Best Heads For Gen-1 SBC
Article by Mark Trotta
One of the small-block Chevy's strong points is the cylinder head design. Even original, unmodified heads from the 1960's (in good condition) will perform pretty well by today's standards.
461 Castings
Back in the day, many performance small-blocks were fitted with 461 castings (#3782461). Even with the 'small' 1.94" intake and 1.50" exhaust valves, they were the best flowing factory heads GM had to offer at the time. They are easily identified by the double-hump shape on the end of each head.
Double-Hump Heads
Casting #3782461 heads became known as "fuelie heads" since they were originally fitted to 327/375-horsepower fuel-injected engines.
461 vs 461X
Casting #3782461 heads featured 160cc intake ports and 62cc combustion chambers.
Casting #3782461X had a larger 172cc intake ports and 64cc combustion chambers.
1.94 vs 2.02 Intake Valves
From 1964 through 1968, some, but not all, double-hump heads had 2.02" intake valves. These larger-valve heads were usually fitted to 327/350-horsepower and 327/365-horsepower carbureted engines.
462 Castings
Another good GM head is casting #3890462. The "462" double-hump castings are similar to the 461's but with the spark plug mounted slightly higher.
Other similar double-hump heads are the "291" (3917291) and "492" (3991492).
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Accessory Mounting Holes
Early Chevy small-block cylinder heads did not have accessory mounting holes on the ends of the head. Except for some early truck applications, it was not until 1969 that all small-block cylinders had factory-equipped accessory holes.
The only double-hump heads to have factory drilled accessory bolts are casting #3927186. These "186" heads were produced from 1968 to 1972.
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Good Used vs New Aftermarket
Finding a set of pre-1973 SBC heads is not an easy task, and finding a set in good condition is even harder.
If you find a pair, you won't really know what you have until you take the valves out and look inside. How many valve jobs has it seen? What other work has been done to them? Many a cylinder head has been ruined by an well-meaning mechanic and a Dremel.
This is where the aftermarket comes in to help us, and no other V8 engine has more performance parts available than the small block Chevy!
There are many excellent choices for performance small-block Chevy heads. Brand names include Dart, Brodix, Edelbrock, and Patriot. If cost is no object, any of these top name brands will give you a solid increase in performance.
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Here's a lower-cost alternative: Flotek 102505 Straight-Plug Heads.
Designed for use on Gen One small blocks up to 1986, they're ready to be bolted up right out of the box.
They're compatible with either solid (mechanical) cam/lifters or hydraulic flat tappet cams with up to .550 lift.
Flotek 102505 heads are very similar to the best factory heads: 2.02" intake valves, 1.60" exhaust valves, 180cc intake ports, and 64cc chamber volume. And since they're machined from aluminum, they're about 20 pounds lighter each than factory cast-iron versions.
And there are bolt holes on the front of the head to mount your accessories.
Slant Plug Heads
Specs on Flotek 101505 Heads are the same as #102505, but they have angled spark plug holes, so stock exhaust manifolds may give you clearance problems.
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Straight vs Slant Spark Plugs
Commonly found on many new replacement SBC heads, angled, or 'slant' spark plug holes set the plugs into a more ideal location for a fuller combustion at higher RPM's. It often helps reduce detonation as well, since the plugs are angled closer to the exhaust valves.
Back in the day, I ran a set of factory slant plug heads on my old 1970 Chevelle. They were the cast-iron, parts-counter-only version.
With a 350-hp camshaft, headers, dual-feed Holley and single-plane intake manifold, they made plenty of power!
Many of today's top header brands are designed for use with the slant plug heads. When shopping for headers, you may see the phrase "for use with angle plugs".
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Compression Ratio
If your 350 SBC has flat-top pistons with valve relief's, any 64cc chamber head will immediately help by adding compression. Going from a factory 76cc chamber head to a 64cc chamber head will raise engine compression from 8.5:1 to 9.7:1 with no other changes.
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Head Bolts For Aluminum Heads
Factory head bolts from a cast-iron head cannot be used with aluminum heads. Why? There are two reasons for this:
Aluminum head bolts need to be installed with a flat washer, so the head of the bolt doesn't "sink" into the soft alloy. This can cause cracks in the head.
And once the correct-size hardened washers are installed, the factory bolts are a bit too short.
ARP 134-3601 head bolts are available with a reduced wrenching hex head or 12-point head, that help eliminate the need for valvetrain removal when re-torqueing cylinder heads.
Aluminum Head Torque Specs
To ensure proper head bolt thread engagement, use the right length bolts and washers, and apply the proper torque value. Torque head bolts with washers in proper sequence to 40, 50, then to 60 ft/lbs. A little engine assembly lube helps prevent galling and improper torque values.
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What Pushrod Length Do I Need?
Any time there's a swap from factory to non-factory heads, pushrod length should be measured and verified. Hardened pushrods in a .100" or .150" longer than stock length are available if needed.
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Horsepower Per Dollar
If you're looking for for SBC replacement heads, aftermarket ones like Flotek will give you the least hassle and most performance for the money.
"The world's best cam combined with a poor set of heads will produce an engine that's a dog. But bolt on a set of great heads even with a poor cam, and that engine will still make great power." - John Lingenfelter
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