350, carb intake manifold

[bru333]

I'm helping a friend with his 350. Cleaning up the intake (after several years of sitting) we popped the stamped steel cover off the bottom side and found a lot of baked on oil crud.

What exactly does this cover plate on the bottom of the intake manifold do? (other than catch oil and bake it) Only thing we could think of was it is a heat shield of sorts. Can he leave it off?

[Injuneer]

The main purpose is to keep hot oil off the bottom of the manifold, so it doesn't put heat in the bottom of the manifold and heat up the air, reducing perfomance. In the manifold in the picture, it looks like it may have an exhaust cross-over passage, from one side of the exhaust manifold to the other. That passage was used on early emissions engines to pre-heat the air going into the intake during warmup. There was a spring loaded valve in one side of the exhaust, that closed and forced the exhaust from that side to flow through the manifold and flow out the other side, heating the bottom. The shield in that case would keep the oil from hitting the bottom, and carboning up - obviously it didn't do a very good job.

For any sort of performance application, you would block the exhaust crossover (if that's what the manifold has), preventing exhuast heat from flowing through that passage. It would delay engine warmup slightly, but would keep the heat from hurting performance after the engine warms up.

On the LT1, that shield is also used as a baffle to keep the oil mist out of the PCV system, which pulls crankcase vapors through slots in the shield, and into slots in the bottom of the manifold, to the PCV valve on the side of the manifold.

I would keep the shield on there.

[bru333]

Thanks Fred!

I told him someone would have a detailed explanation for him...