RB25 gearbox in 32

[Clint32]

I have done a search but not found any real answers.

I have stuffed my rb20 gearbox, now makes some nice noises when you back off, and it gets stuck in reverse.

I want to fit a rb25 gearbox and i just want confirmation everything will go in fine. Im sure the box will bolt to the block and the input shaft is the same. Im only worried about the length and the tail shaft going in.

The speed sensors are different can you just change them?

[Dr_Drift]

The sensors can be swapped, you will need the front yoke from the RB25 tailshaft, and a custom shortened shaft made up, I suggest a single piece one, and you'll need to fabricate a custom gearbox mount. Tail shaft shouldn't cost more than $200.

Doc.

[dabigbolf]

finding a yoke will be. not a lot of people sell the yoke by itself, so try get it with your gearbox.

dr drift who would you go to, for your custom one piece shafts, i been quoted up round the $300 mark.

i am in melb

[greygirl1976]

im pritty sure a rb25 gbox wont fit on a rb20 block different bolt patten i know rb25 and rb26 r the same thou

[dabigbolf]

all rb boxes are interchangeable.

for instance rb30et box can bolt up to rb25det.

the rb30e box is the same as the rb20det box, and that bolts up to the rb25det box.

meggala is running the rb25 box on his rb20 box.

so yeah all interchangeable.

[Dr_Drift]

Meggala isn't running a RB25 box, but all the bolt patterns are the same, just different length boxes....

No idea about tailshaft in melbourne, that's just what it used to cost for my datto coonversions.......

[dabigbolf]

hmm,

i thought he was. my bad.

[Clint32]

Thanks Sam, the gearbox mount is easy, and the tail shaft is not too hard i suppose, just need to find a box and yoke for a decent price.

[meggala]

NP.... I'll keep my ears out for ya...

[MrMayhem]

Mechanical speedo in the 32.... hunt down a 32 gtr speedo drive or convert your dash to elecky as teh 32gts drive isnt going in, as the Dr says go a 1 piece using the same large unis as the 25det yoke has, and cost me $400 for 90mm.

Ive glued a 25det box to my RB20 in my HR31, alterations to the gearbox cross member were straight forward. I do think there is a larger spread in the gear ratios its not as "snappy" as it was before the swap, does anyone have rb20 vs 25det box ratios so I can be sure I am or am not going nuts.......

All in all I did what had to be done...... loose the weakest link in the driveline.

If you get stuck for a local yoke pm me

[Brody]

Im pretty keen on this topic, esp for ratios. Ive been considering for a long time now to swap boxes ova, and now that mines 80% dead, time is coming near...

[Sydneykid]

Hi Guys, following are the R32 GTST RB20DET ratios as I know them....

1 3.321

2 1.902

3 1.308

4 1.000

5 0.759

R 3.382

Diff 4.363

Anyone have the R33 GTST RB25DET ratios?

[meggala]

Sydneykid they are here

http://www.meggala.com/r33transmission.html

1. 3.214

2. 1.925

3. 1.302

4. 1.000

5. 0.752

remeber the r33 has 4.11 gear in manual and 4.3 in auto

cheers

[Brody]

Looking at that, they're both very similar (?), Would the difference in acc. be all that noticeable?

[MrMayhem]

you'd be splitting hairs to notice that difference

[Sydneykid]

Thanks Meg, I have a gear graph chart that I use for circuit racing, I'll stick the two sets of ratios in it and post it later today.

It is later today..................

Following is the kph at 6,000 rpm for the two sets of gearbox ratios with 4.363 diff ratios, plus I have thrown in a third set for the RB25DET with the 4.1 diff ratio. The kph are based on the rolling circumference of a Yokohama A032R 245/45/17.

The.......... RB20DET G'box........ RB25DET G'box........ RB25DET G'box

Gear.........with 4.36 diff...........with 4.36 diff............with 4.1 diff

1 st..........50 kph.................51 kph....................55 kph

2 nd.........87 kph.................86 kph....................91 kph

3 rd.........126 kph................127 kph..................135 kph

4 th.........165 kph................165 kph..................176 kph

5 th.........217 kph................219 kph..................234 kph

As you can see, there is very little difference in the gearbox ratios, the diff ratio change would be much more noticeable.

For those with R33 GTST's (4.1) diff ratio there would be a noticeable improvement in acceleration with an R32 GTST (4.36) diff ratio fitted.

Hope that helps

[Guest drift_me_silly]

q....if r33 auto diff fitted to r32 with r 25 box....would fifth at 100k's drop down to around 2ooorpm?...with a standard 4.3 and standard box fifth is pulling just about 3 grand at 100k's.

also...apart from yoke and tailshaft modifications, would the r32 clutch assy bolt onto the '25 box? i know the gtr's changed between 33/32 but no idea with the rear wheel drives...lastly, does anyone know if the trust 6spd h pattern internals wold fit into a '25 box?....From what i've read it would be cheaper (!) to source an r34 six speed and use those internals...any thoughts?

[Clint32]

I picked up my rb25 gearbox today complete with half the tailshaft for the yoke. It was out of a series 2 that had done 25k, paid $1200 so im happy, some importers want $1800.

Sydneykid would you mind tellling me what you use to work out the speed in each gear is it just a excel program or something different. It would be usefull for me as i work on a 6 speed ICC go kart in the CIK series and while we cant change gearbox rations we do change the final drive ration.

[Sydneykid]

Hi Clint, I designed an Excel spreadsheet a long time ago that we use for selecting gear box and diff ratios when we go to a circuit for the first time or in a new car. I did another one when Son of Sydneykid was racing Karts. I can't seem to find it, probably on the old lap top.

Anyway the formula for a Kart is simple (high school Pi)..

An example for a "J"..................................

circumference of the tyre = 800 mm

multiplied by the engine rpm = 10,250

multiplied by the number of teeth on the engine sprocket = 12

divided by the number of teeth on the axle sprocket = 68

multiplied by the number of minutes in an hour = 60

divided by the number of mm in a kilometre = 1,000,000

equals kph = 87

800 X 10,250 X 12 / 68 X 60 / 1,000,000 = 87 kph

All you need to do is add the gear ratios. Say it has a 3 to 1 first, a 2.5 to 1 second, a 2 to 1 third, a 1.5 to 1 fourth, a 1 to 1 fifth and a .75 to 1 sixth......

First = 800 X 10,250 / 3 X 12 / 68 X 60 / 1,000,000 = 29 kph

Second = 800 X 10,250 / 2.5 X 12 / 68 X 60 / 1,000,000 = 35 kph

Third = 800 X 10,250 / 2 X 12 / 68 X 60 / 1,000,000 = 43 kph

Fourth = 800 X 10,250 / 1.5 X 12 / 68 X 60 / 1,000,000 = 58 kph

Fifth = 800 X 10,250 / 1 X 12 / 68 X 60 / 1,000,000 = 87 kph

Sixth = 800 X 10,250 / .75 X 12 / 68 X 60 / 1,000,000 = 116 kph

Bit tired, been laying concrete all day, hope that makes sense.

[Clint32]

Thanks i will try and set up a spread sheet to make it easy to work out the ratio we use.