Rocker Arms
This post was in response to rocker arm ratio and design on another forum. I have withheld the author for privacy sake. -BB94
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Happy New Year.
I was the dynamometer performance development engineer on the Fox bodied 5.0 GT V8 program from its inception in the late 70s through the late 80s, when I moved on to the new Modular V8 program. [My,my, how time flies...lots of good and humorous memories]
I did the rocker arm study in the early '80s, during the roller cam development period which was slated for the '85 GT, the last of the Holley carbed engines. We were looking to reduce friction in many ways to improve engine efficiency. These ways included low friction valve trains, low friction ring packs, lighter weight lubes, and other similar stuff. Ford historically rated their rocker arm ratios based on the instantaneous rocker arm ratio at the midpoint of the valve lift of the cam that was in use at the time the rocker arm was designed. This makes sense since at the midpoint of the lift the rocker lever arm will be at right angles to the valve stem, where the multiplication would be the greatest. Just because the instantaneous ratio at the mid-point is 1.5:1 does not mean the maximum lift at the valve will be 1.5 times the lobe lift. (Try that experiment on your next cam install with the stamped rocker arm. I guarantee the valve lift will be less than advertised and clearance-to-coil-bind will be greater.)
The rocker arm was not redesigned for the 5.0 GT - it was carry over. The ratio was based off the early, standard issue milder cam. So lets say the earlier standard V8 cam had a lift of .400" and the hipo GT cam had a lift of .500" (I've forgotten the real specs, it was likely less, but for the sake of discussion and keeping the math simple call it .4 vs .5.) That would mean the rocker arm had a ratio of 1.5:1 at .200" valve lift. Clearly that is not the midpoint of the GT cam but the budget did not call for a new rocker arm to match the GT lift profile.
When I looked at rollerizing the rocker I bought several brands to try on the dyno. That was a lot quicker and cheaper than designing our own. To our surprise the performance gains were more than could be explained just by the reduction in motoring friction, which was measured. At first I thought the stamped rocker arm may be distorting and flexing with a more aggressive and higher lift GT cam. But then I plotted valve lift vs lobe lift for all the brands. All the aftermarket brands raised the valve higher. So either the aftermarket rates its ratios in a different way, or more likely looked at the Ford stamping and decided to go more aggressively on the ratio. Of course we did design our own roller CAM to meet the performance criteria we wanted using the stamped rocker arm.
As a side note I have a reverse engineered flat tappet hydraulic cam in one of my hot rods that closely matches the roller cam lift profile. Nice!
Ever since then I've tried to use aftermarket roller rockers whenever the budget will allow. I even put together a 300 recently with roller rockers using the original pressed in studs and Crane cam, yet to be installed, break-in tested only.
So it wasn't any emissions conspiracy. It was a "follow the money" thing. New rocker arms for every cam profile Ford used over the years were never in the budget.
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