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 HistoryThe 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.
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 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
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.
The Bolt Pattern
As you can see by the picture on the left the intake bolt angle for the vortec 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 the vortec 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 the vortec head 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 a indent where it would have been. Since the heat riser has been deleted form the vortec head if you choose to run these heads and have to retain the EGR valve for emissions you will have to change the exhast mainfolds, usually the drivers side at least, and obtain the EGR tube. This pipe feeds exhaust gasses from a port on the exhaust manifold to a port on the intake manifold that feeds the EGR valve.
With this new bolt pattern you will have to have a vortec style intake manifold, or you can drill and tap the cylinder head for the early style intake pattern. I have personally done this a few times but it takes very careful preperation and if not done correctly you can make the heads unusable. If you choose to try this you need to be aware of a few things, The old style intake and gasket may not cover the smaller bolt hole up top, The new bolt hole will intersect the smaller old one, drilling to deep on the outer bolt holes can punch through into the water passage, and the metal is kinda thin in the center where there are no existing bolt holes. I reccomend installing small 5/16 allen plugs in the old bolt holes with red locktite before you drill the new holes. Once drilled and tapped, clean with brake parts cleaner then cover the original holes and allen plugs with JB weld and smooth it down. This will prevent any leaks from sprouting from the old smaller bolt holes. When installing the bolts don't over torque the center 4 bolts or they will strip!!!! No more than 25 ft/lb on the center 4!
GM Vortec intakesPart # 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 Vortec intakesPart # 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
As you can see in the table above, Vortec heads have excellent flow characteristics! In fact GM states that production vortec heads flow better than Bowtie Phase 2 Cast iron heads!!! Vortec heads have been used in many performance applications and by many performance magazines over the years and on average these heads, with standard off the shelf intake, exhaust and conservitive camshafts, make 400 + HP.
When GM designed the vortec 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 vortec head is that the stock valve springs can only attain around
.425" valve lift, mostly due to the oversized valve guide bosses 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 for machine work. Please note that Vortec, and all center bolt valve cover style heads, use a self aligning rocker arms! If you have the screw in studs and guide plates done, you will have to get new non
self -aligning rockers!