since you have and use machine tools,
what about trying to machine a tapered flat onto the inner piston of your present hydraulic lifters?
If it does not work,
you will be changing to new hyd lifters with the new cam anyway.....
http://www.freepatentsonline.com/5623898.htmlsample quote
SUMMARY OF THE INVENTION
The variable duration hydraulic valve lifter described herein is designed to provide favorable characteristics over the entire speed range. At low and intermediate speeds a closely controlled oil leak in the pressure chamber is permitted to prevent pumping up to a wholly solid condition. This is accomplished with uniquely configured grooves in the outer surface of the plunger of the valve lifter. These grooves extend the entire length of the upper portion from its top edge to its bottom edge and also on the bottom portion from its top edge to its bottom edge. Each of these grooves has a greater width at their bottom end than their width at their top end.
The width of the grooves at their top end is in the range of 0.0042-0.0612 inches.
The width of the grooves at their bottom end is in the range of 0.0150-0.0625 inches.
The configuration of these grooves is referred to as a pyramid type cut. Also the depth of the grooves may increase from their top edge to their bottom edge. The depth at the top edge of the grooves is in the range of 0.0075-0.0150 inches. The depth of the grooves at their bottom edge is in the range of 0.0080-0.0180 inches.
Control tests have been conducted on a 1991 Ford pickup truck that was tuned-up to factory specifications. Then it was sent to a California smog station for testing. Once the smog testing was completed, it went to a wheel dyno for horsepower and torque testing. Thus provided with an accurate starting point established, the Ford pickup had the novel variable duration hydraulic valve lifters installed. No modification to the vehicle's engine of any kind was required nor was any retuning of the vehicle necessary following installation of the novel valve lifters. The Ford pickup was tested again at the smog station and on the wheel dyno. The testing revealed that the novel valve lifters made the following improvements: 91% reduction in hydrocarbons at idle, 37.5% reduction in hydrocarbons at 2500 rpm, elimination of deadly carbon dioxide at idle or at 2500 rpm, increased air flow through the engine, and 7.9% increase in horsepower and torque from the engine. The engine's warm-up time was also cut in half. An additional benefit was that there was an increase in gas mileage from 18.6 mpg. to 20.7 mpg.
The use of variable width grooves and/or variable depth grooves in the external surface of the plunger of the variable duration hydraulic valve lifters allows them to be effectively used with multiweight engine oils.
In prior art variable duration valve lifters such as the Rhodes lifters, the external grooves in the plungers had a constant width and depth. It was therefore difficult for the oil in their respective reservoirs to enter the bottom ends of their respective grooves and also insure that there would be a continuous flow of motor oil up the length of the grooves. As a result, spurts of oil would be ejected from the top ends of the grooves instead of a controlled continuous flow and the valve lifters would operate inefficiently at low and mid-range rpm. This produces a lose of horsepower and torque, incomplete combustion causing increased emissions and a decrease in gas mileage.
The use of variable width grooves and/or variable depth grooves in the external surface of the plunger of the variable duration hydraulic valve lifter also decreases the recovery cycle time considerably for the oil to leave the respective reservoir areas at the bottom of the respective upper portion and lower portion of the plunger, pass along their respective external grooves and return to their respective reservoir areas. The recovery time can be reduced by as much as 50 percent or more.
