01/21/07

Subject: Quang Le's 1968 Camaro Z/28 - Chevrolet / Smokey Prototype 
                 “Hemi” 302 

Part Number(s):      Block # BWO-70065-98-B
                                    1968 Camaro - VIN – 124378N22393, Date code – 04D

Historical Perspective/Overview – General

 1968 Camaro Z/28 - Chevrolet / Smokey Prototype “Hemi” 302

The 1968 Chevrolet Camaro Z/28, identified on this page and the subject of this report enjoys the distinction of being one of the most uniquely  appointed marks of its kind in existence.  A rarity with unparalleled individuality since it is the only 1968 Camaro Z/28 with a Chevrolet Engineering built, 302 Cuin, semi- hemispherical head prototype engine.

In addition, to the extraordinary power train is an equally exceptional driveline and brake system.  This production Z/28 was appointed with the Four Wheel Disc Brake System that was available thru Chevrolet parts departments as a Heavy Duty Service Option. What makes it even more unusual is the fact that this equipment along with an electric fuel pump was installed at the dealership prior to vehicle delivery. It should be quite apparent that the intent was for racing.

1968 Camaro Z/28 Original Build Specifications 

• RPO Z/28 VIN# 124378N42239

• Build Date (04D)– Fourth week of April, 1968

• Interior (712) - Black Standard Bucket Seat

• Exterior (UU) - LeMans Blue

• Rear Axle Build Date (D168) April 16 1968 (note that the rear build date coincides with build date of car. (Dealer Installed, “Special Order” Four Wheel Disc Brake HD Service Option upgrade).

• Originally delivered with the standard 302 engine

• Dealer Installed Electric Fuel Pump and special wiring harnesses

The Original owner, Tom Prather of Kansas City, MO., bought the car with a specific intent on racing. Since that time, the car has never been street driven or tagged. Tom prepped the Camaro and raced in the SCCA Amateur Series in the A-Sedan category until late 1977. All original parts deemed unnecessary for racing where stored carefully for the future in the event the Camaro would be returned to stock.

Race History: 

 

     The race chassis enjoyed limited successes over the next several years in Trans Am events. Tom came in seventh overall against some big name racers in the 1970 Road Atlanta A Sedan event. 

 Smokey Yunick’s name appeared on the side of the car in 1977 along with with the new owner Steve Roberts. The special 302 was installed in the Camaro around that same time frame. The Camaro eventually ended up in Smokey’s shop for sale. Earl Rand purchased the Car February 5, 1981 and it was restored back to original condition using the boxed original parts in 1992. The car remained in storage until November 2004 and was sold at that time to Carl Todd. The car changed hands in January 2007, and is now in the possession of Quang Le. 

The SCCA logbook that accompanies this Camaro shows the Identity Number for Camaro VIN# 124378N422393 as 30-093. (Un-verified by Guinn’s)

Photographic Documentation – Restored 1968 Camaro Z/28

     The Camaro has been meticulously restored using it’s original stored parts as is evidenced by the following photos:

The following photos were taken during the restoration process

The following photos were taken during the restoration phase – Rebuild/Refinish

The following photos were taken during the restoration phase – Undercarriage

The following photos were taken after the restoration phase – Chevrolet / Smokey Hemi Engine

 302 Chevrolet / Smokey “Hemi” Engine History

         The Special Chevrolet 302 Hemi engine identified on the cover page (resident to the Camaro identified above) is one of three experimental engines built-up inside Chevrolet Engineering for the evaluation of the special "Bolt-On Head Package", specified for use with the 302 cuin engine.   The package was specifically intended for use in the 1969 Trans-Am events and was scheduled to be released in time for the beginning of the 1969 racing season.

         Three working prototype "Trans-Am" 302 engines were built up for evaluation using the special heads and related componentry under Build Work Order number (BWO) #70065-98-A, B and C. The effort was directed by and charged against Vince Piggins “Special Performance” engineering group.  The BWO appears stamped on both the block and heads. Under the BWO on the heads also appears the letters L.H. and R.H. respectively as the assemblies are unique to each side. The BWO # for the engine identified in this vehicle is 70065-98-B.  Also appearing on the valve covers are O-Dash numbers (0-314634) that identify the components as being experimental, interim or prototypes.

         The package consisted of special "modified semi-hemispherical" design aluminum heads, pistons, camshaft and Related componentry, designed to upgrade the 302 specifically to combat Fords formidable new engine development, the "Cleveland Head".  The Idea was set in motion June of '68 by Vince Piggins (Product Performance Group) and developed by Chevrolet Engineering's V8 Engine Group.  It was a hurried and short lived project ending early in '69, at which time it was dropped from further development primarily because the results were mot equivalent to the expense involved. 

     Test evaluations on the dyno showed the engine sacrificed valuable torque only to gain a small increase in power at the top end.  According to development engineer Bill Howell, the secret to winning (Trans-Am) is not top end horsepower but the overall power band for which the '68-'69 regular engine was famous for.

     The aluminum heads demonstrated no other appreciable advantage over the production iron units.  The killer blow for further development of the package came from early Trans-Am results which indicated the Fords weren't as invincible as was initially feared and therefore, there was no need to continue development to beat Ford. The heads and related components were assigned production part numbers but because they were cancelled early on were not cataloged or produced in mass.

      Regardless of the fate of these experimental pieces there was a great deal learned from the exercise. A small displacement, short stroke engine such as the 302 is easily over ventilated by increasing the intake ports to the point where the incoming fuel charge velocity is decreased. This will not allow the piston during intake stroke to "pack it in".  Thus producing a negative effect on horsepower/torque productivity and/or how it is distributed in the power band.

      The heart of the package are the heads themselves and making them breathe was the foremost consideration concerning development.  The massive port layouts were drawn up by design engineer Dave Martins and chamber design by Charley Turner, a former Chrysler design engineer who was no stranger to the "hemispherical" design.  Initial development was done with out the use of flow box technology.  Design was based on a combination of prior experience with the small block and the adoption of the current popular theory to obtain what might be considered the right combination of port and chamber design. Of course it all had to conform within the constraints of the small block design and be able to meet their specific objective. 

      Essentially the design of the heads was good but flow characteristics were not optimal and probably could have been further developed. The exhaust ports were found to be a major problem. The port shape was greatly compromised by the location the spark plug that required the port to curve around, thus creating a vortex, which made them a little lazy flowing the exhaust gases. 

     Prior to development of these experimental 302 aluminum heads there were various high performance aluminum heads developed that were almost exactly the same design as the production 302 head.  The question is often raised why those heads, since development was done and tooling available were not considered for use. First, it must be understood that it was not for the weight savings alone that these prototype 302 aluminum pieces were developed.

     The development processes of these two differently designed heads were each an individual and specific exercise in power production, each with a unique engine and set of governing factors for which they were developed.  Primarily the first design aluminum head was designed to be used with a normally aspirated engine of lesser power producing capabilities.  The prototype units that were specified for use with the 302 engine were built for use with the cross ram two four barrel carburetor system in conjunction with the "140" cam and header system.

     Specific power band requirements and engine characteristics were taken into account in each instance. Obviously, what applies to one small block does not apply to all, so...  although they existed, the first design aluminum head was not a consideration for use with the 302 racing engines.  Furthermore, development is a key factor, technology does not stand still and Chevrolet utilized their resources, constantly researching and developing new ideas in order to remain a winner.  

     Contrary to what has been previously written, these heads are not scaled down big block versions. Although they look similar to the ZL1 big block aluminum heads, looks are where the similarity ends.  They were designed from "White" having to conform to the small block configuration, any similarities between the two are purely coincidental. In fact they are actually closer in design to Fords Cleveland head, with symmetrical intake port spacing/shape as well as the combustion chamber shape. 

     The two most outstanding similarities visually are aluminum material from which they were cast and the appearance of the large valve covers, necessary due to the canted valve arraignment, which is again is only similar to the big block arrangement.

     Both the big block and prototype aluminum small block valve arraignments are laid out in repeated sequence cylinder to cylinder Example: int./exh, int./exh.  However, positioning of the valves in the head is opposite. The big block sequence front to back is exh./int. where the prototype small block aluminum head sequence is int./exh.  Incidentally, another major difference between the production small block heads and the aluminum prototypes are the valve sequences for the production small block head alternate cylinder to cylinder (exh./int.-int./exh.) where the aluminum prototypes as stated above repeat the int./exh. sequence cylinder to cylinder.  Consequently, special camshaft, Part # 3965556, unique to this package was produced. It was a flat tappet design the same as the "140" profile which was actually a Mark IV lobe.

      The intake ports on the small block prototype units are symmetrically laid-out unlike the double-paired spacing of the big block and production small block.  The larger valve covers were necessary due to the canted valve arraignment, which again is only similar to the big block arrangement. Combustion chamber shape is totally different with different "squish areas".  These combustion chambers are a modified semi-hemispherical chamber in design, due to the inclusion of squish areas.  A true semi-hemispherical head uses a completely rounded dome and piston for the combustion chamber.

Aluminum head casting with modified semi-hemispherical combustion chambers, canted values, 2.05 inch intake land 1.94 inch exhaust, extra large elliptical shaped intake ports and round exhaust ports which led virtually straight into the combustion chambers. The new head used magnesium valve covers which bear an uncanny resemblance to the designs seen on Jim Halls Chaparrals (see image below). The link here being the designer was assigned duties on both projects. 

      The new intake port design required the lower portion of the cross ram manifold to be redesigned to accommodate the larger reshaped, relocated, evenly spaced intake ports. Exhaust ports were also larger, evenly spaced and required newly designed headers.  The area of the water crossover and thermostat housing presented a problem when lower portion of the manifold was revised.  Because of the new port and runner lay out the water crossover had to be recessed into the interior of the manifold.  

    This necessary compromise was found to adversely affect power production due to its heating of the interior of the intake manifold.  Special domed and relieved pistons were developed to complement the new combustion chamber shape.  Compression ratio was 12.5:1 and oversize pistons were to be made available to bring up the cubic inch displacement to the 305 limit.  Lower end of the engine remained essentially the same.  The exception being modifications to the crankshaft counterweights to compensate for the new piston weight difference. The package was a bit more than a bolt on deal in that it required the cylinder block to be notched on the top deck surface in order to clear the exhaust valve push rods.  The push rods themselves were also specific to that package.  Because of the valve new sequences it was necessary to design a new camshaft using the same racing profile found on the "140" lobe.

Consideration for production ended after tests concluded the newly developed heads were not a significant improvement over the old cast iron counter-parts.  Which meant trying to justify 1000 pair of the expensive heads just to satisfy the SCCA ruling was cost prohibitive and ultimately out of the question.  However all was not lost, there was much to be learned from that exercise.  A small displacement, short stroke engine such as the 302 is easily over ventilated by increasing the intake ports to the point where the incoming fuel charge velocity is decreased.  This will not allow the piston during intake stroke to "pack it in" which produces a negative effect on horsepower productivity.  Essentially the design was good but flow characteristics were not optimal and probably could have been further developed, but time and money were the key factors then, just as today.

As previously mentioned, Jim Hall had some interest and influence on the design as did TRACO. However, the most prominent of all consultants employed  by Engineering on this project was Smokey Yunick.

The Smokey Connection (and beyond)

Author and Smokey in Philadelphia, PA (1990)

Chevrolet became frustrated with the project due to their inability to meet expectations of increased power over the TRACO ported 2.02 inch intake valve iron head base line. At that point, they brought-in Smokey Yunick to further develop the heads. His initial evaluation was validated when after four months of development the heads yielded no more significant power gains than were realized by Chevrolet. He knew from his experience working with Ford on the Tunnel Ports that the design was not well suited for the smaller cube engines. In any event he tried some exhaust port reconfigurations but the problem was that the heads over “ventilated” the relatively small cubic inch engine.

It’s interesting to note that at the time Engineering gave the project over to Smokey, Chevrolet had already received directives from Corporate that the Product Performance Group was to be reorganized and that development was shifting to lower performance, economy and SMOG control. This meant almost all performance-oriented development and power production was to cease - immediately. It was a hard decision for the performance Engineers to accept as well as the consultants who worked for Chevrolet Engineering. For them it meant the steady work they performed for Chevrolet would no longer be available.

It might have been a “correct” decision by Chevrolet Corporate since end-development was achieved for both large and small blocks as was demonstrated with the case with the “Hemi 302”. It also meant that the cash / parts flow from Chevrolet that was once was the bread and butter for consultants like TRACO and Yunick was now over. 

This began a very bitter era among the “greatest high performance development team in automotive history”. That being the Chevrolet Product Performance Group and the consultants such as Smokey, TRACO, Roger Penske, Jim Hall, McLaren and many others. So quickly did it change that many were in dispute over compensation due to them by Chevrolet for their services. Smokey was undoubtedly the most disgruntled. So much so, that he had numerous law suits against Chevrolet and to this day some have still not been resolved.

            In an effort to suppress Smokey’s fury, Chevrolet sent him the 302 “Hemi” headed experimental engines as compensation thinking that it was a significant value and that it just might satisfy him. In no way did it come any where close to what he thought he was owed.  Smokey had a much bigger compensation package in mind for the work he did over the years. The gesture just aggravated him even more knowing that the engines were developed to the fullest and could even be considered obsolete.

             In any event, Smokey did some further development on the engines. He had intended to develop a 350-cube version that had some promise due to the increased cubic inches. In fact, he had special pistons made from Ford forgings. But once again the project was put aside in lieu of more lucrative ventures.

             Around 1976, Steve Tate, a close friend of Smokey’s from Gallatin, Missouri, visited the Daytona shop and ended-up taking the three engines home along with the spare heads, pistons etc. Steve was the owner of Gallatin Motor Company and a man who had a real love for Corvettes and exotic Chevrolet racing components. Steve’s intent was to build a  “unique” 1969 Trans-Am styled Camaro using the 302 “Hemi” engine. Steve’s priorities shifted and he offered the engines to the author in a private sale. Not too long after (March, 1980) he listed one of them publicly through Hemmings Motor News along with the 1969 Camaro body.

    The engines were sold to separate concerns over the years. One of which (#70065-98-B) appears to have been sold at an earlier date and is consistent with the engine in this vehicle.

Historical Importance:

Chevrolet / Smokey 302 “Hemi” Engine

·         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.

·         In particular, this Prototype 302 “Hemi” Engine holds a special place in the development of the Z/28 302 as it represents the final stage of development prior to the 350 cube platform change. Essentially having the highest level of all 302 Z/28 engine.

·         The importance of this engine cannot be overstated as it was developed specifically by Engineering and Smokey Yunick to compete in Trans-Am events specifically for Roger Penske and Jim Halls use.

·         The history of this engine is exceptionally spectacular as the trail begins inside Chevrolet engineering - extends out to the most famous race car builder in the United States at the time (Smokey Yunick), and then onto compete in later Trans Am events as it was intended too.

·         An exceptional history with a most dignified and documented pedigree. It would be hard to find another engine that has been touched by as many famous and talented personalities in racing or in power plant development as was this.

302 “Hemi” Engine Specifications

Holley Carbs 

• List 4295 –
• Dated 941
• Part Number #3957859
• Primary Jets              69
• Secondary Jets         71

 Intake Manifold Top Plate            

• PN # 3941130 / PN # 3965549 (Second number appears immediately below the former)

 Valve Cover 

• Dated-            12 -2 –68
• Part Number- 0-314634

 Engine Block - 70065-98-B 

Hemi Heads

§         Dated                       10-14-68

§         Part Number(s)         70065-98-B LH

70065-98-B RH

 Push Rod Length

• Intake-             8.5 INCHES LONG
• Exhaust-         9.5 INCHES LONG

 Pistons                      PN # 3865534

• Clearance      .0068

 Rods and Journals

• Clearance      .003

  Cam

• PN  # 3965556
• Duration at .050          Intake             271

Exhaust          281

Valve Setting

• Intake and Exhaust    .019 Cold

 Oil Pump

• PN # 8704180

 Fuel Pump

PN # G140668

 Distributor

• PN #111480

302 “Hemi” Photographic Documentation 

Copyright Wayne D. Guinn, 2007
All Rights reserved, No portion of this report
may be reproduced without the express permission of Guinns Engineering

www.guinns-engineering.com