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S12 Technical Areas => Engine Tech => ENGINE: Exotic Engine Swap Tech => Topic started by: SyphonS12 on 11:22:06 PM / 17-Mar-11

Title: RB25 w/ Rb20 tranny?!?!?
Post by: SyphonS12 on 11:22:06 PM / 17-Mar-11
i was wondering. if i were to do a RB25 swap if i could use a rb20 tranny. cuz i know the rb25 tranny is huge and would require cutting of my firewall. and the rb20 tranny isnt as bulky


and if this is possible what parts would i need
Title: Re: RB25 w/ Rb20 tranny?!?!?
Post by: Jay on 12:11:05 AM / 18-Mar-11
Yes it is.
You could also use a pathy, or Z31 transmission. Makes it easier in the driveshaft aspect
http://forums.nicoclub.com/pathfinder-transmission-swap-t423440.html
http://www.240sxforums.com/forums/rb-engines/122672-rb20-vs-rb25-trans.html
Title: Re: RB25 w/ Rb20 tranny?!?!?
Post by: SyphonS12 on 12:50:05 AM / 18-Mar-11
So with a rb20 tranny I can use a ka drive shaft?? Or is that only for the s13
Title: Re: RB25 w/ Rb20 tranny?!?!?
Post by: Draconis on 01:03:14 AM / 18-Mar-11
Okay, you can swap all the RB transmissions regardless of what specified RB engine.  In addition, you can even use an Z32 transmission granted you have the correct bell housing.  The best bet is to use an RB20 transmission or a MKII Z31 turbo transmission.

Just a thought though, if you do end up keeping an RB20 transmission, you dont really want to do much more than 350-400 rwhp.  There is a range for it depends on what type of life the transmission has seen.  Some have had harder lives that others so power levels are associated accordingly.  This is a guideline.  If you do use an RB20 transmission, it is best to keep an OEM clutch and flywheel.  If you go aftermarket, you have the chance to shortening the life of the RB20 transmission.

Also, about the Z31 transmission.  Reason I say MKII Turbo is that they are essentially the same as a Z32/R32 25 transmission within a housing that fits quite well into our trans. tunnel for obvious reasons.  It is your best bet but they are hard to come by.  I found one but due to the person's loose description of its history and the shipping costs I declined.  I am currently waiting for a Z31 transmission, which a buddy of mine in the Z community thinks he has a line on.

But for now, my RB20 transmission works out quite well with the 355rwhp/285ft-lbs I am running.  I dont drive hard habitually and always let the car warm up, cool down, and ease into hard driving.  That will do a lot for the life span.

Then there is your question about drive shaft.  That is a tricky one and I suggest you get a one-piece made up for your car.  That very much depends on a couple things.  First, your placement of the engine.  Although all our RB swaps will have the engine sitting in the same general area, small distances can throw things off when measuring distance.  Second, the differential you may have.  The S12 came with three different diffs: H190, R180, and R200.  They will cause some differences in your drive shaft as well.  All are minimal but I cannot guarantee you one answer for all three sets.

Also, for more information that may be of assistance - RB swap into an S12 write up I did: http://www.s12silvia.com/community/index.php?showtopic=5441
Title: Re: RB25 w/ Rb20 tranny?!?!?
Post by: SyphonS12 on 02:03:59 AM / 18-Mar-11
So custom drive shaft?
Title: Re: RB25 w/ Rb20 tranny?!?!?
Post by: RB25sx - SLPR on 02:29:11 AM / 18-Mar-11
It isn't so much the firewall that needs work as the entirety of the stock s12 trans mount needs to be cut out.. If you don't have decent welding gear I wouldn't suggest tackling it as you need to re-make these mounts in some capacity.

I ended up cutting out all my stock trans tunnel.

So far, after a full season of drifting my trans is still holding up to the stock-ish power levels of an RB25 - so thumbs up!

-dan
Title: Re: RB25 w/ Rb20 tranny?!?!?
Post by: SyphonS12 on 03:16:59 PM / 18-Mar-11
what if i have a r33 crossmember would i be able to use stock mounts??

also im not making this my drift car. Im making it my daily
Title: Re: RB25 w/ Rb20 tranny?!?!?
Post by: SyphonS12 on 05:52:59 PM / 21-Mar-11
Ok i have given up on doing this swap to a s12! i havent been able to find one for under 400 so i am getting a s13 shell. and i will be doing this swap to that


RB25det w/ vg30 tranny
Title: Re: RB25 w/ Rb20 tranny?!?!?
Post by: RB25sx - SLPR on 06:22:00 PM / 21-Mar-11
You still need a bellhousing for an RB.
Title: Re: RB25 w/ Rb20 tranny?!?!?
Post by: newby200sx on 06:34:16 PM / 21-Mar-11
yea bro nomatter what your gonna need rb20 bell housing craigslist is your best bet for it or try nico, and from there you can switch out the internals from kade and off you go again bro, just dont forget about that lil gasket in between trust me lol
Title: Re: RB25 w/ Rb20 tranny?!?!?
Post by: SyphonS12 on 06:37:23 PM / 21-Mar-11
i already have the rb25 bell housing from a friend in Okinawa for 40 bucks shipped
Title: Re: RB25 w/ Rb20 tranny?!?!?
Post by: newby200sx on 06:38:10 PM / 21-Mar-11
fuckin awsome dude goodluck, your doing a 20 swap in your s12 dude?