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Originally Posted by na svt
Advancing the cams a few degrees does increase DCR but only very little, the power gain comes mostly from the intake valve being open much further early in the intake stroke.
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If we were talking about a lazy port or a 2 valve combination I would agree but the 4 valve combo is very efficient at filling the cylinder do to its superior low lift flow and high port velocity. That leaves the benefit of placing the valve at a more effective lift when the piston is further down the bore and closer to maximum pressure differential, which helps of course but not to the extent of rendering dynamic compression insignificant.
Advancing the intake centerline 4 degrees on a 4.6 DOHC will pick up a little over a quarter point in dynamic compression. Since we know .10 increase equals 1% additional HP we can figure a little over 8 horsepower on a 350 rwhp combo from DCR alone. That's easily half the gain picked up from advancing the intake centerline. Not huge but certainly not insignificant.
Quote:
Originally Posted by na svt
The 106400s are not a good match for the stock intake or even a short runner (10"). We've gotten 370rwhp with 18 degrees less duration, stock heads and a ported intake and the mid range was much greater than what the 106400s provide. The 106400s need shorter runners (FR500, Sullivan) but in a 281ci engine they would make peak around 7800.
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Would be interesting to back to back some advanced 106400's against the cams you are referring to (20 degrees less duration) on a stock intaked combo.
In terms of average HP produced between 4000 and 7000 RPM I think I'd have go with the 106400's as long as ramp acceleration rates were comparable between the two. But I can see whre alot of people wouldnt consider the adversen drivability and loss of torque down low worth the extra HP.