Ideal Piping Size

[96Turbo]

Hey everyone. I'm currently piecing together my Intercooler/Piping setup for an RB25. What are your suggestions for choosing an intercooler piping size? I'm thinking 3" for the best flow, but could there be negative effects of having such a big pipe? (such as slower spooling since there is more volume to fill up) This isn't going to be a huge horsepower engine any time soon, so would i be better off with 2.5"-2.75" for better response...or would it not make a whole lot of difference? Thanks in advance

[punxva]

yeah i'd go with 3 in since it will be pushing more air, and if your staying twin turbo it won't really affect lag too much with pressure drops

[SILVIA_KIDs14.5]

yeah i'd go with 3 in since it will be pushing more air, and if your staying twin turbo it won't really affect lag too much with pressure drops
he would be staying single turbo its an RB25 not RB26

[orion::S14]

How big is the throttlebody...not the inside diameter, the outside.

Probably 2.75"...so no reason to go any bigger than that on the COLD side.

For the hot pipe, you'll usually have a half-inch step...smaller by a quarter or half inch.

Take a note from GReddy...their kit is 2.25" on the hot side, and 2.75" on the cold side.

That works for 400hp SR's, my 338rwhp KA-T, etc...

There's really no magic here...it's as much fitment as it is performance. But, if you want somethign to base your sizing off of...there you go.

- Brian

[96Turbo]

can someone tell me the O.D. of the compressor outlet, and also the intake pipe? To start out, i'll be using the stock intake manifold. Later i plan to upgrade to the greddy manifold...probably with the stock TB. Is the TB the same size as the stock intake piping? I want the cold side piping to match up to the intake (no reducer) both with the stock manifold and directly to the stock TB (greddy manifold)

[IStop4NoMan]

i have a spec-m intercooler kit with a P2m hot pipe. this is what i know....

cold piping is the same as the O.D. of the throttle body.

there is a reducer pipe from the hot pipe to the intercooler, i think a 1/2 inch.

also, the compressor outlet has a reducer to the hot pipe which is a 1/2 inch.

so whatever the throttle body OD diameter, just keep stepping down i would guess

[garagelu]

Keep in mind that 2.75 piping is really hard to find. Especially 2.75 mandrels. And when you do find it, and sometimes it is more expensive than 3 inch from what I have experienced.

Just depends on what your budget is. It would actually look better if you went with 2.75 because then you wouldnt have to use a reducer coupler. Im not sure what the throttle body diameter is on the rb, but sr is 2.75 and majority of sr intercoolers are 2.75.

And reducer coupler are pretty expensive also. Ive seen 2.5 inch piping used on pretty high horsepower cars so Im sure it is sufficient.

Here is an awesome site I found when I was shopping for piping. They have a wide variety of piping but they are fairly expensive....

http://burnsstainless.com/index.htm

I bought my 2.5 inch Stainless J bends from hybridynamics. They were only 30 or 40 dollars per J bend. I think thats right, its been a while.