12/15/04

Subject:         Rick's First Generation "Smokey" Cross Ram Manifold 

 Part Number(s):     Upper Half – PN# 3941130, Date code 9^.30^.68

Lower Half – PN# 0-310510, Date code 11^.15^.67 Rev. 12^.15^.67

                                    Carburetors – List 6895, Date 1388, Series 4150

General Description:

 Chevrolet Cross Ram Manifold Assembly

 Complete Chevrolet Cross Ram Manifold assembly consisting of lower and upper manifold halves, stamped steel heat (oil splash) shield, carburetors, linkage, fuel distribution block and hard fuel lines. Missing is the throttle cable bracket. All components are original Chevrolet built or distributed with the exception of the carburetors. All appear in excellent condition.

 Historical Perspective/Overview:

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

•  The lower half of the Cross Ram Manifold, identified above, was part of the initial or first working group of prototypes produced by Chevrolet. It was among four or five complete units built up inside Chevrolet Engineering that were 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.

·        Also seen are the remnant traces of flow experiments. Smokey conducted extensive flow testing on this unit by placing sensors directly through the manifold runners while running the manifold assembly atop a full race 302 engine on the dynamometer (pre-flow bench era). Confirmation of the testing is evidenced by repaired openings on the casting consistent with Smokey’s flow evaluation techniques of that period. The material of choice to alter or repair the aluminum manifolds was Devcon aluminum epoxy. It was used to build up areas in order to change flow characteristics and or repair areas where sensors were placed and removed.

• The distribution fixes (made to the manifold floor) 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 were hand laid in the manifold using aluminum wire and aluminized Devcon Epoxy

·       The bolts that normally hold down the top plate and the distributor were replaced with studs consistent with good racing practice and to avoid stripping the threads in the aluminum castings as a result of frequent breakdown and re-assembly as would occur during the testing and evaluation stages.

• The stamped steel splash shield or oil deflector plate was developed for use with the prototypes but was never made part of the production numbered units. The shield was demonstrated not to be necessary since there was no heat crossover to vaporize the oil that came in contact with the manifold. The plate was attached to the manifold bottom using steel rivets.

• Additional alterations to the lower manifold can be seen at the thermostat housing. The addition of a heater hose take-off (nipple) can be seen on the side of the thermostat housing. This location would later be incorporated into the design of the production units. It should also be obvious that the production location was decided based on this unit in conjunction with and in consideration of the later model water pump.

The rear of the thermostat housing was extensively altered in an attempt to work out a coolant return/temp sensor location. A plate with a tapped boss was welded-in and is currently plugged. For the production manifold, the location ended up as a boss on the coolant cross over passage near the manifold flange.

 After Chevrolet received the castings from Winters Foundry, internal testing began. At one point, at least two were sent to Smokey Yunicks Garage for evaluation and clearly, this lower manifold is one of the two.  Once in Smokey’s shop, the manifold was developed extensively. Based on the progression of development, and in comparison to other units of that group that I have examined, it is probable that this was the first manifold to have been tested for flow and to have the hand laid distribution runners placed inside.  Therefore, it was from this initial design layout that the others in the first group followed with slight variations as can be seen on the Daytona Penske unit shown in Camaro Untold Secrets book.

It is also likely that this manifold was the most highly developed unit in Smokey’s hands at the time of the 68 FIA races at Daytona and Sebring and was therefore was the unit put into service on his Number 81 Camaro entry. The car did not pass tech inspection at Daytona but did run at Sebring with Al Unser and Loyd Ruby sharing the driving. It qualified right behind Donohue/Fisher and was lightning fast in the straights, but the Penske Camaro dominated the corners. Unfortunately, after 3 hours the engine blew and the Penske Camaro went on to take the win.

• The upper manifold (top plate) is a later dated production piece consistent with the Cross Ram manifold units sold over the Chevrolet parts counter. The original top plate was probably heavily cobbled during development (flow experiments) and replaced with a later dated production top plate. In addition, the later model carburetors had clearance problems when used on the early plates and for that reason the plates were often switched out.

• The Holley carburetors on this Cross Ram are of a later design 4150 series 6895 (390 CFM). They are the dual feed, double pump, center float bowl and progressive secondary HP variety and have been altered for use on the Cross Ram. The throttle plates have been re-configured to accept the original diagonal linkage with heim ends. The float bowls were reversed front to rear in order to position the inlets to the inside to accommodate the fuel distribution pipes.

• Noteworthy is the alteration to the lower half of the manifold where material was removed to un-shroud the runners and thereby open the plenum. I speculate this alteration was one of the reasons why Smokey was faster in the straights than Penske. In theory, this may have decreased the vortex effect and corrected some fuel distribution problems. The trade off however may have been decreased torque and power in the lower rpm range – which would be consistent with Smokeys slower performance leaving the turns.

 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.

The correlation of written and verbal accounts related to this Cross Ram unit places its development and use in one of the most famous race cars and among the most famous racing and engineering personage of all that time.

 One of the most remarkable aspects concerning the development of this special equipment is that the actual factory prototype units were used on the racecars long before they became production pieces. Making it truly a product of race bred technology.

 Photographic Documentation

Copyright Wayne D. Guinn, 2004 All Rights reserved, No portion of this report may be reproduced without the express permission of Guinns Engineering