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RPM Xtreme (Rectangular Port)
The RPM Xtreme for big-block Chevy is an all new design that is CNC ported where it counts to achieve optimal air-flow for maximum horsepower and torque in high performance street and light duty racing applications. The casting and port design are all new and engineered to be as close to perfect as possible. To ensure consistency from port to port, the RPM Xtreme is treated to a fully CNC ported combustion chamber, and then CNC ported in the bowl area (above the valve) for a smooth transition into the valve seats. The intake runner entries and exhaust runner exits are partially CNC ported for improved air-flow. RPM Xtreme big-block Chevy heads have a 24.5° x 4.4° intake valve angle, 15.5° x 4.2° exhaust valve angle, stock exhaust port locations, and the spark plug angles have been modified to produce a smooth flame front for increased fuel efficiency and maximum power. These heads also feature an exhaust port location that works with readily available, off-the-shelf big block Chevy headers.
Cylinder Head Specifications |
| Combustion chamber volume |
110cc / 118cc |
| Intake runner volume |
348cc (lh) / 356cc (rh) - #51539
344cc (lh) / 352cc (rh) - #51559 |
| Exhaust runner volume |
145cc (#51539) / 142cc (#51559) |
| Intake valve diameter |
2.300" |
| Exhaust valve diameter |
1.88" |
| Valve stem diameter |
11/32" |
| Valve guides |
Manganese Bronze |
| Deck thickness |
5/8" |
| Valve spring diameter |
1.55" |
| Valve spring maximum lift |
.700" |
| Rocker stud |
7/16" |
| Guideplate |
3/8" |
| Pushrod diameter |
3/8" |
| Valve angle |
24.5° x 4.4° (In) / 15.5° x 4.2° (Ex) |
| Exhaust port location |
Accepts stock port location headers |
| Spark plug fitment |
14mm x 3/4 reach, gasket seat |
| Made In |
USA |
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Technical Notes: Match with Edelbrock head gasket sets. |
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| Description |
Bare (single) |
Complete (single) |
| RPM Xtreme Big-Block Chevy (Rectangle Port) Small Chamber (110cc) |
N/A |
51539* |
| RPM Xtreme Big-Block Chevy (Rectangle Port) Large Chamber (118cc) |
N/A |
51559* |
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Flow Numbers as tested by Edelbrock's SuperFlo SF-1020 flow bench @ 28" H2O
| #51539 | #51559 |
| Valve Lift |
.200" |
.300" |
.400" |
.500" |
.600" |
.700" |
.800" |
| Intake |
158.1 |
237.2 |
298.8 |
344.4 |
366.0 |
377.1 |
385.0 |
| Exhaust |
134.0 |
189.7 |
227.5 |
254.9 |
267.4 |
271.9 |
279.7 |
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AMC
Small Block
