6th gear change 2005 MazdaSpeed?

How practical would it be for someone who knows transmissions to
change 6th gear in my 2005 MX-5 to be more of a highway overdrive
gear, say 2500 rpm at 60mph rather than stock 3000 rpm. Seems such a
waste of rpms to be cruising along at 3000 rpm when my 2001 Eldorado
can do it at 1500 rpm and get 30mpg in the process. Thanks

In article
>,
bowman > wrote:

> How practical would it be for someone who knows transmissions to
> change 6th gear in my 2005 MX-5 to be more of a highway overdrive
> gear, say 2500 rpm at 60mph rather than stock 3000 rpm.

I don't think a taller sixth gear is available. You could swap the
differential gearset for the 3.636:1 from an Australian 6-speed MX-5
(part #MA02) if you can find one.

But search the miata.net forum for definitive answers.

--
Lanny Chambers
St. Louis, MO
'94C

It was possible to do this with the 5 speed. (Done that!) Never heard that
parts were available for the 6 speed.
In any event, the ring and pinion change is more effective. The speedometer
calibration can be done by repositioning the needle without changing the
transducer, or the transducer or transducer gear can be changed. 3.6 is a
bit much, due to the low torque at low rpm of the Miata 1.8. 3.9 is a better
match for "normal" use with an unmodified engine, and parts are easier to
obtain. The Miata engine is, by design, a high revving engine. The usual
American car engine develops quite a bit of torque at much lower RPM than
the Miata 1.8, and generally does not get near the ~ 7000 RPM red line of
the Miata engine.


"Lanny Chambers" > wrote in message
...
> In article
> >,
> bowman > wrote:
>
>> How practical would it be for someone who knows transmissions to
>> change 6th gear in my 2005 MX-5 to be more of a highway overdrive
>> gear, say 2500 rpm at 60mph rather than stock 3000 rpm.
>
> I don't think a taller sixth gear is available. You could swap the
> differential gearset for the 3.636:1 from an Australian 6-speed MX-5
> (part #MA02) if you can find one.
>
> But search the miata.net forum for definitive answers.
>
> --
> Lanny Chambers
> St. Louis, MO
> '94C

In article >,
"Chuck" > wrote:

> 3.6 is a
> bit much, due to the low torque at low rpm of the Miata 1.8. 3.9 is a better
> match for "normal" use with an unmodified engine

3.9 is what comes with a 6-speed, so he has one now. Note that he has a
Mazdaspeed Miata; the OEM turbo will probably handle a 3.6 without a
problem.

--
Lanny Chambers
St. Louis, MO
'94C

"Lanny Chambers" > wrote in message
...
> In article >,
> "Chuck" > wrote:
>
>> 3.6 is a
>> bit much, due to the low torque at low rpm of the Miata 1.8. 3.9 is a
>> better
>> match for "normal" use with an unmodified engine
>
> 3.9 is what comes with a 6-speed, so he has one now. Note that he has a
> Mazdaspeed Miata; the OEM turbo will probably handle a 3.6 without a
> problem.
>
> --
> Lanny Chambers
> St. Louis, MO
> '94C

The MSM has a 4.1 final drive- I guess to offset the larger tires. A switch
to the much more common (than 3.6) 3.9 rear ratio will give about a 5%
reduction in rpm vs speed.
The RX-8 might use the same gearbox internals and have a different 6th gear
ratio.

In article >,
"Chas Hurst" > wrote:

> The MSM has a 4.1 final drive-

Ah. I didn't know that. Thanks.

> I guess to offset the larger tires.

More likely, to make them seem actually quick, without dipping too
deeply into the parts bin.

> A switch
> to the much more common (than 3.6) 3.9 rear ratio will give about a 5%
> reduction in rpm vs speed.

That's only a 150 rpm drop at 60. Doesn't seem worth doing.

--
Lanny Chambers
St. Louis, MO
'94C

"Lanny Chambers" > wrote in message
...
> In article >,
> "Chas Hurst" > wrote:
>
>> The MSM has a 4.1 final drive-
>
> Ah. I didn't know that. Thanks.
>
>> I guess to offset the larger tires.
>
> More likely, to make them seem actually quick, without dipping too
> deeply into the parts bin.

The MSM has a turbo, intercooler, 17" wheels, dunno about the brakes. But
I'd say they dipped fairly deep into the parts bin.

>> A switch
>> to the much more common (than 3.6) 3.9 rear ratio will give about a 5%
>> reduction in rpm vs speed.
>
> That's only a 150 rpm drop at 60. Doesn't seem worth doing.

Nope, it don't. Even the taller gear, the 3.63 only drops the rpm about 12%.
The Miata engine doesn't have the power curve to drag the car along at
2500/60 mph.

On Mon, 06 Jul 2009 18:20:36 -0400, Chas Hurst wrote:
> "Lanny Chambers" > wrote in message
> ...
>> In article >, "Chas
>> Hurst" > wrote:
>>
>>> The MSM has a 4.1 final drive-
>>
>> Ah. I didn't know that. Thanks.
>>
>>> I guess to offset the larger tires.
>>
>> More likely, to make them seem actually quick, without dipping too
>> deeply into the parts bin.
>
> The MSM has a turbo, intercooler, 17" wheels, dunno about the brakes.
> But I'd say they dipped fairly deep into the parts bin.
>
>>> A switch to the much more common (than 3.6) 3.9 rear ratio will give
>>> about a 5% reduction in rpm vs speed.
>>
>> That's only a 150 rpm drop at 60. Doesn't seem worth doing.
>
> Nope, it don't. Even the taller gear, the 3.63 only drops the rpm
> about 12%. The Miata engine doesn't have the power curve to drag the
> car along at 2500/60 mph.

The MSM does. I have one.

What I can tell you is that my 99 (turbo,SBB,with 5th gear mod & 4.11 rear)
can be annoying at times, due to the 5th gear change. Seems that around 45
mph, which is a common "speed limit" around here, 5th is a bit too high, and
4th a bit to low. Other than that, the gear change was useful, in that it
helped reduce the noise at normal highway speeds, and may have helped
slightly with fuel consumption during cruise. The tires, while larger than
stock, are within 1% or so of the stock diameter.

One local club member has changed a stock NA to a 3.6 ratio, in order to
save fuel. He was not concerned about other preformance losses. I haven't
heard much about his satisfaction, other than the rear end is/was a bit
noisier than it was before.

"Carbon" > wrote in message
ng.com...
> On Mon, 06 Jul 2009 18:20:36 -0400, Chas Hurst wrote:
>> "Lanny Chambers" > wrote in message
>> ...
>>> In article >, "Chas
>>> Hurst" > wrote:
>>>
>>>> The MSM has a 4.1 final drive-
>>>
>>> Ah. I didn't know that. Thanks.
>>>
>>>> I guess to offset the larger tires.
>>>
>>> More likely, to make them seem actually quick, without dipping too
>>> deeply into the parts bin.
>>
>> The MSM has a turbo, intercooler, 17" wheels, dunno about the brakes.
>> But I'd say they dipped fairly deep into the parts bin.
>>
>>>> A switch to the much more common (than 3.6) 3.9 rear ratio will give
>>>> about a 5% reduction in rpm vs speed.
>>>
>>> That's only a 150 rpm drop at 60. Doesn't seem worth doing.
>>
>> Nope, it don't. Even the taller gear, the 3.63 only drops the rpm
>> about 12%. The Miata engine doesn't have the power curve to drag the
>> car along at 2500/60 mph.
>
> The MSM does. I have one.

Chuck. would love to hear from this club member about his satisfaction and
about what rpm at what speed, he is seeing.

Chris
99BBB

"Chuck" > wrote in message
...
> What I can tell you is that my 99 (turbo,SBB,with 5th gear mod & 4.11
> rear) can be annoying at times, due to the 5th gear change. Seems that
> around 45 mph, which is a common "speed limit" around here, 5th is a bit
> too high, and 4th a bit to low. Other than that, the gear change was
> useful, in that it helped reduce the noise at normal highway speeds, and
> may have helped slightly with fuel consumption during cruise. The tires,
> while larger than stock, are within 1% or so of the stock diameter.
>
> One local club member has changed a stock NA to a 3.6 ratio, in order to
> save fuel. He was not concerned about other preformance losses. I haven't
> heard much about his satisfaction, other than the rear end is/was a bit
> noisier than it was before.
>
> "Carbon" > wrote in message
> ng.com...
>> On Mon, 06 Jul 2009 18:20:36 -0400, Chas Hurst wrote:
>>> "Lanny Chambers" > wrote in message
>>> ...
>>>> In article >, "Chas
>>>> Hurst" > wrote:
>>>>
>>>>> The MSM has a 4.1 final drive-
>>>>
>>>> Ah. I didn't know that. Thanks.
>>>>
>>>>> I guess to offset the larger tires.
>>>>
>>>> More likely, to make them seem actually quick, without dipping too
>>>> deeply into the parts bin.
>>>
>>> The MSM has a turbo, intercooler, 17" wheels, dunno about the brakes.
>>> But I'd say they dipped fairly deep into the parts bin.
>>>
>>>>> A switch to the much more common (than 3.6) 3.9 rear ratio will give
>>>>> about a 5% reduction in rpm vs speed.
>>>>
>>>> That's only a 150 rpm drop at 60. Doesn't seem worth doing.
>>>
>>> Nope, it don't. Even the taller gear, the 3.63 only drops the rpm
>>> about 12%. The Miata engine doesn't have the power curve to drag the
>>> car along at 2500/60 mph.
>>
>> The MSM does. I have one.
>
>