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Gearbox upgrade - MX5 to M series engine

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08 Sep 2020 06:01 #227916 by Busta
Just another observation. 2nd gear in the MX5 isn't really any shorter than the Jimny. 1.888 vs 1.947. That's a 3% differencee. 9.7mph rather than 10mph. 14.55mph rather than 15mph. The MX5 has a much higher 1st (14%) so the gap will be smaller form a standing start, but you'd still be looking at dropping back into 1st gear in the situations where you say 2nd drops out of the power band. And the downside of that significantly higher 1st is that if you do need to take it off-road, your crawling speed is massively higher.

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08 Sep 2020 09:23 #227917 by sniper
Thank you for your advice..... But having driven 1600 MX with just a little more power than and a similar weight, to my car. I have no concerns.... Mazda diff ratio's are similar, the Jimny should be a similar drive, which is what I am aiming for. My last 1600 MX was a pleasure in tight low speed corners.

The taller first would be a benefit off road from my (limited) experience, anything that it won't cope with will be addressed by low range.

sniper

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  • Lambert
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  • The quickest Jimny in Harrogate...(that I own)
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08 Sep 2020 09:41 #227918 by Lambert
Have you thought about the later vvt box? I don't have any trouble pulling from below 1500 rpm in second or any other for that matter it would also be simpler for fitting too?

Temeraire (2018 quasar grey automatic)
One of the last 200ish of the gen3s, probably.
Bellerophon (2024 grello van daily
ADOS Attention Deficit Ooooh Shiny!

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08 Sep 2020 11:33 #227922 by Busta
The gearing might be similar but there are some key differences, namely the extra low end power of the Mazda's bigger engine and the significant difference in tyre size.

I must say, the concept of a higher 1st gear being better off road is a new one to me!

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08 Sep 2020 14:12 #227924 by sniper
Engine power will be equal to the 1.6 Mazda engine even if I stay with the 1.3. 109bhp & 100 lb.ft is not too much of a target and a 1.6 M series would yomp it, should I fit one....

There are low box gears when needed and a slightly higher crawl in first would suit a lot of the very slow driving that I do....... I have a 410 transfer and three selections of diff ratio's to play with..... and then tyre size isn't fixed either....

If the engineers can sort it, I'll be doing it.

Keith very kindly gave me a CAD drawing of the rear block, we should be able to find out if it is a goer next week.

sniper

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08 Sep 2020 16:31 #227925 by Busta
You might manage to match the peak figures of the MX5 if you throw enough money at it but you won't match the bottom end, which is what you would require to overcome the 2nd gear issue you were to hoping the gearbox swap would fix. My old M16A Jimny took just under 12 seconds to get to 60mph. It was a good match for my girlfriends C1 but nowhere near the performance of an MX5. How you think a 1.3 with an exhaust is close I have no idea! The Jimny drivetrain losses are significant. Compared to other cars with a similar bhp/ton it will always be slower.

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