### Re: Flat Tappet vs Roller Specs

Posted:

**Tue Jan 12, 2021 10:32 pm**Home of Racing's Best and Brightest

https://www.speed-talk.com/forum/

Page **2** of **3**

Posted: **Tue Jan 12, 2021 10:32 pm**

Posted: **Wed Jan 13, 2021 1:04 am**

The only real way is to measure both cams in the block ,degree wheel,dial gauge rocker geometry set up already,use actual valve springs and go to town,measure off the retainer and put it on paper.

Posted: **Wed Jan 13, 2021 8:17 am**

A flat tappet set-up is "velocity" limited.

A roller set-up is "acceleration" limited.

Just remember that camshaft lobe velocity is actual lifter rise speed. Acceleration is the rate of change of velocity; + or -.

Posted: **Wed Jan 13, 2021 10:23 am**

The difference is, the lifter radius limits the velocity of the flat tappet, and there's no way around that.Walter R. Malik wrote: ↑Wed Jan 13, 2021 8:17 am A flat tappet set-up is "velocity" limited.

A roller set-up is "acceleration" limited.

On a roller, it's the radius of the grinding wheel that limits the acceleration, and you can get around that, by using a larger base circle, or a smaller radius grinding wheel. That's why we use a 2.5" radius grinding wheel, and 55mm+ journals are common now.

Posted: **Wed Jan 13, 2021 12:10 pm**

On a Ford size lifter is there a specific lift this starts at?

Posted: **Wed Jan 13, 2021 12:17 pm**

No. The flat tappet radius dictates the maximum velocity you can move the lifter, before the lobe runs off the edge of the lifter.

Where max velocity occurs, depends on the shape of the velocity curve.

Posted: **Wed Jan 13, 2021 12:39 pm**

"To me" , when given a flat tappet and roller with the same "at .050" durations , the roller will run like a flat tappet with 8-10 more degrees of duration.

Posted: **Wed Jan 13, 2021 1:09 pm**

That depends on the diameter of the lifter and the aggressiveness of the ramp for that diameter.piston guy wrote: ↑Wed Jan 13, 2021 12:39 pm "To me" , when given a flat tappet and roller with the same "at .050" durations , the roller will run like a flat tappet with 8-10 more degrees of duration.

Posted: **Wed Jan 13, 2021 1:54 pm**

YES ... of course, large diameter base circles and hollow flank lobes on a roller will get around that restriction however, I don't see any mass produced hydraulic roller camshafts for original flat tappet engines, (like the early small block Chevy small journal diameter), being manufactured that way.CamKing wrote: ↑Wed Jan 13, 2021 10:23 amThe difference is, the lifter radius limits the velocity of the flat tappet, and there's no way around that.Walter R. Malik wrote: ↑Wed Jan 13, 2021 8:17 am A flat tappet set-up is "velocity" limited.

A roller set-up is "acceleration" limited.

On a roller, it's the radius of the grinding wheel that limits the acceleration, and you can get around that, by using a larger base circle, or a smaller radius grinding wheel. That's why we use a 2.5" radius grinding wheel, and 55mm+ journals are common now.

Especially for everyday street driving. Something in a competition setting would certainly be a different story.

Posted: **Wed Jan 13, 2021 5:50 pm**

To calculate maximum velocity (Vm) of a flat (actually, it may also be 50" radius convex shape) tappet per degree of camshaft rotation (.040” is a safety margin to prevent edge contact, use whatever number you feel comfortable with):

**Vm = (tappet diameter - .040”) ÷ 114.6**

Maximum for some common tappets

Chev. Gen-3 L6, V8 .842” .00700”/deg.

Ford .875” .00729”/deg.

Chrysler; A.M.C. .904” .00754”/deg.

Oldsmobile V8 .921” .00769”/deg.

Model “T” mushroom .970” .00812”/deg.

Chev. Gen-2 235, 261; GMC L6 .990” .00829”/deg.

VW Type I• 31mm 1.220” .01030”/deg.

To compare, it's linear.

Maximum for some common tappets

Chev. Gen-3 L6, V8 .842” .00700”/deg.

Ford .875” .00729”/deg.

Chrysler; A.M.C. .904” .00754”/deg.

Oldsmobile V8 .921” .00769”/deg.

Model “T” mushroom .970” .00812”/deg.

Chev. Gen-2 235, 261; GMC L6 .990” .00829”/deg.

VW Type I• 31mm 1.220” .01030”/deg.

To compare, it's linear.

Posted: **Thu Jan 14, 2021 10:34 am**

For those that want to understand the math, here's what we use.

Lifter face Radius, minus .012"(safety margin), multiplied by .0174524064373(sin of 1 degree) = Max lifter velocity per degree.

High School Trigonometry.

Lifter face Radius, minus .012"(safety margin), multiplied by .0174524064373(sin of 1 degree) = Max lifter velocity per degree.

High School Trigonometry.

Posted: **Thu Jan 14, 2021 10:58 am**

That's why they pay you the big bucks.

Posted: **Thu Jan 14, 2021 11:15 am**

Mike ,

.842 flat lifter still "around".0025/degree? It was when I was at Erson's in the '70s.

.842 flat lifter still "around".0025/degree? It was when I was at Erson's in the '70s.

Posted: **Thu Jan 14, 2021 11:37 am**

I think you're mistaken. A max velocity of .0025" per degree, would only need a lifter diameter of .287"piston guy wrote: ↑Thu Jan 14, 2021 11:15 am Mike ,

.842 flat lifter still "around".0025/degree? It was when I was at Erson's in the '70s.

Using the equation above.

.842" lifter has a radius of .421", minus .012" safety margin equals .409" multiplied by the sin of 1 degree equals a max velocity of .00713803" per degree.

Posted: **Thu Jan 14, 2021 12:15 pm**

For a given cam lobe lift, shorter duration (not including ramp duration) will increase

velocity and increase required tappet diameter.

For a give duration (not including ramp duration), higher lift will increase velocity and

required tappet diameter.

Depending on the specific lobe design, maximum lift typically occurs at about 72 CS degs

after the end of the ramp.

velocity and increase required tappet diameter.

For a give duration (not including ramp duration), higher lift will increase velocity and

required tappet diameter.

Depending on the specific lobe design, maximum lift typically occurs at about 72 CS degs

after the end of the ramp.