I bought a greddy kit for my del sol si. The turbo is a tdo4 which has the t25 flange. Anyways, I need a boost controller for it so I can max out the boost.
My tuner said that he'd be surprised if it broke 170 whp...I hear that these turbos drop in efficiencyat about 14psi. So, at 13psi what horsepower would I be making? Also, what is the largest turbo that fits on a t25 flange? I don't have the money to scrap the manifold or downpipe for a t3 turbo, so don't suggest it

 

The largest is a GT3076R Wastegated. If you plan to keep that manifold, then you'll need to keep the money saved for a GT-"R" ball-bearing turbo, so that it will fit properly.

 

Jesus christ...way too big for a stock single cam...I bet that when it hits max boost it'll throw the targa top right off...

Anything that will max out in efficiency right around 300whp? Anyone have a list of all turbos that fit on t25 flanges? Technically, any turbo that will fit an sr20 will fit a greddy manifold on a honda single cam?

 

You asked what the largest one was. That was it. On single cam, a GT2860RS or G2871R could work for a bit smaller application

 

I have the greddy 18g on my single cam with greddy manifold. With the stock internal gate, you can expect somewhere in the high 2xxwhp range and MAYBE reach 300wheel...with the stock internal gate.
Switch to an external and you could probably make a few more horses.

 

those gt28rs turbos are great and perfect for the power you are looking at, the 18g is also a suitable choice(turbo from b series greddy turbo kit)