Pure_JDM

Hey guys, new to the s-chassis, and my first question for ya is regarding FMIC piping sizes. I'm no newbie to turboed cars, which in turn is why I'm asking... because I know all turbo setups are different in their own ways. My specific question is should I convert all the 2 inch piping that came with this SR20DET swap to 2.5 to match the inetercooler inlets i have as well as the throttle body, or should I leave it all 2 inch with reducers all over the place?

As it sits, it comes out of the turbo 2 inch through the hotpipe into a reducer coupler to a 2.5 in inlet on the FMIC, then it reduces back to 2 inch after the FMIC, makes a bend, and turns into 2.5in piping right before the throttle body.

My guess would be to make it come out of the turbo 2 inches like it is, turn it immediately into 2.5 inch piping, and have 2.5 all the way through the FMIC to the throttle body.

What do you guys think/ what has been proven most efficient?

- and don't flame. I did search but came up with SOOO many off the wall topics (as you can guess searching pipe, intercooler, and size on a forum like this)

HYPNOTIK

Are you still using a stock turbo? If so it's probly fine how it is. If you were running a bigger turbo I'd match the turbo side piping to whatever the outlet on the turbo is and match the other side to the throttle body. That might not be the correct way but that's how I would do it. I know there is a scientific way to do this so it keeps a balance of the most flow and velocity but I don't know what it is.

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Pure_JDM

in theory, i would think that it should be 2 inch until the intercooler, and then 2.5 from the intercooler to the throttle body if anything... hot air is expanded (less dense). so hot air in a smaller pipe would be closer to the same psi as cooler air in a larger pipe, right? im no engineer, nor have i taken a fluids class, but this is what i would assume. just wanting experienced feedback.

GripIt

^sounds like it makes sense but for some reason beg to differ. With what you are saying then the piping would have to be the other way around 2.5 from turbo and 2.0 from ic. Think about it your tire psi drops when its cold out that dosent mean that the amount of air that was in there is less it just means that the air is more dense now(not as expanded) and you can fit more air in. So back to what you were saying if you want to keep the same flow of the air(from hot to cold) the same then the hot pipe would have to be 2.5 and cold side would be 2.0. Im just going by the point you were trying to make.

S14DB

Piping should always be getting bigger or staying the same size. Never getting bigger then smaller. Smaller will give you more response(less lag) cause of less piping to charge when going into boost. But, too small may not flow enough(surge).

So if,
Turbo is 2"
IC is 2.5"
TB is 2.5"

Turbo to IC should be 2~2.5"
IC to TB should be 2.5"

Note: stock SR20DET TB plate is only 2" in a 2.5" housing. Unless your are running a KA
or NA SR TB, you could run 2" the whole run with 2 to 2.5" couplers at the IC cause you are changing size in the IC endtanks anyways.

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Comments should be taken as Opinions not as Statements of Fact.

jr_ss

My 3071R is 2" out, then to 2.5" and finally to 2.75" on the hot side of my HKS intercooler. Cold side is 2.75" all the way to my 65mm TB for an FYI.

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Built 95' S14....

Pure_JDM

This was more of what i was looking for... I can't believe no one else has responded. I didn't think i would only be getting a couple responses to this type of question.

Are more people running 2 inch piping all the way on sr20dets with 13ish psi on the stock turbo? or 2.5?

jr_ss

I would assume that most people running Sr's have FMIC's. In which case, usually just the pipe from the turbo to the IC is of smaller diameter, whatever it may be. Then it bumps up on the hot side like stated.

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Built 95' S14....

Ceepo

my redtop has 2.5(hot side) and 2.75(cold side)

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1995 240sx SE (current)

shogun!

Nice thread!

One other thing to consider is the losses in the piping (bends going over to straights etc). This must also be compensated for.

I have a slightly different engine setup so I use 3.15" piping all the way from the outlet (cone shaped up sizing) on the turbo to the TB.
The FMIC has 3.15" in and out.

Pure_JDM

No, i think you're backwards, the hot side is smaller. The cold side should be the larger diameter according to everyone else.

I can agree with this... and VERY nice build. I'm thinking I will do 2 inches from the turbo to the FMIC inlet, which i will step up to 2.5 so when it enters the tank, it will leave as 2.5 the rest of the way to the throttle body. I think this is my best bet. Just still wish I had more input.

jr_ss

Yeah, I meant cold side...

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Built 95' S14....