Gen1GT said:
You can't 'ram air' a turbo set up. The turbine and the turbine alone controls the amount of air feeding the engine. It will always draw in more air than the speed you're going anyway. The hole in the front is just to allow for the least restriction possible.
This is not true. High performance piston-engined aircraft that used superchargers, 2-stage set-ups using turbos blowing into superchargers (such as the P-38 Lightning) or turbochargers alone all made use of ram air to increase the the inlet air density at the inlet to the blower. Since the forward velocity of high speed aircraft actually generated a positive boost independent of the blower, the inlet air was already above atmospheric at low altitudes or above the density/pressure altitude at any given flight level. The increased air density at the blower inlet (over and above that which would have occurred without ram) added to the increase in density due to the blower alone yielding a greater blower output air density than would have been possible without ram.
At this point you're probably laughing your head off since obviously at the road speeds our vehicles travel, positive boost will never be achieved from forward velocity alone. That's correct, but remember that inlet air density is primarily a function of two factors: pressure and temperature. Considering just the effect of pressure alone, it has been demonstrated that well-designed ram air systems on passenger cars can lead to a reduction in negative pressure in the inlet duct such that both the blower intake air density and cosequently the blower output air density is measureably increased over that possible without ram. In some cases, the use of ram has resulted in the onset of detonation in blown vehicles because of the resultant increased air density in the combustion chamber, as compared with the same vehicle w/o ram.
In fact, one passenger car ram air design was able to provide positive pressure in the inlet duct up to the atmosphere side of the air filter in most driving modes at higher speeds. Since this particular car was turboed, unwanted detonation was produced. The increased inlet air density due both to ram air and ambient temperature air clearly shows that the statement, "The turbine and the turbine alone controls the amount of air feeding the engine.", does not hold up. It's not the AMOUNT of air drawn in by the engine but rather its DENSITY that determines HP output.
Finally, I know that this is an NA thread but the beneficial effects of increasing air inlet density and providing air at the ambient temperature is equally applicable to FI or NA engines.
Incidently, if necessary I can provide references for every statement I have made in this post.
02 DX Millenium Red
