11-08-2009, 03:32 PM
To see what you can make from a 351-C 2V, look at a comparison of stock cams for the 351-C 2V & 4V, 351W 2V & 4V, Boss 302, Boss 351, and other high performance 351 engines for various years. Then you can see how easy it is to boost the 351-C 2V. The top line of specs is for when the cam first starts to move the valve. The second line is for 0.050" lift, which is commonly used by cam manufacturers.
You can see that the 351-C 2V cam is rather mild in that the duration is low (Intake=258° & Exhaust=266°) as compared to the 351-C CJ (I=270° & E=290°) or the 351-C High Output (I=275° & E=275°) hydraulic cams. Note that the only difference between the '71 and '72 CJ cams is a 4 degrees, achieved through a different cam timing gear setting. The cams are exactly the same profile. Also, note that the stock 2V cam has only 0.400" lift.
Calculating Duration:
Intake Duration = Degrees before TDC + Degrees after BDC + 180. In the case of the stock 351C-2V, the duration is 12+66+180=258.
Exhaust Duration = Degrees before BDC + Degrees after TDC + 180. In this case it is 66+20+180=266.
Since the exhaust valve opens before the intake valve is closed, both valves are open at the same time. The exhaust actually helps scavenge the cylinder and suck gas in through the intake. This allows unburned gas to go out the exhaust, but it gets a larger amount of new gas into the cylinder more quickly. So this overlap can increase power, but is terrible for mileage.
The timings in the chart below are based on the position of the crank (degrees of rotation) when the valve first starts to open. An alternative is to specify the cam based on when the valve has opened 0.050 inches. This is often a better method and is frequently used by the cam manufacturers. You will see from the table above, the specifications can appear to change significantly using this alternative method.
You can see that the 351-C 2V cam is rather mild in that the duration is low (Intake=258° & Exhaust=266°) as compared to the 351-C CJ (I=270° & E=290°) or the 351-C High Output (I=275° & E=275°) hydraulic cams. Note that the only difference between the '71 and '72 CJ cams is a 4 degrees, achieved through a different cam timing gear setting. The cams are exactly the same profile. Also, note that the stock 2V cam has only 0.400" lift.
Calculating Duration:
Intake Duration = Degrees before TDC + Degrees after BDC + 180. In the case of the stock 351C-2V, the duration is 12+66+180=258.
Exhaust Duration = Degrees before BDC + Degrees after TDC + 180. In this case it is 66+20+180=266.
Since the exhaust valve opens before the intake valve is closed, both valves are open at the same time. The exhaust actually helps scavenge the cylinder and suck gas in through the intake. This allows unburned gas to go out the exhaust, but it gets a larger amount of new gas into the cylinder more quickly. So this overlap can increase power, but is terrible for mileage.
The timings in the chart below are based on the position of the crank (degrees of rotation) when the valve first starts to open. An alternative is to specify the cam based on when the valve has opened 0.050 inches. This is often a better method and is frequently used by the cam manufacturers. You will see from the table above, the specifications can appear to change significantly using this alternative method.
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