Original Posted By: "Richard Navratril"
Does anyone have an opinion (boy, wrong question here!) on the merits ofusing a reground camshaft that can be purchased from Bratton's for $50versus Dan Price's new ones for $250?Obviously new versus used is a consideration, but if it's not a weak point,does it justify the price difference? Also, Price cams are "stepped up,"whatever that means, still don't know if it's worth it.Gene Rambo________________________________________________________________________________
Pietenpol-List: Re: Model A camshaft
RE: Pietenpol-List: Re: Model A camshaft
Original Posted By: owner-pietenpol-list-server(at)matronics.com
Gene,As Les said, longer duration and higher lift. Longer duration will meanlonger overlap. This means the intake valve will open sonner and theexhaust valve will close later. This is good for high RPM operation but isreally bad for idling. Idling means a lot to us because the biggest brake,both in the air and on the ground, we have on the ship is the engine idlingthe propeller at low speed. We don't want the engine to idle at 800 rpm aswe need 400-600 rpm. We don't want it to quit on final either.High lift is usually where you can pick up meaningful low end torque whichis what we want. The downside of high lift is the springs are worked harderand more likely to fail. The good side is that with an L head, the springbreaking will not allow the valve to fall into the cylinder which we know isreally bad. The higher lift means more rapid acceleration of the valvetrain on opening and closing. This is not a big deal for us because at thePiet's rpms, inertia is not a big deal.To recap, short duration and high lift is generally what we want in the lowrpm band that we operate the A. A little extra lift will go a long way.This will maximize torque at the low end and have good idling. Hope thishelps.chris bobka-----Original Message-----
Gene,As Les said, longer duration and higher lift. Longer duration will meanlonger overlap. This means the intake valve will open sonner and theexhaust valve will close later. This is good for high RPM operation but isreally bad for idling. Idling means a lot to us because the biggest brake,both in the air and on the ground, we have on the ship is the engine idlingthe propeller at low speed. We don't want the engine to idle at 800 rpm aswe need 400-600 rpm. We don't want it to quit on final either.High lift is usually where you can pick up meaningful low end torque whichis what we want. The downside of high lift is the springs are worked harderand more likely to fail. The good side is that with an L head, the springbreaking will not allow the valve to fall into the cylinder which we know isreally bad. The higher lift means more rapid acceleration of the valvetrain on opening and closing. This is not a big deal for us because at thePiet's rpms, inertia is not a big deal.To recap, short duration and high lift is generally what we want in the lowrpm band that we operate the A. A little extra lift will go a long way.This will maximize torque at the low end and have good idling. Hope thishelps.chris bobka-----Original Message-----
RE: Pietenpol-List: Re: Model A camshaft
Original Posted By: owner-pietenpol-list-server(at)matronics.com
Gene,I forgot to add that most aftermarket cams will be designed with racing inmind. Racing means high rpm and we don't care for high rpm. With that, Iwould say the stock cam is better than an aftermarket.In addition, the standards used to measure overlap and duration (they aredirectly related) differs from cam manufacturer to cam manufacturer so thenumbers cannot necessarily be readily compared unlessyou are looking at twocams made by the same manufacturer.Also, a cam designed for use in a GPU application or something similar, willbe designed to optimally run at the design RPM, which for an A in a GPU typeapplicationm would be around 1900-2000 rpm. If it was a cam in an A thatwas used on some piece of farm equipment that ran at 1900 rpm all day long,then that would be a good cam design because it is trying to maximize thetorque at that RPM.Chris Bobka-----Original Message-----
Gene,I forgot to add that most aftermarket cams will be designed with racing inmind. Racing means high rpm and we don't care for high rpm. With that, Iwould say the stock cam is better than an aftermarket.In addition, the standards used to measure overlap and duration (they aredirectly related) differs from cam manufacturer to cam manufacturer so thenumbers cannot necessarily be readily compared unlessyou are looking at twocams made by the same manufacturer.Also, a cam designed for use in a GPU application or something similar, willbe designed to optimally run at the design RPM, which for an A in a GPU typeapplicationm would be around 1900-2000 rpm. If it was a cam in an A thatwas used on some piece of farm equipment that ran at 1900 rpm all day long,then that would be a good cam design because it is trying to maximize thetorque at that RPM.Chris Bobka-----Original Message-----