Poly 318, 390, 402 Camshafts
(applicable to 277, 301, 303, 313, 318, and 326 engines)
Introduction
This page discusses misinformation about the poly A-block camshaft and lifters, camshaft selection, and common camshaft profiles. While the 1957 – 1958 “Dual Fury V-800” poly 318 boasted the hottest factory cam, it was still undersized for what the engine can make use of with factory spec equipment and certainly for high-performance modifications. While mainstream cam manufacturers have given up on the A-block and we have lost some cam grinders like Chris Nielson (2017), we are lucky to have some custom cam grinders still around, including Schneider, CamCraft, and Racer Brown. Do not throw out old A-block camshafts since blanks are no longer produced and a regrind might be the most viable option. Cam selection is a precise process that depends on multiple vehicle variables from the engine back to the rear tires and should be discussed with the cam manufacturer. The following profiles are ballpark examples and should not be considered the definitive cams for every application. All specs below are with factory 1.5:1 ratio rocker arms.
Camshaft Misinformation
Before we dive into bump sticks, I want to debunk two claims that float around online: A-block and LA camshafts and lifters do not interchange. The LA camshaft will physically slide into an A-block and accept the timing set, but LA cam lobes are aligned for the inline valves of LA wedge heads, whereas the A-block’s cam lobes are aligned for a canted valve configuration (Figure 1). Similarly, LA lifters will physically fit into the A-block lifter bores, but the LA lifters are taller than A-block lifters and will create adjustment and binding issues if run with the A-block pushrods. To use LA lifters in an A-block, like I did on my 390 stroker build, you need to order shorter custom-length pushrods.
Factory Cam Profiles for Historical Comparison
“Dual Fury V800” 2×4-barrel
| Intake Duration (gross): | 256 |
| Exhaust Duration (gross): | 256 |
| Intake Duration (.050”): | 208 |
| Exhaust Duration (.050”): | 208 |
| Intake Valve Lift*: | .405″ |
| Exhaust Valve Lift*: | .405″ |
| Lobe Separation: | 110 |
| Valve Lash: | .017″ hot |
| RPM Range: | 1800-5500 |
“V800 Super-Pak” 4-barrel and “Fury V800” 2-barrel
| Intake Duration (gross): | 240 |
| Exhaust Duration (gross): | 240 |
| Intake Duration (.050”): | 198 |
| Exhaust Duration (.050”): | 198 |
| Intake Valve Lift: | .400″ |
| Exhaust Valve Lift: | .400″ |
| Lobe Separation: | 111 |
| RPM Range | 1500-4400 |
Popular Grinds for Mild Street Build Poly 318
- 3.23:1 or lower gearing, slightly higher stall converter, and headers beneficial but not necessary. Mild lope with good vacuum.
- Contact the manufacturers for comparable hydraulic grind availability.
EH-2 (courtesy Racer Brown)
| Intake Duration (gross): | 264 |
| Exhaust Duration (gross): | 264 |
| Intake Duration (.050”): | 220 |
| Exhaust Duration (.050”): | 220 |
| Intake Valve Lift: | .450″ |
| Exhaust Valve Lift: | .450″ |
| Lobe Separation: | 110 |
| RPM Range: | 2000-6000 |
264H (courtesy Schneider)
| Intake Duration (gross): | 264 |
| Exhaust Duration (gross): | 264 |
| Intake Duration (.050”): | 208 |
| Exhaust Duration (.050”): | 208 |
| Intake Valve Lift: | .435″ |
| Exhaust Valve Lift: | .435″ |
| Lobe Separation: | 112 |
| RPM Range: | 1800-4800 |
Popular Grinds for Performance Street/Strip Poly 318 and Mild 390 or 402 Strokers
- 3.54 or lower gearing, headers, and high-stall converter necessary. Decent lope and vacuum.
- Warning: Checking valve clearance at or above .480” lift is a must with A-block pistons.
SSH50 (courtesy Racer Brown)
| Intake Duration (gross): | 274 |
| Exhaust Duration (gross): | 274 |
| Intake Duration (.050”): | 222 |
| Exhaust Duration (.050”): | 222 |
| Intake Valve Lift: | .477″ |
| Exhaust Valve Lift: | .477″ |
| Lobe Separation: | 110 |
| Valve Lash: | 0.015″ hot |
| RPM Range: | 2400-6500 |
274F (courtesy Schneider)
| Intake Duration (gross): | 274 |
| Exhaust Duration (gross): | 274 |
| Intake Duration (.050”): | 230 |
| Exhaust Duration (.050”): | 230 |
| Intake Valve Lift: | .480″ |
| Exhaust Valve Lift: | .480″ |
| Lobe Separation: | 110 |
| Valve Lash: | 0.014″ hot |
| RPM Range: | 2500-6500 |
Popular Grinds for Performance Street/Strip 390 and 402 Strokers
- 3.73 or lower gearing, headers, and high-stall converter necessary. Strong lope with lower vacuum.
- Warning: Checking valve clearance at or above .480” lift is a must with A-block pistons.
SSH25 (courtesy Racer Brown)
| Intake Duration (gross): | 286 |
| Exhaust Duration (gross): | 286 |
| Intake Duration (.050”): | 238 |
| Exhaust Duration (.050”): | 238 |
| Intake Valve Lift: | .485″ |
| Exhaust Valve Lift: | .485″ |
| Lobe Separation: | 110 |
| Valve Lash: | 0.015″ hot |
| RPM Range: | 3000-7000 |
284F (courtesy Schneider Cams)
| Intake Duration (gross): | 284 |
| Exhaust Duration (gross): | 284 |
| Intake Duration (.050”): | 240 |
| Exhaust Duration (.050”): | 240 |
| Intake Valve Lift: | .480″ |
| Exhaust Valve Lift: | .480″ |
| Lobe Separation: | 110 |
| Valve Lash: | 0.015″ hot |
| RPM Range: | 3000-7000 |
Acknowledgement
My thanks to Gary Pavlovich and the tech support at Schneider, CamCraft, and Racer Brown for fielding my questions on the following profiles and my description notes.