Problem: Won't past 3K RPM. Any help?

[TTPrince]

I have an '87 turbo automatic. Ever since I got the car I have never been able to enjoy it's full potential because of this annoying mechanical problem because I do not have the experience to remedy it:

When I full gas the car will not push itself with noticable torque, at all. Rather, it will rattle, discharge bad odour and black smoke in the exhaust, and continue so, if kept pushing. (this happens less now, maybe 'cuz I know to avoid it). If I let off the gas and gas much less then the car will move but slowly and gradually, this was the only way to drive it, there was no way going fast with this one. On highways it was slow to reach appropriate speeds - very annoying!


I think these are worth mentioning:

-I have an aftermarket cat converter, not Toyota's.
-The head gaskets came with the replacement engine with 170KM on it. Now:230KM.
-One of my RX7 fanatic friend told me my turbo was leaking.


I'm thinking of making a monster out of this ride with a 5-speed (maybe getrag?) 1jz, after I got this problem solved.



Thanks
TT