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I can never seem to get a clear answer on this but really is the best size for intercooler piping?
I tried on the 323gtx boards and they say 2 and 1/2, Then I have seen others say that you should have it smaller coming from the turbo and bigger after the intercooler towards the throttle body.

Can someone tell me without a doubt what size is best for the gtx bpt?

Honestly it depends on the turbo and amount of HP you are shooting for. For the stock turbo 2.5 would work well if your going to turn up the boost. For a little less lag use 2.25 from the turbo to the IC then 2.5 from the IC to the throttle. For the fastest response and if your only planing on around 200-250HP run 2.25 all the way. There is no true single answer honestly. Trial and error with your setup and dyno time is the only way to find a single answer for you. Every car is different.

well on a stock BPT w/VJ20 they use 2". i would assume that if your using the stock turbo that 2" would be the most efficent. i start boosting at 2300 rpm, and hit 8 psi at 2800 rpm, with the VJ14 hybrid. i know several Honda guys running T3's with 2" piping all the way. i dont think i would change it unless i upgraded the turbo to a bigger one.

I measured the piping that is on the engine today and it is 2 and 1/4 so I guess that is the size that I am gonna go with

I was running 2.25 on my VJ-14 setup.

If its for your street car and you want the best performance, responce and spool up to about 250 to 300 whp. 2 inch will be great.

yah i am going to go bigger when i get a bigger turbo. i figured anything bigger than the exit of the turbo is just going to create more lag. so i stayed small with the 2".