Reproduced with permission from: http://www.chevymania.com/
Many people are talking about Vortec heads these days. While the Vortec head is a very powerful and inexpensive production head, there is some confusion as to exactly what makes a head the Vortec head. This article will explain the Vortec head and give you picture comparisons so the next swap meet you will know for sure your buying a set of 'Vortec' heads!
A Little History
The Vortec name first appeared on 4.3L V-6 engines in 1986.These engines were the first to use a new "Vortex technology" designed to create a vortex (powerful swirl like a tornado) inside the combustion chamber. The Idea behind this is to create a more even and well-mixed air/fuel charge that both generates more power and is more efficient. Over the years, this Vortex technology has changed and improved to develop many new changes in the GM power train division. In today's world 'Vortec' means power and here is where the confusion starts. There are literally thousands of cylinder heads that have been made with the Vortex technology since 86 and many people refer to 87 and later small block heads as 'Vortec' heads. While this is a half-truth, the heads that GM sells under the Vortec name and the ones everybody is buzzing about did not exist until 1996.
Outside Appearance
From the exhaust side of the head you can't tell a Vortec from any other head. They look nearly identical to all other Chevy heads. The ends also look more or less the same. All the accessory holes on the outer edges look just like any other 87 and newer center bolt head.
The intake bolt pattern is different! It uses an 8 bolt attachment. This unique bolt pattern and the casting numbers are the quickest way to tell them apart from other heads. You also can tell by the casting mark on the end of the head since the Vortec head has a 3 triangle or 'saw tooth' casting mark. They are available under 2 casting numbers 10239906 and 12558062. Both casting are good and performance wise they have no difference.
The Combustion Chamber
The above left picture is a comparison of the 87 to date center bolt head combustion chamber (left in picture) and the Vortec combustion chamber (right in picture). The Picture on the right is a comparison of the 87 to date center bolt head and a 461 double hump head
(87 head on left in picture, 461 on right).
As you can see the Vortec head as a smaller chamber much like the early 461's but the spark plug is more centrally located in the in the chamber. The kidney shaped chamber promotes better combustion thus making more power. While they are 'advertised' with a 64 CC chamber they can vary from 64-68 CC's in production.
These heads are all produced with 1.94/1.50 valves but they can be machined to accept 2.02/1.60 valves.
The Bolt Pattern
As you can see by the picture on the left, the intake bolt angle is different, 72 degrees vs. 90 degrees of earlier heads. It is also located in the upper 1/3 of the head and uses a 5/16 coarse thread instead of the usual 3/8 coarse thread of earlier heads. When these heads are bolted on an engine, all 8 attachment bolts are almost strait up.
You can also see by the picture on the right that it has only the outer bolts and the center bolts are no longer used. If you look at the bottom right of that pic you will also notice that there is no heat riser passage either but there is an indent where it would have been.
With this new bolt pattern, you will have to have a Vortec style intake manifold!
GM
Part # 12496820 is a low-rise dual plane with EGR provision and dual carb bolt pattern.
Part # 12366573 is a high rise dual plane manifold with a Holley carb flange.
Part # 12496822 is a high rise single plane manifold with a Holley carb flange.
Part # 12496821 is a Throttle Body Injection manifold with EGR.
Part # 12498060 is the SDPC TPI Vortec base manifold.
Edelbrock
Part # 2116 Performer manifold non-EGR
Part # 7116 Performer RPM manifold
Part # 7516 Performer RPM Air Gap manifold
Part # 2912 Victor Reports 2-Barrel manifold
Part # 2913 Super Victor 4-barrel 4150 flange
A Word on Power
Valve Lift Intake Exhaust
.100 70 48
.200 139 101
.300 190 121
.400 227 140
.500 239 147
.600 229 151
As you can see in the table above that Vortec heads have excellent flow characteristics! In fact, GM states that these production heads flow better than Bowtie Phase 2 Cast iron heads!!! These heads have been used in many performance applications and 400 + HP is becoming a common figure with these heads!
When GM designed this head, they basically took the intake and exhaust ports from the now infamous LT1 cast iron heads (the ones installed on SS Impalas) and packaged them in a standard water flow cast iron head with a new bolt pattern. GM uses a new 'Cast Port' head process that make for a very good port shape that is consistent from runner to runner and cylinder head to cylinder head. The only drawback to the head is that the stock valve springs can only attain around .425" valve lift Mostly due to the oversized guide and tall seal height. Machining the valve spring pockets for larger valve springs and reducing the seal height will allow for lifts into the .550 range. Adding screw in studs and guide plates makes these heads quite good performance pieces but it can set you back about $200. Please note that these heads use a self-aligning rocker arm! If you have the screw in studs and guide plates done, you will have to get new non-self -aligning rockers!
Since these heads have been in production since 1996, you can find more than a few sets at swap meets and even salvage yards. GM sells them at the parts counter in 2 versions, a bare casting Part # 12529093 and fully assembled part # 12558060. The assembled version comes with 1.94/1.50 valves and stock valve springs. Both heads have 64 cc chambers, 170 cc Intake runners and 3/8" press in rocker studs.
Reproduced with permission from: http://www.chevymania.com/ ©
305 VORTEC HEADS
305 Head Casting ID
The 305 Combustion Chamber
Left:993 head with 2.02 intakes & 1.6 exhaust Right:Stock 305 Vortec
(The combustion chamber is unlike the 350 Vortec)
Edited by Dougofthenorth
Rev. 18JAN05
305 information & pictures contributed by SmallBlock
