I just bought some IC piping off someone and it looks pretty good... the only problem is he told me it was 2.5", but it's smaller in the pre-intercooler pipes and bigger aftwerward. Isn't that backwards, if anything shoudln't the piping get smaller since the air compacts as it gets smaller. Here I have some pics


The right pieces are smaller than the left in diameter.



The pipes on the right are small enough to fit inside the other pipes

 

When the air gets colder it becomes more dense in the same amount of space or volume, or it can have the same density in a larger volume, so that makes sense in theory

 

Exactly... I've seen setups where the pipes will get smaller after it is compacted (so the air doesn't lose it's velocity), but this just seems backwards.

Hot air takes up more volume than cold air. This would ram the hot air into the intercooler, make the molecules more compact due to cooling, the basically let them float through the bigger piping, losing a lot of speed and increasing lag. I'll be pissed if I got the shaft on this... paid good money for it.

EDIT: the pre-intercooler piping is only 2"... the charge piping after is 2.5"

 

I don't think you'll have any problems...won't speeding air up increase heat? so it rams it into the IC to cool it off and then slows it downa bit to kee it cool? i don't know doubt it will make a difference unless you are running really low boost level, just hook up your wastegate to the intake mani and then you'll get acutrate boost levels and you will probably loose more pressure from an IC that is too large

 

Yes the air will get to the intercooler faster with smaller piping, but that is not necessarily a good thing. You want the air velocity to remain constant. To compensate for the air getting smaller through the intercooler, you can decrease the piping size AFTER the intcercooler to keep the speed the same. Most people, including myself wanted to keep the piping the same size just because it's a lot easier... but the guy that sold it to me didn't say anything about a size difference.

 

rule of thumb is whatever your compressor outlet size(2" for example) keep it the same size all the way to the entry of the intercooler, than you can step it up a size to match the throttlebody.