Does the advantage of a roller cam compared to a flat tappet increase, as duration increases?

[plovett]

I know both roller and flat tappet cams can be ground in a multitude of ways, but in general, would you say, "the bigger the cam the bigger the advantage" for roller cams.

My thinking is that with a small duration cam the flat tappet can get off the mark faster. Unlimited acceleration. But the max velocity is limited. A roller has limited acceleration, but is not limited in velocity in the same way. So on a very short duration cam, the flat tappet gets a head start and the roller might not have time (duration) to catch up and pass it, at least not in a way that significantly affects the area under the curve.

With a large duration cam the roller has time to blast past the flat tappet and create more area under the curve. The greater the duration, the more time to increase the advantage? True?

thanks,

paulie

[RDY4WAR]

IIRC, David Vizard made mention of this transition happening around 270 degrees of seat to seat duration. Below that number, the flat tappet has more area and above it, the roller wins. I could be wrong about that, but I think that's what I remember reading in one of his posts a while back.

[GARY C]

IIRC, David Vizard made mention of this transition happening around 270 degrees of seat to seat duration. Below that number, the flat tappet has more area and above it, the roller wins. I could be wrong about that, but I think that's what I remember reading in one of his posts a while back.

You are correct and I think he was correct at the time but with modern hyd roller lobes and the better lifter we have now I think the hyd roller would win out in most every occasion plus the better heads now like lift and you can get more with a hyd roller.

Also with the cost of a flat tappet special core and treating plus the lifter needed to live with a competitive hyd roller lobe the cost would be very similar.

[MadBill]

Concave flank roller lobes probably shift the crossover point down by 20° or more. Maybe camking will weigh in with the facts.
(And then there's the nail-biting break in process to contend with...)

[hoffman900]

Yeah, that would be old information. Looking through Comp, Crane's, Jones, Bullet, etc. shows that does not apply, not even close.

Enjoy..

Comp: www.compcams.com/Technical/Catalogs/Cam ... atalog.pdf
Crane: www.cranecams.com/uploads/lobe/masterlisting.pdf
Jones: http://jonescams.com/lobe-profiles/
Bullet / Ultradyne: http://www.bulletcams.com/Masters/Masters.htm / http://www.bulletcams.com/Masters/ultradynemasters.html (the Ultradyne ones are old. Harold worked through the 2000s updating a lot of these).

[Krooser]

Yeah, that would be old information. Looking through Comp, Crane's, Jones, Bullet, etc. shows that does not apply, not even close.

Enjoy..

Comp: www.compcams.com/Technical/Catalogs/Cam ... atalog.pdf
Crane: www.cranecams.com/uploads/lobe/masterlisting.pdf
Jones: http://jonescams.com/lobe-profiles/
Bullet / Ultradyne: http://www.bulletcams.com/Masters/Masters.htm / http://www.bulletcams.com/Masters/ultradynemasters.html (the Ultradyne ones are old. Harold worked through the 2000s updating a lot of these).

Here's my new reading material for the next four weeks... guess the wife will have to finish the bathroom remodel herself.

[hoffman900]

Yeah, that would be old information. Looking through Comp, Crane's, Jones, Bullet, etc. shows that does not apply, not even close.

Enjoy..

Comp: www.compcams.com/Technical/Catalogs/Cam ... atalog.pdf
Crane: www.cranecams.com/uploads/lobe/masterlisting.pdf
Jones: http://jonescams.com/lobe-profiles/
Bullet / Ultradyne: http://www.bulletcams.com/Masters/Masters.htm / http://www.bulletcams.com/Masters/ultradynemasters.html (the Ultradyne ones are old. Harold worked through the 2000s updating a lot of these).

Here's my new reading material for the next four weeks... guess the wife will have to finish the bathroom remodel herself.

There is a lot more out there than that. I wish they would all post them in a catalog format; Lunati, LSM, Cam Motion, Crower, etc.

[plovett]

Yeah, that would be old information. Looking through Comp, Crane's, Jones, Bullet, etc. shows that does not apply, not even close.

Enjoy..

Comp: www.compcams.com/Technical/Catalogs/Cam ... atalog.pdf
Crane: www.cranecams.com/uploads/lobe/masterlisting.pdf
Jones: http://jonescams.com/lobe-profiles/
Bullet / Ultradyne: http://www.bulletcams.com/Masters/Masters.htm / http://www.bulletcams.com/Masters/ultradynemasters.html (the Ultradyne ones are old. Harold worked through the 2000s updating a lot of these).

How can you tell that Vizard's rule of thumb does not apply? Are you comparing advertised, 0.050", and 0.200" durations?
Not saying you're wrong, just wondering where you are coming from.

thanks,

paulie

[CamKing]

How can you tell that Vizard's rule of thumb does not apply?

It hasn't applied in 40 years.

With the availability of a 2.5" radius grinding wheel, I can design roller cams with an acceleration rate higher then what a cast iron flat tappet cam would allow, due to the amount of spring it would require to control it. If the pressure required to control the acceleration rate will cause the flat tappet material to fail, you can't really use that acceleration rate.

[plovett]

So a roller can get more area under the curve, compared to ANY flat tappet cam, even a tiny one?

[CamKing]

So a roller can get more area under the curve, compared to ANY flat tappet cam, even a tiny one?

Yes, and the larger journals on today's engines allow for larger base circles, and that favors the roller, even more.

[psychomotors]

So a roller can get more area under the curve, compared to ANY flat tappet cam, even a tiny one?

Yes, and the larger journals on today's engines allow for larger base circles, and that favors the roller, even more.

But what about old school engines such as SBC, SBF & small block Chrysler?

[CamKing]

So a roller can get more area under the curve, compared to ANY flat tappet cam, even a tiny one?

Yes, and the larger journals on today's engines allow for larger base circles, and that favors the roller, even more.

But what about old school engines such as SBC, SBF & small block Chrysler?

Roller still wins, it just may take a 5" grinding wheel to grind it.

[plovett]

So a roller can get more area under the curve, compared to ANY flat tappet cam, even a tiny one?

Yes, and the larger journals on today's engines allow for larger base circles, and that favors the roller, even more.

Thanks! Can I ask this, too? Does the difference in area between the two, the roller and the flat tappet, become more and more with added duration?

paulie

[DaveMcLain]

Yes, and the larger journals on today's engines allow for larger base circles, and that favors the roller, even more.

But what about old school engines such as SBC, SBF & small block Chrysler?

Roller still wins, it just may take a 5" grinding wheel to grind it.

How much does the overall quality of the roller lifter come into play when you grind a lobe with a lot of positive acceleration? Does the greater pressure angle have a dramatic effect on the life of the lifter and the lifter bores in the engine? Do you have any recommendations in that department? Do you recommend a coated lifter, a bushed lifter bore etc?... Is it one of those things where it gets to a certain point and then service life really drops off quickly and the technique is only suitable to short duration applications?

Just curious.