enjoyed this post! Well written, good luck with the build. Iām only 200% jealous
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Thanks mate! I always worry I bore everyone to tears!
Absolutely loving this! Iād love to do a rocketeer conversion myself so I admire this a lot!
As far as your seat dilemma, they arenāt lotus seats but thought Iād throw my wee two pence in just in case they were something you like?
Couple of these
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I was actually looking at these at GSM - are they Cobra ones? I do like them!
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They are, aye.
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Are they for sale? I notice they arenāt fitted to anything 
Absolutely they can be for sale, though, Iām a horrible business man and havenāt an earthly clue what they are worthā¦?
Also where are you? Iām in Scotland but I work 3 on and 3 off so I could take a jolly to deliver them to you on my time off, would love to have a look around this wee beaut!
haha well, iām in Lincolnshire!! Thatās a long way for a jaunt! Iāll PM you.
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I heartily recommend using threaded rod couplers instead of nuts. This sort of thing: Easyfix Carbon Steel Threaded Rod Connecting Nuts M10 10 Pack | Threaded Rod | Screwfix.com
They have plenty of length so you donāt need to worry about using multiple nuts to stop their thread stripping when you wind them up tight.
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Thanks again Martin!
Right, about to get dirty.
Whilst iām gearing up for it (mornings arenāt my friend!), iāve been thinking about and searching for diffs. Now, iām quite keen on a Fuji diff; sounds like they are preferred by a lot of racers, but theyāre cheaper than Torsenās. However, it seems that the Fujiās mostly come in 3.6 (and less so in 3.9) ratios. Obviously 3.6 on a standard 5 speed mx5 would be a struggle. Bruce @ Rocketeer says his preferred setup is 5 speed and a 3.9 or if you can find out, a 3.6 diff. I donāt want acceleration to be blunted too much, but there are of course the added benefits of a lower RPM at motorway speeds, and I will be using this once a week to do 200 miles on the motorway.
This website gives a great overview of all the options:
https://beavismotorsport.com/guides-tech/differential-guide-for-miata-mx5/
Iāve found a good value, low mileage Fuji 3.6 - I was just wondering whether anyone had any opinions or experiences they could share?
Andrew
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The 3.6 diff was designed for the 6 speed box. Six and five speed ratios are very different. 6th gear with 3.9 diff is virtually the same ratio as 5th gear with 4.1 diff.
So if you use a 3.6 diff with a 5 speed box the ratios will be way off. Youāll have a very leggy box in all gears. Some people with turbo conversions like this because it means the car has a much higher top speed, but at the expense of instant response low down.
5speed with a 3.9 might be OK, the only place you will find these is on either a mk2 3th anniversary or a mk2 Eunos RS.
Unless your car is an early mk1 with a 4.3 diff it probably has the 4.1 which is not a bad compromise. I would try that for now and see how you like the ratios.
5 or 6 speed? Itās personal preference but after having both I prefer the 5speed
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Thanks Carl,
Iāve got a 91 Eunos with a 2004 NB Manual Gearbox.
I spoke to another Rocketeer who took the route of 5 speed and 3.6 - what you say is what I was initially worried about. I know swapping over a diff isnāt the end of the world, but iād rather make the right decision first time!
Sounds like finding a 3.9 or a 4.1 ight be the best bet.
The diff I currenty have is from my auto, which clearly isnāt suitable 
The. Gearbox. Is. Mounted. To. The. Engine.
Never, ever, ever try and do that on your own. Iāll come and help you!
I did not enjoy that very much haha, it took me about 4 hours, hurt a lot and lots of swear words were used (I didnāt have a beard when I startedā¦)!
So, my first job was to file a 2mm chamfer around the inner edge of the bell housing, just to give a little bit more clearance to the flywheel.
Then, I tensioned the lift and lowererd the subframe and engine assembly to the floor.
Using a succession of jacks and swear words, I slowly mated the gearbox to the engine.
I had forgotten that the PPF does not actually mount to the car, and because I havenāt got a diff yet, I could not fit that. It was interesting to see the difference between the manual PPF and the auto one. I wonder what that means for the effectiveness of the PPF? Is the difference in length mitigated by the size of the comparative gearboxes?
I also used a combination of heat (maybe too much at times) and power (not mine!) to remove the main bushes from the Suspensions arms. Having used Hydrate 80 to treat and paint the arms, iām not happy with the finish. I think I may take them back to metal again and try something else. I know it seems like a lot of work for very little end product (not to mention the fact nobody will see them!) but it seems a shame to put shonky arms back on what will be a beautiful car. Alternatively I could buy new arms, but then iād have to remove more bushes and I think the metal is actually in good condition, so would be a waste of money and metal!
New parts ordered over the weekend:
- Tie rod ends
- DaveFAB jacking bar
- IL Motorsports calipers/brackets
- Clutch Pedal Bush
- Fuel Filter
- ARB Drop Links, bolts and nuts
Next lot of new parts needed:
- Diff
- Diff mountings
- Seats
- Electronics Pack from Rocketeer (about 4 weeks away)
- Maybe wheelsā¦
I keep changing my mind about wheels. Originally, I didnāt like the daisies. Frankly, the car I purchased was the MX5 I always hated. Standard red and standard wheels. However I grew to like both, so I decided to keep both. The only nagging issue I have is the width of the wheels; because of the lack of any from of traction control, the fact I want to use it to do the odd commute and the odd track day. I like the idea of it looking like a fairly standard MX5, but I also need to be sensible about the fact that I could probably do with more grip. Anyone got any thoughts?
Next Job
Itās almost time for the Carbon Fibre! 
But first, exhaust mounting, which actually is almost as exciting because its slowly beginning to look a lot more like a car! 
Anyway, sorry - this was a fairly long post! Hope you all had good weekends, and thanks very much for the constant encouragement!
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If you like standard wheels then I would look at something like the 15ā mk2 sport wheels. These are very light and fit over big brakes.
The daisies are going to limit you on brakes and 14ā tyre choice is low these days. Also they are narrower than the 15ās so you are going to struggle for grip with all that hp. You could compensate by using semi-track tyres like NS2R and add wheel spacers to move them out to fill the arches
On the gearbox side, canāt you offer up the whole engine and box on the subframe in one?
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I ran a 3.6 Fuji on a 5-speed with a supercharger. In fact I experienced each combo - 4.1 diff with the blower, 3.6 normally aspirated and 3.6 with the blower. As you can imagine the 3.6 on an NA car is distinctly slow off the mark. Other than that itās fine. Once youāre moving you just have longer in 1st gear before you shift to 2nd etc. It was like swapping gears 1-5 for gears 2-6 or perhaps 1Ā½ to 5Ā½ if you see what I mean.
With the extra torque of the supercharger it didnāt feel slow getting away any more and it was nice to have a first gear you could use instead of a frantic launch-and-shift which the 4.1 had felt like. Winding out 2nd gear to well over 60mph is rather good too.
TL/DR: Yes I would happily recommend a 3.6 / 5-speed combo for a car with a power upgrade.
Howeverā¦
Caveat emptor. The Fuji diff in its NB incarnation is notorious for breaking off the tabs inside itās friction cones. They tend to appear stuck to the magnetic drain plug. In unlucky cases they can chip gears which bite on them. I stripped and removed all such chunks from the one I got and just ran it as a semi-open diff. Since then a chap in Northern Ireland has started up a business fitting stronger replacement friction cones. (The manufacturer do not supply spares.)
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Hi chaps,
After readjusting and reasjusting again, I canāt get all the subframe bolt holes lined up and the gearbox true centre. the easiest way to show this is by taking a picture of the gear stick in situ.
Is this something that will straighten up once the PPF is fitted, is that difference within any sort of expected tolerance, or do I need to unbolt and try again? To me it looks too far out, which has me worried about all sorts of things!
Thanks in advance!
Andrew
I could have done that yes, I just decided for reasons unknown to even me, to do it piece by piece.
I think I thought it would be somehow easier! You live and you learn.
Thanks Martin!
OK, this has given me lots of food for thought.
So the ppf isnāt fitted? whatās supporting the back of the gearbox at the moment. I would not tighten the engine mounts fully until the ppf is on. Without a ppf I wouldnāt expect the gearshift to be centre, unlike most cars that have engine mounts + gearbox mounts - the MX5 only has engine mounts and the gearbox is held in position by the ppf frame which is bolted to the rear subframe with the diff āwingsā