Frequently Asked Questions

Small Block Chevy Aluminum Cylinder Heads

1. What spark plug should I use in my AFR Chevy Cylinder Head?
2. What should I torque my head bolts to?
3. Do I need Offset Rocker Arms with my AFR Heads
4. Does my 400ci Block require steam holes
5. How do I determine correct pushrod lenght?
6. Where can I purchase CNC ported AFR Aluminum Cylinder Heads?

 

Answers

1) Spark Plugs:

(14mm x 3/4" gasket) no tapered seat style! For race applications Champion C59YC, Autolite 3910 or 51, A/C R41CXLS & NGK R41 CXLS are good starting points. For street applications use AC FR3LS or RC9YC Spark Plugs or equivalent. Spark Plug selection is of course dictated by many factors including RPM level, compression ratio and type of fuel. All the above Spark Plugs are at a starting heat range; blowers or nitrous applications usually require 1 to 2 heat ranges colder. Spark Plug gap should be determined by the ignition manufacturer.

2) Head bolt torque:

All Aluminum Cylinder Heads should be torqued to 65-70ft./lbs. This should be done in the proper General Motors sequence in 10ft./lbs. Increments beginning at 40ft./lbs. All high compression, supercharged, turbocharged & nitrous motors should receive a re-torque after the first running and complete cool-down. Bolts containing a 12 point head are suggested in 3 areas on each head near the exhaust valve springs where it may be difficult to fit a standard 5/8 hex head sockets. In case of head studs use 12 point nuts. Air Flow Research stocks complete and partial Head Bolt kits, Studs and Washers for your convenience. Proper ARP #'s for Head Bolt kit, use #134-3701 and Head Stud kit, use #234-4301.

Torquing: We suggest not using a Torque Wrench on intake and exhaust manifold bolts, accessory bolts,or spark plugs, as inaccurate torque wrench values can easily strip the smaller threads. Just snug up hand tight with a wrench only.

3) Rocker Stud Location:

AFR Cylinder Heads feature two Rocker Arm Stud locations, standard GM L98 and an offset (for maximum intake port volume). The 180, 195, 210, & 220 Heads all use the standard GM Stud locations. The 227 & 235 guide plates are stamped with cylinder numbers. Install guide plates onto corresponding cylinders. Heads use the offset location which will require a matching Stud Girdle. AFR stocks both standard and offset Girdles and Adjusting Nuts for your convenience.

Guide Plates:

Use only the guide plates supplied by Air Flow Research! Push Rod Guideplates are supplied with each set of AFR Aluminum Cylinder Heads and installed correctly as shipped. Studs should be torqued to 60ft./lbs. Silicone sealer is recommended on aplications where the stud hole intersects the intake port. The 180, 195, 210, & 220 Heads use AFR #6110. The 227 & 235 heads use AFR # 6105. . For proper alignment of the rocker arms over the center of the valve, simply loosen the rocker studs and shift the guide plate back and forth until the proper alignment is achieved, then torque to 60ft./lbs.

4) 400 Blocks:

Steam holes are recommended for all 400 block applications (GM blocks only). Use a 400 Gasket as a template and drill the three holes, nearest the spark plug side of the head, straight down. The other three which are very near the head bolt holes should be drilled at a 30° angle away from the bolt hole. The center hole will intersect water about 1" down and the two outboard holes to a depth of 2 1/4". Use 1/8 drill.

5) Pushrods:

Visit the following sites for information regarding choosing the correct push rod length.

Holley Valve Train Technical Info
Holley Valve Train Geometry Info

6) Purchasing AFR Cylinder Heads:

You may purchase your AFR Cylinder Heads directly from Air Flow Research or any one of our authorized distributors.