Tuning the C20LET - Breathing/Pipes

Pipe Airbox->turbo

The OEM version of this hose is substandard. It looks ribbed, reinforced, big and bad. Try squeezing it and it's not that hard though. Maybe as it ages it gets worse, who cares. It has no place on a modified LET. At about -0.1 bar the upper third of the hose is half-collapsed. That's rubbish performance, and in real life it would feel like the engine suddenly cuts out. Note that this might not be visible while someone simply revs the car, as there is no load on the engine. It needs to be revving (and boosting) on a road (rolling or real!).

A proper, thick, silicon hose is needed here. It's got to be specially made (i.e. pricey), as it's a bit crooked and the two diameters are different.

It will look something like this: Don't worry, you can reuse the OEM pipe for the RamAir feed!

The pipe can be wrapped in aluminum tape to help it reflect the heat of the engine bay. Black isn't exactly the best colour for something to stay cool in a hot confined area (it absorbes all light wavelengths, while this one reflects them away again)

This is another option, a DIY attempt by a ClubCalibra enthusiast. Total cost is similar to that of a commercial silicone item, and it certainly looks more robust and shiny! Being made of straight pipe bits stitched together, the inside will be nowhere as smooth as the silicone equivalent. On the other hand, the thicker skin is also heat-reflective, so overall performance should not be compromised. This one would be ideal for fitting pre-compressor water injection, as the nozzle won't need an extra boss to screw on.

Compressor->intercooler

These need to be as smooth and gentle as possible. Short, too, but only if sharp bends are avoided.

Only mandrel bends are permitted (no bending of straight pipes!) and even then pressure is lost by anything more than 45degrees. In theory around 5% of flow is lost for every 90degree turn, and many are unavoidable. Also note that the turns at the intercooler caps are not as restrictive, because the diameter on one side is much larger.

For high-flow engines a larger pipe diameter is preferred, a 300bhp LET would like 2.5"~2.75" pipes (inner diameter).

As far as material quality goes, the stock pipes are borderline even for stock engines. Good quality silicon hoses are the only ones acceptable on a serious engine, because the temperatures and pressures involved are considerable. At 20psi the air exiting the compressor can exceed 140C, cheap pipes won't last long.

Intercooler->Throttle Body

This is normally a short silicon pipe followed by a steel tube. The silicon pipes attached to the intercooler give it some flexibility to move relative to the engine (which rocks under load, while the intercooler is firmly attached to the frame!)

Sometimes the silicon hoses pop off under full boost, no matter how hard they're clamped. In that case, bracing is a no-nonsense way of tackling the issue one and for good:

 

Heatsoak

we spend a lot of effort to cool down the charge air with the intercooler. It would be stupid to let it get hot again as it passes through the hot engine bay. A metal pipe exposed in there ain't gonna be cool then. It's a good idea to 'dress' the long steel pipe in a heat-insulating jacket.

The one I prefer is sold by CarpetRight (or something similar) and it's sold as a thermal underlay for home carpets:

It's flexible and insulating, with aluminium shiny side outwards. Just cut it into shape with a Stanley knife and keep it in place with cable-ties. Reusable, too.

Marvelous.

...On to the Turbo