Building A 302 Chevy
Correct Cylinder Head:
Cylinder heads used on the 302s can be a bit confusing. In 1967, two different cylinder head castings were used on the 302, 3917291 and 3890462. Both heads used 2.02" intake and 1.60" exhaust valves. The confusion arises from the fact that the 3890462 casting was also produced using smaller 1.94" intake and 1.50" exhaust valves, although this head was never used on the 302. 1968 heads were also produced using casting number 3917291, but 1968 heads included a provision for a water temperature sensor not included on 1967 heads. Valve sizes were again 2.02" and 1.60" intake and exhaust respectively. To further complicate matters a small valve version of the 3917291 head using 1.94" and 1.50" intakes and exhausts was used on the SS 350 engines in 1968. So far that's two different versions of the 3890462 cylinder head and three versions of the 3917291 cylinder head! Both castings had the familiar "double hump" machined pad located on each end of the head. 1969 engines used head casting number 3927186 and featured the large 2.02" intake and 1.60" exhaust valves of the earlier heads. 1969 heads also have holes drilled and tapped in the ends due to a change in the alternator mounting method. All of the 302 cylinder heads, regardless of casting number, had the same characteristics. Large port volumes and large valves were used to facilitate breathing at high rpm, at the expense of low to midrange efficiency.
12480092 Cast Iron High-Performance Head (Large Valve)
This casting identification, "double bump," was originally introduced on the 1960 Corvette 283 CI with casting number 3782461. It was used on several high performance small-blocks such as the 327 Corvette Fuel Injection, 302 Z-28, and 350 LT-1 over the years, with many different casting numbers. In 1970 casting number 3991492 was first introduced and is still used to identify this casting today. (See chart for specifications.)
Technical Notes: The Cast Iron High-Performance Head (Large Valve) does not include 3/8" studs or guideplates.
3946882 High Performance Piston
This piston is for 68-69 Z28. This 302 .030 over-size bore, floating pin, high performance piston has a 11:1 compression ratio with 64cc head chamber volume (ID# 372176).
Chevrolet used many variations of their basic connecting rod over the years. All the rods were similar. Small block rods were 5.70 center length, and all rods produced prior to 1968 had a 2 inch rod journal diameter. All rods from 1968 on, including 1967 350 rods, have a 2.1 inch rod journal diameter. In addition, rods built until May 1967 have V groove holes in the rod cap.
All big block rods have a 6.135 center length and a 2.325 inch rod journal diameter.
The part numbers for Chevrolet rods are identical for each year Camaro, but there were variations in the rod design with the same number.
small journal, 11/32 rod bolts in 1967
large journal, 3/8 rod bolts 1968, 1969
magnafluxed (known as "pink rods" due to the pink residue)
1967 - early 1968 pressed pin
late 1968 - 1969 floating pin
Scatt BrandChevy Small Block Premium 4340 Forged I-Beam Connecting Rods with ARP 3/8" Cap Screw Bolts
Part # Description
2-ICR5700-2000 5.700" Bushed, ARP 8740 Bolts
Gen.I, "Small Journal"
Gen.I, "Medium Journal"
To arrive at the SCCA legal 302 cubic inches, Chevrolet used a 4.00" bore and a 3.00" stroke for 67-69 Z-28 engines.
The crankshafts used were forged steel, tufftrided pieces in all three years. 1967 models used a small journal crank with 2.00" rod journals and 2.30" main journals. 1968 and 1969 models used a large journal crank featuring 2.10" rod journals and 2.45" main journals.
SCAT CRANKSHAFT: Chevrolet Forged Custom 4340 Series 7000
Available in any stroke, pin size, main size, and counterweight style; aero-wing design counterweights for reduced windage on Pro Comp and Superlight style; nitride hardened for superior wear resistance; pendulum undercut counterweights on Superlight models; lightening holes in all rod throws; .140” fillet radius on all rod & main journals.
The blocks used in 1967 were casting number 3892657. These small journal blocks were also used for 327 and 350 cubic inch engines as well (all three engines used a 4.00" bore). 1968 models used block casting number 3914678 and featured the new style large journals. The 1968 block was also used for the 327/210 hp and 350 295 hp SS engines. The blocks used in 1969 featured thicker webbing around the mains and used nodular iron 4 bolt caps. A common misconception is that 1967 and 1968 302's were 4 bolt blocks, while actually the only engine to use 4 bolt main caps was the 1969 version.
10185047 350ci Bow Tie Block
This block, which can be used for 302ci, 327ci, and 350ci engines, is the same as the cast iron Bow Tie bare block P/N 10051183, except that it has a "straight" nodular 4-bolt main bearing cap. It also features "siamesed" cylinder walls which could give it a maximum bore of 4.090". It has a crankshaft diameter of 2.45" and the newer (1986 and later) one-piece type rear main seal. It replaces the older P/N 366287 4-bolt block, the difference being the one-piece rear seal rather than older 2-piece rear main seal. Block weight is 208 lbs. Main bearing torque specifications for all Bow-Tie blocks are 65 lbs. inner bolts, 60 lbs. outer bolts and 40 lbs. on 3/8" front bolts with light oil.
10051183 Cast Iron Bow Tie Bare Block (3.98" bore)
This updated design has a decidedly different appearance, but retains its original part number. New tooling procedures have significantly improved the quality and dura-bility of this third-generation casting. This heavy-duty cast iron Bow Tie block has rough-bored 3.98" diameter cylinders, which can be bored to a maximum diameter of 4.090". This block is recommended for maximum effort competition engines. The deck surfaces are thicker than production blocks, and the head bolt holes are blind tapped to improve head gasket sealing. The main bearing bulkheads are .900" thick and the front and rear bulkheads are reinforced with strengthening ribs.
The updated design on this Bow Tie block's oil galleries now extend flush to the front and rear faces of the cylinder case and can interfere with some camshaft drive systems. Therefore, timing system clearance should be checked before engine assembly. The revised Bow Tie block has a boss below the bellhousing flange behind the #8 cylinder that can be drilled and tapped for lifter valley oil scavenging. The outer water jacket walls have bosses to allow coolant passages to be drilled between adjacent "siamesed" cylinders. Oil drainback holes in the lifter valley are drilled. The updated design provides more consistency in the thickness of the cylinder walls and water jackets. The "siamesed" cylinder bores have a nominal wall thickness of .340" at the casting parting line (measured 2" below the deck surface).
Technical Notes: Oil dipstick hole is not drilled and the lifter holes are finish bored to production diameter .842".
2-bolt main bearing caps are installed to simplify the installation of the heavy-duty steel main caps with splayed outer bolts. Bow Tie blocks are designed for crankshafts with 2.45" diameter main bearing journals. The Bow Tie casting block P/N 10051184 is machined for a one-piece rear main bearing seal used on 1986 and later production small- block Chevrolet V8s. Crankshafts designed for two-piece rear main seals can be installed in Bow Tie blocks using crankshaft seal adapter P/N 10051118. These blocks weigh 187 lbs. Main bearing torque specifications for all Bow-Tie blocks are 65 lbs. inner bolts, 60 lbs. outer bolts and 40 lbs. on 3/8" front bolts with light oil.
10066034 350ci Bare Block
This 350ci iron bare block is used on the 1973-85 GM Goodwrench 350 engine and has the early-style 2-piece rear main seal. Its main bearing caps are the straight type four-bolt design. The block has a standard 4.00" cylinder bore.
Technical Notes: Can be used for 302, 327 and 350 engines. (Does not include oil galley plugs or dowel pins.)
All 302s used a special baffled oil pan (the baffles prevented the uncovering of the oil pump pickup as a result of the g-forces generated during acceleration, braking and cornering) and a high pressure oil pump.
360450 Oil Pan
Five quart Z28 oil pan with internal baffling. Left hand dipstick.
Technical Notes: Use gasket P/N 14079399.
12555884 Oil Pump
Production high-pressure Z-28/LT-1 oil pump with 1.20" gears. Will produce 60-70 psi oil pressure.
Technical Notes: Does not include screen.
Single four barrel aluminum high rise intake manifold: The basic design of the manifold remained unchanged from 1967 to 1969 although two different casting numbers were used. 1967 and 1968 engines used casting number 3917610, and the intake featured the thermostat hole located off-center toward the drivers side of the car. The engine temperature sensor on 1967 models was located in a drilled and tapped hole next to the thermostat opening. On 1968 intakes, this hole is plugged due to the relocation of the sensor to the head. 1969 intakes, casting number 3932472, centered the thermostat hole and are otherwise unchanged from the earlier intake. As an over the counter option in 1969 (available through the parts department, never installed by the factory), the Z/28 buyer could order a dual four barrel aluminum cross ram intake manifold (casting number 3940077). This intake was designed so that longer intake runners and two carburetors could be used while fitting under the stock hood. In 1969, the intake came with a special ZL2 cowl induction hood and air cleaner. This intake performed poorly on the street, but when used on high rpm competition engines (the engine was designed for SCCA racing, after all) really came into it's element.
All Chevrolet intake manifolds were either cast iron or aluminum. The aluminum intakes were built by Winters Industries and carry the Winters "snowflake" logo on the intake.
Aluminum Intake Manifolds:
3917610 4BBL Holley 1967-68 302 290 (Z/28)
3932472 4 BBL Holley 1969 302 290 (Z/28)
3941126 2X4BBL Holley 1968-69 302 290 (Z/28 crossram bottom half)
3941130 2X4BBL Holley 1968-69 302 290 (Z/28 crossram top half)
10185063 Intake Manifold
This manifold is used on all ZZ series 350 HO engines and also can be used on all small-block Chevrolet's thru 1986. This aluminum manifold produces the same horsepower as the previous high-rise design, but provides increased hood clearance and more versatility. It has a dual-pattern flange that can accommodate both standard-flange Holley and spread-bore Quadrajet four-barrel carburetors. This manifold has provisions for all late-model accessory brackets, EGR (exhaust gas recirculation), and an integral hot air choke. A heat shield can be mounted underneath the manifold to prevent coking when EGR is used.
Technical Notes: This manifold carburetor flange is approximately 1/2" lower than the LT1 manifold.
1969 Camaro Z-28 CrossRam: New licensed GM restoration parts crossram intake manifold complete bolt on package
Pt# 3940077 1969 Camaro Z-28. New licensed GM restoration parts crossram intake manifold complete bolt on package. The package includes top section, pt#3941130 dated 8/20/69 with Winters logo, bottom section, pt#3941126 dated 10/1/69 with Winters logo, 6 piece gasket set, top/bottom section attaching bolts, pipe plug, heater hose fitting, Holley List #3957859 4295 carburators, camshaft and lifters, fuel line kit with plated "Y" block, throttle linkage, linkage return spring and bracket, air cleaner, accelerator cable, accelerator cable bracket, flame arrestor, breather elbow arm. and anternator bracket.
All parts will be available seperatly also.
Last edited by Scorpio Shaping Flow; 02-08-2005 at 11:43 PM.
All three year model 302s used the famed solid lifter "30/30" Duntov camshaft, so named because of the .030" intake and .030" exhaust valve lash adjustments. This camshaft was also used in the 1964 and 1965 special high performance and fuel injected 327's installed in the Corvette. Again, due to the high rpm nature of the 302, a solid lifter camshaft was chosen.
Specifications for the cam are .452" intake and .455" exhaust lift, 229 degrees intake duration and 237 degrees exhaust duration (both measured at .050" tappet lift) and 78 degrees of overlap (at 0 lift).
Comp Cams Nostalgia Series 30-30+ Duntov 12-673-4
A proper custom roller cam optimized for a 302 would need to have a bit shorter lift compared with the small block Chevy norm. And the duration would of course have to reflect the rpm band within which the cam operated, but would probably need to be a bit longer to keep horsepower levels up with the shorter lift. So a good three-quarter race roller cam for a 302 might have between 245 and 265 degrees of duration at .05 inches of lift, but instead of .576" lift at the valve, it might need .556" lift. It would need to have a bit less in the way of lift to help neutralize the threat a high RPM, short stroke engine represents to its own valvetrain. Lower lift means less stress on the valvetrain components. This makes useful high RPM function more feasible. Even just a little bit lower a lift profile helps. Lobe profile optimization could also help in this area. The 302 is just a bit more of a race motor at a given horsepower level.
Last edited by Scorpio Shaping Flow; 02-11-2005 at 04:03 AM.
The 4150HP 600 CFM Holley carbutetor on an Edelbrock Performer EPS is just about right for a 302 Chevy. The engine will breath efficiently almost right up to an 8,200 RPM outer limit, which is about three-quarters race limit. On super stock race motors, 8,200 RPM represents a shift point, so a 650 CFM 4150HP and a Performer Plus Air Gap or Victor JR would work for a full race motor depending on application (600 would still work fine I imagine). The 800 CFM Holly which would historically belong to the 302 was good out to nearly 10,000 RPM in the breathing department - mini-modern-NASCAR.
Last edited by Scorpio Shaping Flow; 02-10-2005 at 08:53 PM.
What kind of horse power are we looking at when building a 302? Can I get more from my 350? The reason I ask is that I have a option to build a 327 or 350. I love the 327 but with the 350 I am already starting with more cubic inches.
Yea the question is what would be a better engine to build A) 327 or B) 350. I have a choice of the two and can't decide what to go with.
|Recent Hotrodding Basics posts with photos|
|Currently Active Users Viewing This Thread: 2 (0 members and 2 guests)|