Lowering
 

I have a 88 supra turbo and considering lowering it, will that effect the TEMS?

I don't believe it will effect the TEMS. I looked into this, and found 2 companies that make drop-in springs. Range is from 1" or 2" drop.

It seems like a waste of all that work to only go 1".

Lower than that, and you may have trouble with TEMS, I don't know.

from what I understand as long as you stay with the stock type shocks (TEMS compatible) they will work fine. Obviously if you go with coilovers, the TEMS become unusable.

Catalytic Converter
 

Thanks for the feedback regarding lowering my car, one more question; I know my 1988 Supra has two catalytic converters has anyone taken one or both off and if so how much louder was the car.

I am about to install a down pipe and 3" exhaust

I installed full 3" (including 3" elbow from turbo) It was very very loud at first.

The whole system was custom made, and only had one resonator and large (kinda cheap) muffler.

I have since had a further resonator installed, and am looking at a good quality sports muffler.
It sounds awesome when ideling, and when you give it heaps on motorway... but it gets very annoying after a while at around 2 - 3k rpm. Sound is a constant drone...

also, on the lowering... I have lowered mine 2" (50mm)
hasent effected TEMS at all, makes the ride very solid! heaps more fun to drive!