Throttle Body Coolant Bypass

[bszopi]

This isn't so much a myth, as it is exaggerated. The lines were put in by GM for cold climate conditions, which is said to cause ice to form on TB, which could cause a lot of problems, like a stuck open condition that can cause an accident. There have been no known reports of this happening, but there hasn't been any research either.

The idea behind removing it has nothing to do with the ice though, it is removed to keep the hotter coolant from heating up the TB. Cold air is good for a motor's performance, but the air moves so fast that the TB temp isn't really going to make a difference. Cooling the TB and Intake manifolds will help however.

The real gain from this mod is to eliminate one area that "can" leak, and if you tear the motor apart at all, those coolant lines can be a pain to remove when you want to remove the TB or the plenum. Because this is a really cheap modification, it is still recommeneded to remove the lines if you don't have to worry about ice forming on the intake (only because it would be bad to recommend something that could be potentially dangerous). Every little bit helps when cooling the intake, just don't think you will notice anything from it. Not only will you not notice anything, you won't get anything on a dyno because of it either (on its own).

[danbettis]

I agree wiht your conclusion. I was told years ago they were there to prevent iceing and the throttle body from sticking. Now I dorve my 92 Z4 for about five years with the throttle body bypased and had no problems, even in cold weather.

Dan Bettis

[Andromeda451]

Icing??

Icing was a common issue in or on carburetor equipped engines. This was due to the fact that at the carburetor mixed fuel and air in the carb body. The act of atomizing a liquid like gasoline into an air stream causes a drop in the gases temperature. As the carburetor vaporizes fuel, it cools the intake air by evaporation. The carburetor venturi also cools the air by adiabatically expanding the intake air, known as the Joule-Thomson Effect. If the air temperature drops below the dew point, moisture in the intake air stream condenses into water droplets. Thus, water can be present in the carburetor even when driving on clear, relatively dry days.
Ice also forms near the carburetor butterfly when condensate water droplets strike the parts of the carburetor (typically the butterfly and venturi) that are freezing. Freezing is determined by: the outside air temperature, the temperature drop, and heat absorption from the engine. With the throttle partly closed, you may have a 10" Hg or more pressure drop across the throttle butterfly.
The more gasoline the carburetor evaporates, the colder the carburetor becomes. As your engine idles, little fuel is evaporating and the carburetor's temperature may be above freezing. Adding power increases the rate of fuel evaporation. Now the carburetor may be cold enough to form carburetor ice. A carburetor can get pretty cold. The heat loss from evaporation of gasoline at the stoichiometric ratio (~14:1 air/fuel ration) creates a theoretical temperature drop of 40 degrees F. The adiabatic expansion of gas across the carburetor's venturi also lowers the temperature but to a much lesser degree. Thus, you could drop the carburetor temperature to freezing and form carburetor ice at an ambient temperature of 72 degrees or higher. Stoichiometric is the leanest possible mixture for good emissions and a clean burn of the airfuel mixture. At richer mixtures the ambient temperature at which carburetor ice forms is even higher.
Adding alcohol to gasoline dramatically increases the ambient temperature where ice can form. Evaporating methyl alcohol creates a temperature drop of about 300 degrees F. As a result, carburetor ice can occur over a wider range of temperatures.
A fuel injected engine set up like the V6 used in GM vehicles will generally exhibit much less icing on the throttle body because the adiabatic expansion across the throttle without the coincident introduction of gasoline at the throttle body results in a much reduced temperature drop effect. The injectors are at each port so the cooling of the air stream by the injection of fuel is downstream of the throttle and within the "heat envelope" of the operating engine. This is not to say that ice cannot form in the throttle body. It would just be a bit more difficult.

My 2 cents,

Andromeda451

[Ray Hamilton]

How do you "by-pass" it?

[SappySE107]

Depends on the motor.