09/30/05

Subject: Rick’s Edelbrock / Chevrolet Cross Ram Manifold

Part Number(s):      Upper Half – PN# 0-310512, Date code – 12-8-67 (No Rev.)
                                    Lower Half – PN# 0-310510, Date code – 11-15-67 (12-14-67)
                                    Carburetors – LH & RH - List 4210, PN #3906631-DA

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 four or five complete prototype units built up inside Chevrolet Engineering slated for performance evaluation. Each of the units was O-Dashed Numbered (0-310510/0-310512) 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 now cast into the lower half. The oil 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.

Rick’s Edelbrock / Chevrolet Cross Ram - Subject

General Description:

Chevrolet Cross Ram Manifold assembly consisting of lower and upper manifold halves, first design carburetors, carburetor linkage, fuel distribution hardware, stamped steel heat (oil splash) shield, production oil fill tube, and accessory fuel filter. All components appear in good condition, some have been altered from the original configuration by design.

The manifold identified on the cover page and the subject of this document is consistent with the initial or first working group of prototypes produced by Chevrolet. It was among those four or five complete units built up inside Chevrolet Engineering and evaluated for performance by Engineering’s Product Performance Group and by Smokey Yunick at his shop in Daytona Beach.

The distribution fixes (made to the manifold floor - see image below) were accomplished primarily by gas analyzation methods, that is, obtaining readings by taking samples at the exhaust ports. Also utilized was the more gross method of "reading the plugs" after dyno runs following changes that were made based on educated guess work.

This particular area of development was complicated in that an intake port that is rich at low rpm can also demonstrate itself to be lean at high rpm. Needless to say, time spent in this area is crucial for the best obtainable performance results. It was through much educated guess work and extensive trial and error that the final runner configurations were made.

Some flow work occurred simultaneously inside Chevrolet Engineering and it’s interesting to compare the manifolds developed by both camps to observe the variations. The distribution fixes seen in this manifold were hand laid using aluminum wire and aluminized Devcon Epoxy.

IDENTIFYING FEATURES (Specific to Rick’s Edelbrock / Chevrolet Cross Ram)

Special Interest Historical Components:

Late in December 1967, Chevrolet Engineering sent the prototype identified in this report to Victor Edelbrock. Vic went on to modify the manifold and evaluate it for possible Edelbrock production. GM was not involved with the evaluation and further development work performed by Vic. Rather; it was solely an attempt by Vic to improve the product with the intent to compete in the aftermarket. As it turned out, the results were quite good and Vic began marketing Edelbrock’s “Street Tunnel Ram, STR-10”. The development work was driven by the requirement of universal application.

The following outstanding hallmarks distinguish this prototype unit as unique and easily identifiable:

Top Plate

The top plate was altered by removing the rear most carburetor throttle plate recess. This indentation is required on the Chevrolet prototype to provide clearance for the rear carburetor throttle arm. The indentation was no longer necessary since Vic decided to run both carburetors primaries facing forward. The recess was cutout and a flat aluminum plate Heli-arced fitted in its place flush with the top (see documentation section). The front recess was then downsized and streamlined since the Chevrolet linkage was not used. The new linkage developed by Vic was less obtrusive and therefore took less space from the interior of the manifold. The least amount of space taken from the interior means less internal disruptions and better flow characteristics.

A boss was added at the rear of the top plate to accommodate the power brake unit. The take-off on the Chevrolet Prototype was located in an awkward position on the front of the lower manifold half. It made sense to move it and create a more universal position for other models and chassis applications.

Good overall shot of the Chevrolet Prototype Top Plate (subject) that Vic altered. Insert on upper right depicts the O-Dash number (0-310512) and date 12-8-67. See photos below for details.

Lower Manifold

The lower half of the subject manifold was unchanged by Vic.


Subject lower manifold half above was un-altered.	Underside of the subject manifold with the oil splash shield removed shows Prototype Number 0-310510 and Date code 11-15-67 (revision 12-14-67)

Carburetors

The subject carburetors are PN #3906631-DA List # 3810. Chevrolet engineering modified these carburetors to conform to the #4210 configuration. They were once again were modified by Vic, having the air horns milled-off and float bowls reversed front to rear on the front carburetor in order to move the fuel lines out board.

Vic further modified the carburetors by adding secondary accelerator pumps to create to the double accelerator pump configuration. It could be conceived that these alterations influenced the later list # 4295 design. The only difference being the progressive secondary opening rate of the later design.


Engineering built (prototype) List # 4210 using PN# 3906631-DA carburetor is shown above. Note the List Number is hand scribed, the original List Number (3810) has been eradicated while the original PN# 3906631-DA remains.	Subject carburetor: Vic altered the List # 4210 by milling the air horns off. At one point, It was determined that the air horns were too close to the air cleaner lid when the low AFP 22 air filter was used. This situation resulted in restricted airflow and turbulence caused by air flow being forced to turn too acutely which adversely affected performance.
	Left: List # 4210 carburetor (subject) as altered by Vic to accommodate secondary pump system

Peripheral Hardware

Due to the re-configuration of the carburetor position(s) from the front carburetor primaries facing forward and rear carburetor primaries facing rearward, to both carburetors primaries facing forward, the linkage, plumbing and associated hardware was changed out. A special bell crank was devised to fit on the manifold top (see photo below). The linkage once again was a universal design in order to easily accommodate a mechanical accelerator rod from different models and chassis applications

Plumbing consisted partially of 1968 Z/28 Holley dual feed hard lines and fuel blocks tied together with braided line. A special one-piece bracket was made to incorporate a fuel filter and also act as a spring return.

Multi-use bracket devised for Fuel Filter and Spring return above. Below: special Bell Crank Vic Devised

With the exception of the fuel lines and brackets, all of concepts actualized by Vic on this Chevrolet Prototype manifold went into the production of Edelbrock’s STR-10 manifold including the throttle bell crank. In addition to the above modifications, the production STR-10 had a more streamlined tub (see photo documentation section) in order to correct fuel flow. This alteration in conjunction with the new carburetor configuration virtually eliminated the need for the distribution fixes.

Engineering Usage:

Evaluation of these components within Engineering consisted of a visual inspection as well as a functional assessment for form, fit and function and was gauged against performance expectations and pre-specifications set forth by Chevrolet Engineering. Therefore, these components would have been fitted and run on an engine dynamometer within the Engineering’s Product Development engine test cell and tweaked accordingly before it was sent out.

Additionally, it was not unusual for a pre-production prototype or evaluation piece to be pressed into service due to the high demand and short supply of these components. Victor was “in” with Engineering, and therefore great consideration was given to him by sending one of these first prototype units out to him.

Above is a rare glimpse of the Edelbrock Research & Testing Center "Manifold Field Test Car"

Historical Importance:

This research attempt concludes with the successful and comprehensive documentation of a significant prototypical race bred Chevrolet development. A works in-progress touched by the greatest engineering and racing talents in the world. One in which Chevrolet Engineering and one of the most influential aftermarket concerns synergized to the benefit of the racing public.

· The subject Cross Ram holds a most significant place in Chevrolet / Camaro history as it stands proof as to the degree of influence Chevrolet had on the public and how it helped shape aftermarket development once outside of Engineerig

Once again it should be noted that this Prototype has the fingerprints and hallmarks of some of the greatest talents in racing history. Victor Edelbrock, Bill Howell, Jerry Thompson and others.

Photographic Documentation – Rick’s Edelbrock / Chevrolet Cross Ram

Chevrolet Prototype as it left Engineering

Edelbrock Altered Chevrolet Prototype

To the left is the Chevrolet Cross Ram Vic modified (subject) to come up with his STR-10 Design. Compare Vic’s alterations to the photo of the Edelbrock STR-10 below. Note that all alterations to the top can be seen on the production STR-10 below

Edelbrock STR-10

Note how Vic streamlined the manifold tub (See Arrows) helping smooth the design and aid flow. This design change eliminated the need for distribution runners and facilitated the forward facing carburetor primaries.

Chevrolet Prototype Top Plate (underside)

Exactly as it left Chevrolet Engineering. Compare to the Vic’s altered plate immediately to the right.

Vic altered Prototype Top Plate (underside)

Note how the carburetor throttle arm recesses were altered to accommodate Vic’s new dual forward facing (primaries) carburetor design. The rear carburetor recess was removed completely, and the front indent was reconfigured. Also note the vacuum take-off was relocated to the rear of the top plate for a closer proximity to the brake booster. All of the top modifications were carried over to the Edelbrock STR-10 shown immediately to the right. Compare the two.

Production Edelbrock STR-10 Top Plate (underside)

The Edelbrock STR-10 top plate above is a direct descendent of Vic’s experimentation on the Chevrolet Prototype Cross Ram and subject of this report.


Chevrolet Prototype as it left Engineering	Edelbrock Altered Chevrolet Prototype Note both carburetor primaries both face forward. This alteration eliminated the need for the rear most top indent by placing the rear carburetor throttle actuator to the outside as noted above. Also note the linkage transfer set-up and compare to the transfer mounting boss holes on the STR-10 to the right.	Edelbrock STR-10 Most apparent is the change to the thermostat coolant outlet. This design was intended to make the manifold universal for all chassis applications with the use of a common flex hose.

Chevrolet Prototype as it left Engineering The vacuum take off on the Chevrolet Prototype was awkwardly located on the front of the bottom half of the manifold.	Edelbrock Altered Chevrolet Prototype Vic neatly heli-arced a vacuum take-off boss for the brake booster on the rear of the top plate.	Edelbrock STR-10 Here again we see that Vic’s Chevrolet prototype design went directly into the production STR-10.

Thanks to Jon Mello and the CRG for use of the STR-10 Manifold Images