Yeah same hear, running 3 engins in that thing, if your a sub you want speed underwater
b/c this equals more kills, faster and easyier time chasing ships, and getting out of hot
spots faster. Faster subs can/get to do more than a slower sub.

There are actually four extra slots,three support and one R.

I'm running three engys in the support slots and my 2nd torper in the R slot.

Can't remember my SD off hand but I think its right around 800

I hate T4 so I'm not using it(yes I do have the lvl for it)

but if I did

I wouled put

1 - 2nd torper, just in case IJN gets back tubes or just in case SDE acctually trows
out T5...wich wouled be overkill but be ready

2 - Engine

3 - Engine OR Seaman

as for SD I have no idea :)
on T3 I have oround 250-300 SD if thet helps :)

cheers
Megadone