1979 Ford F-150 5.8L Cam Specifications

Print this articleWhile Ford's 351M and 400M engines (as used in F-150s of this vintage) may have gotten something of a bad rap over the years, their basic architecture does hearken back to the company's legendary Cleveland block. Essentially, a Cleveland block and heads with Windsor internals, the 351 "modified" engine is in some ways the best of both worlds. After all, that's the same basic recipe used for Boss 302s (except for the Windsor block), and you'll have a hard time finding anything bad to say about that.

Related Searches: Duration

Duration is one of the most basic of all camshaft measurements, and indicates how long the cam stays open. Duration comes in two varieties: "Advertised" duration (measured at 0.006-inch after the valve opens to 0.006-inch from when it closes), and duration at 0.050-inch, which is how long the valve actually allows air to flow through. The 351M's cam comes in at 282 intake and 292 exhaust (advertised) and 204 degrees intake and 214 degrees exhaust at 0.050-inch lift. If you're comparing notes, this is the exact same duration specified for the 351M's larger 400-cubic-inch cousin.

Lift

Like most cams, the 351M's rating comes in assuming the stock 1.72-to-1 rocker arm ratio; assuming that, the 351M's cam lift measures 0.484-inch at the intake and 0.510-inch on the exhaust valve. Lift at the cam lobe itself specs out at 0.281-inch on the intake and 0.296-inch at the exhaust. If you're using aftermarket 1.80-to-1 rockers, lift at the valve will increase to 0.505-inch intake and 0.532-inch exhaust. In 351M trim, this cam's duration and lift measurements give it an effective powerband of idle to about 5,500 for the 351M and idle to 5,200 for the 400M.

Lobe Separation and Overlap

Lobe separation angle is the distance in crankshaft degrees from the peak of one cam lobe to the peak of the next; LSA is intricately tied to valve overlap, which has an enormous impact on the camshaft's top-end power potential, torque, idle quality and fuel economy. Cams with more lobe separation angle have less overlap, meaning that the intake and exhaust valves spend less time open at the same time. This reduced overlap increases torque, idle quality and fuel economy but hurts top-end horsepower. A typical street cam will exhibit an LSA of around 112 to 114 degrees, while more performance-oriented cams may check in at 108 degrees. The 351M's cam has 112 degrees of lobe separation and 63 degrees of overlap; pretty typical for an emissions-era V-8.

Valve Opening and Closing

Intake valve opening and closing are important indicators of the "steepness" of a lobe's profile, or how fast the valve opens and closes. This is important because it tells you how long the valve stays at maximum lift, which determines its outright potential. The valves' open and close times measure in crankshaft degrees relative to the position of the piston; i.e. if it's at the top of its travel or the bottom. The 351M's intake valve opens 31 degrees before top-dead-center and closes 71 degrees after bottom-dead-center. The exhaust valve opens 80 degrees after top-dead-center and closes 32 degrees before bottom-dead-center.

References"The Ultimate American V-8 Engine Data Book, 2nd Edition"; Peter Sessler; 2010Wallace Racing: Automotive CalculatorsRead Next:

Print this articleCommentsFollow eHowFollow

View the Original article