Rb20Det Box Vs Rb25Det Box

[clip14]

hi all,

running a rb25de+t with currently 200rwkw @9psi, going in for a retune with bigger injectors, afm, custom ecu etc, shooting for 230rwkw+

at the moment its surviving with a rb20det gearbox with a 3000lb pressure plate, full face carbon kevlar clutch, unsprung.

So i think the gearbox is going to take all the load. The gearbox has held up so far, but not to any sustained abuse at the increased power level.

i'm wondering, should i take my chances with the 20det box and just pray it holds up/wait for it to blow

or pre-empt the blown box and source a 25det box and new clutch etc?

bear in mind this is in a budget build car, and in new zealand, a complete 25det box swap including clutch will run me 3-4g incl parts and labour.

anyone running decent power through a 20det box? it will get rarely abused (mostly a street car with some gymkhana work), but the clutch is harsh.

cheers for any input

[StevenCJR31]

suggest you be gentle with the 20 box, ie dont side step off the clutch, until you have a good 25 box on your hands

[GTSBoy]

The 20 box is lucky to be holding the torque you're giving it now. The 25 box is close on double the diameter of the 20 box! All that size reflects on the strength difference.

[2LV8ETR]

I was running 350hp though mine and went through 4 20DET boxes, keep in mind that there were track days involved.

The 20 box will hold up as long as you baby it, but then, where's the fun in that? Saying that, I have also lunched a 25DET box.

Start sourcing a 25DET box, spigot bearing (larger) and tailshaft yoke.

[GTSBoy]

Start sourcing a 25DET box, spigot bearing (larger) and tailshaft yoke.

And quite possibly a clutch slave, and a gearbox crossmember. I've got an auto R32 chassis that has been through manual conversion and now RB25 box, and it's had a number of different crossmembers in it to make things fit. I don't think the RB25 box and the RB20 box sit on the same crossmember. There's 3 types that are useful in Skylines. Marked A, B and C.

[clip14]

thanks for the replies. Hopefully the 20det box will hold up on the dyno - since there will be no dynamic loading on the gear set, just static loading mostly.

Then I will take care of the 20det box until I can save up enough for a 25det replacement. The mods required will be simple enough.

Also has anyone here decided to rwd a GTR box instead? Here in NZ we can get GTR boxes at about half the price as 25det boxes, but some modification is needed to remove the front axle transfer mechanism etc.

i have seen in some performance car magazines drift skylines running 300+rwkw through 20det boxes, which is odd. do you think its anything to do with driving style?

With drift I would think that if you are breaking traction easily, and have a sprung clutch, that the low traction on the tyres act as a fuse - i.e. the tyres will break traction before too much load is applied to the gearset.

In my case, I am running 18's and 245's on the rear of my skyline, and a harsh clutch, so all the shock loads will be at the gearbox.

thoughts?

[GTSBoy]

Plenty of people have RWD converted GTR boxes. But if you're paying someone else to do a RB25 box conversion for you then it sounds like you're paying someone to do the work on a GTR box also, which would probably eat the price difference.

RB20's running high power don't make any torque down low, whereas RB25s make a fair bit more torque, which is probably what helps the 20 boxes to survive behind 20s. And yes, drifting is all about not loading the gearbox. Although drifters will say that something holds up really well if it lasts 3 laps. So you have to take what they say with a grain of salt.

[2LV8ETR]

And quite possibly a clutch slave, and a gearbox crossmember. I've got an auto R32 chassis that has been through manual conversion and now RB25 box, and it's had a number of different crossmembers in it to make things fit. I don't think the RB25 box and the RB20 box sit on the same crossmember. There's 3 types that are useful in Skylines. Marked A, B and C.

Yeah, the slave is different (bolt config), I forgot about that one.

As I went from auto to manual I had to use the S13 auto crossmember backwards, but I used the same between the 20 and 25 box.

[blind_elk]

I'm still running the RB20 box in my GTS4, after an upgrade to a RB25DET (up to 180kW at all 4). No sign of it giving way (has had a few track days as well, a trip around the great roads in Tas, and places like the Great Ocean Road).

In my experience, Nissan's gearboxes are near indestructible. To lunch 4 of them is mind boggling.

[2LV8ETR]

I'm still running the RB20 box in my GTS4, after an upgrade to a RB25DET (up to 180kW at all 4). No sign of it giving way (has had a few track days as well, a trip around the great roads in Tas, and places like the Great Ocean Road).

In my experience, Nissan's gearboxes are near indestructible. To lunch 4 of them is mind boggling.

I'm not easy on them, that's why I've done a few.

A couple of other guys I know have had to convert to 25DET boxes because of the same reason. The only reason I went back to the 20 box this last time was because I was breaking the converted speedo sender units. While I rebuild the 25DET box, I'll be buying and using the Navara sender unit instead of a modded 20/25. It will be out a few km/h, but I can live with that

Are you still using the Gts-4 box? If so, they are basically equivalent internally to a 25DET box, they're not skinny little mongrels like a 20DET box.

[GTSBoy]

Yuh, I was going to say the same thing. The GTS4 box is essentially a GTR box. Unburstable by comparison.

I put an RB20DET box in my 32 when converting to manual and it lasted a couple of years, but went out with thrashed input shaft bearing. My car wasn't spastically fast....was just stock stuff wound up, so ~155rwkW or so I suppose. That was enough torque to make the RB20 box feel the pinch though. Replaced with RB25DE box. Same basic box, but has at least held up. Running more like 170rwkW for the last couple of years.

Would not even contemplate keeping that box behind the Neo that has just gone into the car though. Not an option. Rather sell the box as working than scrap it a few months later.

[Sir Lord Van Von Vader'ham]

i run 20box's behined my rb30 powerd 315rwkw/650nm track car, so far i get about 8 track days out of one. (including motorkhanas)

From what i've be told, 1-2 track days = 1 years worth of normal driving strain on the car.