Is this the same one you posted a few months ago on SVTP?
Quote:
Originally Posted by tmhutch
Advancing ICL
Advancing the intake lobe opening point can help performance in a couple ways. Opening the valve sooner increases overlap and allows the exhaust to have a greater influence on the intake charge as the intake valve is opening. Advancing the entire lobe also moves the centerline and effective lift of the opening ramp closer to the pistons highest point of velocity where it produces the most suction or pressure differential. Both of these attributes help kick start airflow allowing a weaker inlet path to appear bigger to the cylinder. As David Vizard said; what happens at the beginning of the intake valve opening determines the success of the entire intake event.
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This is the reason that a lower lobe center (LC) works well much better than a higher LC. However, advancing both cams and leaving the LSA the same works great in 4vs as the valve diameter/cylinder volume ratio is very high. Some overlap is needed but it's not undeard of to run an exhaust LC of 120 and an intake LC of 108 or less. Additionally, the higher the cubic inch of the engine the more overlap and to a greater extent, the lower the intake LC must be to ensure adequate filling of the cylinder. For example, in a recent buildup of a BB 5.4 by John mihovetz he set the LCs atsomething like 106/108 which is unheard of in mod motors. The result was some pretty impressive mid range and upper rpm power with cams no more aggressive than what a lot of people on M1R put in their 4.6s...think they overcammed they're engines?
There is a problem though and that is that 4.6 design results in little PTV clearance and this limits how far you can advance the intake cams. For this reason most aftermarket cams have 111 and 114 intake lobe centers. remember, higher intake lobe centers reduce tq and delay the onset of power. They make up for the later opening by adding duration, but combined the two result in lower hp and tq than what could be made by a lower duration, lower intake LC cam set.
Now these wide LSA, and high intake LC cams are okay for FI but for someone who wants to make big n/a power they flat suck. Ever see someone install comp 106400s, ported heads/intake and only make 370rwhp? If you've been on the boards long enough you have and the cams are the reason...well that and the thought that "stg 3" ported heads are needed to make power. Those people would have been better off with less duration and a lower intake LC. The result would be more tq and hp and a lot more average hp through the entire range.