A few of the local Sports sedan racers here with big rubber went straight to the rb25det box instead of constantly replacing 71 b and C boxes. It seems the 71 series is not as strong as the Toyota W58 series which are similar in weight and size then there is the rb25det box (FS5R30A) which is almost equivalent to the toyota R or R154 but not the tremec V160 series. All big units, made for big numbers yet the Nissan Big boxes seem to be always behind Toyota.

Jmac supercharged with turbo is my guess.

This an interesting cut and shut for turbo SR engined cars that could help with the ideas of 71 series onto the A series block then maybe not.
http://www.youtube.com/watch?v=mgeqePIFya8

A friend I know runs an sr20de NA with big rubber and chews up SR20 boxes quite easily and has no choice but to go the R series box, 2nd pic below shows the size difference of the R & W (Rb or 300zx is longer) vs the C.

This one from the top (very fat unit?) supposedly first available on VG30DETT
http://cdn.mkimg.carview.co.jp/minkar ... 76/p1.jpg?ct=a8cdf4b6d056

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  rb25det box vs sr20det.jpg (186.42 KB)

R33 (or Z32 boxes) are common upgrades for Silvias and R32s once they go over about 250rwkw seems to be the consensus on when you really need to upgrade from a 71C for reliability.

Your mate with an NA SR20 chewing up SR20 71C's must be a hamfisted brutal driver. They can handle 200rwkw pretty safely for track use with big sticky semi slicks. Pretty safe to say your mate has nothing like that from his NA SR20! And more importantly, would certainly have nothing like the torque of a turbo motor.

Tremec V160 series? The toyota V160 is the Getrag 6spd used in early MKIV Supra twin turbos like I owned, not a Tremec box.

Drives a very nice 120y coupe with gigantic flares and highly worked sr20 NA. He has gone through 3 sr boxes, they were second hand boxes unknown miles but his slicks wich I think are either on 10 inch wide or there abouts quite massive things are supposedly very sticky but he loves it and yes he is brutally angry to it, no sympathy at all. He believes its the tyre/wheel combo but loves the traction he feels totally safe. Stand corrected had a late night "getrag" confused it with a totally different beast a Tremec TR in a Mazda rx4 build nearby.

in a light car like the 120Y, the gearbox should last even longer.

I had 10" rears on my much heavier 200rwkw 180SX with R888 and FZ201 semis and Kumho S700 slicks at one stage. Never broke a box in the three years of track work it copped.

I was surprised as well with the breakages, he did let on he has no mechanical sympathy, likes to let it all out on the track. He has had it parked for a while after the 3rd box went and was contemplating going straight to the rb25det box conversion as he couldnt be bothered wasting more money buying more sr boxes.

jmac good price for this one
http://www.gumtree.com.au/s-ad/yolla/ ... -speed-gearbox/1015339326

Interesting how none of those ratios have a direct 5th gear..

also they are 1500aud in japan not Landed in oz and to your door-step.Shipping,taxes etc add on very quickly.

and in most cases from what i've heard, gearbox breakages are dependent on the driver of the vehicle and how skilled or un-skilled they are.

I was under the impression the rpm could also play a factor as his tacho had 9300 and he is a very strong framed bloke who works with steel all day so not going to label his driving ability in case he is reading this! :)

I know all boxes are different from make to make but Mazda rotary boxes seem to suffer big torque in turbo setups but fine for high rpm work yet the toyota boxes used in the turbo drag cars often suffer stripping gears when changing gears at high rpm levels in NA rotaries. This is what I understood from Rohan Ambrose a rotary pioneer & very able driver but cant remember why the design had this trait.

Maybe above 9000 rpm causes problems in the 71 series? just speculating

The place in Argentina have can make the input shaft & 5 chosen gears for around 1000-1100usd for any box make (as my contact Chizito has helped me understand) but as mentioned their communication is in spanish or german and via a landline as they rarely do email. Chizito holds a world record for an NA swift gti and was happy to deal with them if ready to put an order in.

You could use the FS5R90A, but the 71C is reportedly just as strong.

Nissan is great because they don't fit overly heavy gearboxes unlike Toyota what adds the weight whether needed or not.

The toyota boxes are actually lighter, better synchros, shifting & gear strength
Also bonus of removable bolt up bellhousing so popular for conversions all over the world for different engine makes and fits many toyota rwd/fwd engines.

The W58 was 35.5kg dry 20RE engine (most sought after box)
The T50 same as above 29kg 2tc engine
The T50 drained not rebuilt 31kg 4age engine

The stumpy 71B from R30 is 38kg dry L24E engine
The 71C long box from R31 is 42kg RB30E engine
The 71C silvia is 43kg ca18de engine
Still to weight the slightly longer stumpy d21 box

Even the world class mustang and S10 T5 is 35kg (77lbs)

the A10 4 speed 56a box is the king of lightweight boxes
surprisingly strong for such a measly designed contraption