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RB20 with a RB25 G'box

Roy

By Roy,
in Engines & Forced Induction

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Roy Grand Master

Roy

Posted
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So who is running an RB20 with an RB25 box. Interested to hear ppls feedback.

My concerns are they are heavier then the RB20 box:(

Also the ratios are wider, so with a TD06 on my RB20 the last thing i want is taller gearing, would you really notice the difference? Crunch the numbers and they suggest you would.

Also the cost for an unknown quantity. Most boxes are drained, so cant really check the drain plug for synchros or swarf/filings...how do you tell the general condition of a g'box when its on the deck?

Has anyone heard of a way to beef up the RB20 box? I recall someone mentioning they can be re-built using CA18DET gearsets etc etc. I like the idea of a strong light gearbox, but cant see the budget stretching to a new custom gearset for the old girl unless the CA18 stuff goes in?

Last question, is the RB25 box the only solution, Z32 5-spds are plenty strong and cheaper, also thinking about a Supra 5 spd, S15 6 spd, though these ideas most likely suck.:)

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Nugget_GTR Collaborator

Nugget_GTR

Posted
Posted

I have a mate with a R31 with an RB20 and he got a 25 box put in about two years ago. i havent noticed any difference in how it drives... like the gearing. the only thing was the speedo cable didnt fit and he had to get an adaptor which was a hundred or so extra. he was running a 20box before the 25 too.

Bl4cK32 Grand Master

Bl4cK32

Posted
Posted

Ive got a r33 box in my 32 Roy. You can hardly notice the difference in ratios...well i cant when going from Joels car to mine it feels the same.

The only way not to get stung with a dud box is buying one with a warranty, or a recent rebuild history...

I didnt think you could "beef up" a manual box, but autos can be played with. If you decide to go for another box it would mean custom fabrication (like cutting welding bellhousings)....

R33 box is a damn good bolt on soultion for a r32, its just buying the worn out box you have to be careful with......

R31Nismoid Grand Master

R31Nismoid

Posted
Posted

the S15 box is weaker than the S14 one anyway.

get the 25 one and be done with it.

I noticed no diff in my car either troy.

It sits a litle higher in the R31 Coupe due to the underbody config. But the 32s are fine i think benno said

dangerous_daveo Grand Master

dangerous_daveo

Posted
Posted

A Z32 box is cheaper? I thought they were exxy as and also the pick of the bunch, but too hard and too costly to put in, as in rb25/26 box being the better cheaper option, even if they are a wisker weaker. No idea if its true tho, just what I have heard/read.

Id also be looking long term Roy, I mean if you ever do get sick of the RB20 (god forbid!) and go to the RB30 or something, how would a beefed up RB20 box hold then?

Roy Grand Master

Roy

Posted
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I'm surprised your gearbox is holding up at all Roy!  

s15 box - wouldn't bother.. Supra box - too expensive.  

getting the rb20 box beefed up could be an interesting proposition...

When cold and at low revs is now a bit notchy, but when warm or when shifting over 3,200rpm its fine...

I was thinking more an old school Supra 5 spd, not the 6 spd. Looks like it may be best to go RB25, but they weigh like an extra 20kgs.

It costs what it costs:( Just dont want to go throwing more weight into the car.

browny Proficient

browny

Posted
Posted
I was thinking more an old school Supra 5 spd

There are two 'old school' Supra boxes that I can think of:

The W58 supra box that's commonly referred to as the "Supra 5spd" is actually from the NA engines and by all reports it's about the same strength as the RB20 box (definitely about the same size and weight). About the same cost as well. I have heard some people say that the W58 can hold up fine behind 1UZ and 1/2JZGTE but i'd assume that this is only if it's treated carefully.

The big Supra box (R154) from the turboed engines is from all reports pretty much on par with the RB25 box in terms of strength, size, weight and cost. At least as difficult to find, possibly more.

So unless there is something about the Supra boxes that is overwhelmingly attractive (ie gearing), I can't see either being a really attractive option over the Nissan boxes, which are essentially a bolt in proposition and won't need a bunch of stuffing around and $ to fit.

Roy Grand Master

Roy

Posted
  • Author
Posted

Fair call then, put that idea to bed. Ppl use them behind 304/308s and 13Bs so thought they may be up to the job.

As for removing more weight, i doubt the HICAS system in my car weighed 30kgs. I have already removed it all with the exception of the lines that run rearward. Anyway, was dreading the thought of putting in a cage because of weight, with the g'box my car could end up weighing 80kg more then std, time to drain my wash bottle of water, thats 2L/2kg:)

geordie Proficient

geordie

Posted
Posted

Sound deadening? I had a good look at the rear hicas setup in a gtr the otherday.....the thing is huge, i can see where the mechanic quoted his 30kg figure from, that was including lines and everything to do with the system though.

Roy Grand Master

Roy

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Ahh, what is the normal manula diff ratio? Ive got a spreadhseet at home with all that guff, is it 4.11 or something.

I may try to track down an auto diff when getting mine re-shimmed, didnt realise they were a different ratio. Seriously who cares if you only get a top speed of 240km/h, there arent too many places inlcuding the straights at PI/Sandown where you get up to that speed anyway.

Oosh Veteran

Oosh

Posted
Posted
Ahh, what is the normal manula diff ratio? Ive got a spreadhseet at home with all that guff, is it 4.11 or something.

I may try to track down an auto diff when getting mine re-shimmed, didnt realise they were a different ratio. Seriously who cares if you only get a top speed of 240km/h, there arent too many places inlcuding the straights at PI/Sandown where you get up to that speed anyway.

I don't have anything concrete to back it up but everything I've read says manual = 4.11 and auto = 4.33.

My car WAS an auto (g'box) and converted to manual, and my speedo reads high leading me belive the diff ratio is different. However, it reads higher than the 5% you'd expect from a manual g'box mated to an auto diff, so perhaps i have other issues (such as the speedo gear thingy) causing (or further compounding) the error.

predator Grand Master

predator

Posted
Posted

I'm not sure whether on the r32's they have a different ratio diff.. I think I remember reading there wasn't any difference on R32's.. but R33's and plenty of other cars there is a difference. Somebody quote the model number off their diff, and i'll crawl under and see whether mine has a different one (auto atm)

The W58 supra box that's commonly referred to as the "Supra 5spd" is actually from the NA engines and by all reports it's about the same strength as the RB20 box (definitely about the same size and weight). About the same cost as well. I have heard some people say that the W58 can hold up fine behind 1UZ and 1/2JZGTE but i'd assume that this is only if it's treated carefully.

I don't think thats much chop like you say. Guy up here put one in his HR31, and I think it didn't take long to destroy it at low 200rwkw levels. If its anything like the HR31, he said it was a bit of a stuff around to get it in and the shifter doesn't align properly in the cabin anyhow.

dangerous_daveo Grand Master

dangerous_daveo

Posted
Posted

Roy! I just had a tremendous thought!

More weight would make more load correct? More load could = less lag! :(

[edit] also Mark on here (summoner) he was using a RB30ET box. He said its the same as a RB25 box just without the double syncros. So a bit stronger than the RB20 box, and not quite up there with the 25. But Im guessing one lot less syncros should be less weight.

Roy Grand Master

Roy

Posted
  • Author
Posted

Im a porky 103kgs at the moment, time to lose some weight, i can lose an easy 10kgs, it all helps. Now to find an RB25 box and soemone to install it, i couldnt be bothered doing it myselef then only to get the car towed for the new tailshaft/balancing etc. Say goodbye to another 2k:(

LOL...on another note im starting a diary this weekend, noting cylinder pressures etc. I want to get some decent rubber, then i have to talk to the guy that tuned my car to see if the tune is ok for 1.4-1.5bar, i want an 11.99sec pass at around 116-118mph before i can sleep at night...fear my attempts will kill the g'box well before the engine, and at 2k ill wait until the g'box dies rather then pre-empt it:)

Right now im feeling pretty shitty, and reasdy to destroy something, may as well see if i can be in someway constructive with my anger:)

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