1990 Toyota Corolla Downpipes

Hi,

Do you have any info on specs for a downpipe system for a 1.6L 4cl engine?

Engine is 1.6L 4cl DOHC

I'm planning to install new headers, a 4-1 type header
What diameter should I use for the headers pipes?

I'm running it to a downpipe, no muffler, no resonator.
What diameter should I use for the pipe?
It will just be a straight pipe from the header collector end.

Thanks and more power.
Jack