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The intake manifold is an important part of the induction system. Basically it connects the carburetor or throttle body to the intake ports of the cylinder head and in some cases like the small block and big block Chevy engine, it seals the lifter valley and provides a means of mounting the distributor and water neck.
But that is just the tip of the iceberg. The intake manifold design has a lot to do with how the engine will perform and an radically influence the shape of the power band. Matching the intake type to the engine and vehicle specs is an important part of making a balanced combination, and the choice of what intake best suits the circumstances should not be taken lightly.
Factory intakes have run the gambit from simple log intakes with no concern for efficiency or high flow, to aluminum high rise intakes designed for multiple carbs (tri power and dual 4 barrels).
There have been "oddities" like Ford using a Q-jet on the 429 Cobra Jet, seen below:
Types of intakes
As of 2012 the Edelbrock Performer RPM/RPM Air-Gap intake manifold is considered to be the best of the breed. It consistently makes as good if not better power over a wider range than any of it's competitors. In fact, it rivals the open plenum intakes like the Edelbrock Vic/Vic Jr.- even at the top of the powerband, unless the cam and cylinder head intake volume are up there pretty good. It will always make more bottom end than the open plenum intakes but that is to be expected. But what is surprising is how well the RPM performs at the top of the power band.
The original Weiand Stealth p/n 8016, which has been discontinued and replaced by p/n 8150, is considered by some who are "in the know" to be an equal to the Edelbrock RPM.
The original Holley p/n 300-36 was possibly the best of breed in its day, and it isn't made any longer either. The replacement Holley p/n 300-36S is NOT the same manifold.
The Edelbrock RPM 7101, Weiand Stealth 8016 and Holley Street Dominator 300-36 were all patterned after the dual plane, high rise intake first used on the Z-28 and LT-1 in the late '60s and early '70s. Those original aluminum Chevy manifolds were cast by the Winters Foundry and will have the Winters "snowflake" cast into the aluminum.
Professional Products makes a knock-off of this design also, called the Typhoon, p/n 52021 for satin finish.
The so-called "air gap" intake concept has been around since the late '40s-early '50s. It has been used by various auto makers through the years, like Pontiac, as original equipment. Air can circulate beneath the plenum; the plenum is separated from the hot motor oil being splashed onto the bottom of the intake where it seals the lifter valley.]]
Only because the Chevy V8 uses the intake bottom to seal the lifter valley is this called to attention. Other engine that use a separate plate to cover the lifter valley have had "air gap" intakes all along.
The Edelbrock Air-Gap intakes will require a longer warm-up. In cold weather this can lead to driveability problems, almost like a tunnel ram. The air/fuel mixture- if tuned for a fully warmed up engine- will be lean until the engine is up to temp. This can be compensated for by the choke, but if using the choke, spirited driving is out until the choke is fully open.
Multiple carb intakes
Dual 4 barrel
One of the more iconic intake set-ups is the tunnel ram. First used in competition in drag racing, it was made a household word by driver/engine builder/tuners like Grumpy Jenkins (RIP). He used a 331 SBC with a tunnel ram/dual Holley 4 barrel carbs against engines ~100 ci larger than his in A/Stock- and won.
Adaptors have been used since the beginning. There are adaptors to mount dual carbs to a single carb intake, to mount 4 barrel carbs to 2 barrel intakes and vice versa, there are adaptors to mount a squarebore carb on a spreadbore intake and vice versa, there are adaptors to mount a squarebore carb on a Dominator intake, etc.
One of the more useful adaptors (if it can be called that; Edelbrock does) is the Edelbrock p/n 2732. It is a simple flat steel plate and a pair of gaskets used to prevent vacuum leaks at the secondary side of the intake when mounting a squarebore carb onto an intake having a carb flange designed to accept either a squarebore or spreadbore carb.
L30/L31 Vortec engines use fasteners made specially for the plastic intake they use. To prevent over torquing the fasteners and crushing the intake gaskets, the bolts come with a longer shank, designed to bottom out before the gasket is compromised.
Below the OEM bolt is on the left, an ARP bolt, right: