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Flat Tappet vs Roller Specs

General engine tech -- Drag Racing to Circle Track

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skinny z
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Re: Flat Tappet vs Roller Specs

Post by skinny z »

cgarb wrote: Tue Jan 12, 2021 10:29 pm What was so secretive about that build?
No secrets. I just wanted an answer to the original question. I wasn't looking for a cam recommendation but rather some info on how to compare different cam type specs.
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Re: Flat Tappet vs Roller Specs

Post by steve cowan »

skinny z wrote: Tue Jan 12, 2021 10:32 pm
cgarb wrote: Tue Jan 12, 2021 10:29 pm What was so secretive about that build?
No secrets. I just wanted an answer to the original question. I wasn't looking for a cam recommendation but rather some info on how to compare different cam type specs.
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.
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Re: Flat Tappet vs Roller Specs

Post by Walter R. Malik »

skinny z wrote: Tue Jan 12, 2021 10:32 pm
cgarb wrote: Tue Jan 12, 2021 10:29 pm What was so secretive about that build?
No secrets. I just wanted an answer to the original question. I wasn't looking for a cam recommendation but rather some info on how to compare different cam type specs.
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 -.
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Re: Flat Tappet vs Roller Specs

Post by CamKing »

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.
The difference is, the lifter radius limits the velocity of the flat tappet, and there's no way around that.
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.
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Re: Flat Tappet vs Roller Specs

Post by Steve.k »

On a Ford size lifter is there a specific lift this starts at?
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Re: Flat Tappet vs Roller Specs

Post by CamKing »

Steve.k wrote: Wed Jan 13, 2021 12:10 pm On a Ford size lifter is there a specific lift this starts at?
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.
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Re: Flat Tappet vs Roller Specs

Post by piston guy »

"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.
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Re: Flat Tappet vs Roller Specs

Post by frnkeore »

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.
That depends on the diameter of the lifter and the aggressiveness of the ramp for that diameter.
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Re: Flat Tappet vs Roller Specs

Post by Walter R. Malik »

CamKing wrote: Wed Jan 13, 2021 10:23 am
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.
The difference is, the lifter radius limits the velocity of the flat tappet, and there's no way around that.
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.
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.
Especially for everyday street driving. Something in a competition setting would certainly be a different story.
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Re: Flat Tappet vs Roller Specs

Post by panic »

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.
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Re: Flat Tappet vs Roller Specs

Post by CamKing »

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. :lol:
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Re: Flat Tappet vs Roller Specs

Post by xxdabroxx »

That's why they pay you the big bucks. =D>
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Re: Flat Tappet vs Roller Specs

Post by piston guy »

Mike ,
.842 flat lifter still "around".0025/degree? It was when I was at Erson's in the '70s.
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Re: Flat Tappet vs Roller Specs

Post by CamKing »

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.
I think you're mistaken. A max velocity of .0025" per degree, would only need a lifter diameter of .287"

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.
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Re: Flat Tappet vs Roller Specs

Post by David Redszus »

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.
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