COMP461
Comp Diesel Sponsor
- Joined
- Apr 23, 2006
- Messages
- 4,009
The reason to increase spring pressure specifications on an engine is to avoid uncontrolled valve action. In a turbo application it is compounded by the fact that you have boost to some degree working on the back side of the valve. It’s not as big a factor as most think, in that the pressure is in both the intake [Boost] and the exhaust, [turbine inlet pressure].
A critical factor in making a diesel cam program work, is to keep seat timing [ .006 ] as short as possible, while making the valve timing during the critical aspects [.200 ] generous . Numbers at [.200] are where significant amounts of airflow gain are achieved.
In the past many people would use cam masters with very slow ramps that overly extended seat timing and bleed off precious cylinder pressure, but didn’t contribute to airflow, and ultimately led to a cam changes in a diesel being thought of as non productive.
Another aspect is valve lift, and if the spring has the capacity to work with a given lift. The stock spring installs at 1.380 @ 70 lbs and coil binds at .930 , give it a safety margin of .040 off coil bind and that only allows you a maximum of lift .410 not really a problem on a stock head , the port stalls out before that , and you can remove the valve and not achieve any more flow . The flow numbers on a 24V/CR stock head are in the range of 145 to 150 cfm at 28 inches on a SuperFlow 600
Now take a worked head with a ZZ manifold and you’re approaching numbers in the 235 to 250cfm range with valve lifts extending to the .500 range. This is where power in made with 30% less boost, and an equal amount of Back pressure. Less heat and less chance of melting something.
Now you need more spring and the cam profile can take advantage of the port. I use springs that set up at installed height of 125 lbs @ 1.400 and coil bind at .780 you can set these springs at .040 off CB and have 580 valve lift. If you want to set them to stock installed height you can have 145 lbs on the seat. In The NitroFlash truck these springs will go to 6000+ rpm time and time again. We have never had one break.
In reality springs are a little extra insurance, but a lot of people don’t install springs and have had no problems The MaxSpool series can run with or with out them, until you get to the 3.0 and this requires a spring to cover the valve lift, and the acceleration rate of the lobe.
A critical factor in making a diesel cam program work, is to keep seat timing [ .006 ] as short as possible, while making the valve timing during the critical aspects [.200 ] generous . Numbers at [.200] are where significant amounts of airflow gain are achieved.
In the past many people would use cam masters with very slow ramps that overly extended seat timing and bleed off precious cylinder pressure, but didn’t contribute to airflow, and ultimately led to a cam changes in a diesel being thought of as non productive.
Another aspect is valve lift, and if the spring has the capacity to work with a given lift. The stock spring installs at 1.380 @ 70 lbs and coil binds at .930 , give it a safety margin of .040 off coil bind and that only allows you a maximum of lift .410 not really a problem on a stock head , the port stalls out before that , and you can remove the valve and not achieve any more flow . The flow numbers on a 24V/CR stock head are in the range of 145 to 150 cfm at 28 inches on a SuperFlow 600
Now take a worked head with a ZZ manifold and you’re approaching numbers in the 235 to 250cfm range with valve lifts extending to the .500 range. This is where power in made with 30% less boost, and an equal amount of Back pressure. Less heat and less chance of melting something.
Now you need more spring and the cam profile can take advantage of the port. I use springs that set up at installed height of 125 lbs @ 1.400 and coil bind at .780 you can set these springs at .040 off CB and have 580 valve lift. If you want to set them to stock installed height you can have 145 lbs on the seat. In The NitroFlash truck these springs will go to 6000+ rpm time and time again. We have never had one break.
In reality springs are a little extra insurance, but a lot of people don’t install springs and have had no problems The MaxSpool series can run with or with out them, until you get to the 3.0 and this requires a spring to cover the valve lift, and the acceleration rate of the lobe.
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