[ZX3TUNING]

SVT MBRP exhaust are 2.5" and will fit ZX3's just fine.
you may be able to ask the guys at MBRP to make a special tail section for the seadn in 2.5".

also, even though Meford has graciously brought me up, sadly he is wrong once again. I do not have the best price on 2.5" flex pipes as i sadly do not even carry them.

I'm not the biggest fan of the sound of MBRP's i find that they drone alot at highway speeds.
I personnally like the sound of Magnaflow muffled focus'.

as a rough guide:
for FI you do not NEED a 2.5" exhaust.
2.25" is good for about 170fwhp before it becomes a restriction.
2.5" will start to show gains in the low 160s at extremely high rpms but really shows gains everywhere at above 185fwhp and is not a restriction untill around 250-270fwhp.
3" takes over on turbo cars at about 240fwhp if faster responce from the turbo is required and not suggested on SC'ed cars untill approaching 260-280fwhp...

this is all in reference when "complete" exhuats are used. ports back defines a complete exhaust.

oh and most companies do not design any form of FI around the stock exhaust, some use it on test mules but those kits are not designed around it.