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Performance Chevy Cylinder Head Comparison - Go With The Flow

When It Comes To Cylinder Heads, How Much Is Enough? Glad You Asked ...

By Mike Petralia, Photography by Mike Petralia

The valve angle changes I'm referring to here are the angle of the valve's face in relation to the piston's flat surface. Way back when, in order to fit the wide 90-degree V-8 inside a stock engine compartment, OEM engineers angled the top of the valve stem in toward the intake manifold, compromising flow. Race engine builders then started angle-milling cylinder heads to move the valve stem back out toward the exhaust side, which puts the valve in a better relation to the piston. This produced a better-breathing cylinder head, and as such more power came along with it. But angle-milling the heads meant that you also had to move everything else to match.

Today, cylinder head companies are simply moving the valve angles within the heads, but the intake manifold and rocker arm companies have a tough time keeping up with the varying angles. And so far I've only talked about rolling the valves toward the motor's exhaust side.

Canted valve heads' intake and exhaust valves are at different angles, and splayed valve heads' valve centerlines point out from each other as viewed from the top of the heads. This allows large valves room to open in small cylinders. Actually, canted/splayed valve technology is nothing new. Big-block Chevys have had it since their birth, which might explain why a stock oval-port big-block head can flow just about as much as many race small-block heads. The most important thing to keep in mind here is that whenever you move the valve angles around, it's going to cost more money to build the engine.

This illustration highlights how complicated the end of a normal V-8 valve can become. Study it carefully. All these angles, widths, and dimensions can be modified for increased performance. It takes days, even years to develop the perfect setup, and only the guys with the biggest budgets have the resources to find minute differences in power here.

The three-angle valve job you've heard so much about refers to the angle of the seat cuts on the valve and in the head. Typically, the valve actually has only two of the angles (highlighted in the circles), and the head has the third, a transition cut commonly called a "throat cut," used to blend the valve seat into the cast area of the port's bowl. It does not have a corresponding cut on the valve face, and the valve will never touch this area.

THE FOLLOWING IS BASED ON A COMP CAMS 292H MAGNUM HYDRAULIC CAM
DEGREES DURATION @
LOBE LIFT 1.46:1 1.60:1 DIFFERENCE
.006 289.5 291.1 +1.6
.020 273.9 276.0 +2.1
.050 253.4 256.2 +2.8
.200 188.1 195.1 +7
.400 98.6 118.1 +19.5
SOURCES
Air Flow Research (AFR)
Valencia
CA
N/A
www.airflowresearch.com
GM PERFORMANCE PARTS (GMPP)
Alabama Cylinder Head/Patriot Performance Cylinder Heads High Velocity Heads (HVH)
Knoxville
TN
www.highvelocityheads.com
All Pro Aluminum Cylinder Heads Holley Performance Products
1801 Russellville Rd.
Bowling Green, KY 42101
KY  42101
270-782-2900
www.holley.com
Arao Engineering, Inc. Indy Cylinder Head/Aerohead Industries
BMF Racing Heads Mike Petralia's Hardcore Horsepower
Brodix, Inc.
301 Maple
Mena
AR  71953
Performance Heads
Canfield Cylinder Heads
580 West Main Street,
Dept. MMFF
Canfield
OH  44406
Racing Head Service (RHS)
8-77/-776-4323
www.racingheadservice.com
Chapman Racing Heads
Woods Cross
UT
801-292-3909
www.chapmanracingheads.com
Summit Racing Equipment
P.O. Box 909
Akron
OH  44309
Dart Machinery
353 Oliver St.
Troy
MI  48084
248-362-1188
www.dartheads.com
Trick Flow Specialties
1248 Southeast Ave.
Tallmadge
OH  44278
330-630-1555
Edelbrock
Dept. 5.0
2700 California St.
Torrance
CA  90503
310-781-2222
www.edelbrock.com
World Products
Ronkonkoma
NY
6-31/-981-1918
www.worldcastings.com
By Mike Petralia
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