i have the Z1 test pipes on to the Greddy TIC Turbo exhaust. Never heard of cutting test pipes before.

It would be a pain in the ***. There's not enough room in there if you've got external wastegates. You'd have to weld them in way downstream. You'd also have to get another map for when the cutouts are open. And electric cutouts fail all the time. And they're not cheap.

I've thought about cutouts before, you could install them just after the test pipes and it would still be a big improvement, but you absolutely do not need another tune for a larger exhaust, I wish people would stop spreading information like this when they don't fully understand things. They certainly seem prone to failure though which is a concern.

You don't need to retune unless boost starts spiking to stupidly high levels, I have seen eclipses with cutouts spike upwards of 5psi with the cutout open vs closed.

Also the more expensive cutouts have low failure rates with good warranties. QTP(I think that's the companies name) has an extremely low failure rate and has a leak proof design, but their cutouts are expensive, close to 300 for one. The cutouts that use the butterfly valve design always leak eventually due to soot build up preventing the valve from fully closing.

You don't need a retune for a larger exhaust, but you do for the cutout. You're essentially going from a 2.5 in to no exhaust.

no. no you don't.

You would just run the cutouts with no adjustment to the tune? I would absolutely get it on the dyno and see if anything needed to be adjusted.

if you're on a stock block and afraid of making too much power, sure put it on a dyno and see if you want to turn down the boost. as far as AFR and timing goes, going from a 2.5" to 3" cutouts won't require a change to the tune

Are there bigger test pipes(GTM?)
i am running with no cats.

GTM has 3" downpipes, but they won't mate up to a 2.5" exhaust without some work.