New rockers...
Each to their own but that seems like a hell of a lot of work for a few horsepower!!
Ill ask a dumb question, can't you order a cam with the specs you need?
It's not a dumb question at all. It's a really good question, and deserves an answer. I'll do the best I can:
Our motor is turbocharged. That means that whenever the boost (pressure) in the intake manifold is making its way into a cylinder, through an open intake valve, it's always trying to find another way out... ANY way out...
When the intake valve opens, at the start of the intake cycle, if the exhaust valve is still open (this phenomenon is called "overlap" in techno-circles,) some of that pressurized air (boost) from the intake port, will escape into the exhaust port, never making it into the cylinder where it belongs, doing nothing good for the power output... Less boost = less power, usually.
So, overlap is a bad thing on a motor like ours. Having the cam designed with wide lobe-center separation , helps reduce overlap; we use 115 degrees of lobe separation.
But, you can only go just so far with that crutch...
That leaves actual duration, sometimes measured at .050"-lift, for purposes of comparison.
When you get right doewn to it, reducing duration is the most basic way to reduce overlap and not risk blowing a significant amount of boost out the exhaust valve and port.
Our cam has 210-degrees of duration @ .050"-lift, much like a stock cam... certainly a mild cam by any accepted standards. More duration = more overlap, generally speaking... not a good thing when running a turbo or a supercharger.
Therein lies the rub in getting the amount of lift at the valve we wanted; (slightly over .500".)
With such a short amount of duration, the cam lobe profile necessary to raise the valve that much (over .500") requires a lobe design that steepens the angle of attack at the cam/lifter interface, to the point that the edge of the lifter is actually digging into the lobe and will grind it off in short order. So, to have a cam that will "live," something has to give... and, in this case, it's the amount of lift.
The highest-lift cam I could buy with 210 degrees of duration, was .484".... not as much as I wanted.
So....don't raise the drawbridge; lower the river!
Increasing the rocker arm ratio from 1.5:1 (nominal; they are usually not that high,) to 1.6:1 gave me the increased lift I was after without changing the lifter/cam interface geometry, and without increasing the duration. It increases the "effective" duration, but the opening/closing specs stay the same, but with more area "under the curve"... so hopefully, it can make more power.
There's more than one way to skin a cat...:cheers:
The aluminum 1.6:1 arms are very nice, but we just couldn't afford them, so we did the next-best thing. And yes, it was a lot of work, but, ultimately, satisfying.
Thanks for asking!
Hope this helps!
