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BigJimnyMeet (North) 2024 (12 Jan 2024)


BigJimnyMeet 2024

14th July 2024
Parkwood Nr. Leeds

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Gearbox upgrade - MX5 to M series engine

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07 Sep 2020 13:21 #227873 by sniper
I am having a lot of fun in my car at moment..... dare I say... on TARMAC...

The new exhaust has allowed my 1300 to breathe much better and I have little complaint about the engine now, the gearbox however is a different story. The biggest issue is the big hole at the bottom of 2nd gear, the car bogs in slow 2nd gear corners.

I have considered many options but the one that has presented itself as financially viable (but still quite costly) is the MX box. It has a shorter 2nd and will allow the engine to stay within its power band in those tight 2nd gear corners. In addition, the box is close ratio'ed and very short shift, a pleasure to drive with.

A local engineering company that is quite heavily involved in motorsport has said that they will produce a bell housing to mate the engine and box together.

The conversion kit will be around £500 if I can get a batch of 10 produced, would there be any interest from other forum members ?

sniper

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07 Sep 2020 17:00 #227879 by Lambert
I'm trying to remember the hole in 2nd you refer to it certainly didn't seem too boggy when I had a wee drive?

Temeraire (2018 quasar grey automatic)
One of the last 200ish of the gen3s, probably.
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07 Sep 2020 17:14 #227880 by Riccy
I know what John means. There is a larger 'gap' between 1st and 2nd, than between 2nd and 3rd, 3rd and 4th, etc. I notice it as increased noise from the rocklobster at low revs, as well as not getting going very well from low revs

The ratios for the Jimny are in the wiki (look at M13 R7me gearbox for this comparison):
www.bigjimny.com/mediawiki/index.php?tit...ssion_gearing_ratios

And the MX5 has much smoother progression through the ratios (and is 6 speed):
www.miata.net/garage/KnowYourCar/S8_Gears.html

The £500 kit sounds interesting, does that include a mini prop (assume it'll need a custom one?) and some form of mounting bracket altering probably too?

J999 MNY, ULYSSES M18 VVT with ITB's Dyno tested at 130hp

Pickup/tipper, R7me gearbox & 6.4 Rocklobster, 31" Toyo MT, 2x ARB air locker 3.9 diffs in braced axles, 6" total lift, Floating rear conversion, Raptor painted, CB, Recaro's, Caged, etc, etc...

www.youtube.com/user/riclemus

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07 Sep 2020 17:41 #227882 by sniper
Lambert - It only "bogs down" in tight slow corners with no punch to get going, you'd almost shift to first but then you have still got the big gap to get around... Not really a problem on a normal car, you just tolerate it and accept that momentary lack of progress. Being a gentleman, you didn't push my car that hard when you drove it.... or have the type of corner that causes a problem...

Riccy - No prop or mounts, it's just the bell housing and maybe some flywheel work.... It will need to be fitted and the mounting problems resolved but it does look doable... The shifter location will be very slightly back from standard but a kinked gearstick should make it good.

sniper
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07 Sep 2020 18:11 #227885 by Busta
I don't want to burst your bubble but my the MX5 gearbox is a massive 32" long compared to 19" for the Jimny. It leaves barely 6" for a transfer case propshaft.

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07 Sep 2020 18:15 #227886 by Busta
Also, if you are going to the trouble of fitting the gearbox, you might as well leave the MX5 engine attached and spend the £500 on an ECU instead. I bought an MX5 for precisely for this reason but the length of the gearbox made it massively more complicated than I had initially hoped. I took the alternative route of lifting the MX5 and fitting some all-terrains and it's epic.

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07 Sep 2020 18:49 #227888 by Lambert
Any chance of pictures of your mx4by2?

Temeraire (2018 quasar grey automatic)
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07 Sep 2020 18:59 #227890 by sniper
Busta - The motorsport engineers I've spoken to today fit the boxes in a number of different cars and according to their CAD, it can be done with just a small shifter move and a modified gearstick, as mentioned... No bubble burst... A £500 ECU won't resolve an iron blocked engine weighing nearly twice as much as an all alloy M series... Oh and apparently 6" is plenty....:laugh: :laugh: :laugh: :laugh:

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07 Sep 2020 19:00 #227891 by Busta
Here you go. I'll upload a video of it in action...
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07 Sep 2020 19:06 #227893 by Riccy
6" mini prop? that'll be interesting :laugh: You might as well have the t-box attached as in a vitara. The amount mine squirms about on the standard engine mounts that would never work properly :unsure:

J999 MNY, ULYSSES M18 VVT with ITB's Dyno tested at 130hp

Pickup/tipper, R7me gearbox & 6.4 Rocklobster, 31" Toyo MT, 2x ARB air locker 3.9 diffs in braced axles, 6" total lift, Floating rear conversion, Raptor painted, CB, Recaro's, Caged, etc, etc...

www.youtube.com/user/riclemus

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07 Sep 2020 19:12 #227894 by sniper
The prop was mentioned and dismissed as an easily resolved issue.... Viscous couplings are made in house...

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07 Sep 2020 19:27 - 07 Sep 2020 19:27 #227895 by Riccy
Viscous coupling? what is the idea there then? The standard mini-prop is a solid thing with UJs, no slip joint or anything other than a simple prop (mine is an SJ one to allow for RW t-box, but essentially the same thing as a normal Jimny)

J999 MNY, ULYSSES M18 VVT with ITB's Dyno tested at 130hp

Pickup/tipper, R7me gearbox & 6.4 Rocklobster, 31" Toyo MT, 2x ARB air locker 3.9 diffs in braced axles, 6" total lift, Floating rear conversion, Raptor painted, CB, Recaro's, Caged, etc, etc...

www.youtube.com/user/riclemus
Last edit: 07 Sep 2020 19:27 by Riccy.

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