I'm getting close to switching to a roller cam in the big block!

[HawkRod]

Your new springs will be 400# for a few days or running until they settle in to the upper 300s. Unless you really want to upgrade, I suggest you save your money. If you had a race car doing 7000 RPM and your springs were in the 500# range and up I'd worry about it, but for a street car I think you'll be fine.

 

[BSB67]

View attachment 1926914

By looking at the two cams in the attachment, you cannot say which is more aggressive.

Aggressive speaks to the rate that the lifter and valve moves. The contact point between a roller lifter and a roller cam lobe is completely different than the contact point between a FT lifter and FT cam lobe. The contact point effects how the lifter accelerates.

Said differently, if you put a roller lifter on a FT cam lobe, it would move the lifter and valve way slower than a FT lifter on the same lobe. The valve and motor would see it as a smaller cam, and it would make a bunch less power.

 

[Geoff 2]

The contact point does NOT affect how the lifter accelerates. It is merely the contact point. The lifter does not know what is to come after the initial contact has been made.

 

[BSB67]

The contact point does NOT affect how the lifter accelerates. It is merely the contact point. The lifter does not know what is to come after the initial contact has been made.

Okay. It is the contact point between the lobe and the lifter relative to the centerline of the lifter.

 

[BSB67]

Here is a diagram that shows why a roller cam lobe profile “looks” more aggressive than a FT lobe profile to get the same lift rate as the FT.

The diagram would be an example of what happens with a roller lifter relative to a FT lifter on the same cam lobe. To get the same rate of lift for a roller lifter, the cam lobe needs a more aggressive shape.

 

[icetech]

Here is a diagram that shows why a roller cam lobe profile “looks” more aggressive than a FT lobe profile to get the same lift rate as the FT.

The diagram would be an example of what happens with a roller lifter relative to a FT lifter on the same cam lobe. To get the same rate of lift for a roller lifter, the cam lobe needs a more aggressive shape.

View attachment 1933573

thanks for that drawing , i had never considered how much farther into the lifter the contact point is on a roller.. had never really thought bout it though

 

[Geoff 2]

The rate of lift of a FT cam is limited by lifter diam because the edge of the lifter will 'dig in' to the lobe. Bigger diam lifter, more aggressive rate of lift & more lobe lift. That is why mushroom lifters were invented to get more lift & more area under the curve. Roller lifters do not have this limitation.

 

[6872n73]

Tried to post the link but it would do it, this is close to your build Kern and close to what I'm wanting as well.

 

[Kern Dog]

Are YOU Mopar Joe?
If so, WELCOME to the forum. I have enjoyed your videos for awhile now.
I bought most of what I needed to do this swap and have been putting it off. I keep finding other things around here to do but it is still on the list!

 

[Mopar Hunter]

Tried to post the link but it would do it, this is close to your build Kern and close to what I'm wanting as well.

This one?

 

[6872n73]

This one?

That's it!

And no I'm not Mopar Joe, I stumbled across his videos and this hits close to home.

 

[Kern Dog]

I don't know if I had asked this before but....
Why is the camshaft supposed to be limited to just .010 movement fore/aft? I understand the need to control some movement but why is it limited to such a small amount ? If the lifter wheels are still in contact with the lobes beyond .010, why such a narrow range of movement?
I'm not looking to be a hack here, I just wonder why...

 

[66 Sat]

Maybe to limit the wear from the "scraping" that will occur - rather than the 2 surfaces rotating against each other they will also be rubbing against each other horizontally?

 

[Geoff 2]

Because it:
- changes the ign timing
- moving the helical gear contact off centre [ with the pump drive ] increases the gap between the gear teeth; this causes ign timing variations & may increase tooth wear because of the 'hammering' from increased gaps.

 

[Kern Dog]

I'd agree with that if the flat tappet cam setups also had to be limited the same way.
Lobe taper....I understand that it pushes the cam forward or rearward, I don't recall which direction. I don't quite understand if it does push it rearward in a small or big block because that would put the last cam journal against the cam plug that seems to be a variable as to where it actually sits in regards to the depth in the block. The timing gear ultimately keeps the whole thing from going too far, I guess. Still, is the back side of the timing sprocket supposed to rub the block? I bought a set with a Torrington bearing in it for this project.
In a small block, there is a retainer plate that stops forward movement. I could see the reasoning for pushing the cam forward.

 

[Hemirunner]

I'd agree with that if the flat tappet cam setups also had to be limited the same way.
Lobe taper....I understand that it pushes the cam forward or rearward, I don't recall which direction. I don't quite understand if it does push it rearward in a small or big block because that would put the last cam journal against the cam plug that seems to be a variable as to where it actually sits in regards to the depth in the block. The timing gear ultimately keeps the whole thing from going too far, I guess. Still, is the back side of the timing sprocket supposed to rub the block? I bought a set with a Torrington bearing in it for this project.
In a small block, there is a retainer plate that stops forward movement. I could see the reasoning for pushing the cam forward.

You’ve really answered your own question. Lobe taper on a flat tappet cam will be ground so that it keeps the cam pulled rearward, into the block and the front sprocket rides against the block with a film of oil in between.
Lobe taper can also be ground to push in opposing directions to hold the cam in place without being biased to one direction or the other.
It would make sense that most BBM cams use a rearward thrust, and that the torrington bearing equipped sprockets would reduce some amount of friction. You’ll still get a slight bit of movement with a flat tappet cam and this can be confirmed with a timing light on a locked out distributor. A cam button on these can be beneficial in reducing or eliminating that movement.
The roller cams are flat ground and need the cam button to prevent any movement in either direction as it will change the engine timing in an undesirable manner.
Besides a poor running engine, this movement will also prematurely stretch a timing chain and ultimately allow the cam bolt heads to become the “thrust button”, so to speak, and grind out the inside of the timing cover. It will also eat a bronze distributor gear pretty quickly.

Here’s a link to an older discussion on Speedtalk. There’s a lot of engine theory discussed on this sight, if you’re into that sort of thing.
Cam Lobe Taper