cam/lifter questions

[iceman]

What would happen if I replaced a set of solid lifters with solid roller lifters? Would there be damage to the lifters? The cam? What would it change as far as performance? I've asked these questions before and have always managed to get people that jump on the "just buy a roller cam" band wagon. The roller cam that I would have to get would have to be custom ground, and that's a little out of the price range for what I'm looking to do.

[mod71m]

You absolutely do not want to do that. The camshaft will not have anywhere near the same specs when putting a roller tappet on a camshaft that was ground for a flat tappet. The profile of the cam must change dramatically in order to get the same valve events when going from a flat tappet to a roller tappet. If you don't believe me then put the camshaft in an engine, degree it as you would with a flat tappet, then change to a roller tappet and see what you have. This is why the dial indicators that you insert into the lifter bore have a flat tappet and a rounded tappet side, so that you can get the correct readings!

There is a reason that everybody tells you to quit trying to do this and buy a cam that is made for roller lifters. It's because what you intend to do WILL NOT work correctly!!! The engine will run, but it will not run the way you want it to.

[50j]

I wouldn't try it. Not only are the valve events going to be different but good solid roller cams are ground on a billet core and need a lot more valve spring. To do it right would cost around 1k. Doing it wrong would probably cost the engine.

[iceman]

Thanks for the reply. What I'm trying to do is tame down an over-cammed engine. I was thinking that the differrent shapes of the lifter bottoms would reduce duration and move the RPM band down. My first concern is that they would damage components. But I am also concerned about what happens at the top of the lobe. But you've given me an idea. I can graph the differences using a degree wheel and a dial indicator in conjuntion with the two different lifters.
Thanks again!

[iceman]

50j, That's exactly what I'm afraid of. I'm hoping to find out if someone has actually done this and can give first hand results.

[mod71m]

It's a bit of a different story if you intend to decrease duration but there are still some drawbacks.

The biggest problem I can see with it is that the camshaft lobes are ground on a slight angle in order to spin the flat tappet lifters. The rollers of the lifters will be sitting on one edge of the cam for the most part and it's possible that it could cause problems with the roller and or bearings in the roller lifter. I would not increase valve spring pressure too far above what you would run on a typical solid flat tappet cam. Maybe 400 pounds open pressure at the max.

The issue for making power is that it will produce a very lazy, slow rising lobe with a lot of seat to seat duration. This is the opposite direction that camshaft technology has gone in the past 30 years.

I would guess that you will end up with less than desirable results but there's only one way to find out.

You can get a solid cam and lifters in the $300 range or less and I'm pretty sure you could find something off the shelf that is close enough (assuming you are working with a SBC)

[perfconn]

If you insist on trying it,be prepared to replace a broken cam.Flat tappet cams are made out of cast iron and will break with the spring pressure that roller cams need.Suck it up and buy a cam,they are only $300.00

[lazermod3]

Thanks for the reply. What I'm trying to do is tame down an over-cammed engine. I was thinking that the differrent shapes of the lifter bottoms would reduce duration and move the RPM band down. My first concern is that they would damage components. But I am also concerned about what happens at the top of the lobe. But you've given me an idea. I can graph the differences using a degree wheel and a dial indicator in conjuntion with the two different lifters.
Thanks again!

What you are attempting to do will happen.You will tame down the engine by carrying it home in a basket!