What size fmic pipe are you guys running?

[RB20DETodd]

Hello just curious what size pipe you guys are running on your rb's.

[armysweitzer]

i double the question, really not sure what to buy. IVe been looking at getting the pre made piping from rbmotoring.com but that only works with certian fmics (ex greddy vspl and a couple otheres)

[JonPowell]

There is a formula for this to get it precise, but it depends on turbo, fmic pressure less, throttle body size, etc. Most common "quick answer" is same size as the throttle body opening.

[Nameless EJ6]

I'm personally going to run 2.75" or 2.5" if I must.

Jon's right though.. should be approx. the same diameter as the throttle body.

[hannibal]

hot and cold pipes should both match the throttle body??

[RBTALLY]

I used 2.5" on the hot and 3" on the cold

[Phat_Optimo]

I am using the stock 3" piping all the way around. If your engine is stock I would stick with the stock size piping...

[Sil240]

im using 2.75 all the waystock TB and RB25 Turbo

[SillyRB]

I used 2.5" on the hot and 3" on the cold

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I did the same2.5 from turbo to Inlet on ICthen 3.0 from the TB to the Intercooler

[JonPowell]

hot and cold pipes should both match the throttle body??

Why do you want BIG pipes that once the intake charge hits the throttle body back up pressure.....to some extent smalle rpipes on intake are better because the help keep air velocity at the maximum to allow for better fuel atomization/mixture.

The reason I am using 3.5 is because of the Q45 throttle body...its 3.5" so the piping is gonna match. I got 3" feeding the turbo(Z32 MAF size and turbo inlet size) 2.5 feeding the intercooler(same size as turbo outlet) and 3.5 feeding the throttle body. I think thats gonna work decent. Igot transitions to go from the 2.5-3.0 for the intercooler inlet and 3.0-3.5 for the intercooler outlet.

I have the formula to figure the optimum piping size to allow for the optimum intake velocity.flow but not here in front of me...and its a hell of a formula also.

My basic rule of thumb, match the throttle body size.

[hannibal]

Ive seen that formula in 'Maximum Boost'. He suggests using as small a pipe as possible, as long as air velocity doesnt exceed this magic number.

I understand the reasoning behind matching the cold pipe to the throttle body size. I was wondering if the hot pipe should match the throttle body as well, or if it could be a little smaller. I should go back and read Maximum Boost, but why do some guys run smaller hot pipe than cold pipe??

[JonPowell]

Insid ethe intercooler alot of funky things happen to air flow....maximizing pressure and velocity TO the intercoole ris key because it will minimize loss and maximize outlet velocity....this number is ALWAYS less than the inlet velocity by the nature of the intercooler itself, cooling the air slows molecules as does the resistance of the air having to seperate and flow through the fins.

Running a bigger pipe will allow that air to flow OUT of the intercooler in an easier manner, instead of creating more backup and forcing that air to "get back in line". It also allwos an easier transition into the throttlebody if you are running a large one like the Q45 when the cold pipe & TB match.

[hannibal]

Gotcha, thanks for the education

[Yellow4g63]

I'm running 2.75 for the cold pipe. The intercooler endtanks are 2.75 on mine so I'm matching it all the way. But for right now since it's on the stock turbo I'm going to run the stock size hot pipe going into the fender and prob step it up to a 2.5 to the intercooler. btw what the hell size is the stock hotpipe?

[RB20DETodd]

Thanks for the info guys!, tell me how this sounds 3 inch for the hot pipe and 2.5 or 2.75 via a reducer coupler for the cold pipe, now for the pipe i was thinking of using already bent exhaust pipe from a autoparts store or pvc pipe painted black with engine paint. Yes some people can say pvc pipe looks ghetto or rice but they can kiss my *** cause its connected to a rb motor and there is nothing rice about that im thinking that pvc pipe wont attract heat as easy as aluminum pipe or exhaust pipe, any thoughts?

[JonPowell]

Sounds like a bad idea unless the outlet of your turbo is 3"... As I said the concept is to keep velocity UP until you hit the intercooler which is a "disturbance in the force" and then larger piping after to help the turbulent air escape the intercooler.

Switch your sizes around and you should be fine.

PVC is not a good idea by nature of the couplers which will introduce MAJOR turbulence in the intake tract. Buckle down and buy some REAL pipes. If you are gonna get any exhaust pipes make sure they are mandrel bent, not crush bent because your 3" pipe will become 1.75 REAL QUICK in the corners.