currently have the greddy TDO5H-18G turbo, heard through some freinds thought that all it can really make is 300hp if im lucky. what size turbo manifold can support the 350-400 hp range? already know i'll need to upgrade to a 3" DP.

 

need more info on what you going to do. are you just tryin to get a bigger snal and bolt it on to make that kind of power? are you lookin for a bigger turbo or and manifold that can support big power? if your lookin for 350-400whp by boltin on a bigger turbo... thats not going to cut it. maybe for a lil while but not that long. why you need a 3"downpipe? you can... but dont have to...i cant start, i think the people need more info on your plans, dont want you and you whip to be

 

THe 18G from the Greddy kit, needs a LOT of work in order to hit about 350whp. It won't do 400whp, so don't even get there. The turbine has to be converted to an external wastegate, larger downpipe, (getting rid of the "adapter" and 2" downpipe that comes included), as well as really good management. Even at 350whp, on a stock block, the tuning has to be dead on, and even THEN that is not a guaranteed of reliable success.

 

I thought the 18g kit downpipe elbow has a 2.5" diameter opening?

 

the elbow does, but not the downpipe itself.

 

sorry, posted it when i had trouble sleeping so left otu a few things lol.
i have a fully built GSR (full arp, port and polished head, block bored to 81.5mm, 9:1 comp pistons eagle rods) skunk2 intake mani and edelbrock TB. was looking at a few GSR builds that are around the 400-450 range and my build is pretty close to some of them, really the turbo is the only difference and sometimes .5 on the bore. just curious what manifold i can replace the greddy one with for more power. wanting it to be reliable 350-400ish for atleast 1/4 mile and trying to save some $ by not getting a whole new kit

 

or is it just unrealistic?