I have posted this in the Race Car Tech forum as well... just hoping for more responses from those who may browse only either:

I've got an '85 GSL-SE that I am slowly molding into a track car (track = the kind that involve turns lol). In the meantime however, it is still being used as a daily driver.

I was looking through the available list of gearsets available from Mazdatrix, and saw that between the 4.44, 4.875, and 5.12, the 4.875 were cheaper. How would the 4.875 set work on my car? I do mostly city driving, but some freeway driving. However, I like to obey the speed limit nowadays (speeding tickets + youth = high insurance). I'll usually cruise on the freeway at around 70mph, which equates to about 3000rpm.

As for power, my car is currently running the stock ports with the aux ports wired open. I have a header, and a collector into a 2.25" single exhaust all the way back, so I'm not making too much power.

I am, however building an engine to go along with an IDA throttle setup, and hoping to make over 200rwhp.

How would the 4.875 gearset compare with the different amount of power I have now vs. in the near future?

As for the tracks I will be getting to: most of the ones in Southern California. The fastest one we have down here is WSIR. I was there last year in my dad's '95 M3 and was getting up to ~125mph on the back straights. However, the car is a full ~3200lbs, has shitty tires and doesn't have much power (only mods are intake, chip, and cat-back). If I was able to exit turn 6 & 7 faster, I'm sure I could have squeezed another 5+mph down that straight.

I know it's hard to say, but might I be able to reach those speeds with the 4.875 gears on my current car at the stock 7000rpm redline?

Thanks in advance for your time

*edit: BTW, I will be running either 50 or 60 series tires on a 14" wheel.

 

With n/a motors the shorter the better as far as I'm concerned.

 

I love my 4.778's.

Find a Kia Sportage ('98-02?) and get the front pumpkin.

It isn't limited slip, BUT the pinion flange is the same as '83-85 RX-7 so you don't have to mess with that, just pop the ring gear on your LSD and set backlash to what it was originally (and get side bearing preload right but this is easy with this type of diff).

Only downside is, if you have a driveline vibration now, you will make it much worse. My car used to get shaky over 65, now it's shaky at about 45, so it's not really driveable yet except for around-town.

 

Thanks, but I think it's much harder to find a Kia Sportage here in SoCal than to just go to Mazdatrix to buy a set of gears. I'm also not very confident in my ability to set everything in the rear end up to specs, so I will probably have Mazdatrix do it for me as well.

BTW, I got many awesome responses in my clone thread in the "Race Car Tech" forum, so if anyone else was wondering the answers, you could check out that thread as well.

 

Save some dough, autocross the 7 and get a membership with mazdamotorsports.com Get the gears, new diff clutch plates which are prolly worn out on your car already, and any other part @ cost. 4.875 is a great gearset, motor revvs up mad quick. Gets it into the powrband *now*. But expect MPG to go down.

My REPU has factory 4.675 and 245/50/15 on the rears, 4200rpms on the freeway in 5th. It's all compromise.

Many more tire and wheel options w/15" rims.

 

if you really wanted to save on gas you can always switch to a miata geabox yet still have closer gear ratios. either that or swap your 5th gear cog to a miata one.