
1st: 3.674
2nd: 2.217
3rd: 1.432
4th: 1.00
5th: 0.825

87-88 turbo ii
1st: 3.458
2nd: 2.015
3rd: 1.391
4th: 1.00
5th: 0.762 (0.806 Japan)

Renesis
1st: 3.815
2nd: 2.260
3rd: 1.536
4th: 1.177
5th: 1.00
6th: 0.787

miata
1st: 3.136
2nd: 1.888
3rd: 1.330
4th: 1.00
5th: 0.814

the downside is, all the oem boxes we can readily get these days basically suck. The "best option" would actually be a kennedy T5 adapter then a proper motorsport gearset for the T5 (since they are cheap). Other options would be OS giken if they are still making things, or maybe Pfitzner.

the miata box is about the best due to a longer first but is still nothing like the comp box. the shift into second isnt bad. The rx8 essentially has a typical, streetability useless for racing first gear.

the final drive is more or less relative to the speed of the track your driving on, with consideration given to the torque produced by the engine. choosing a gearset that gives the best rpm drop between shifts keeps you in the power band. adjusting the final drive essentially adjusts overall acceleration and speed in gears.

the factory Rx-8 final drive was bumped up after 09 to about a 4.77 as i recall, which is not the same thing as a kia sporage gearing swap. I am unaware in the ring and pinion works in the 8.

eage8

iTrader: (9)

it doesn't matter if the RX-8 has a useless first gear if it's 2nd gear (and the rest of the gears) are about the same as the mazda comp set's 1st gear...

Whizbang

your correct that the 2-3, 3-4, 4-5 shifts of the Rx-8 box are damn close to the mazda comp box for 1-2, 2-3, 3-4.

[2813 vs. 2876, 2061 vs. 2084, 1725 vs. 1375, 1050 vs. 1898, respectively]

So for the prices, its a nice gig, but you still have a worthless first (hard to start from stop, or real low speed in 2nd), the 4 to 5 shift on the 8 is actually a little TOO short and your losing some powerband use, and the overdrive drop is almost twice of the comp, which makes sense because commuting on the freeway isnt the same as hauling *** on a raceway.

but obviously the 8 box ISNT a comp box, its a decent attempt by Mazda to make a compromise street transmission.

but that isnt the point of the this thread. The final drive, pure and simple, changes your acceleration at the cost of top speed (and and increase in rpm while cruising at a given speed).