UN1 Box Fitment to an 807 Series Engine
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Thread: UN1 Box Fitment to an 807 Series Engine

  1. #1
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    Default UN1 Box Fitment to an 807 Series Engine

    So pretty sure I already know the answer to this, but is it possible to fit a UN1 box to an 807 series engine?

    I mean anything is possible if you throw enough money at it, but I am more thinking of a simple bellhousing swap rather than a custom CNC job.

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    And I guess the follow up question, does anyone know if a UN1 will fit into a 17G chassis without having to massage the gearbox hump in the floor too much?

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    1000+ Posts geckoeng's Avatar
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    A 17G should have the bump already. But why a UN1 ??? R18 395 is the answer.

    Another R17 owner planning to upgrade

    807 needs to be the R15/17 block, then engine mouts bolt straight up.

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    The NG* series boxes will with a bell housing change as well and also some fabrication of mounting brackets.
    Regards Col

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    The trick with regard to the bellhousing is to use the R17 bellhousing and fabricate an adaptor
    plate at the bellhousing to gearbox casing interface.
    having said that, the rest will be a headache- mounts, input shaft, driveshafts, selestors etc etc.

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    It has a 365 in it already, but I was under the impression that the UN1 from the R21 Turbo was a much stronger box than the 365.
    I was just spit-balling ideas for a strong/reliable box for an R17 turbo project that may or may not happen.

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    I take it you have located the UN1 box already.

    If not, do that first. Not that many found their way here. Besides, once you have the UN1 on the bench in front of you the challenges should become apparent.

    The 17G box is strong, the diff is not. I have looked into swapping a NG3 diff and pinion in my 365 but it's not that easy. The pinion has completely different splines so the 17G gears can not be used. The other option is to use NG3 internals, but it's more work than using the whole box. Then the gears are all wrong. Not sure about the UN1 gears, but I would guess they should be better.

    I assume swapping internals from the UN1 to the 365 casing is another headache because of the relative positions of the diff and pinion.

    Hmmm. Not easy.
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    To just put it out there, perhaps an R25 2.2L motor with its UN1 would be possible, and still turbo it. Don't know if height would be a problem, but they will fit in an R18 with its lowish bonnet line. I've not seen one fitted to an R17 or 12.
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    Umm I think you need to swap something into it.. I don’t care what, but when you do take the 365 out, you’ll want to dispose of it... I’ll kindly take it off your hands.

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    I wonder though, would NG3 be a better way to go... not anywhere near as strong as un1, but stronger than 365/395, relitively easy conversion, and much much easier to find and less expensive to replace than either un1 or 365.
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    This guy made it fit...

    https://www.youtube.com/watch?v=DhLJ6oZoT78

    the 21 engine that is..

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    Does using a UN1 involve custom drive shafts as well as an adaptor plate or an impossible to find bell housing?

    If it does then there are many options including Subaru and Audi. I know it isn't Renault but they are much easier to come by, the Subaru anyway.

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    I mis-spoke in my original post, the concern wasn't really with the strength of the box, it was the diff, as has been pointed out above. So will fitting a quaife LSD solve the strength issue with the spider gears in the 365?

    I have looked at the subaru and audi boxes but they both appear to require some floor pan modifications as well as adaptor plates, so I wasn't too keen on that.

    And if the 365 is replaced at some point, it'll stay in the shed as a spare,right next to my pile of rocking horse poo.

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    Quote Originally Posted by 3006882 View Post
    I mis-spoke in my original post, the concern wasn't really with the strength of the box, it was the diff, as has been pointed out above. So will fitting a quaife LSD solve the strength issue with the spider gears in the 365?

    I have looked at the subaru and audi boxes but they both appear to require some floor pan modifications as well as adaptor plates, so I wasn't too keen on that.

    And if the 365 is replaced at some point, it'll stay in the shed as a spare,right next to my pile of rocking horse poo.
    I have fitted a UN1 gearbox to a 807 engine in the Bob Watson R5Turbo Group B Rally car
    It requires a tricky spacer fitted between the gearbox and the bell housing
    The drive shafts the car uses are modified Commodore units and I run a Hewland limited slip diff.
    Unless you have deep pockets or very friendly machining shop,as there is a lot of grafting work required

    Rob Sealey

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    The 365 gearbox weakness wasn’t the Centre diff, it was the crow wheel/pinion.. the 365 gearbox had 4 spider diff which was hard to break... problem was that having that stronger meant that instead of breaking that part (which would be relatively easy to replace), you’d break the crown wheel pinion set or the first second gear of the primary shaft.. the crown wheel/pinion for a 365 is extremely expensive if you can find one, and the primary shaft cluster is pretty much impossible to get. In a lot of ways the 395 gearbox used in the late 17g is a bit safer as they only have 2 spiders in the diff.. this means the weakest link is the Centre diff and you’re more likely to break that than other components.
    Depending on what your torque curve looks like with the turbo motor, I’d still be thinking the ng3 might be the better gearbox for you.
    Last edited by angru; 17th March 2019 at 01:30 PM.

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