ND Overdrive (additional, not final drive change)

Conza · Postby **Conza** » Thu Dec 22, 2016 10:29 pm

So how can you get overdrive without just changing the final drive size?

I was sort of thinking, replace 6th to 5th gear and then have a larger gear where 6 is. I just want 1 overdrive gear, what's the engine RPM at 110kph in 6th? 2.5k would probably be ok, but I'm thinking it'll be 3/3.5k (rpm)?

smy0003 · Postby **smy0003** » Thu Dec 22, 2016 10:44 pm

It's all relative, yes there's no box over drive but the final drive is extremely long at 2.8:1 which puts 100kph in sixth around 2600RPM if I've done that right. That's very tame for an MX5.

Conza · Postby **Conza** » Thu Dec 22, 2016 11:24 pm

Alright, well I guess it's less than 3 grand at 110kph. Anything faster an I guess I'll be on a track, so seems like I can give up on this one.

pcmx5 · Postby **pcmx5** » Mon Jan 02, 2017 2:02 pm

Conza wrote:Alright, well I guess it's less than 3 grand at 110kph. Anything faster an I guess I'll be on a track, so seems like I can give up on this one.

An indicated 100 klph is a smiggen over 2500rpm so certainly no need for a longer 6th!Yanks keep on about the short gearing of the ND and they have the same as us ,2.8 diff 6 speed 1 to1.
Even more amazing that they would think that when they had a 4.1 in manual NC's where we had a 3.7!!

Peter.

Conza · Postby **Conza** » Mon Jan 02, 2017 2:37 pm

I think its more important to keep in mind the total ratio of gear and differential, which Mazda would've taken into account with this car. Considering that, an overdrive gear, on this differential anyway is pointless.

Yes 1:1 6th gear sounds like the gears are short, and they are, but 1:1 on a 2.866 diff, is just that, 2.866 (tallest gear ever in an MX-5 from the factory?).

Found a great google doc on this on reddit using data from http://flyinmiata.com/tech/gearing.php

https://docs.google.com/spreadsheets/d/ ... edit#gid=0

I'll do some substitutions for AU cars if I can find the data. Wheel torque for lower gears and engine rpm at highway speeds are really all that matters (to me).

93_Clubman · Postby **93_Clubman** » Mon Jan 02, 2017 4:15 pm

Conza wrote:AU cars if I can find the data.

https://www.miata.net/garage/KnowYourCar/S8_Gears.html
Note, ADM 10AE diff ratio was 3.6 as opposed to 3.9 quoted in above link.

sailaholic · Postby **sailaholic** » Tue Jan 03, 2017 10:31 am

We plotted the gear ratio of the ND vs the NA when the numbers first came out. It's almost a perfect match for gears 1-5 with 6 as an "overdrive". This is unlike the NB6 speed which brought the gears closer together and actually had a shorter ratio in 6th than the 5 speeds 5th.

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Postby **beavis** » Tue Jan 03, 2017 12:11 pm

93_Clubman wrote:
Conza wrote:AU cars if I can find the data.

https://www.miata.net/garage/KnowYourCar/S8_Gears.html
Note, ADM 10AE diff ratio was 3.6 as opposed to 3.9 quoted in above link.

No I'm pretty sure the 10AE were 3.9

pcmx5 · Postby **pcmx5** » Tue Jan 03, 2017 1:02 pm

sailaholic wrote:We plotted the gear ratio of the ND vs the NA when the numbers first came out. It's almost a perfect match for gears 1-5 with 6 as an "overdrive". This is unlike the NB6 speed which brought the gears closer together and actually had a shorter ratio in 6th than the 5 speeds 5th.

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The NA6 was a 4.3 diff and the NA8 was 4.1 so although the gear ratios may have been the same the overall gearing is different with the ND doing 90 klph in 2nd and 130 in third!

Peter.

sailaholic · Postby **sailaholic** » Tue Jan 03, 2017 3:00 pm

Incorrect Peter!

The ratios and diff and tire diameter are all different but, if you plot road speed vs engine rpm for each gear, gears 1-5 are nearly identical road speed for the NA and the ND. The ND 6th gear is then above the 5th as an "overdrive".

For memory this was worked out against a 4.3 diff (as per the JDM cars) as that is what Plohl and I run in our NA8s.

And yes my na8 does 130 in 3rd.

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pcmx5 · Postby **pcmx5** » Tue Jan 03, 2017 3:07 pm

Ok . Sorry I stand corrected,memory must be going but I didn't think I got near my ND figures in either of my NA's in 2nd or 3rd,but it is a about 10 years ago since I had either in standard form having done the 6 speed 3.9 conversion to NA8A in about 2006.

Peter.

Conza · Postby **Conza** » Tue Jan 03, 2017 3:09 pm

sailaholic wrote:We plotted the gear ratio of the ND vs the NA when the numbers first came out. It's almost a perfect match for gears 1-5 with 6 as an "overdrive". This is unlike the NB6 speed which brought the gears closer together and actually had a shorter ratio in 6th than the 5 speeds 5th.

Yeah how great is that! The more you know huh, I'm actually really happy with the 1:1 on a 2.8 final drive, sub 3k at 110kph is perfectly fine.

93_Clubman wrote:
Conza wrote:AU cars if I can find the data.

https://www.miata.net/garage/KnowYourCar/S8_Gears.html
Note, ADM 10AE diff ratio was 3.6 as opposed to 3.9 quoted in above link.

sailaholic wrote:Incorrect Peter!

The ratios and diff and tire diameter are all different but, if you plot road speed vs engine rpm for each gear, gears 1-5 are nearly identical road speed for the NA and the ND. The ND 6th gear is then above the 5th as an "overdrive".

For memory this was worked out against a 4.3 diff as that is what Plohl and I run in our NA8s.

Hey guys, didn't mean to start an argument, apologies for that, perhaps we can all use references when quoting information? clubman has a reference to miata.net, sailaholic, have you found another reference which conflicts perhaps?

EDIT: Never mind, saw Peter has agreed with sailaholic now, doesn't matter.

sailaholic · Postby **sailaholic** » Tue Jan 03, 2017 3:09 pm

Maybe your foot has got heavier with age Peter?

My info is just the standard car data for na8 and ND , don't see the point in referencing it.

I'm not touching the 10AE discussion, seen that go back and forward WAY too many times.

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