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Old 05-31-2007, 10:42 PM   #1
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Default Question about pipeing size for a t25

the compressor outlet has an outter diameter of 2 inches. Does that mean I must use 2 inch pipe? What if I used 2.25 inch pipe? would that reduce spool time? thanks.
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Old 05-31-2007, 11:08 PM   #2
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nope not one bit

you're going to want to make it 2.5" by the time you get to the TB....typically we do 2" in the intercooler and 2.5" out.
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Old 05-31-2007, 11:23 PM   #3
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Whatever piping sizes you decide to use you have the option of using transition couplers or you can weld transitions on the pipes themselves.
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Old 05-31-2007, 11:28 PM   #4
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ok, thanks! you guys are great!
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Old 06-01-2007, 12:02 AM   #5
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I run 2" from compressor to throttle body.. no problems, car spins through first and second..
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Old 06-01-2007, 01:03 AM   #6
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The smaller the better, right? Ideally you want the pipes to have as little volume as possible so they take the least amount of time to fill up, correct?

For instance, if you've got an IC with 2.5" inlet/outlet, it'd be best to run 2" to a transition coupler, then out the other side to another transition coupler, up to the TB to a 90° transition coupler. Difficult, but ideal, right?
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Old 06-01-2007, 01:07 AM   #7
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Seriously, I feel that ideal is whatever fits the best. For the power levels we're aiming for, going to big pipes doesn't add much benefit, and the "throttled volume" decrease in small pipes is not very important with a turbo.
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Old 06-01-2007, 09:39 AM   #8
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Quote:
Originally Posted by Savington View Post
The smaller the better, right? Ideally you want the pipes to have as little volume as possible so they take the least amount of time to fill up, correct?
you could use 4" piping and the volume will fill up just as fast...
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Old 06-01-2007, 04:05 PM   #9
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What? 2" pipes will fill faster than 4" pipes.
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Old 06-01-2007, 04:18 PM   #10
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The flow of CFM relative to the volume of the intercooler, pipes and distance involved in whatever sort of plumbing you utilize...have virtually zero influence.

yeah they will fill faster, but will you be able to measure/feel the difference?

Last edited by Braineack; 06-04-2007 at 09:58 AM.
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Old 06-03-2007, 10:21 PM   #11
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AND.... 4" pipes would look kickass
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Old 06-03-2007, 10:48 PM   #12
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Only 4"??? You guys must drive girl cars.....:gay:

FWIW I use 2.5" plumbing on pretty much everything because thats what size the intercooler inlet and outlet are.
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Old 06-03-2007, 11:34 PM   #13
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use whatever fits best/is cheapest
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Old 06-04-2007, 02:58 AM   #14
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At 200bhp 2.0" puts you at about mach .27 in the pipe and 2.5" is at about .18. Corky Bell says that frictional losses get noticeable at about mach .4, so 2" would work good. He also says to resist the urge to go larger because the volume of the system is directly proportional to the time it takes for the boost pressure to get to the engine.

Time = (volume / flow rate) X 2
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Old 06-04-2007, 09:52 AM   #15
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Now your getting crossed with Supercharger talk:

Quote:
Originally Posted by Corky Bell
The throttled volume doesn't change with the turbo. Throttle stays in the original place.

I see no change in the throttle response regardless of intake tract. Isn't throttle response sort of defined as the engine's response to a throttle position change? Turbo/no turbo.... I don't see how it affects it.

Lag is a different deal. Would the large volume intake path from turbo to throttle affect the lag? Maybe, if the volume is as big as my office.

Try this: estimate the volume from turbo to throttle, estimate the cfm in the system when typically nailing the throttle, then calc the air velocity in the tube, then calc the time the air will spend in the tube. The results are kinda cool. And slightly surprising.

Another thought: Use an improper anti-surge valve (bypass valve) and the turbo will keep 3 or 4 psi packed into the throttle inlet tube all the time. With some boost already there, the throttle need only let it in. Not much for lag.
I think this post clearly states what I'm saying.
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Old 06-04-2007, 04:52 PM   #16
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This discussion comes around every other month or so. If I remember correctly, Corky did expiriments and found for power levels in the sub-300whp range, there was ZERO difference between around 1.75"-4" piping. I think he even talks about this in Maximum Boost.

Keep it a uniform size, make the routing as straight as possible, and use a properly sized IC.

My 2" pipes were super easy to route.
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