Has anyone installed the isr y pipe while keeping the stock midpipe, & if so did you experience leaks or any other negative effects? I purchased with the intention of getting the SOHO single exit exhaust, but after reviewing more pictures/videos I've decided I no longer want to do that. I've heard the piping diameter difference between the isr & stock mid pipe creates turbulence=power loss, but then I've also seen videos of people running it with stock midpipe claiming no leaks or power loss, & at this point I just need help deciding if I should go through with the install or send it back.

 

It's a huge difference in size and it will require your best effort with a good metal gasket for it to not leak and even then it might end up leaking months to a year later.
Finding a flange that matches the Y pipe and welding a flange to the mid pipe will be the best you can do at optimizing flow. That sharp edge on the step down will overheat from heat and exhaust gas friction and start to warp the flange as time passes.
You'll be fine for a bit until it starts to give you issues.

 

Thanks for the reply, I'll look into the time/cost to have a flange welded to the midpipe, but tbh I'm thinking I should just scrap the isr & shoot for a true dual catback; After researching more there appears to be a consensus that the isr's 3" outlet is overkill for an n/a car (Which is how mine will be staying). Thanks again.

 

Quite the contrary if you're going single.
You don't want a true dual, many benefits from merging both pipes, the trick is where, how, style and size of merger since one bank will help the other move the exhaust out.

 

In that case would the Stillen catback be a good choice? It merges when connecting the y pipe to the midpipe (From 2.25" to 2.5" I believe) & I've heard good things about it but Stillen advertises it as a "true dual" catback so I'm confused on that terminology.

 

In my opinion a true dual would never connec the left and right pipes coming after your cats. Most manufacturers including aftermarket ones merge both pipes at one point. Many times in form of a Y after the cats or by the mid pipe.
The Stillen has a Y desing and merge by the flange from the Y to the Mid pipe. Stillen provides looks and performance plus bolt in ability for a decent price.
As the car ages look out for used accesories, for some people Tomei's are just right for them and for others Stillen would be way too loud for them same goes for the muffler delete folks.

The cool aspect about the Stillen is the mufflers, if you ever got tired of the setup you could make your own mid pipes to change the sound overall or sell since they seem to keep their value.

 

Understood, I'm gonna go with Stillen in that case, the sound clips I've heard sound like what I'm shooting for, & as you said I can always alter the setup if need be. Thanks for the help.