Late SSP type 1 box upgrades

[modnrod]

Can I ask a few dumb questions please?
The box is in my '73 Superbug 1303 1600. I'm going to run a baby motor in it, under 1700, and lower revs too, but I know what I'm like  .......... and I have bottles and bits in the shed. If I can't keep up with mates, it WILL happen. 

The main question is, I know it's not the revs but the torque that pops them (well, besides abuse), but HOW MUCH torque roughly? Eg, can they take 150 lb/ft? 180 lb/ft? 200 lb/ft?

What are the main upgrade items for these later boxes, and in what sort of order? Stronger side plate? Superdiff? 3rd/4th gearset? Steel shift forks? CrMo super-duper doohickey thing?

Also, I wanted to put it a 4.37 ratio to help out the little motor too. I know they aren't as strong as the 3.88, but which ratio set? I've seen ads for the OEM 4.37, but not sure if it is suitable. Do I look for a "splined" set, a "keyed" set, a "threaded" set? (Told you I didn't know!  ). They can't be that weak really, I had a '63 1641 with a stock 1200 SA 4.37 box that must have endured literally over a hundred launches at the track, although that was using a 195/205 radial with 1.9/1.8 60ft, but enough so I still felt sorry for the poor little thing every time I broke yet another front mount.

The idea is a 6000rpm 1600-1700, launched off 185/195 radials pushing probably 900kg total, so it should run 15s all day just (like my last few did), but this time I'm also considering a bit of NO2 to help it keep up, and send it deep into the 14s, like about 40-60HP in 2nd/3rd/4th. This thing will never have slicks, or turbos, or 2.5L etc, just stay a small motor sweet streeter.
Hence the  dumb questions about how much torque, I'm too damn stiff and sore to keep fixing stuff, it sucks!

[modnrod]

 
Uhmmm, I take it my dumb question about if I need upgrades for this box for my planned uses is, well, dumb?
 

I was worried 60HP of NO2 in 2nd/3rd/4th might strain the box.
Obviously not I guess........

[dangerous]

I think the question was too long winded dave!

The late 4.375 will bolt in, and those boxes, when in good shape,
can handle plenty of torque.

I like to add a good billet side cover(not cast) to these if using the 4.375.

Superdiffs are available, and the main shaft is designated as the 002 style
which means it has a splined hub instead of the earlier keyed hub for the3rd/4th selection.
They have steel forks standard.

The only negatives are the weak and "always renew at rebuild time" reverse idler gear,
and the fine tooth 3rd and 4th can handle a lot of power.
 (well, as much as you plan anyhow),
unless the main shft ball race has been run worn, allowing them to come out of mesh.

It is also very common for these to have more wear than previous models in the 3rd/4th shift rail hole.
It may be a weaker magnesium in these, or just perhaps, more often, higher milage.

[modnrod]

I think the question was too long winded dave!

Uhmmm, yeah, maybe. Sorry mate!  HAHA!
I would have PMd you on our own site, but didn't want to ask you too many questions all over again.......because I didn't fully understand you're last answers way back when!
*sigh*
Anyway, thank you very much once again. Now, finally, I think it's clear.

I would love to just send the damn box over to you and say "here you go", but I suspect the freight is more than the car.

Thanks very much Dave. Good luck in Sydney man.