Hate to sound like a newb, but...

65LoveAffair said

Okay, I was reading about upgrading intake and exhaust manifolds at various locations, and I kept coming across a recurring theme. A lot of what I read said that some "aftermarket" manifolds will cause you to lose intake manifold heat. What exactly does this mean? Thanks, and sorry for the newb question.

Click to expand...

No problem. On the /6, the intake manifold bolts onto and is heated by the exhaust manifold. This heat is very useful when the engine is very cold and it is hard to maintain the flow of fuel vapor to the engine. Most aftermarket manifolds to not have the provision to bolt up to the heat riser on the exhaust manifold, though some do.

No intake heat

Pro:

1. Denser fuel/air charge introduced into cylinder (more power).
2. Possible to run slightly leaner jetting on carburetor.
3. Less tendency to "lean out" when engine is running hot.
4. No EGR.

Con:

1. Takes longer for engine to warm up and run smoother.
2. Less fuel mileage, especially on short runs.
3. Automatic choke less efficient.
4. Increased harmful emissions.

Since /6 carb heat depends on the exhaust manifold as a source, similar things happen when an aftermarket exhaust system is used. The only exception to this are the Dutra Duals and manifolds with a hot water provision. The Dutra Duals twin manifolds are based on the stock manifold and retain the heat riser for use with a manifold that is compatible.