slow_talon

Well I want to know what's the gear ration on the 93-95 rx-7, a friend of mine is selling his rx-8 ring and pinion which are 4.44's and I was wondering if this are an upgrade for my car and if they will fit...Thanks

bewtew

iTrader: (7)

3.90 for auto and 4.10 for manual

slow_talon

Would Rx8 gears fit my 93 rx7??

dial8

iTrader: (4)

Doubt it, but there are handful of JDM companies that sell 4.77, and I believe Racing Beat has a 4.30.

bewtew

iTrader: (7)

some one told me rx8 gears would fit. i was going to try it but it was going to be overkill at 750+ whp. 4.77 sound insane to me and you will get horrible gas milage i would go with 4.30 but they are kinda expensive

arghx

iTrader: (3)

i'm pretty sure it wouldn't fit... Icemark might know, he has an Rx-8

7syawedis

iTrader: (1)

i want to say ive heard of it being done

cosmo105

It can be done as I am in the process of using the 4.44 ratio out of an RX-8 (there are two ratios RX-8's use: 4.44 and 4.30)

jeff p

go with the 4.3 Mazda RZ gears. I love mine, made it a whole new car. very responsive . by far the best mod I did.

Jeff

dial8

iTrader: (4)

I wouldn't say that, but we'll find out. I have a 4.77 thats getting installed once I find someone who can set the proper backlash...

AnthonyNYC

iTrader: (3)

Yes, they would fit.

Monkman33

iTrader: (28)

AnthonyNYC, any more info on your response? I am curious.

Also, would the gears from the RX8 rear end hold up to 425hp? 350 ft/lbs?

Eastwood

Why would you want to change it. Won't it lower your top speed considerably. What would the new top speed be with 4.44.

Also whats the topspeed with 4.10's?

dial8

iTrader: (4)

This argument always gets lost on me, because who really gives a **** what your top speed is and how much you lose? Do you hit the top speed of your car every time you drive? Lower gear ratios make it easier to gain accel without adding tons of power, and I'd like to use what I have between 25mph-115mph, and if I can't push beyond 145 with a 4.30, 4.44, 4.77 then so ******' what?!? I don't understand why this always gets thrown out. Its as if the guy who mentioned changing rear ends gears hasn't thought things through and doesn't know their top speed is going to change, or the RPM the engine will be running on the freeway. Keep your 4.10. As a bonus I'll give you mine as well.

bewtew

iTrader: (7)

^--- +1

Wargasm

The correct rear end ratio depends on what you want the car to do, what the dyno curve looks like, what the gearbox ratios are, and finally - how much can you put down safely?

What will it do?

A) Street Car
B) Road Race
C) Autocross
D) Dragstrip

Dyno?
A) Near-stock
B) mild mods
C) Smaller single (~400 rwhp)
D) Bigger single (~500 rwhp)
E) Warp 10, Engage! (~600 and up)

Gearbox Ratios?
A) Stock
B) Customized

Tires/Drivetrain?
A) Stock
B) Upgraded for street/track with some larger rubber
C) tubbed-out, huge slicks, crazy stuff

You want to look at everything together and then figure out the best pick for you. You probably want to make an excel spreadsheet that figures all this out (I did, it's on my other computer). Inputs are tire size, gearbox ratios, final drive, and the actual dyno torque curve.

Most people on this site use their cars on the street 99.99% of the time, and have the factory twins making sub-350 rwhp (last time I checked anyhow - I don't post much).

For those guys -

In general, since most FDs are from 220-350 rwhp with 225/50/16 or 245/45/16 tires (or similar) and stock gearboxes, the stock 4.1 (manual tranny) is actually just about perfect. You could do a 4.33 for a little bit more pull, but if you're already at around 350 rwhp, my guess is that you don't have traction. If you are closer to stock levels (220-275 rwhp), I think the 4.33 makes more sense because you aren't having as many traction issues. Sure, you sacrifice some top speed, but who needs to go 200+ mph in 5th gear? You sure aren't getting there with "only" 300 rwhp anyhow. Fuel economy? C'mon, this is a sports car - who cares?

For the mid-range HP guys 400-500.. I bet most of them agree that first gear is way too short, second is somewhat too short, and 5th is still too long - even though with 400-500 rwhp, you should be able to hit 200+ mph, who goes that fast? Changing the rear end for these cars can help solve 1st and 2nd by making them a little taller, but now your 5th gear is retardedly long. You dont' want to go too tall on the final drive because even a 500 rwhp 13B engine still makes **** for torque below 4000 rpm - so you need a usable first gear to get started from a stop on the street (see - this doesn't apply for road race track cars as much).

Anyhow, I'm going way off on a long and wandering rant now... so let me just close by saying... you need to evaluate your car as a whole unit and then figure out what to do with it.

For most cars with mild mods, 4.1 is just fine. If you feel the need, a 4.3 or 4.44 (if it fits) could work, but as your power level goes up, I bet you will regret it.

jeff p

look the 4.10 is great for the man trans cars driven on the street up to 500 hp or better. since I have an auto I needed a little more advantage to make the car more exciting. but for most the 4.10 is just fine.

Jeff

Wargasm

Here's a graph I made. It is sort of specific.

It compares power-to-the-ground (I just did dyno torque x gear ratio x final drive - so I guess technically this measures force at the axles) of my RX-7 (with my dyno and my customized 5th gear ratio) vs. some guy's modified Dodge Viper GTS that I found on the web.

BLUE is my single turbo FD - 405 rwhp / 335 rwtq
PINK is the modded Viper - 450 rwhp / 490 rwtq



I don't remember the mods for the Viper, but this info was derived from his dyno sheet + assuming he has the factory gearbox/final drive/tire size. So the speeds should be pretty close.

My final drive is 4.1 (stock) and installed a shorter ratio 5th that is 0.806:1 so I lose some top speed in 5th.

Things to notice...

My car is making MORE power to the ground in first at peak. 15% more force at a lower speed on much more narrow tires. Traction? I have none. This power does not actually make it to the ground. Instead, I have to go half-throttle or so until I get into second where I can use full throttle. First gear is way too short in my car. Or put another way, I need drag slicks or something (I do not drag my car - just saying).

As we follow each car's progress up in the gears, you see that the Viper puts down a little more force than me the whole way, but do not forget, he is about 500 lbs heavier than I am. Overall - this would be a close race.

My modified shorter 5th gear really helps me at 140+ mph compared to the econo-fifth in a stock FD. You can see from the graph that just as my 4th gear is running out (hitting redline) around 145 mph, my shorter 5th is right there to pick up and keep pulling hard to 180 mph redline-limited top speed. I think 180 mph would be sufficient for ANY street car and probably every road course in america (not sure?).

I guess in a hypothetical street race, this Viper would get the last laugh as we were approximately even up to 180 mph (maybe 190 mph if I pass redline) and he kept going to about 200 (or more - keep in mind, he actually has 6 gears although I only graphed 5 here).

I am cool with that.

Brian

cosmo105

I only use my car for drags, autocross, hillclimbs and the occasional drive around town. I am putting down 391 whp and don't plan on making any hp mods for the upcoming race season so I decided to change the rearend ratio to see if it will give me a couple of more tenths (My best is 11.7 using 26.5 ET Streets) at the drag and bring up the rpms in second gear while autoxing. I bought a complete different diff to try this new setup so incase I didn't like it, I'd be able to go right back to my 4.1 ratio.

Top speed doesn't really matter to me. All I care about is not having to shift into 5th at the end of the 1/4.

slow_talon

well i'll be using my car for drag racing/street driven so I think this will be a good idea thanks for the imput guys as alway helping the newbies...

cosmo105

Just got my diff back from the shop. The RX-8 ring and pinion worked fine.