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Thread: SR20 conversion using RB25DET gearbox

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    Senior Member Sprinter Freak's Avatar
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    Default SR20 conversion using RB25DET gearbox


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    hey guys


    Am at the stage of choosing which Gearbox to go with in my conversion, i was originally looking at RB20 gearboxes but don't think these are going to be tough enough for what i need.

    Has anyone got experience's with using an RB25 box in there conversion? i know you will have to get a new firewall/tunnel made up, gearbox cross member and drive shaft. But are there any other things needed?

    anyone got some pics of where it puts the shifter position?


    any help/advice is much appreciated

    cheers

    Ryan

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    Veteran ae8zn6's Avatar
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    I Ok, I know a lot of the silvia guys do the RB25det gearbox conversion, but there are a few potential differences. First up, how much power are you planning on running and what size tyre are you going to use?

    I mean a lot of silvia guys complain that the SR/RB20 gearboxes aren't strong enough, but then you have to remember they typically run 250+rwkw (about twice s13 factory power) onto 295s and then put in heavy brutal clutches as well.

    If you are running less than those figures I would strongly recommend sticking with an sr/rb combo box.

    Here is a photo of both (RB20 box is on the right)


    So the body of the rb25 gearbox is significantly larger too, but the shifter looks to be a little further forward.

    Keep in mind that I had to modify the tunnel/firewall to fit the sr/rb box in recently. If you stick with that box you don't NEED to do a full boxed up tunnel, but I can't see any way that you could avoid it with a rb25 box! Also from the research I have done the RB25det is about 20-25kg heavier

    Finnally if you do choose to go the RB25 box make sure you get the rb25DET box, as apparently some rb25DE cars came with the same box as an rb20det.

    Hope some of that is useful

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    Veteran willa's Avatar
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    Pm matt99 , pretty sure he runs sr+25box in his 86
    SuperFunHappySliders

    SR's are ghey.

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    Senior Member Sprinter Freak's Avatar
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    Quote Originally Posted by ae8zn6 View Post
    I Ok, I know a lot of the silvia guys do the RB25det gearbox conversion, but there are a few potential differences. First up, how much power are you planning on running and what size tyre are you going to use?

    I mean a lot of silvia guys complain that the SR/RB20 gearboxes aren't strong enough, but then you have to remember they typically run 250+rwkw (about twice s13 factory power) onto 295s and then put in heavy brutal clutches as well.

    If you are running less than those figures I would strongly recommend sticking with an sr/rb combo box.

    Here is a photo of both (RB20 box is on the right)


    So the body of the rb25 gearbox is significantly larger too, but the shifter looks to be a little further forward.

    Keep in mind that I had to modify the tunnel/firewall to fit the sr/rb box in recently. If you stick with that box you don't NEED to do a full boxed up tunnel, but I can't see any way that you could avoid it with a rb25 box! Also from the research I have done the RB25det is about 20-25kg heavier

    Finnally if you do choose to go the RB25 box make sure you get the rb25DET box, as apparently some rb25DE cars came with the same box as an rb20det.

    Hope some of that is useful

    Im aiming for around the 300kw( i know its a lot and probably dont need that much, but why not) mark and will be running between 185 to 205 tyre. with Theres a guy in qld who runs the sr20 in his ke, his making about 275kw and has been through 4 sr boxes(same gear set as rb20 only slightly different ratios)in a year of drifting:/

    Was going to box out the tunnel and the firewall anyway to make gearbox removal easier so thats not too bad. And as for the weight i'm going to be putting a Heavy R31 diff in so 25kg shouldnt make too much difference

    your right about rb25de's coming with out with rb20 boxes, as i picked up one off my mate the other day. Was out of an r33 non turbo and it looks exactly the same as the rb20 box in that photo.

    cheers for your input man

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    Senior Member Sprinter Freak's Avatar
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    Quote Originally Posted by willa View Post
    Pm matt99 , pretty sure he runs sr+25box in his 86

    sweet will pm now, cheers

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    Uhh, what cluth is he running? You can destroy transmissions at at like 250whp/220wtq (from memory) by running a dumb clutch. You can get the same trans to last 3 years of drifting at ~380 dynojet hp by running a nice clutch. ORC 409 in this case. Exedy stage 2, nismo coppermix, exedy hypersingle will keep 'em alive. And then you're on 195/205 not a 235-265 in a lighter car. You're doing something wrong if you're going through gearboxes so often.

    Oh and which gear breaks and how? Is he running a kouki trans? Being qr, a gearbox oil cooler would probably have saved those.

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    Yeah it's a lot to do with the clutch, I'd be inclined to just go SR box seeing as you'll have 195/205 and just run a HD or standard clutch, there really is no need for a super heavy duty clutch. See so many people chucking in button clutches then complaining about breaking gearboxes all the time.

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    You can also use the Z32 vg30dett? Box aswell.
    Obviously the RB25det and Z32dett box's don't bolt up to an SR and require bell mods and adapter plates etc.
    Nigel Petrie (engineered to slide) sells adapter kits for both box's.
    I don't really see the point in going rb20 box, may aswell stay with the SR box and shift a little smoother, run a good oil, tranny cooler, warm it up and don't try pull 4th in a 3rd gear corner..

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    That's always an option but I think people prefer RB25DET trans simply because it's newer and more likely to be in better condition. VG30DE is also usable instead of VD30DETT. Front housing is different but the difference is machined off anyway. VG30 trans is cool because of the remote shifter. You can place the shifter where you want it instead of dealing with wherever it ends up. Not really a problem for corolla since the shorter trans (apparently the RB25 trans is 65mm shorter than SR trans) works well for us.

    You sure SR trans shifts better? I always read they are the same across the cars for the given production year and the only real difference was kouki (and probably S2 R33 NA) getting the gated centre section.

    I reckon trans cooler would save a whole bunch of gearboxes that weren't rediculously overpowered.

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    Nah wasn't saying they shift smoother... Just saying to shift smoother to save the box

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