Rear axle ratio modification!
 

I've got an 05 rx8 and I'm thinkin about changing the rear axle ratio to give myself some more torque in the lower RPMs of my lower gears. I mainly use my car for city driving so this change might do well with MPG too!

I'm pretty sure the rear axle ratio in the stock 05 RX8 is 411 (but im not completely sure on that). So my question is - What should i change it to? 510? If i do change it to 510 - What will be the difference in my RPMs?

Maybe this is a stupid idea? I have heard people say countless times that Mazda already tuned the RX8 to perfection and that it shouldn't be changed. Please let me know what you guys think about this.

There's no maybe about it.

And why do you say that?

your rpm will be higher, you may have a bit more torque at same gear than old rear end, but your 2nd gear red line speed is gonna suffer. 0-60 might be slower cuz you might need 3rd gear to get to that.

at 510 where do you think my 2nd gear will red line at? Somewhere between 50-55 mph?

a 5.12 gear set installed will cost you about $2200 installed, plus you'll be filling your gas tank twice as often

Where did you find that number? Also if i am only driving in the city then my mpg would be better therefore I wouldn't have to fill up as much.

Your talent is clearly wasted here .....



.

Talk to RX8thunder
He changed from stock 4.44 to 4.77

How do you figure that? Your cruising down the street at 45mph and taching around 4k in 4th, how is that better for MPG? Are you really going to use 6th gear for city driving? I dont see any benefit from going any higher than stock. I dont see any torque gain because essentially all your doing is taking away some of the load from the engine, making it not work as hard. How do you "gain" torque by adding a higher gear?

Thanks darkbrew - Thats the most helpful thing i have yet to hear so far.

Does he work at mazdatrix? if so iv'e already talked to him about it

And teamrx8 please understand that my knowledge on this topic is very limited - If theres something that i don't know - then tell me. Don't sit around and post useless information like you have been.

PhantomRX-8 you bring up a good point. Obviously that is a strong hold back from getting a mod like this. And you are right about there being no ACTUAL torque gain too, however there would be a good amount of "get up and go".

Seems like this would be something to do if I wanted to invest into a supercharger.

Welcome

No he's just a rotary crazed friend.... ;)

For a race car it is a distinct advantage to have your final drive ratio matched to the highest speed you are ever going to see - at that particular track . This keeps the ratios close meaning you can stay in a slightly higher rev range .
For the street i don't really see much advantage in changing what you have already . You want your cruise gear to put you in a rev range that is suitable for the torque available . Anythiong below 2500rpm is just lugging your engine and above 3500 is wasting gas .

I like this question. Maybe some auto x guys would be more help. I drive on the highway every day but still, interesting.

Every car I know of has worse gas mileage in city driving than highway, including the RX-8. This mod will lower it further. Plus it doesn't make any sense for that use.

You and your bank account are going nowhere fast, literally.

So it seems the purpose of changing the rear axle rotation is for a specific track; guess its a bad idea for a street car like what TeamRX8 said in the 1st place. Thanks for the feedback Brettus. It was exactly what I was looking for.

Now I need to find something else to put on my car ... Any suggestions?

I agree with you that this mod won't save gas, but wont it give him a lot more low end? Not torque, just revs. I'm thinking of my GT3 Playstation days but isn't that why people do this mod?? Like Mustangs that only go 1/4 mile. They don't need to go over 150 (or whatever) because their race is over in 11 seconds... So if you're driving in the city and you can rev up twice as fast, isn't that a huge advantage? Like rally cars....

If you still want instant power (and torque) get a penny bank and save for the Pettit sc ($6,000 give or take (...give)). But if that's too much I would suggest SUSPENSION! Out of all mods for any car imo suspension is the best as far as bang for the buck. Nothing beats that first drive after some tweaking.... Then make sure your 8 is running good (ignition, pre-mix, starter, spark plugs.....).

Think I am going to go with a rear strut bar.

You are going from changing the rear end gear ratio to a strut bar? You wont even notice a change in the car with a rear strut bar change.

I have thought about a gear ratio change, but I would go the other way. I installed a supercharger I could afford the higher gear ratio and for the track I could use a little more gear on some straight and it would be nice to save a shift. However, because of the price of such a mod, I will just leave it alone and maybe, just maybe I will install a larger diameter tire instead.

To the OP, if you want a little more get up and go, just get a smaller tire the next time you buy tires. On the plus side you might save some money on the tire purchase. Try something like a 225/40/18 or a 245/35/18. It wont make a huge difference but it will be something.

I believe he is modding for the sake of modding lol

nothing wrong with modding for the sake of modding. Just bloody tiring reading thread after thread of "hey guys, i read on a bathroom wall somewhere that this is awesome, what do you think?"

We're a nation of instant gratification seekers, no one wants to put in any leg work on research anymore. By "no one" i mean people who start threads like this.

Thats crazy! I DID find it on a bathroom wall!!! :O

Anyways - I'm slowly loosing hope with this car ... seems there is nothing I can do to it other than buy pointless bolt-ons.

But don't get me wrong; I wouldn't trade this car for the world.

Any other ideas?

take it, as is, to a track event in your area. something tells me you will regain all the hope you had when you bought it

The rx8 is a great track car, made for the twisties. So focus on its strengths.

Lower the car with a nice set of coilovers KW Variant 3 is a great coilover and can be had for around $1700, if you want a more basic lower spring/strut the tokico d-specs are nice $700 range.)

Sway bars. An adjustable set like the progress techs will improve cornering g's and wont brake the bank.

Reduce unspung weight and improve the brakes with racing brake 2-piece rotors. $1000 range. I will be posting a used set up for sale soon with SS brake lines. $700 for all corners.

Lightweight wheels and a good set of tires. Improves handling, braking and acceleration (a little)

3" exhaust with a davesport 100 CPI cat, you will feel an improvement in power and acceleration with this one. 10-15 WHP.

AEM intake. BHR ignition and if you can get an AP and tune the car. This will add maybe 5-10 HP, will improve throttle response, driveability and MPG.

All these mods will make owning an RX8 much more fun and if you decide to add a turbo or supercharger latter, they can be used. Lots of reading to do but you have to pick a goal and then mod the car to meet that goal.