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I am fitting a new smaller cooling pro intercooler. 300 x 220 x 60 with an inlet of 46 mm OD to my Garrett T25 Turbo.

I have a BIG question for the turbo gurus:-

Q What will the existing pipework do to the air charge?
Maybe introduce lag, maybe nothing??? It may be expensive to find out.

The air charge will go (turbo) small - large - small - large - small - large (manifold)

Pipe diameters:
T25 outlet 50 mm OD
pipe 63 mm OD
intercooler inlet / outlet 46 mm OD
pipe 63 mm OD
NA6 inlet Manifold 50 mm OD ???

Any ideas??

Regards LRR

Ive probably spent too long researching on US sites, so forgive me for speaking in old school measurements.

I think 46mm inlet/outlet for the intercooler is maybe too small. My intercooler piping is 2in on the hotside, and 2.5in on the cool side. The 1.6l inlet manifold is 2.5in, so as the rest of your piping is 63mm you should also get a 2.5in/63mm intercooler.

Find the throttle body ID, then keep the piping, AND INTERCOOLER entry and exit, at that same ID. Going to smaller ID for the cooler is a backward step. The most important thing to be looking at is the pressure loss across the intercooler. If you then run the piping to and from as smoothly as possible you'll be on your way to a reasonable setup. If you want to go bigger for some reason, start with a bigger throttle body and work back along the line from there...

Thank you all for the good advice.
I've sent back the small intercooler. I'm replacing it with a 63 mm IL/OL unit that follows the shape & size of the front mouth.
All pipes and intercooler will be the same size start to finish.
Blue chilli