Small Block Chevy Head Identification Guide | Casting Numbers Explained
The GM Small-Block Chevy engine is the single most prolific powerplant ever made. With OEM production spanning almost 50 years, there is a reason it became the go-to engine for eons. In fact, it is still going, as the LS- and LT-series small blocks are just that—small-block Chevy engines, albeit with quite different overall architecture. This article focuses on the classic SBC, the Gen I (and Gen II LT-series) SBC cylinder heads.
How to Identify SBC Cylinder Heads
There are at least 20 distinct versions of OE Small Block Chevy heads, varying by port length and size, valve size, chamber volume, intake/exhaust port shape and size, and build material. These cylinder heads are mostly ID’d through the casting numbers (located under the valve cover), the casting marks (double hump, twin tower, etc.), and the valve cover bolt pattern. With nearly 300 casting numbers for Gen I/II SBC heads, SBC head identification comes down to knowing what to look for.
SBC Cylinder Head Identification by Year & Style
As demands changed, so did the cylinder heads. Some updates were internal, such as hardened valve seats, while others were external, like accessory holes. These differences simplify SBC head identification, which often starts with the last three digits of the casting number.
How Do I Find Casting Numbers on SBC Heads?
All Gen I/II/Vortec SBC heads have the full casting number located under the valve cover, between the first and second sets of valves. The casting block is on the end of the head. Gen III and up (LS- and LT-series) have three-digit casting numbers machined or cast into a block on the outside edge of the valve cover mounting flange. Check out our guide on Small Block Chevy casting codes to identify which engine block you’re working with.
Early Cast Iron SBC Heads (1955–1968)
The original SBC was a 265 cubic-inch “Turbo-Fire” making a whopping 162 horsepower. The first three years (1955-1957) used a 3.75-inch cylinder bore and 1.72-inch intake/1.50-inch exhaust valves. These heads have no accessory drive holes in the heads, as the generator was block mounted. In 1957, SBCs changed to a 3.875-inch bore to make 283ci and 307ci engines. The valve cover bolt pattern was staggered for 1955-1959 heads and changed to a square perimeter pattern (top and bottom holes are parallel), which remained until the center-bolt heads came out in 1987.
The 1957 283ci head (#3836842) is noted as the genesis for all future SBC heads. This head helped the 283 make one horsepower per cubic inch with the Rochester mechanical fuel injection system. Once the cylinders changed to a 4.00-inch bore GM used this head design in five versions (there are seven casting numbers).
Camel Hump, Double Hump, and Fuelie SBC Heads (1962–1970 Performance Models)
In 1962, the hottest heads were the #3767462, otherwise known as the “fuelie” head. When coupled with fuel injection and the Duntov solid lifter grind cam, these heads will make 340-360hp on a 327 block. This is the cylinder head that helped usher in the horsepower wars. There are five casting numbers for “double hump” heads: #3767462, #3814462, #3890462, #3927186, and #3917291. They all have the same casting block. These heads vary by valve sizes, while the three #XXXX462 heads use 1.94-inch intake valves, the other two use 2.02-inch valves. Heads with #3767462 and #3890462 casting numbers do not have accessory holes, whereas the others do. You’ll find a number of earlier heads without accessory holes that were modified over the years by adding the holes, so you must check when looking at original heads.
The #3932441 castings have a single large rectangular casting block. The large 76.26cc chamber opened up the heads to handle larger valves while increasing flow, making these heads popular with circle track racers of the day. These were only available in ’69-’70 Chevelle, Camaro, Nova, and handful of passenger cars fitted with the 255hp 350 Chevy heads.
Unless you are building a restoration or “original parts” vehicle, the camel hump heads are a bit dated. They use outdated port designs and have less flow than modern castings. Additionally, cast iron cylinder heads are prone to warps and cracks, and many still have the soft iron valve seats, which don’t do well with modern unleaded fuel. For stock heads, these are great, but they don’t hold up against modern technology. Speedway’s aluminum 461 SBC double hump heads are a terrific way to update an early SBC with modern cylinder head benefits wrapped up in a period correct exterior design.
Why Are They Called "Double Hump" Or "Camel Hump" Heads?
The casting block on the end of the head notes the overall design and era. The casting block on these heads features two round “humps” on a rectangular block (later models have slight angle on the exhaust-side of the head), somewhat resembling a camel’s twin humps. These heads were the go-to performance heads in the 1960s and 1970s due to their flow. Heads with 2.02-inch intake valves could hit 400hp without much effort.
Are Double Hump Heads Still Good for Performance?
Yes, double hump heads can support up to about 400 horsepower on a small-block Chevy when properly rebuilt, and slightly more if they are ported. They work best for performance builds that retain mostly stock components. However, if your goal is maximum horsepower, modern aftermarket cylinder heads are a better choice because they use updated airflow and combustion chamber technology. For Factory Appearing Stock Tire (FAST) racing classes, original “double hump” castings remain popular because they deliver impressive performance while maintaining a factory-correct appearance.
Late Cast Iron SBC Heads (1970–1986)
Do you want mediocre power and non-existent torque? Then boy, oh boy, do we have the era for you! While the high-performance engines of the 1970s used the same heads (with different casting numbers) as the high-performance 1960s models, the rest were smog-era junk, let’s be honest. These heads have three tapped holes for the driver’s side, and one for the passenger side.
All OEM cast iron ’70-up SBC heads have 3-5/8-inch center-to-center spacing between the top two holes on the driver’s side. Aftermarket heads have dual accessory patterns on the passenger side, and the factory aluminum Corvette, ZZ to ZZ4 heads have three holes on the passenger side with 3-1/4-inch center-to-center spacing between the top holes. You must use the correct bracketry for the heads you have, as later accessory drives will not fit the earlier pattern.
The reality is that the money it would take to port and install larger valves into a smog-era head would be much better spent on a new set of heads, cast iron or aluminum. The most powerful GM SBC built between 1973 and 1986 was the L82 in the C3 Corvette, maxing out at 250 whole horsepower. In fact, the most powerful Gen I SBC came quite early in the 1965 L84 327 at 375hp, followed by the 1970 LT1 at 370hp. This number would not be topped until the Gen III LS platform.
Corvette & ZZ-Series Aluminum SBC Heads (1980s–1990s)
The advent of electronic fuel injection into the GM stable brought us some pretty great cylinder heads, specifically the L98 and ZZ series. With Tuned Port Injection (TPI), these engines received aluminum heads for the first time. Casting numbers #14101128 and #14101083 both featured 1.94-inch intake/1.50-inch exhaust valves, with the aluminum 128s getting a 58cc chamber; the later cast iron 083 heads were 64cc. The 083 heads were EFI-specific, with angled center intake bolts (87-up), marking the last significant head design from GM until the Vortec head arrived.
The ZZ350 crate engines were released in 1989 for performance engine swaps. These were the first “real” performance crate engine, backed up by a GM 50k mile warranty, which was unheard of at the time. Using the L98’s 128 heads, these were the business back in the ’90s. The ZZ4 crate engine also uses 128 heads.
The L98’s heads suffer from lower high rpm air flow above 4,500 rpm, causing several issues, including blown head gaskets. They were still smog-era heads, better than the 1970s offerings, but still restrictive. These were great for mild street builds. Both L98 versions are still suitable. These heads require the use of the L98 accessory drive, which fits tight to the block. The Camaro/Firebird TPI drive is different and does not fit directly. You’ll need the entire accessory drive, including the crankshaft balancer.
Vortec Cast Iron SBC Heads (1996–2002)
In 1992, the second generation of small block Chevy engines was released as the LT1 in the Corvette, and then to GM full-size cars in 1996. Plagued by a terrible distributor placement behind the water pump (the famed Opti-Spark unit driven off the camshaft), these never really caught on. Never fear, GM was there with the Vortec heads.
Designed for trucks, the cast iron L31 Vortec head was a full departure from previous designs. These heads fit any SBC back to 1955 but require a Vortec-compatible intake manifold. Casting numbers #10239906 and #12558062 help ID these heads. Based on the LT1 heads, which was the highest flowing head, the Vortec heads were built to fit all SBCs, unlike the reverse-cooled LT1. 906 castings used a single-angle valve job, whereas the 062s got a typical 3-angle valve job.
Unaltered stock Vortec heads flow 190-240 cfm on the intake runners, and 130-150 cfm on the exhaust side. The intake ports were designed to have maximum flow from a .300- to .500-inch lift, making these heads perfect for engines with relatively small camshafts. In factory form, these heads can support up to about 480hp. On the dark side, these heads are cast iron, with thin areas that allow them to warp and crack when overheated. Valve lift is limited to .450-inch, reducing their power potential. Vortec heads require a Vortec-compatible intake and use center-bolt valve covers, just like all 1987-up heads. They also require special guided rocker arms.
Fast Burn Vortec Aluminum SBC Heads (1990s–2000s)
To update the Vortec heads for the aftermarket, the “Fast Burn” heads were released. These are 23-degree aluminum heads capable of supporting well over 500hp. Billed as budget heads that flow as well as CNC-ported heads, the Fast Burn Vortecs are a solid choice for any SBC build.
Which SBC Heads Are Most Sought After?
There are two sets of heads that match this question; double hump and Vortec head castings are the most popular for two specific build styles. The 462 castings without accessory holes are desirable for era-correct builds, 186 and 492 castings have similar performance with the accessory holes for later-model engines. For anything that does not need to be era-correct, the Vortec SBC heads are the best option for stock heads.
What’s the Difference Between Vortec and Non-Vortec Heads?
Vortec heads have eight vertical bolt holes for the intake, whereas Gen I heads use twelve angled bolts. The combustion chamber is a 64cc heart-shape for Vortec heads, yielding better flow and efficiency. Everything, from the head gaskets up, must match the Vortec or Gen I SBC heads, including the exhaust manifolds, intake manifold, and gaskets.
When it comes to your Gen I SBC build, finding the best cylinder heads are paramount to getting the performance you are after. Whether you are building a 283 for your Tri-Five or a factory-appearing Stock race car, finding the right set of original heads makes all the difference in the world. Either way you go, Speedway Motors has the goods to get your ride back on the road.
