Here's the factory cam specs:
___________________________________________________________
1971 351C-4V (M code) camshaft, D0AZ-6250-C
268°/280° advertised duration
duration @ 0.050” not available
0.427"/0.453" valve lift
118.5° lobe separation angle
Int lobe mathematic centerline = 116° ATDC
Ex lobe mathematic centerline = 121° BTDC
Exhaust valve opening = 81° BBDC
Intake valve opening = 18° BTDC
37° overlap
Exhaust valve closing = 19° ATDC
Intake valve closing = 70° ABDC
_____________________________________
1971 Cobra Jet (Q code) camshaft, D1ZZ-6250-A
270°/290° advertised duration
205°/220° duration @ 0.050”
0.481"/0.490" valve lift
117° lobe separation angle
Int lobe mathematic centerline = 117° ATDC
Ex lobe mathematic centerline = 117° BTDC
Exhaust valve opening = 82° BBDC
Intake valve opening = 18° BTDC
46° overlap
Exhaust valve closing = 28° ATDC
Intake valve closing = 72° ABDC
_____________________________________
1972 through 1974 Cobra Jet (Q code) camshaft, D2ZZ-6250-B
(Same as the 1971 camshaft except the camshaft timing was ground 4° retarded to reduce the dynamic compression ratio)
270°/290° advertised duration
205°/220° duration @ 0.050”
0.481"/0.490" valve lift
117° lobe separation angle
Int lobe mathematic centerline = 121° ATDC
Ex lobe mathematic centerline = 113° BTDC
Exhaust valve opening = 78° BBDC
Intake valve opening = 14° BTDC
46° overlap
Exhaust valve closing = 32° ATDC
Intake valve closing = 76° ABDC
_____________________________________
If you're considering replacing a factory cam with an equivalent cam, the Cobra Jet cam is still available. This cam was rated by Ford for 29 additional horsepower over the M code camshaft, the basic RPM Range is rated as 1700-4200 rpm. To the best of my knowledge these modern versions are ground on 115° lobe separation angles, and I recommend timing them for intake lobe mathematic centerline = 115° ATDC.
Blue Racer #972227
Melling #SYB-29
Clevite #229-1883
Sealed Power #CS-650
Manley #MS700
Lunati #11104LUN
Crane #C580
__________________________________________________
There were 2 other well liked cams sold by Ford in the 1970s and 1980s, and reproduced by many aftermarket companies. These are both a little hotter than the Cobra Jet cam.
The 505 cam (1970s) D1ZZ-6250-BX
Described as having a fair idle with lope, and a wide power band – its a hydraulic version of the Boss 351 cam. This camshaft was rated by Ford for 50 additional horsepower over the M code camshaft, 21 additional horsepower over the Q code camshaft, and 7 additional horsepower over the Boss 351 solid tappet camshaft.
290°/290° advertised duration
219°/219° duration @ 0.050”
62° overlap
0.505"/0.505" valve lift
114° lobe separation angle
Basic RPM 2100-5000
Blue Racer #972803
Melling #24224
Clevite #229-2072
Sealed Power #CS-173R
Lunati #11101
The SVO A341 cam (1980s) M-6250-A341
Described as having a good idle with lope, and good low to mid-rpm torque. This cam does not have as much high rpm pull as the 505 cam.
280°/290° advertised duration
214°/224° duration @ 0.050”
61° overlap
0.510"/0.536" valve lift
112° lobe separation angle
Basic RPM 2000-4800
Blue Racer #972836
Melling #24204
Clevite #2055
Sealed Power #CS-1021R
Crane #523941
______________________________________________________
If you're considering a modern performance cam with specs similar to the factory cams the Crane Cams H-278-2 hydraulic flat tappet camshaft or the Crane Cams HR-216 hydraulic roller tappet camshaft are modern off the shelf cams with similar drivability characterisitics (but higher lift and more horsepower).
I can also provide specs for custom cams ground by Bullet Cams that emulate the 1971 M code cam and will provide excellent drivability, excellent intake manifold vacuum, excellent low rpm power with even better performance and horsepower than the cams from Crane Cams. They use somewhat hotter cam lobes but not so hot to cause exessive valvetrain wear.
Here's feedback from someone running one of the cams ground by Bullet Cams
quote:
"... My engine is a 393 stroker, 10:1 compression, dished pistons, iron 4V closed chamber heads, 66cc polished chambers, blended bowls, hand ported by me, 2.19/1.71 valves, 7/16 studs, guide plates, beehive springs w/steel retainers, roller rockers, all good Comp Cams stuff; Edelbrock RPM AirGap intake, Demon 750 vac sec (annular boosters) carb, Pertronix ignition, 8° initial, 34° total advance. The exhaust uses 1-7/8" headers, 2-1/2" intermediate pipes, and magnaflow mufflers.
I was running a Comp Cams custom hyd roller 224°/230° @ 050, 0.572"/0.584" lift, 110° LSA, 110° ICL. The motor switched on @ 2200 rpm and was all done by 5600. 10" vac idling @ 1000 rpm; The motor had difficulty passing the smog idle test.
I installed the hyd flat tappet cam you specified, ... I needed a 9 way timing set to get the timing correct (straight up), but it installed perfectly and matched the cam card; the Bullet guys had it done in 3 days.
Anyway, I am ECSTATIC about the results so far! The motor will even idle down at 650 rpm now (wouldn't idle below 950 before) Vacuum at idle has jumped from 10 to 17 inches! And it idles cleanly (couldn't stand beside the car before at idle, it stunk so bad due to emissions) It has a nice lope to it, but still idles very well. I'd recommend this cam to anyone.
... the motor "turns on" at 1700 rpm now (was 2200 with the other cam) and pulls hard past 6200; just blipping the throttle, it revs so freely now to 4500 it makes me laugh; and it melts the tires at will and even breaks them loose shifting into second gear now (never did that before); its been all you said it would and more! I'm going to need more tires under it though (laugh) ..."
Regards!"
351C 4V Street Camshaft Shopping
______________________________________________________
A motor equipped with 4V cylinder heads is capable of excellent low rpm power and throttle response with the right cam and with a dual plane intake manifold. If somebody is having problems with the lower rpm performance of their 351C 4V it’s not the cylinder heads that are the problem, it’s the camshaft selection, the intake manifold design, the tune of the carburetor, the tune of the ignition, or the general condition of the engine (i.e. rings & valves).
The other small block in-line valve motors people are more familiar with have small ports and small valves for the given displacement of the motor, thus pushing the motor’s power band into the very lower end of the rpm range. Such motors rely upon camshaft and intake manifold design to widen the power band and promote mid and upper rpm power. The 351C 4V is just the opposite, the intake ports and valves were sized to give the motor response to 7000 rpm, the 351C 4V relies upon the camshaft design and intake manifold design for its lower rpm performance.
Camshaft selection for a street driven Cleveland motor with 4V heads should be limited to camshafts with advertised intake duration in the range of 270° to 290° (advertised duration) to prevent pushing the powerband too high in the rpm range. Overlap should be in the range of 50° to 62° for good low rpm power and good manifold vacuum. Exhaust valves should open approximately 78° to 84° BBDC (based on advertised duration) for good upper rpm performance and/or to help the motor cope with restrictive exhaust systems. Intake valves should close approximately 68° to 74° ABDC to steer clear of reversion. Camshafts having 112° to 115° lobe separation provide best drivability and compliment the design of the cylinder heads in supporting a wide flat powerband. Cams with 8° to 14° split duration (more exhaust duration than intake duration) allow the cam designer to center the overlap event around top dead center, thus aiding low rpm power. Many of the most popular 351C camshafts were (and still are) Crane Cams grinds.
Street Cams
LSA ...... Average Duration ........ Overlap
115° ... 280° through 292° ...... 50° through 62°
114° ... 282° through 290° ...... 54° through 62°
113° ... 284° through 288° ...... 58° through 62°
112° ... 286° ........................... 62°
average duration = (advertised intake duration + advertised exhaust duration) ÷ 2
The heads will provide good upper rpm performance as long as they are not strangled by restrictive intake or exhaust systems. The 351C 4V will make peak horspower at 6000 rpm with cams varying as widely as the Cobra Jet cam (270° advertised intake duration, 205° intake duration at 0.050), the Boss 351 cam (290° advertised intake duration, 235° intake duration at 0.050), the Crane HR-216 cam (278° advertised intake duration, 216° intake duration at 0.050) or the Crane H-278-2 cam (278° advertised intake duration, 222° intake duration at 0.050).
With the 4V heads and powerbands up to 7000 rpm the cam is the tool for shaping the motor's low rpm performance, but it takes a back seat to the induction system in regards to shaping high rpm performance. The way to increase horsepower at higher engine speeds is to improve the volumetric efficiency. Valve lift, cam lobe design, and the associated valve train play a part in that. But so do the heads, the intake manifold, the carburetor and the exhaust system.
To make my point, there is a Pantera owner whose Pantera is equipped with a standard displacement 4V Cleveland that makes over 500 BHP at 6000 rpm with the very small Crane HR-216 hydraulic roller cam! Only 216 degrees @ 0.050" intake duration. The Pantera's motor has independent runner induction and a bundle of snakes type exhaust with very open mufflers. The cam is obviously not responsible for all that power ... its the intake & exhaust systems, plus the iron 4V cylinder heads (which are mildly ported). The volumetric efficiency of his Pantera's motor is very high. The 4V heads are capable of very high volumentric efficiency, the intake and exhaust systems of that Pantera's motor are not hindering that performance.
-G