6 speed and 3.63 diff ratio

tiggsh · Postby **tiggsh** » Thu Oct 10, 2013 5:24 pm

From the numbers, it looks like a 6 speed is quite similar to a 5 speed + 4.3 setup with the extra sixth gear for cruising.

A lot of miataturbo guys highly recommend the setup but they are also running boosted cars with a decent amount of power.

How is the acceleration of the 6 speed + 3.63 compared to a 5 speed with 4.3 or 4.1? On a stock engine power levels?

zoomzoom · Postby **zoomzoom** » Thu Oct 10, 2013 10:55 pm

I highly recommend NOT doing this if you have any performance in mind. I loved the 6 speed with the 4.3 but have recently changed to a 4.1 to target a couple of corners in particular at lakeside. The 4.3 drove out of the corners great and still from memory only sat at about 3400rpm at 100kph which is still livable on the highway, or if you regularly highway drive and this bothers you then a 4.1 will drop that by about 5% or a couple hundred rpm.

Don't believe everything (or most things) you see on the american forums, they don't always get it right...

Cheers,

Tim

tiggsh · Postby **tiggsh** » Fri Oct 11, 2013 1:38 pm

Highway cruising rpm doesn't bother me much as long as it is crazy high, ie above 4K

So why is that the Miataturbo boys highly recommending the 6 speed + 3.63 FGR? I assume at high HP levels it's good but not at stock power levels?

Still trying to understand gearing ratios but if the two setups are similar in numbers, how wouldn't that make it the same in drivability? Is it the power an engine makes that determines whether I'm going gonna be flat stick shifting all the time and not going anywhere and vice versa?

plohl · Postby **plohl** » Fri Oct 11, 2013 2:06 pm

this might help... Seems that 1st and 2nd are pretty much the same, and it is a bit shorter up until 6th...

5sp 4.3 vs 6sp 3.63 by plohl, on Flickr

calculated using 225/45R15 tyres

Postby **NitroDann** » Fri Oct 11, 2013 2:18 pm

The MT guys only suggest going to a 6 speed for strength, they care not for 'feel' just for performance.

Once you are at the levels of power and torque where you need a 6 speed, the 3.6 is mathematically the quickest.

Dann

zoomzoom · Postby **zoomzoom** » Fri Oct 11, 2013 9:48 pm

The benefit of the 6 speed apart from the extra strength is the better geometric progression allowing you to better keep the car in the narrow power band about peak power.

NitroDann wrote:
Once you are at the levels of power and torque where you need a 6 speed, the 3.6 is mathematically the quickest.

Maybe with an electric motor.

Postby **NitroDann** » Fri Oct 11, 2013 10:07 pm

You mean because of the flat power band?

Well developed turbo cars do have a flat power band.

Dann

zoomzoom · Postby **zoomzoom** » Fri Oct 11, 2013 10:24 pm

Righto.

Steampunk · Postby **Steampunk** » Sat Oct 12, 2013 4:05 am

tiggsh wrote:Highway cruising rpm doesn't bother me much as long as it is crazy high, ie above 4K

So why is that the Miataturbo boys highly recommending the 6 speed + 3.63 FGR? I assume at high HP levels it's good but not at stock power levels?

Still trying to understand gearing ratios but if the two setups are similar in numbers, how wouldn't that make it the same in drivability? Is it the power an engine makes that determines whether I'm going gonna be flat stick shifting all the time and not going anywhere and vice versa?

two things: firstly,torque. Gearbox/transmission and diffs are torque multipliers. The more powerful the engine is in terms of torque, the less it is dependent on gearing for punch. Secondly, Americans really value comfort and ease of highway cruising, so they recommend lower ratios. As mentioned, the combo you are looking at is rubbish for stock NA power. As zoomzoom alluded to, yankees are a different breed so dont buy/use something just because the "cool" guys are doing it.