Question on the operation of a Intake Manifold

[Larry E.]

I see on Ebay and at Swap Meets Intake Manifolds for sale that the Oil Splash Shield(underneath of carb on back side of I/M)
is missing. I know they did not put those on there for nothing but if a I/M was installed
w/o the Splash Shield would the engine still run OK? How much of a difference does
it make? Has anybody ever tried this? Thanks in Advance-Larry

[Bill M.]

Re: Question on the operation of a Intake Manifold

Here are the bottom of a '62 340 carbureted intake and the bottom of a '62 FI intake.
The shield on the bottom of the carb intake is to shield the heat riser area from the oil.
The FI intake doesn't have a heat riser, so no shield is necessary.
Some OE carb intakes don't have the heat shield.

[John H.]

Re: Question on the operation of a Intake Manifold

Larry -

LOTS of OEM aluminum intake manifolds don't have an oil splash shield. The shield isn't there to to keep oil from heating up the manifold - it's there to keep the oil from "coking" on the hot bottom surface of the exhaust crossover passage, and to contain any that does form there.

[Stuart F.]

Re: Question on the operation of a Intake Manifold

Thanks John for explaining that. The "heat riser" analogy was a new one on me.

Stu Fox

[Larry E.]

Re: Question on the operation of a Intake Manifold

Larry -

LOTS of OEM aluminum intake manifolds don't have an oil splash shield. The shield isn't there to to keep oil from heating up the manifold - it's there to keep the oil from "coking" on the hot bottom surface of the exhaust crossover passage, and to contain any that does form there.

John:

Thanks for the explaination; new one on me also. Larry

[John H.]

Re: Question on the operation of a Intake Manifold

Thanks John for explaining that. The "heat riser" analogy was a new one on me.

Stu Fox

Stu -

Virtually all 60's-70's OEM intake manifolds (except Rochester F.I. baseplates) have exhaust crossover passages that run below the floor of the plenum, from one side to the other; the flow of exhaust gases through them (to preheat the incoming air/fuel charge in a cold engine and improve atomization and cold driveability by minimizing "wetting-out" of the charge on the cold manifold walls) is controlled by the "heat riser" valve on the passenger side exhaust manifold.

[Stuart F.]

Re: Question on the operation of a Intake Manifold

I often wondered what they were for on the 40 or so I handled back in the day. Perhaps if I would have known that I could have bettered my "B" stock record by a few more tenths at Great Lakes Dragway (270 hp 57 Chevy post w/ 4-speed & 4.56 final; 13.27 et @ 106.4 mph w/street tires). Actually, I used FI intake gaskets w/the small oval holes, no heat riser valve w/ headers of course.

Stu Fox