Hi all,
Does anyone know if Mazda made a 6 speed box for the MK1 or do any of the MK2/2.5’s have a 6 speed box that would fit a MK1?
Cheers.
I’m prettty sure that that all MX5 gearboxes, including the 6 speed, are interchangeable
MMMM! six speed in a Mk1 with std diff
That’ll give you
Stump pulling low first gear
Slightly lower top gear
Thanks guys.
Just found out the Mk2’s have an electronic speedo cable unlike the Mk1’s so it can present a problem if you fit one apparently.
Mechanical drive fits in the same place
Before you consider a 6-speed consider the ratios
5 Speed 6 Speed
1st 3.136 3.760
2nd 1.888 2.269
3rd 1.330 1.645
4th 1.000 1.257
5th 0.814 1.000
6th n/a 0.843
With ratios like that it does make you woder why they didn’t take the opprtunity to keep the first 5 the same and use sixth gear more like an overdrive , so reduce the revs for motorway cruising.
Or is the final drive a lot lower ?
Cheers for the info guys, think I’ll stick with the 5 speeder.
Diff ratio on a 6-speed is numerically lower (higher geared)
My car does about 3200rpm in 6th gear at an indicated 70mph.
For less technically minded MX5 owners like myself (I could have said I had a friend who doesn’t understand all this ratio stuff but went for the honesty angle), I probably do more motorway driving than anything else and would if possible like to improve fuel efficiency for these journeys. Would fitting a six speed box and possibly a different ‘diff’ give me what I want. I am not as interested in speed/ performance etc as I am enjoying driving with the top down on nice sunny days so tearing away from the lights etc is not an issue.
Cheers
Paul
Originally the diff on Mk1 1.6 models had a final drive ratio of 4.3:1. When the 1.8 Mk1 was introduced a larger, stronger diff was fitted with a final drive ratio of 4.1:1 initially (I believe it reverted to 4:3:1 later, possibly when the Mk2 was introduced)
Overal gearing in top gear on the Mk1 1.6 with 4.3:1 diff and 5-speed box is 3.50:1 (4.3 x 0.814).
Overall gearing in top gear with a 4.1:1 diff and 6-speed box would be 3.46:1 (4.1 x 0.843).
So a 4:1.1 diff from a 1.8 with a 6-speed box would give you a slightly higher overall gearing in 6th gear. You would also have the advantage of closer ratios in the box and the ability to have a Torsen LSD if desired.
A 4.1:1 diff from a 1.8 with the original 5-speed box would give an even longer drive ratio
You would also need to use a 1.8 propshaft and driveshafts if you wanted to use the 1.8 diff in a 1.6 Mk1.
Hi Niggle
Thanks for th ereply. Sorry, left the club for a short while. Too busy doing other things (work) 
I really am a ludite when it comes to all this engineering stuff. I have a 1.8i and as I said in my initial post I am looking to improve MPG. The 5 is high reving even when cruising on the M’s and am interested to know if fitting a six speed box would drop the revs and give a little better MPG.
Cheers
Paul
No, fitting the diff from a 6-speed car would
Thanks
Has anybody tried fitting a dif off of a six speed 5.
Driving at a steady 65 instead of 70 improves economy and is quite relaxing too. 
After posting my question, I have just come across this useful post.
It looks like a 6 speed box on a MkI would not give me what I was hoping for. It would still be interesting to find out if anyone has done this. As a matter of interest, which LSD would be be best to fit to my 1.8?
A chap I know is running 195/65/15 tyres on his 1.8 Automatic Mk1, reckons he is seeing 40mpg on motorway trips (he is from Cardigan mind
)
Trouble is his insurance might not be too happy that he is running on a tyre size not specified for the car…not what i would advise but it is another option to consider 
With that tyre size and a 4.1:1 axle ratio on a 5 speed manual gearbox you would be pulling 3500rpm @ 75mph as opposed to 71mph if you were on 195/50/15
I have the 6 speed and diff from a Mk2 RS in my California that diff is a 3.909:1 with Torsen LSD
I know of a turbo Mk1 with the six speed and Tochigi Fuji Super LSD from a 2.5 sport 3.636:1
Highest gearing using standard parts is a 5 speed with the 3.636:1