if you are sticking with t3's then you could go up to 67mm. but you would run out of turbine well before the compressor is done. 62mm turbo could be made to work well. are you 57's maxed? what kind of power do you have? what are your goals.
A Pair of 57's is more than enough.to make 700 at the crank. Do you have other issues within the combo holding you back? Whos turbos are they? ebay specials? Precision 3431E's are 57 mm inducer units rated at 545 hp a piece. Thats over 1k hp of airflow capability. The problem is the turbine side is pretty small and would probably choke up being the biggest A/r housing.offered is a .63 T3.
How do your downpipes attach? 3inch Vband or 4 bolt?
If you have 4 bolt round flanges, the 6076E is a 59mm inducer compressor coupled with a P trim turbine wheel and the option of a .63 or .82 a/r housing a pair of these would be 1200 horsepower capable. 599.99 each. This turbo with the .63 housing would spool damn near instantly on 347 inches and the P trim wheel is big enough it wouldnt choke.
If you have V bands you could buy a couple and weld the correct halves directly to a pair of 4 bolt flanges and bolt them to these turbos. The price and size jumps up pretty good to the first turbo offered with a Vband Flange. Thats the 6365. Its 700 hp capable each with a T3 3inch Vband housing available in .63 and .82. this turbo lists at 849.99 per Precisions website.
All these units came from the entry level section of thier website.
I believe a pair of the 6076E's would be an excellent fit on your motor and be easy on the wallet.... Not many turbo combinations can be had for 1 dollar per hp. I think the .63's might come on too quickly making boost happen instantly. Id probably go with the .82 housings. These units could give you 1000 hp easily and with your description of your combo it sounds like the engine has the parts to take it.
There are some 60-66mm offerings from Borg Warner as well. Reed at Work Turbo could help you out with specing and pricing on those. He is who Iwould call before making a final decision on your upgrade.
thank u liljohn,very informative, the turbo s on there now are ebay special chinese junk..... they r a 2.5 inch vband outlet,so i just ran 2.5 inch down pipes, when i swap to bigger/better turbos, im prolly gonna do a set of 4 inch downpipes
some of the new billet precision 61's would be awesome and something you would have room to grow if you decide to turn up the wick. plus the many options with turbine AR's and choice of a wide variety of T3 or T4 options. like someone had mentioned the Borg stuff is an option also.. although they have less options for AR sizings compared to the Garrett/ Precision options. Bullseye power is having a lot of luck with the "BatMoWheel" turbos and have a good size inducer selection. depends on what money you want to spend really.
I think 4 inch downpipes would be a tad bit Overkill BUT the best exhaust is NO exhaust for a turbo motor. 3 inch pipe off of a T3 .82 housing would easily support 600-650 horsepower per side. So 3 would be enough for 1200+ hp easy. And probably be easiee to fit too.