What is positraction?. Does the RX8 has it?
Thanks

 

Positraction is the trade name GM uses for it's limited slip differentials. They allow the drive shaft to turn both rear wheels together, rather than one wheel spinning and wasting power.

Yes, the '8 has an LSD, a fancy hi-tech 'torque sensing' one.
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doc

 

Than you Doc

 

Anyone know the exact ratio between the transmission and the diffrential to the wheels on the rx8?

My initial maths suggests around 4.5589 : 1

/twospoons

 

4.444:1

you can find it on the mazda web page, look for the rx-8 specs

 

Just realized the RX-8 has 4.44's in it, (my S2000 has 4.31's I believe), and everyone that's upgraded the S2K to 4.57's (too close to what the rx-8 has already) or 4.77 has been THRILLED with the results.

Since few people actualyl need to go 140+ mph.. it makes good sense, and its "cheap" to change the final gear ratio (at least for the S2K its about $500 for the gear and parts + your cost to install, or DYI).

Is there any talk of changing the final pinion gear? Cheap way to get some amazing performance.

-- Aaron

 

Always been a good option for RX-7's. I'm sure final drive gears will be made available in the near future.

 

It's also in the owners manual, along with the gear ratios for each gear.

I think there's a PDF version of the manual posted somewhere on the forum here if you don't have one.

 

I like the idea, but the 8 would need a taller 6th gear imop. Well, I would'nt mind a taller 6th with the stock gearing either though....but I have ran .488s on the street before in anouther one of my rotary cars, and loved it. CJ

 

.488 also depends on the gearing for how it feels.

I did a topic a while ago about increasing the rear diff ratio. I hope someone comes out with a ring and pinion for the rear diff sometime soon!!

Also, it's not a simple install. It looks very easy on paper, but you must check tolerances before final assembly, and make sure those tolerances are there after final torquing of the boltls.

 

...you could just use much smaller rear wheels

 

smaller tires also leads to less inertia (mass closer to the center of the wheel) which should yield better results.

/twospoons

 

I was wondering if anyone had some problem downshifting to 1st gear on lower speeds. Im having difficulty downshifting to 1st at about 8-11 mph. The shifter wont let me in until I drop a little more speed unless I force it. I just had my fly wheel changed since it had some defects on it, but I'm still having the problem anyone know? Could this be the gearbox or something else?

 

Stop doing that! It's normal for any (and every) car to have significant resistance trying to downshift from 2nd to 1st like that - because of the wide difference in the gear ratios from 1st to 2nd, when you do that downshift you are forcing the synchronisers to do a huge amount of work. So? Well, that's a great way to wear out your gearbox syncros very early (known as driver abuse). If you really need to get into 1st gear at 10 mph, learn to double-clutch. Otherwise, leave it in 2nd, or slow down as you noted.

Regards,
Gordon

 

Double clutching is the answer. 10 mph is about 3000 rpms in 1st gear. While in neutral, spin the engine up to about 3500 rpms and try putting it into 1st gear.

I use the same technique for all downshifts... Makes your 6th to 3rd downshift less punishing.

 

Hmm I understand now, thank you for the reply. I was just wodnering coz I never had this issue with the VTEC civic I had. I guess to each its own. But I appreciate the info on this been wondering about this for the past 2 months but I never forced the downshift I always waited for the reduction in speed. And yes double clutching does help get it in but I ll just rather not abuse the clutch.

 

Double-clutching does absolutely NO abuse to the clutch - far, far less than forcing the gearbox into the lower gear and letting the clutch speed up the engine (engine braking) when you let the clutch out.

Are you double-clutching correctly? Here's how it should be done:

- Cruising in 2nd gear, 10 mph, revs are approx 2000rpm (just guessing, for the purposes of illustrating the point)
- push in clutch, shift from 2nd to neutral
- release clutch with gearbox in neutral, blip the throttle to rev to 3000 rpm
- push in clutch, shift from neutral to 1st, release clutch.

If you do it quickly, then the throttle blip in neutral (with the clutch released) brings the gearbox input shaft up to the speed it needs in 1st gear, 1st gear engages without requiring much load on the synchronisers, and there will be no slip on the clutch when you release it the second time since the gearbox input shaft speed already matches the engine speed (3000 rpm for this example). No clutch abuse at all.

Regards,
Gordon

 

hey thats exactly how i clutch but a little slower between the 2 clutch depressions

 

im just curious, i dont see why go through all that when you can just leave it in neutral until coming to a complete stop then throwing it into first or rolling stop and start from 2nd. i know it is not very difficult to double clutch but I just wanted to know what you guys thought.

 

Under 14 mph in 2nd gear is below 2k rpms. IMO lugging the engine at that low speed is not good for the engine. Also with no power, it's hard to squirt through traffic or get the car rotated through a hair pin curve.

I'm guessing bia619 is coming from a big displacement engine or a truck background... I was surprised that in big trucks, first gear is used only during launch going up hill.