05/05/06
Subject: Grimaldi Chevrolet Cross Ram Manifold and Carburetor Assembly
Part Number(s): Upper Half – PN# 3941130, Date code – 8.18.69
Lower Half – PN# 3941126, Date code – 9.29.69
Holley Carburetors – PN# 3957859, List 4295, Date code - 891
Historical Perspective/Overview - General
1967 was the first year for Camaro in the SCCA Trans-Am Series. It was a hard fought season with a single four-barrel induction system as per SCCA rule limits. For the 1968 Trans-Am racing season the SCCA changed the rules from "Not more than one four barrel" to "Not more than two four barrels". This change was largely in response to unofficial factory prodding with the intention of creating a "More exciting Trans-Am series".
As a result, Chevrolet developed and released the "2X4 Carburetor Conversion Unit" PN #3940077 for use with the 302 Z/28 cuin engine. This special "Cross Ram Induction" system was made available over the counter through Chevrolet parts departments as a "Heavy Duty Service" option beginning December 1967.
Cross Ram Components - General
Prototypes: Initially, there were two groups consisting of four to five complete prototype units built up inside Chevrolet Engineering slated for performance evaluation. Each of the units was O-Dashed Numbered (0-310510) identifying them as pre-production or prototype components. These prototypes were exceptional in the sense that they would later be used in the SCCA Trans-Am Racing Series on various well-known racing chassis.
Performance evaluation on the first manifolds was conducted inside Chevrolet Engineering by the Product Performance Group and by Smokey Yunick at his shop in Daytona Beach. It was on these first prototypes that specific upgrades and corrections were made in an effort to extract the full potential of the components. Some of these corrections are quite evident and appear distinct from the original casting having been accomplished by hand. These alterations include the critically significant fuel distribution fixes (runners and dams) inside the lower manifold and the addition and removal of material for flow correction.
- Production: The production manifold was assigned production part numbers for top and bottom halves and the final configuration of the distribution runners were cast into the lower half. The splash shield that was part of the prototype was dropped as it was determined not to be necessary since there was no heat crossover to vaporize the oil that came in contact with the manifold. The water jacket was in its final configuration and the heater hose outlets redesigned with the 1969 water pump in mind.
Grimaldi Chevrolet Cross Ram and Carburetor Assembly - Subject
General Description:
Chevrolet Cross Ram Manifold assembly consisting of upper (PN# 3941130) and lower (PN# 3941126) manifold parts and special Holley carburetors (PN# 3957859). The components present in excellent, restored condition (restoration details to follow).
The manifold identified on the cover page and the subject of this report is an all-original, production Cross Ram assembly, cast by Winters Foundry for Chevrolet. It was made available through Chevrolet service/parts departments to the public as “Heavy Duty Service” optional equipment for the Z/28 - 302.
The carburetors are original Chevrolet production (PN# 3957859), matching date units (891) manufactured by Holley (List 4295) for Chevrolet.
The current owner, Mark Grimaldi, purchased the subject manifold and carburetors through Rick’s First Generation Camaro (Cross Ram Specialists). The components have been fully restored by Jerry MacNeish's Camaro Hi-Performance, Inc. The manifold surfaces were cleaned and reconditioned (re-skinned) using non-destructive techniques. The carburetors were disassembled, cleaned, re-colored and rebuilt to factory specifications.
Grimaldi manifold and carburetors in original used condition prior to
restoration.
As above in
restored condition. Components closely resemble factory new condition.
Photographic Documentation
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Subject manifold and carburetors as purchased though Rick’s First Generation Camaros. |
Subject manifold and carburetors after complete cosmetic and functional restoration by Camaro High Performance, Inc. |
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Subject manifold prior to clean-up and restoration |
Subject manifold after the restoration process (re-skin) is applied. Restored is the bright, factory like finish. |
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Above is the subject, original GM carburetor in used condition prior to restoration. Note 585 R on the front float bowl – This number more accurately represents the actual flow of the carburetor. |
Above is the carburetor on the left after cosmetic restoration and functional rebuild with close attention to detail. Chevrolet Part number, Holley List and Date are shown in the upper left hand side of the photo. |
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Inside the lower half of the manifold showing the production cast-in distribution runners and the winters snowflake and PN# 3941126 on the front intake runner. |
Underside of the unit showing (circle) the location of the production casting date. The subject unit was cast 9.29.69 |
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Quality Control Inspection stamps can be seen above the part number on the lower intake manifold. The “Circle IMP” stamp is relatively common on production pieces and is indicative of minor casting flaws that have been repaired in-house at Winters and approved for release. |
Two additional areas on the lower manifold exhibit inspection stamp “8”. One appears on top of the water outlet housing and the other in the tub on the second intake runner. Inspection stamps appear in different areas and represent various types of inspection operations ranging from mold release to machining operations. Some designate task confirmation and others QA checks for form fit and function. |
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Circled area depicts location of the cast production part number - PN# 3941130 with the Winters trade mark snowflake appearing directly above it. |
The underside of top plate revels the production casting date 8.18.69 |
