Hello any ideas on what gear box would be best on a A15 turbo max 10psi thinking the 5 speed 63 gearbox if i can find one or the 60 any other ideas don't want to go to mad with modifying the tunnel and would like to keep it sort of old skool age appropriate.

just fishing for ideas any help will be, well helpfull :)

I believe that the best value for money 5 speed gearbox for a datsun is still the toyota T50 box.

They fit into the existing tunnel with only minor mods (bolting locations)
are as expensive as chasing down a datsun 5 speed (~$1000 including the belhousing)
will need a custom propshaft (toyota output to datsun diff housing)
and are considered stronger that the datsun box.

Datsun box
has a 2 different shift patterns (std and dogleg)
has several ratio gear sets (some overdrive 5th others 1:1 5th)
can be hard to track down
pricey at around $700-900 for a reasonable 2nd hand unit.
still needs aaptors made to fit the bolting points
fits into std tunnell, but the reverse switch will need to be modified/removed.
can use a std datsun propshaft.

For an A15 turbo go with the T50 box.

And don't forget to upgrade the diff while your at it

Turbo/Supercharged setups are an interesting scenario.

Gearboxes (and axles and diffs) break for two main reasons (not talking about the eventual wear and tear over the yesrs which finally requires a rebuild, Im talking about breaking 'relatively new' or good condition ones.

They are

1. the engine's torque and the weight of the vehicle (the higher either of them are, or worse still if you have both - heavy car and motor with lots of torque) - eventually exceeds the strength of the gearbox an breaks things inside.

2. Shockloading. This is a violent sudden application of force (and possibly helped by inertia of the rotating assembly - the flywheel for example). Even with a 'stock' a12 with 56 series gearbox - well if you repeatedly rev it up to 5000rpm (and I mean this hypothetically, I'm not saying anyone is doing this in real life) and keep dropping the clutch to either launch hard, or do a burnout or whatever - well that'll break a gearbox, diff or axle (or if you are lucky the clutch might slip and accidentally end up reducing the shock loading) in no time.

Obviously we can impact on #2 very easily - don't jump off the clutch hard. SLip it a little on launch (and if you know what you are doing, on street tyres, this slippage combined with decent accelerator input can actually get you to launch smoothly, safely and believe it or not _quicker_ than just jumping off the clutch (because if that spins the tyres, it's lost grip and prevents maximum acceleration). Similarly, we can all practice and perfect shifting 'quite' fast but not shifting the gearstick as if trying to rip the shifter handle right off, and not jumping off the clutch too quickly (and not applying the accelerator again too early before lifting off the clutch pedal , and also of course not 'flat shifting' (where there is a rev-limiter installed and once you hit the redline in one gear, you leave the accelerator floored, hit the clutch and take the next gear and let off the clutch with the motor at redline rpms (bouncing off the limited). If you had an indestructible drivetrain and very grippy tyres, flat shifting 'is' quicker, but in all other scenarios it's mostly just a way to break parts if you do it often enough. Heck even F1 cars with all their advancement and being able to replace motors and boxes semi-regularly (in the case of transmissions, they arguably run different ratios for each circuit, so the gearboxes 'sort of' only have to last each race meeting) - well even with all that development - they still get the ecu to cut engine power (I don't know if they do it via spark or fuel or what) as they perform the upshift. Obviously, being computer controlled, this 'cut off' of engine output happens in the blink of an eye, almost imperceptible to anyone watching and listening, but they do it.

OK, so we can 'address' number 2 easily - but what about # 1?? That's where it gets just a little bit tricky. And here's why.

When you modify a non turbo engine, you do your best to maximise torque. Torque goes hand in hand with cylinder filling. So in very basic terms, when the engine combo gets the most volume of air into the cylinder per intake cycle, the best cylinder filling, that'll be where it makes peak torque.. All well and good. So we maximise torque as best we can. Horsepower is very important too. whilst torque is just a measure of the actual force the engine makes in any revolution, horsepower is a factor of the torque produced and the rpm it is produced at.

So if you had 100 ft lbs of torque at 5252rpm (that's the cross over point where hp will be higher than torque on a dyno chart) it would make 100bhp at that rpm. We do our best and max it out to 120 ft/lbs of torque, same rpm, now we have 120 bhp at that rpm. no matter what we do we just can't get more torque/more cylinder filling. So what next for the non turbo engine builder? Well if we can't get more torque, what about if we modify things so that it gets the same cylinder filling at a higher rpm? well if we made 100ft lbs at 5252rpm, and we could modify it all so it made 100ft lbs at 10504 rpm - well since hp is a combination of torque and rpm, then same torque at double the rpm = double the hp! So the engine that makes 100ft lbs of torque at 10504rpm has 200bhp. Then you go back and alter the diff ratio, so it still makes decent top speed (as this new engine can rev a lot higher safely, hypothetically) but hte lower gears mean more torque multiplication, so quicker acceleration. I chose those 2 rpm points since the math is simpler. but if you hypothetically made 100ft lbs at 7000rpm, you'd have approx 133bhp for a more real world example.

The interesting thing here is that despite the much greater horsepower, this engine doesn't make more torque, so the 'strain' on the gearbox wouldn't be much different. Of course a modded non turbo engine makes more torque than a stock undeveloped a12, so there is _some_ more stress on it, but it's not so bad. Harking back the the F! engines - whilst they make incredible bhp per litre, they're spinning to what - 18000rpm I think now (some were apparently topping 20,000rpm before rule changes made a max of 18000 or thereabouts the legal maximum) - so again, incredible power - but they don't actually make a hell of a lot more torque per litre than some (comparatively) much more down to earth modified engines built from production cars/engines.

Turbos and blowers (and nitrous) do it differently. With them, there's no real need to have to push the powerband up into 5 digit rpm ranges.Whilst an NA engine will only ever get X amount of cylinder filling, the boosted engine can double (or triple, or more, with enough boost) the amount of air (and obviously fuel is added to it in proportion so the air is actually utilised) they can pack into a cylinder is astronomical. So in effect they can (and easily do, even on fairly budget minded diy turbo setups) double the torque or more. SO going back to our hypothetical engine - unboosted it made 100ft lbs and 100bhp at 5252rpm, and modified it made 100ft lbs and 200bhp But with enough boost this 'latest' imaginary engine could make 200bhp at 5252rpm - simply by doubling the torque. This means unlike the 200bhp NA engine, which has 100 ft lbs, this 200bhp boosted engine has 200ft lbs at 5252rpm. SO it will 'sneakily' be putting the gearbox under twice as much stress as a 200bhp NA engine that spins to twice the rpm.

It's not 100% as clear cut as that (for example the turbo/supercharged motors tend to have a longer power stroke - they push on the piston for much longer after TDC by which time the NA engine would no longer be pushing hard on the piston. So it's more of a gradual sustained push than the NA engine's one which is a bit sharper - so it's a little less stressfuil than truly double, but it's still more stressful than an NA engine by a mile.

Nitrous is similar - it sends a specific rate of nitrous and enrichment fuel per minute. So it will boost hp by the same amount at any rpm. BUT if you applied a 100bhp nitrous shot at 5000rpm, it'd boost torque by approx 105ft lbs (I didn't do the math on that, it is an approximation),. Most drivetrains (assuming a big V8) won't expire. But if you activated it at 2500rpm, it'd boost bhp by the same 100bhp, but it would raise torque by over 210ft lbs. If you activated it at 2000rpm, it'd be even more severe, and that's generally how nitous can break cranks and drivetrains for unsuspecting car modifiers - activating too much of it at too low an rpm. Of course it's all relative, but I'm using it to illustrate a point.

So the result of all that - you nominated the a15 engine - one which has the longest stroke, and potentially the highest torque of any A-series if you compare apples to apples - i.e. same levels of modification, a15 should always produce the most torque. So you've started there, and now are adding boost (and for the record, it's definitely the way to go, great bhp and great torque from a boosted a15 to be sure) - so you take a motor with far more torque than an a12, then add boost. So basically it'll be attacking the gearbox considerably. And so a gearbox that might survive behind a modestly modified a12 would start to have trouble with a near stock a15, and any gearbox that a mild a15 can damage, a boosted a15 will be able to destroy quicker than a politician breaks an election promise!

So short version of all that is that with a boosted a15 - even with 10psi or so - you're going to want to look for a box that has a very good reputation and was/is factory fitted to heavier cars than our 1200s and/or factory fitted behind decent output engines, relatively good torque, of 2 litres or more. If they lasted very well (even when abused a bit) in heavier cars behind larger motors, they'll do the job for you.

Meaning - you're reallly going to need either a toyota T50, which has an establised conversion kit available, or one of the nissan 71 series boxes, which are plenty strong, and easy/cheap to find, but the adaptation process you'd have to diy involving some lathe/milling machine work and some tig welding, since there's no 'off the shelf' kit for it (nor really can be - one of the reasons the toyota boxes have been used in so many different cars is their easily removable bellhousing that means a different one can be bolted on to mate to whatever engine you like. So that (71 series box) is a bigger obstacle, but either of those boxes are strong enough.

If you wanted to go auto - I'm not sure if later jatco autos can be adapted to an a-series (since there's more than a few types, whereas in Aus, most people who use the term 'jatco' - use it to exclusively refer to the jatco fitted behind vl commodores and skylines (i.e. behind an rb series 6 cylinder). What _might_ be possible is to start with a 4 cylinder trimatic, modify a starfire 4cyl bellhousing (or alternatively there were some local ke30-55 (somewhere in there) corollas in Aus with trimatic autos behind them) - modify an existing bellhousing to suit and use a combo of 6 and v8 trimatic internals inside. The trimatic is no powerglide in terms of strength, but a suitably built one would have absolutely no trouble behind a turbo a15

Dont forget to upgrade the brakes aswell, its very important to be able to stop, brake fade can happen when you least want it to.

Wow thanks for the info lots of good advice

was going to run the r31 rear diff with rx7 brake convertion maddat.com.au will probabaly be my first call for most, having built a few cars in the past i decided to take all the easyer options like buying pre made parts to keep overall costs and time down as time is money :) as the toyota box keeps coming up and has support behine it looks like that will be the route i will go.

Thanks jmac some stuff there i wasn't aware off and good to know