A Guide to Vortec vs OE Small Block Chevy Heads


Small block Chevy heads have been manufactured since 1955, and have been used in high performance applications as soon as the first one rolled off the assembly line. Fifty-five years of manufacturing have left us with an endless number of different cylinder heads for the SBC engines. General Motors estimated that through 2005, more than 90 million small block Chevys have been produced, which means that there have been at least that same number of SBC cylinder heads produced. Add in the amount of high performance heads that GM Performance Parts have sold over the counter and the number is astronomical.

Enthusiasts continue to search for the best combination for their applications, and despite the environmental regulations, it is clear that technology has advanced and GM’s cylinder heads have gotten even better with age. When the Vortec heads made their V-8 appearance in the late 90’s, it was inevitable that the question would be asked: how do old school cast heads compare to the newer Votec heads? We take a look back at the Vortec offerings and pack you full of info on the SBC OE head vs. Vortec debate! Read on!

Small-block Chevy Gen I combustion chamber.

Old School Gen I Cylinder Heads

The GM small block was specifically designed as a compact sized engine to embrace the economical use of iron and to streamline the production process. Part of the design process that was carried through to the Gen III design in 1997 was to create lightweight rocker arms for higher rpm operation, wedge combustion chambers for a broader power band, and deliver 4.4 inch bore centers (from the center of one bore to the center of the next bore).

The first small block with a 4 inch bore came in the ’62 Corvette 327, and it really opened eyes. Featuring the famous double hump marking on the ends of the heads, the #3782461 and #3782461X heads used 1.94/1.50 inch valves. These were commonly called “Fuelie” heads because they were released with mechanical Rochester fuel injection on the stock engines. The only difference between the two casting numbers was that the #3782461 featured 160cc intake port, 62cc exhaust port and the #3782461X had the larger 172cc intake port, 64cc exhaust port. The double hump heads continued to be a favorite with performance minded enthusiasts into the new millennium.

Casting number location on the Gen I style cylinder heads.

High performance enthusiasts separated the stock Gen I heads into closed chamber and open chamber heads. By far, the closed chamber factory heads were favored over the open chamber for making power due to the poor burn characteristics and no swirl (quench) inside the combustion chamber of the open chamber heads. Furthermore, the cylinder heads that were capable of making decent power were all manufactured when lead was prevalent in fuel and the valve seats stayed lubricated. Unless you were using leaded racing gasoline, the valve seats needed to be replaced with hardened valve seat inserts. By the time a racer was done modifying the heads, there was substantial monetary resources invested in the cylinder heads and it was hard to justify the modifications unless you were running in a class that dictated hardened valve seats in a cast iron head.

Casting markings and numbers on the old school cast iron heads.

Some of the More Popular Gen I Cast Iron GM Cylinder Heads

#3767754 – Manufactured from 1959-1961 on 283 Cubic Inch engines. Called the “Power Pack” cylinder heads. 1.72˝ intake valves and 1.50˝ exhaust valves. 60cc Combustion Chambers.

#3774692 – Manufactured from 1958-1964 on 283 Cubic Inch engines. Called the “Power Pack” cylinder heads. 1.72˝ intake valves and 1.50˝ exhaust valves. 60cc Combustion Chambers.

#3795896 – Manufactured from 1963-1965 on 283 Cubic Inch engines. Called the “Power Pack” cylinder heads. 1.72˝ intake valves and 1.50˝ exhaust valves. 60cc Combustion Chambers.

#3782461 – Manufactured from 1964-1966 on 327 Cubic Inch engines. 161/62 cc port volumes, 62cc combustion chamber. Identified by Double Camel hump symbol.

#3782461X – Manufactured from 1960-1963 on 283 and 327 Cubic Inch engines. 172/64 cc port volumes, 62cc combustion chamber. Identified by Double Camel hump symbol.

#3890462 – Manufactured from 1966-1967 on 302, 327, and 350 Cubic Inch engines. 64cc combustion chamber. Identified by Camel hump symbol. No accessory mounting holes.

#3917291 – Manufactured from 1967-1968 on 302, 327, and 350 Cubic Inch engines. 64cc combustion chamber. Identified by Camel hump symbol.

#3932441 – Manufactured from 1969-1970 on 350 Cubic Inch engines. 161-165cc intake port. 76cc combustion chamber.

#3932441X – Manufactured from 1969-1970 on 350 and 400 Cubic Inch engines. 161/65cc ports. 80cc combustion chamber. 1.94″ intake/1.5″ exhaust valves.

#333881 – Manufactured from 1974-1975 on 350 Cubic Inch engines. 76cc combustion chamber. 2.02″ intake/1.6″ Exhaust valves.

#3991492 – Manufactured from 1970 on 350 Cubic Inch engines. Available on the LT1 engine and over the counter. 64cc combustion chamber. Either straight or angled plugs.

Don McBride of McBride Performance Engine and Machining in Lake Elsinore, California, still prefers the old school cast heads because his shop specializes in building engines for circle track racing and desert racing. According to Don, “The old style heads were built with a lot of metal. You have room to manipulate and improve the flow on these heads. Of course we still have to build the engines according to the rules of the tracks that our customers are running at, and for the most part, the old style heads are what they are mandated to use by the rules. The newer style Vortec heads have a lot cleaner castings, however. In the 60’s and ’70’s, the factory didn’t pay much attention to how much metal was in each casting like they do today, so there is a lot more areas to clean up in the old style heads. Because of the extra metal, the old style heads seem to be less prone to heating problems, and circle track engines get pretty hot.”

In the 80’s, GM Performance Parts came out with their famous Bowtie performance heads for the small block. GMPP introduced the Phase I Bowtie small block Chevy cylinder head in 1981 for racing applications. Subsequent variations such as Phase II and Phase VI were later released, as well as NASCAR approved SB2.2 series. The Phase II was the most popular for hot rodders and featured a 184cc intake port volume, and 64cc combustion chamber. These worked well into the mid 80’s when after-market cylinder heads became the hot ticket.

Enter the Vortec Heads

Starting in 1996 on several GM Trucks and Vans, the L31 Vortec heads came on the scene. Not just a modification of existing heads, but complete redesign using the 1996 Caprice/Impala SS LT1 cast-iron head castings as a base. The biggest change GM made in the new design was revising the water jacket so the new Vortec heads could be used on conventionally cooled small blocks. The idea of using the 1996 LT1 cast iron head as a starting point for a new performance stock head came from the fact that it was the highest flowing LT head used by GM. The 1996 Caprice/Impala heads outflowed the Corvette Aluminum LT1 heads by as much as 20 cfm on the intake side. The cast iron Vortec head was in development six months longer than the aluminum head, and during that time, GM engineers tweaked the intake and exhaust ports for additional flow. The cast iron Vortec heads was one of the first to purposely integrate tumble instead of large swirl numbers in the design.

Vortec’s “heart-shaped” combustion chamber.

The newly redesigned Vortec cylinder heads were intended to replace the swirl-port Throttle Body Injection heads that were previously used on GM 350 trucks. What got the power merchants attention was the increase in horsepower from 200 to 255 solely based on the power generated by these heads. By the time you purchased a used double hump cylinder head and had it reworked, the cost was the same as buying a new Vortec head that produced more power. Circle track racers were tossing their double hump heads as fast as they could buy the new Vortec heads.

Location of the Vortec heads casting number.

How Many Types of Vortec Heads are Offered?

  • GM L-31 Vortec (Cast Iron)
  • GMPP ‘small port’ Vortec Bowtie (Cast Iron)
  • GMPP ‘large port’ Vortec Bowtie (Cast Iron)
  • GMPP ‘Fast Burn’ (Aluminum)
  • Edelbrock E-Tec 170 (Aluminum) 170cc intake runner
  • Edelbrock E-Tec 200 (Aluminum) 200 cc intake runner
  • Dart OE Vortec replacement head 165cc intake runner
  • RHS Vortec (available with either 1.940/1.500 or 2.02/1.600 valves)
  • EQ “Lightning” Vortec Style Cylinder Heads (Cast Iron)

On the non-bow tie L31 Vortec heads, the ports are larger than the older cast steel heads, so they outflow the older heads. The Vortec heads are a little bit lighter than the older heads and have a “kidney” or “heart” shaped combustion chamber that is more efficient than the double hump chamber.

The L31 Vortec comes in two different casting numbers, 10239906 (#906) or 12558062 (#062). Originally, the stock #906 casting head was available in two versions. One version had an Inconel exhaust seat with single angle valve grind and was available on 1 ton trucks. The other version was the traditional three angle valve grind. Other than that, the #906 is the same as the #062 head.

The Vortec head “saw tooth” casting marking.

GM Performance Parts Bowtie Vortecs are offered in “small port” (#25534351), which has 185cc intake ports/65cc exhaust ports, or the “large port” (#25534445), which features 225cc intake ports/77cc exhaust ports. Both GM factory and GM Performance Parts Vortecs come with 1.94 intake/1.50 exhaust valves. According to the engineers at GM, “Stepping them up to 2.02 valves doesn’t help them any, so it’s not recommended. The port was designed to match the 1.94 valves. With the Vortec flow velocity, you need less spark advance to make power which is a clear indication of a more efficient burn.”

Air-flow in the Vortec heads begin to decrease between .500″ and .550″ valve lift. Their true strength is low lift flow which gives more area under the total flow curve which is where valves spend most of their time during engine operation. Valves spend much more time at .400″ lift and below, which is where the Vortec outperforms most other heads. Combine this with high velocity, lack of turbulence, and superior combustion chamber design, and this is where the Vortecs really stand out. Even the GM Fast Burn heads can’t touch the Vortecs at low lift because their ports are too big which makes their air flow similar but with less swirl.

There are a couple schools of thought on the cast iron Vortec heads vs. the old school GM cast iron heads. The “bolt on” crowd likes Vortec’s advancements. Gaining 35-40 horses by simply bolting on a new set of heads is definitely a plus. The hardcore circle track racers that are subject to rules that mandate the use of stock cast iron Gen I heads view things a bit differently. We talked with Bobby Thomas at Bobby Thomas Motorsports who agreed, “Vortech heads are newer technology and make more horsepower out of the box and off of the manufacturing line, but they have less material to work with and are more prone to heat issues.”

How are Vortec Heads Different from Other GM Cast Iron Heads?

  • The intake port is designed with a cast “ski jump” on the port roof which is there to increase port flow velocity.
  • Port flow was designed to be high in the .300″-.500″ valve lift area to make power with relatively low-lift truck camshafts, whereas the old school Gen I heads liked higher-lift camshafts to make their power.
  • The bowl area is wide around the valve guide – much wider than the old GM cast iron ‘camel-hump’ heads.
  • The intake and exhaust valves and valve seats have a 3-angle grind from the factory.
  • The intake and exhaust valves are back-cut from the factory.
  • The combustion chamber has a “heart-shaped” design (‘double-quench’ design), whereas the Gen I cast heads were either open or closed chamber designs.
  • Best power is made with 32° total timing, although these heads can make power with timing reduced to 29° when used with short-duration camshafts. Older heads needed 32° and up to ensure a more complete burn.
  • Stock out-of-the-box Vortec heads have approx. 480 hp potential naturally-aspirated. Out of the box double hump cast heads produced from 25 to 40 hp less, depending on valve size.

Side by side.

Side by Side Comparison

We talked with Bill Hendren at Hendren Racing Engines about the flow characteristics of the Vortec heads compared to the old style cast heads. Bill explained that they had performed a lot of testing early on with the 906 Vortec heads and were initially surprised at the flow numbers. According to Bill, “The Vortecs required less work to get them to flow better. We tested our 906 Vortec heads with the larger 2.02 intake valves and it flowed in the 530 to 540 horsepower range where the old style cast heads flow in the 480 horsepower range.” Bill went on to explain that the Vortec heads were “limited on how much you could do with them though. We could only run the intake valves to 2.05″ where they started to lose air flow. And you can’t do much porting with them. If you get too wild with porting, you run into overheating and cracking issues.”
Other Vortec Tips and Tricks

  • Maximum valve lift on Vortec cylinder heads is .460″ to .480″. This range is due to production line machining and casting variance. It is highly recommended to check for clearance on anything over .460″ lift.
  • Vortec heads require a Vortec style 8 bolt intake. They should not be modified for older 12 bolt style intakes because there is not enough section thickness for proper bolt retention at the location of the center bolts. Besides, most intakes can’t be ported enough to match the raised intake ports on the Vortecs.
  • If porting the Vortec heads, a little clean-up on the Vortecs is alright. However, if you dramatically open up the ports you will lose the venturi effect in the intakes that makes them flow and perform as well as they do.
  • Use flat top or dished pistons to enhance flame travel and intake swirl.
  • Larger valves will increase flow but chamber modification is not needed. The trade off between shrouded vs unshrouded valves not worth the decrease in laminar flow and swirl.
  • Bill Hendren of Hendren Motorsports explained how they brought up the compression ratio by milling the head surface down. “The stock Vortec combustion chamber on the 906 heads is about 63cc’s. When we angle milled the heads 45 thousandths, we got the combustion chamber down to 56.8cc. When we angle milled them to 85 thousandths + 15 thousandths flat, we ended up with 51.6 cc combustion chambers.”

The Vortec heads (top) lack the heat riser and center intake manifold bolts that the old style heads have.

The Winner

Based on our information gathering, discussions with GM Performance Parts and Engine builders, and our own experiences, we found the Vortec heads to be the real deal. They are very economical, easy to get your hands on, and out perform the old style heads. The Vortec heads reigned supreme in every category except the “amount of work hours to make them flow better” category where the old style heads still rule. Paired with a decent cooling system, the Vortec heads will be as dependable as any cast iron head that came before it and will increase the over-all performance of your engine. That makes Vortec a real winner in my book!

Recommended Spark Plugs for Vortec Heads

  • AC Delco Rapid Fire Spark Plugs R44LTS
  • AC Delco Rapid Fire Spark Plugs MR43LTS
  • AC Delco RapidFire No 3 Sparkplug
  • ACCEL P526S U-Groove “SHORTY” Double Platinum (approximately 3/16″ shorter then R44LTS)
  • ACCEL 516
  • Autolite 26
  • Autolite 104
  • Champion RS12YC
  • Bosch HR10B
  • Bosch HR10BX
  • Bosch HR9DC

Article Sources

About the author

Bobby Kimbrough

Bobby grew up in the heart of Illinois, becoming an avid dirt track race fan which has developed into a life long passion. Taking a break from the Midwest dirt tracks to fight evil doers in the world, he completed a full 21 year career in the Marine Corps.
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