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Old 02-01-2010, 06:26 PM
oldbogie oldbogie is online now
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Originally Posted by hotroddin78
Well first off I want to say that ya'll have been a huge help to me in the past. I know that cams are all different between hydraulic flat, solid tappet, hydraulic roller and solid roller. my question is why? I know that roller cams are generally made out of billet and flat tappet cams are generally made from cast right? So why would I not be able to use roller lifters on a flat tappet cam? I am just curious. Is it because the spring pressures required for a roller cam are so much greater than what is required for flat tappet? Hence the stronger material for rollers? Well thanks again everyone. I was just messin around on my desktop dyno and realized that i can get more power out of the cam I just had in it but I am SICK to death of dealing with flat tappet cams and shaved lobes and have decided that I am most definitely going with hydraulic Roller this time around... Its a bit redic that in 30'000 miles and 8 years I have had to rebuild my 402 BBC four times cause i keep shavin cam lobes. Gettin a little tired of it. Anyway thanks for your input!
In addition to all you've been told about lobe angles there are several other issues. BIG ones!

You're kind of on the right track about force between the roller lifter and cam being higher than for a flat tappet. That's true without regard to greater spring pressure needed for high performance engines. Run of the mill grocery getters use the same spring between flat tappet and rollers but still need better material for the cam because the contact between the roller is much smaller than for a flat tappet so the loads per unit of area are much higher. If you ran a roller lifter against a flat tappet cam with the same spring pressure the flat tappet cam would surface crack and flake away very quickly.

The other issue you'd have running a roller tappet on a flat tappet cam would be a sudden loss of power. Roller cams always look like they have gigantic lobes compared to a flat tappet. This would be true if you took a flat tappet and a roller of the same timing and lift at the valve and laid them side by side. The reason is the lobes are shaped differently because of how the lifter rides them. The lobe of a roller cam more closely looks like the same curve as the motion of the valve. Because the roller lifter only provides a point of contact with the lobe. However, the flat tappet cam lobe looks very little like the motion of the valve if you graphed each. This is because the top of the lobe sweeps across the width of the lifter's diameter which takes time which is a measure of duration.

There is a secondary issue under flat tappets which is the often talked about but seldom adequately explained: the use of larger diameter Ford or Chrysler lifters in a Chevy engine. Their use requires that the Chevrolet cam have lobes that are custom ground to Ford or Chrysler contours, otherwise going over the top would hold the valve open too long and collisions would occur with the pistons. What these larger diameter tappets do is to allow a more aggressive rate of lift before the side edge of the lifter would dig into the lobe.

Bogie
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