2.5" or 3" i/c piping

[deaf_rattle]

for my supra.
want to see 300rwkws at some stage so will need to support that.

im thinking 2.5" will be big enough, but heard conflicting info.

[Malcolm]

At the end of the day, they'll both allow enough air to flow to reach your target, but the 2.5" will (probably) cause more restriction and therefore lower power. 3" will (probably) have lower losses, but it'll take a bit longer from when you put your foot down before you see positive pressure in the intake manifold.

[tsoob]

what about 2.5 from the turbo to the cooler, and 3 inch in to the inlet (providied you have a simalar size throtle body) we did it to the BMW and is added a reasonable number of wkw (around 20)

[Malcolm]

that seems a bit backward, I would think it would be better to have the cooler (and therefore lower volume) air flowing through the smaller pipe. When you say you gained 20kw, what was the previous system?

[4bid1n 2jz]

ive got 3" but dont have anything to compare it to its a bit laggy off the line if not spooled up first thats with after market turbo tho

[deaf_rattle]

ive got 3" but dont have anything to compare it to its a bit laggy off the line if not spooled up first thats with after market turbo tho

dont think ill make 500hp without an aftermarket turbo...

2.5" will be easier to plumb. will see how it goes i guess.

[blitza]

that seems a bit backward, I would think it would be better to have the cooler (and therefore lower volume) air flowing through the smaller pipe. When you say you gained 20kw, what was the previous system?

but that big finned thing will slow flow down, so surely the larger diameter is required after the intercooler to keep the same flow rate?
Aside from that, a 3" t/b and a 2" (ish) compressor outlet kinda dictate tube sizing. no point changing size/charge velocity just because.

[iOnic]

but that big finned thing will slow flow down, so surely the larger diameter is required after the intercooler to keep the same flow rate?

bigger piping = less velocity

All you'll be doing is slowing the air down even more by increasing the size of the piping after the intercooler...think of it as a small stream suddenly joining into an ocean - water won't be moving as quickly.

You are right about the throttle body and turbo dictating piping sizes though. Decide what turbo and throttle body you'll be using for the power you want and then use the piping that works with both.

[postfach]

He's already got his turbo and throttle body AFAIK.

Go with whatever is easiest to fit, 300rwkw is easy on your motor and IMO you won't have any issues with either of those sizes, they're both plenty big enough for that much air.

No point worrying about the technical bullshit unless you're going for big numbers and the maximum throughput of a specific diameter tube actually starts being a factor.

[4bid1n 2jz]

yea i only used 3" because i already had some pipe that size that i got real cheap but by the time i got enough bends i only used bout half a metre

[strx7]

those 1000+hp porsche lemans looking racecars from back in the 80's used to use 2 or 2 1/4 inch pipe..........

[cat007]

2.5" will do way more than 300rwkw - easy.....

IIRC John S (audiman) was/is using 2.5" intercooler piping and he's +450rwkw....

[Py7h0n]

John was using 2.5" till he changed his I/C a couple of years ago, now he's 3" and 500rwkw+.

2.5" will do up to around the 400wkw mark.

[cat007]

John was using 2.5" till he changed his I/C a couple of years ago, now he's 3" and 500rwkw+.

2.5" will do up to around the 400wkw mark.

Its still 2.5 out of the turbo though so......

[deaf_rattle]

turbo is gt3582R (aka gt3540)
t/b size is 60mm i think

[postfach]

Use 2.5, it will be cheaper, and whoever ends up doing the plumbing for you will thank you for making it that much easier.

[QikStarlie]

no point going bigger than throttle body. 60mm throttle suits 2.5" tube. you will find that turbo also suits 2.5" tube

[tsoob]

that seems a bit backward, I would think it would be better to have the cooler (and therefore lower volume) air flowing through the smaller pipe. When you say you gained 20kw, what was the previous system?

2" in to cooler 2.5" out of cooler

really as alex said later in the thread 2.5 is prolly gonna be best for his setup, and easier for the fab guy

[strx7]

the smaller diameter the tighter radius bends too which makes it easier to plumb

[postfach]

I would think it would be better to have the cooler (and therefore lower volume) air flowing through the smaller pipe

I don't think this statement is true - if the air is cooler, it becomes more dense, and since the entire system is pressurised with probably less than 1psi difference between pre-and post-cooler, then the volume of air after the cooler is actually going to be greater than before it.