| Message |
All credit to Greg @ SpecialtyZ. Pretty sure he has this posted on a site somewhere with some graphs, etc. I got this from an email where he dropped this great knowledge-bomb on me. Hope this helps: Here is some more info on the breather parts, remember it all has to work together for each part to offer what it can, the system is only as good as the smallest restriction in it.
Here is some info that will help you understand the system...
Engines make power based on the volume of air they can move...
The 2 ways that allow more power in a turbo set up are, removing restrictions so that more air can move at the same pressure, and turning up the boost and forcing more air through the system.
If you remove restrictions for the system, you make a larger power band and can make more power with the same fuel octane.
If you force more air through a restricted system with more boost, you make more heat that requires higher octane fuel to resist detonation.
The stock intercooler pipe is 2 inches, the stock exhaust pipes are 2 inches, both are crazy restriction for even stock turbos.
The next size up exhaust pipes (2.5") help a lot, but still are a major restriction for even stock turbos. A full 2.5" turbo back exhaust has 6 PSI backpressure in the downpipes at 15 PSI boost. This backpressure causes the turbo to spool more slowly and limits the possible power due to the heat created by the resistance. The exhaust is hottest and most expanded coming out of the turbo and requires the most room, this is why expansion pipes make such a dramatic difference that go to 3 inches. The turbo is driven by the difference in temperature and pressure on each side of the exhaust wheel. More heat before the turbo, less heat after the turbo. More pressure before the turbo, less pressure after the turbo.
The 3 inch expansion pipes have less than 1/2 a PSI backpressure at 25 PSI with sport 700 turbos, zero with stock turbos at full boost.
The 2.5" intercooler pipes also make a dramatic difference over the stock 2 inch intercooler pipes because they remove restriction/resistance from the system and allow the turbo to self feed faster and allow more air flow volume without needing more pressure. The Ash massive intercoolers also allow much more air to more to move by reducing resistance and offer a much better cooling effect with the large core. The air speed of the stock 2 inch intercooler pipe is way to fast with even stock turbos and above the critical Reynolds number, this causes the air flow to go from laminar flow to turbulent flow. When the air speed is so high, it causes pressure drop, this occurs because the speed causes the air to form bubbles on the surface of the pipe from the heat (similar to boiling water) and make the flow area even smaller. The stock pipes have a 2 pound pressure drop at 15 PSI boost with stock turbos. The 2.5" pipes only have .2 pressure drop at up to 25 PSI with sport 700 turbos.
Larger turbos allow more air to flow through the engine because they remove restriction of the smaller wheels on both the intake and exhaust side, but if the rest of the parts are restricting the flow, it is going to take longer to force the air through to drive the turbos.
A good way to look at it is that you can only get so much water out of a garden hose.....You can turn up the pressure and you will more out of it, but it is still limited by the size of the hose.
Take a fire hose and even at low pressure the volume is much greater than the garden hose running full blast. Now turn up the pressure on the garden hose....
The turbos are not the biggest restriction in the system, in order to get good higher power with bigger turbos on pump fuel, the rest of the systems restrictions need to be removed.
|
 |
