03/22/05

 Subject:        Parr Chevrolet Cross Ram Air Cleaner Components

 Part Number(s):        Upper Half – PN# 3941146, Date code - None
                                        Lower Half – PN# 3941144, Date code - None

 Historical 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 Cross Ram 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.

Air Cleaner Lid and Base - Subject

General Description:

Chevrolet Cross Ram Manifold Air Cleaner - consisting of upper and lower Air Cleaner halves, stamped steel construction, chrome plated.  Components are original Chevrolet built and/or distributed and appear in good condition.

 The Air Cleaner components identified as the subject of this document are consistent with prototypical parts.

•  Most apparent and noteworthy are the imperfections in the chrome plating left by rods that were silver soldered to the plates in order to suspend them during the plating process. The marks appear on both ends of the top and bottom plates on the inside surfaces. The imperfections left by the rods required abrasive action to smooth the surface after the rods were removed. In addition, the solder interfered with the plating process causing a slight dis-colorization in a “halo” pattern around the affected areas. Production pieces that followed used a different suspension process (magnets) and do not have, to the same extent, the equivalent degree of discoloration and plating flaws.

• Hard shellac appears on the inside of the Air Cleaner lid around the carburetor stud holes. This material was used as a locking compound and was applied to the stud, wing nut and air cleaner surfaces. All other fasteners (nuts/bolts/pins) used on the engine and chassis were safety wired. This exception was necessary due to the inevitable need to quickly disassemble the Air Cleaner assembly with out too much difficulty but at the same time assure the wing nut would not loosen under the extreme vibrations of racing. This practice was consistent with Penske Racing protocol especially during the 24 and 12-hour events. The material that would have been seen on the top of the lid (wing nut recesses) appears to have been cleaned off at some point.

•  The lack of provision for a crankcase breather connector is consistent with the first assemblies made. All of these pieces were built up and pushed out the “back door” of Engineering to racers to help complete the Cross Ram package. The famous Cross Ram “Carburetor Installation Instructions” were issued on 3-20-68, several months following the release of these parts. The sheets show the final configuration of the plate with a provision for Air Cleaner Connector to satisfy National AIR Regulation mandates for production. The state of configuration, distinct anomalies and the time of build are consistent with units pushed out to Penske for use in Daytona. Shortly afterward, Penske replaced the Chevrolet supplied Air Cleaner with an all aluminum air box because the flimsy plastic air box was demonstrated to be incapable of holding up in competition.  In addition, it is highly probable that this air cleaner was evaluated and appeared on the 1968 16M541 Press Evaluation Car before it left Chevrolet Engineering (see Photo Documentation section).

Engineering Usage:

• Evaluation of 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.

•  In addition, 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.  Often times Chevrolet Engineering and Product Performance would send out what they had on hand to racers/combines who were considered “insiders”. Many of the parts processed through the ‘back door’ were pre-production pieces or prototypes that were clearly marked as such. Due to the specific state, estimated build time and evidence of Shellac consistent with Penske practice, it is likely that this unit was pushed to Penske Racing.

•  Based on the timing of sequences and the state of configuration, it is highly probable that these components were part of the Cross Ram unit tested on Engineering’s Technical Evaluation Camaro and the 1968 16M541 Press Car for press evaluations (See Photographic Documentation section)

 Historical Importance:

• This research attempt represents the successful and comprehensive documenting of a significant prototypical race bred Chevrolet development. A works in-progress touched by the greatest engineering talents in the world. An effort that changed the course of racing history and facilitated the most successful automotive marketing strategy for Chevrolet to date by helping capture the prestigious SCCA Trans-Am Series Manufacturers Cup for two consecutive years.

• In particular, these Cross Ram Air Cleaner components hold a special place in the development of the Cross Ram concept as it represents the final stage before production. Essentially having the highest level of development prior to going into service as Chevrolet Heavy Duty cataloged components with full production numbers as evaluated by the very designers who conceptualized it.

Photographic Documentation

Copyright Wayne D. Guinn, 2005
All Rights reserved, No portion of this report
may be reproduced without the express permission of Guinns Engineering